National Academies Press: OpenBook

Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges (2001)

Chapter: 6 Scientific and Technical Issues in Radioactive Waste Management

« Previous: 5 Societal Issues in Radioactive Waste Management
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 85

6

Scientific and Technical Issues in Radioactive Waste Management

Geological disposition of high-level radioactive waste (HLW) and spent nuclear fuel (SNF) is scientifically sound, but important challenges remain. This chapter discusses how scientists and technologists are addressing the challenge of analyzing the long-term behavior of a geological repository and endeavoring to present their results convincingly to other scientists, regulators, and concerned members of the public. The first part of the chapter describes the scientific basis on which repository behavior can be analyzed. The second part of the chapter describes the quantitative methodology, known as performance assessment, which has been developed for such analyses by the waste management community, and the measures taken to enhance confidence in its reliability. Emphasis is placed on the necessity for the methodology and for the results it delivers to be acceptable not just to scientists employing it, but also to a wider circle of interested and affected parties, including the broad scientific community, regulators, and the public. The third part of the chapter highlights the specific problems faced by a regulatory body in arriving at binding decisions in light of the unavoidable uncertainties remaining in the technical analyses. Finally, some examples are given of how policy decisions can ultimately affect technical issues in program implementation. The chapter ends with the committee's conclusions on the methodology and results of performance assessments for geological repositories.

GEOLOGICAL DISPOSAL

Practically, geological disposal does not represent a major construction challenge. All of the techniques required to build a repository, encap-

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 86

sulate the waste in a series of containers and barriers, emplace the waste, and close the repository are established or could be developed from established practices, and the associated cost is entirely compatible with the economics of energy production. A well-designed repository represents, after closure, a passive system containing a succession of robust safety barriers. These barriers are designed not solely to provide increasing levels of safety, but also to give increasing confidence that the overall system will remain safe even if individual barriers do not perform as well as they are designed to do. Our present civilization designs, builds, and lives with technological facilities of much greater complexity and higher hazard potential. In spite of these facts, there is a long-standing, intense debate on the feasibility of implementing “safe” repositories, that is, repositories that cause no harm to humans or to the environment.

The reason for much discussion is that extraordinarily long time scales must be considered explicitly in the analyses of repositories. There are inevitable uncertainties in the models and data used for these analyses and in the nature of events that might occur far into the future. There are particular uncertainties due to the role of the geological medium in isolating waste placed into a repository. Earth scientists are accustomed to descriptive, deductive reconstruction of the past, but for the purpose of a repository, they must develop quantified, inductive assessments of future system behavior. These factors make it a challenging task to analyze reliably the future evolution of the system. In practice, these difficulties are mitigated by two important facts. First, the engineered barriers can partially compensate for uncertainties in the understanding of the geological medium. Second, a single exact prediction is not needed; rather, understanding the range of potential future changes and assuring that these do not present unacceptable risks is a more correct description of the challenge. Long-term uncertainties also arise in analyses for the disposal of nonradioactive toxic wastes and for managing fossil fuel reserves. All such analyses require good science that will illuminate the physics, chemistry, and other mechanisms that will dominate repository behavior over the long time scales involved.

Nevertheless, the common perception is that for geological disposal specifically, one must be able to predict the future accurately—and it is beyond established engineering practices to predict accurately for many thousands of years how the waste and the repository will behave. It is also beyond established practice to predict accurately whether or not some of the radionuclides disposed in the repository may move through the geological formations and eventually come in contact with human beings and the environment in the future and cause them harm. As emphasized above, however, the challenge is not to accomplish these impossible tasks, but rather to assess the range of potential future behaviors with sufficient confidence to allow the appropriate societal decisions to be made.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 87

Another important issue when evaluating the geological disposal option is physical security. Assuring security requires that safeguard controls over the fissile materials (particularly spent fuel or plutonium) be maintained in order to prevent their clandestine use for nuclear weapons development or to prevent the misuse of highly hazardous radioactive materials by terrorists (NAS, 1994). Disposal in deep sealed repositories is considered one of the most effective ways to prevent undetected recovery of nuclear material (Peterson, 1998). Although it is not impossible to reopen a repository and recover the stored material, such an action would require heavy equipment, long times, voluminous extraction of earth and sealing material, and high costs.

SCIENTIFIC BASIS FOR MODELING

The time scales of concern for deep disposal are so long that direct observations or measurements of temporal alterations in actual repository system components are of limited value (although much can be learned from studies of analogous systems existing in nature). Assessment of future repository performance must be based upon modeling of the physical and chemical processes involved. The basic considerations for modeling are the following:

  • The laws of natural science that govern key processes such as corrosion, fluid flow, and mass transport do not change with time. However, our knowledge of these laws may be incomplete and may develop as more experience is gained. The issue is to know which laws apply during the relevant time scales so that we can assure proper application of current knowledge to be able to identify key parameters with sufficient accuracy.

  • The retrospective geological database actually extends over very much longer time scales (billions of years) than the lifetimes of most radioactive elements. Although knowing the past does not mean that one knows the future, history does give some confidence-building information about geological processes and rates of change.

  • Predictions of actual system behavior are not required. It suffices to provide conservative (or pessimistic) estimates of impacts that can reasonably be expected. However, this assumes that unknown effects—those neither expected nor accounted for in the analysis—will not materialize in significantly detrimental ways. The problem is to know whether the underlying concepts being used will result in a truly conservative estimate.

  • As long as one can be accurate in assuring that the levels of release are low, precise estimates are not needed; even with some orders of magnitude of residual uncertainty, the calculated release may be clearly within defined safety goals or limits.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 88

The major models that are needed for making these predictions can be grouped into three categories: (1) behavior of the waste package (i.e., the waste itself and its surrounding containment), (2) behavior of the host rock in the immediate vicinity of the waste, and (3) transport of nuclides from the waste package to the environment. These are described below.

The Behavior of the Waste Package

The approach used in modeling the waste package is to conduct short-term experiments (up to a few years) that bring the material (i.e., the canister, spent fuel, or solidified waste material) into contact with a leachant. The leachant is typically water containing additives so that its composition matches the expected composition of water within the repository. Corrosion or leaching models are fitted to the experimental results, and a model is used to extrapolate the results to very long time periods.

Understanding of the interaction mechanisms (such as surface corrosion, pit corrosion, solubility, or coating of waste by insoluble films) has made very significant progress in the past 20 years and has benefited from progress in materials science. Furthermore, significant efforts have been devoted to studying ancient natural objects as analogues of the waste package material (e.g., volcanic glass, archaeological copper, bronze, or iron) to determine if the models can reproduce the inferred degradation. There is little experience, however, in modeling the behavior of modern materials derived from new compositions and fabrication methods. Quantifying the uncertainty of extrapolations with these models from short-term experiments to tens or hundreds of thousands of years is still a major challenge. Nevertheless, it is accepted by the scientific community that wastes encapsulated in glass or ceramic material can last for many thousands of years in a suitable geological environment and that containers can be designed and built with similar lifetimes.

Other challenges are to predict the oxidation state of the leached radionuclides, and therefore their solubility (the effect of radiolysis being taken into account), and to predict the potential chemical forms of these radionuclides. Some of these chemical forms, or “species,” may have much greater mobility in the environment than others.

The Behavior of the Host Rock in the Immediate Vicinity of the Waste Package (the “Near-Field”)

The behavior of the host rock will be affected by the temperature of the waste package, the chemical composition (as a function of time) of the water contacting the waste package, the mechanical properties of the rock, and the water content and water velocity close to the waste package.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 89

Conductive heat transport is probably the best-understood phenomenon. As long as conduction is the dominant heat transport mechanism, one can be confident of being able to predict temperatures in space and time. This is because the uncertainty and spatial variability of heat conduction parameters of both man-made material and natural geological media are small, and therefore the uncertainty in the temperature distribution as a function of time is small.

Numerous heat transfer experiments have been made worldwide, including large-scale in situ tests in rock laboratories, for example, in Sweden (Stripa and Äspö), Belgium (Mol), Germany (Asse), France (Fanay-Augères), Spain (El Berrocal), Switzerland (Grimsel), and the United States Waste Isolation Pilot Plant [WIPP] (Brewitz et al., 1999). In the United States, a major, more complex heat transfer experiment at Yucca Mountain is in progress. It includes measurement of convective heat transport, water vaporization, and condensation in the geological medium, which are difficult to analyze. If a decision is made to allow temperatures in the volcanic tuffs to rise well above 100 °C, then there is considerable additional uncertainty because of the effects described above.

Methodologies for hydrogeochemical modeling of the near-field environment have also been developed and tested. They are generally based on the measurement of the present composition of the water; on its potential evolution due to temperature increases; and on the nature of the host rock, the waste package, and possibly a surrounding buffer material. The roles of the buffer are to protect the waste physically and to restrict access of water and transport of radionuclides. Most often, clays and sometimes salt are used as a buffer material. At Yucca Mountain in the United States, the waste package, according to the current design, is surrounded by air, and possibly shielded by an “umbrella” constructed of titanium alloy, which would prevent drops of water from falling on the canisters (DOE, 1998b).

Laboratory or in situ experiments are also being conducted to confirm the hydrogeochemical modeling. A large body of results (see, for example, NEA, 1999d, 2000c) gives confidence in the scientific approaches developed, although some residual uncertainties deserve more work, for example:

  • Modeling the complex interactions between some wastes, waste forms, and buffers. These interactions occur for intensely radioactive waste from fuel reprocessing or if cement, bitumen, or degradable cellulosic material is present. The latter two materials are generally excluded from geological repositories because they may be flammable or support biological activity.

  • Understanding the potential natural evolution of the chemical composition of the groundwater. In some cases, there already is spatial variability in

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 90

the observed composition, and it may be anticipated that changes will occur. The salinity is often variable (e.g., in Sweden), which is assumed to derive from past events during a glaciation or upward percolation of deep fluids. The oxygen content may also change with time, and there is evidence in the mineralogy of the rock that some oxidizing phases occurred. Predicting these changes is very uncertain and difficult.

The mechanical behavior of the rock is a complex function of its physical properties, the natural in situ state of stress, the geometry of the openings, and the thermal and chemical evolution. Thermal stresses are particularly important to determine and have been studied extensively during in situ thermal experiments. Depending on the rock type, stress can produce additional fracturing, or increased plasticity and convergence of the openings. The transport and geochemical evolution of fluids in the near-field may seal or open fractures and thus locally change the permeability. The main issue in mechanical modeling is the evolution of the permeability of the host rock in the vicinity of the waste and, for those repositories that are backfilled or are constructed in a plastic rock (clay, salt), to assess the effectiveness of the natural sealing of the voids and discontinuities surrounding the waste.

The natural evolution of the stress field due to tectonics, the probability and effects of earthquakes, and the effects of mechanical loading by ice during glaciation have also been studied in various programs. Historical records of earthquakes, plate tectonics, and theoretical modeling are used. The residual uncertainties are a function of the host rock (crystalline and volcanic rocks being much more sensitive to fracturing than clay and salt). The uncertainties potentially are significant and must be compensated for as far as possible by conservative repository design.

Knowing the flux of water in contact with the waste package is necessary to model the chemical degradation of the waste. This flux will vary throughout the repository due to small-scale spatial variability of the rock. There have been attempts to estimate this variability (e.g., in granite in Sweden) by using stochastic discrete fracture flow models at the small scale (SKI, 1996). The validity of these models is still debated, and the data base on which they are built is site specific. The models depend on detailed observations of the frequency distribution of natural fractures, plus those generated by mechanical effects. In many cases, an average fluid flux or maximum fluid flux is assumed. During the construction of a repository, observations of the flux at the time of the opening of the deposition cavity can be made and, for emplacements in which the fluid flux would be high, discarded. Even so, the evolution of this fluid flux due to thermomechanical and hydrogeochemical mechanisms, and to tectonic evolution in the long term, is quite uncertain. Upper bounds based on judgment are generally used in evaluations of safety.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 91

Transport of Radionuclides from the Near-Field Environment

Radionuclide transport out of the waste form and repository (the near-field environment) through the more distant geological host medium (often called the far-field or the geosphere) to that part of the environment accessible by humans (the accessible environment) is probably the most uncertain area of modeling. The theory for transport of solutes in natural media is reasonably well developed, but actual measurements have yielded surprises in the magnitude of the travel distance and direction (see Sidebar 6.1 and Sidebar 6.2 ). These measurements force examination of whether the established theories apply in all cases. Even if classical behavior is assumed, transport models require detailed information on both near-field and far-field properties (i.e., properties of the geological medium between the repository and the accessible environment) of the repository system. Given the spatial variability of natural media, this is a formidable task. Clays and salt, which are relatively homogeneous media, generally have less spatial variability in physical and chemical properties than crystalline and volcanic rocks but are harder to characterize because low-permeability experiments are very difficult at large spatial scales.

Moreover, radionuclide migration experiments in a medium that has been chosen because it should confine the waste for very long times can be conducted only over very short distances (e.g., meters) for periods of a few years. Such migration experiments have been conducted in several underground research laboratories (URLs), for example, at Mol (Belgium), Grimsel (Switzerland), Stripa and Äspö (Sweden), El Berrocal (Spain), and Fanay-Augères (France) (see, for example, Kickmaier and McKinley 1997; Brewitz et al., 1999). These experiments have very significantly improved understanding of radionuclide transport in geological media.

It is, however, well known from experiments done elsewhere in more permeable media that transport parameters are scale dependent; consequently, the parameters measured at small scales cannot always be used to represent phenomena at larger scales (Matheron and de Marsily, 1980). The scale issue is related to the heterogeneity of natural media and, in particular, fractured media.

Another difficulty encountered in modeling radionuclide transport in geological media is that of properly accounting for the numerous coupled hydrogeochemical interactions that take place among the solutes, host rock, and particulate or colloidal matter that may be present. Much has been learned about these complex interactions, mostly in laboratory experiments and also in some of the transport experiments done in URLs, as mentioned above. A large number of thermodynamic equilibrium constants for these interactions have been measured for the most important nuclides and the most common rock types. Studies of these interactions

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 92

are made more difficult by the spatial heterogeneity in rock properties, which so far has not been included in the models.

Beyond the difficulties of measuring the properties of geological media at large spatial scales and understanding the complex coupled processes that occur therein, accurate representation of these properties and processes in the transport model remains a major challenge. This challenge is sometimes referred to as the conceptual model problem (NRC, 2000a). Simply stated, a transport model is only as good as the conceptualizations of the properties and processes that govern radionuclide transport on which it is based. If the model does not properly account for the physical, hydrogeochemical, and when appropriate, biological processes and system properties that actually control radionuclide migration in both the near- and far-fields of the repository system, then model-derived estimates of radionuclide transport are very likely to have very large—even orders-of-magnitude—systematic errors (see Sidebar 6.1 ).

The present state of the art for transport modeling involves the use of many different kinds of numerical models to represent radionuclide migration in the environment. These models have large numbers of parameters that are difficult to estimate. Further, they are frequently based on highly simplified or even incorrect conceptualizations of the highly uncertain physical and chemical properties along the transport pathway. Special complications arise from the fact that in deep crystal systems very saline waters that contain methane and other gases are expected. Geochemical models for such fluids are not yet fully developed and transport considerations are very difficult. Only short-scale (tens of meters) direct validation of these models have been done.

Attempts have also been made to use natural analogues to understand long-term behaviors of natural systems (see, for example, Miller et al., 1994; McKinley and McCombie, 1995; Smellie et al., 1997; EC, 1998). Analogues are natural or man-made systems that have existed for long times, whose characteristics can be measured today and whose evolution through time can be modeled using the same methodologies employed in safety assessments (see the following section). In contrast to laboratory experiments that have well-defined initial conditions but limited time scales, some analogue systems have evolved over time periods even longer than those envisioned for repositories. Although there are often inherent difficulties in specifying precisely the conditions at the outset and throughout the history of the analogue system, the study of relevant systems can provide useful data for the analyst, enhanced understanding for the scientist, and increased transparency for the public.

It is, however, difficult to transpose the data inferred from the study of analogues to actual disposal sites, since the parameters of the models are site specific. Consequently, the use of environmental tracers (such as oxygen-18, deuterium, tritium, carbon-14, noble gases, and strontium iso-

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 93

topes) to provide a better understanding of transport at potential repository sites is a very active area of current research.

The implication of the foregoing discussion of the scientific basis for modeling seems clear to the committee. To the extent that repository systems rely on geological media to provide a long-term barrier to radionuclide migration to the environment, it is essential that the fundamental system properties and processes that govern transport behavior be well understood and appropriately implemented in those models. In many disposal concepts, one approach to this challenge of understanding complex geology is to use other safety barriers to reduce the importance of the geological medium. A durable waste form and container, along with an effective, low-permeability buffer material around the waste packages, will reduce the performance requirements on the geology. However, long-term safety cannot be achieved and demonstrated without an adequate understanding of the geological structures and processes. Hence, gaining this understanding remains a major scientific challenge for repository development programs (see Sidebar 6.2 ).

Sidebar 6.1: The Conceptual Model Problem

The importance of accurate conceptualizations of subsurface properties and processes in radionuclide transport models can perhaps be best illustrated using two examples from the ongoing effort to clean up environmental contamination at U.S. national defense sites, which is being undertaken by the U.S. Department of Energy (DOE). Several major defense sites are located in the arid western United States, where the groundwater table is located tens to hundreds of meters below the earth's surface and the unsaturated zone above the water table is composed of highly heterogeneous rocks and sediments. When the sites were first established during and following the Second World War, it was thought that the arid climates and thick unsaturated zones would protect the groundwater from radioactive and chemical wastes discharged into the shallow subsurface. This is the same argument made to support a geological repository in a deep, fractured unsaturated zone at Yucca Mountain.

Transport models seemed to confirm these initial predictions and further indicated that radionuclide transport through the unsaturated zone to the groundwater at these sites would not occur for hundreds or even thousands of years. Recent “surprise” discoveries of radionuclides in groundwater at two of these sites (Idaho National Engineering and Environmental Laboratory [INEEL] in east-central Idaho and the Hanford Site in eastern Washington), however, have prompted a reevaluation of this assumption. Now, similar data involving bomb-era radionuclides (chlorine-36) from the Yucca Mountain site provides further evidence that the observations at INEEL and Hanford may apply to a geological repository site (see Sidebar 6.2 ).

At INEEL, recent monitoring of groundwater near a shallow land burial site (the Radioactive Waste Management Complex) containing radioactive and chemically hazardous waste confirmed the transport of low levels of plutonium and other con-

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 94

taminants through the unsaturated zone to the aquifer some 200 meters below. This migration was neither expected nor predicted from existing transport models, even though radionuclide travel time through the unsaturated zone has been the subject of intense debate at INEEL for almost four decades. In the 1960s, the National Research Council Committee on Geologic Aspects of Radioactive Waste Disposal visited the site and published a report on this issue (NRC, 1966). The report noted (p. 5) that

The protection afforded by aridity can lead to overconfidence: at both sites it seemed to be assumed that no water from surface precipitation percolates downward to the water table, whereas there appears to be as yet no conclusive evidence that this is the case, especially during periods of low evapotranspiration and heavier-than-average precipitation, as when winter snows are melted.

Indeed, since 1960, estimates for travel time through the unsaturated zone at INEEL have decreased by almost four orders of magnitude, as illustrated in the figure below.

At the Hanford Site, billions of gallons of liquid waste containing millions of curies of radioactivity have been disposed in the ground on the central plateau (referred to as the “200 Area”) of the site. Initial field investigations of this site and subsequent transport models suggested that the 90-meter-thick unsaturated zone underlying the 200 Area would bind many of the released radionuclides, preventing their migration to groundwater (GAO, 1989, 1998). In 1997, however, DOE reported that cesium-137, technetium-99, and cobalt-60 had migrated deeper than expected, in some cases to groundwater (DOE, 1999b), along with some metals and chemicals.

Image: jpg
~ enlarge ~
Figure 6.1 Changing estimates of travel time for measurable amounts of any mobile radionuclide to reach the water table beneath INEEL (NRC, 2000a)

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 95

The lack of accuracy of model predictions in these two examples can be attributed to incorrect conceptualizations of the hydrogeologic system at the sites, including improper simplifying assumptions, incorrect transport parameters, and overlooked transport phenomena. These problems reflect both an inadequate understanding of transport processes in geological media and poor implementation of current understanding in the transport models.

The impact of this “conceptual uncertainty” is very difficult to determine in performance assessment (see discussion in text). This is well captured in a quote from Konikow and Ewing (1999) who, comparing long-term predictions of natural systems with a game of chance, remark:

In hydrogeologic and geochemical systems, . . . we do not know the odds. In fact, we probably do not even know all of the rules of the game (or perhaps even which game we are playing); that is, for these natural systems there will be uncertainty in the conceptual models and in the complex non-linear coupling between models.

Most national programs have responded to conceptual uncertainties in the modeling of transport in geological media by placing more reliance on engineered barriers. Within the geological setting, the engineered barriers can be well characterized and can be emplaced under quality-assured conditions. This increases confidence in the understanding of their behavior, although it does not remove all conceptual uncertainties associated with understanding the far-future evolution of the engineered barriers and does not obviate a need to understand the behavior of the geological media.

Sidebar 6.2: Geological Barriers in Repository Systems

The geological media surrounding a repository provides a barrier to migration of radionuclides to the accessible environment. The geological media may retard the movement of groundwater or bind (sorb) many of the radionuclides that escape from the repository; alternatively, the groundwater flow system itself may provide effective isolation from the accessible environment. The net effect is to increase groundwater travel times from the repository to the accessible environment and thereby allow time for radioactive decay to reduce radionuclide concentrations.

Most repository designs utilize geological media as one of several barriers to radionuclide migration to the accessible environment. The Swedish design, for example, calls for a repository constructed in a fractured granite formation with a clay backfill below the groundwater table, with SNF encapsulated in copper canisters. The clay functions as a low-permeability buffer that greatly limits access of groundwater to the container and also retards any radionuclides that may be released from the wastes. The U.S. design, on the other hand, calls for the construction of a repository in the unsaturated zone in an oxidizing environment. The waste will be encapsulated in corrosion-resistant metal canisters, and the canisters will be surrounded by titanium drip shields to protect them from percolating water (DOE, 1998b). Figure 6.2 illustrates this engineered barrier option for Yucca Mountain, as well as the general concept of engineered barriers.

Predicting the long-term behavior of water and radionuclide transport in the near- and far-field environments is a major challenge in all of these programs. In the U.S. program at Yucca Mountain, for example, it was initially assumed that

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 96

water flow from the surface, through the repository some 250 meters below, and then into the groundwater some 350 meters below the repository horizon, would occur over thousands of years. It was further assumed that any radionuclides released from the repository would be readily sorbed onto the volcanic rocks that surround and underlie the repository. Recent scientific work suggests that some of these initial assumptions may reflect an oversimplified understanding of the geological system at Yucca Mountain. Recent geochemical and isotopic measurements suggest that some water has migrated from the surface of Yucca Mountain to the repository level during the past 40 years (Fabryka-Martin et al., 1998). Other research under way at the nearby Nevada Test Site suggests that small amounts of plutonium may be capable of being transported through groundwater on microscopic particles known as colloids (Kersting et al., 1999). Both of these findings remain to be confirmed through additional work at the site.

These recent findings have had at least two significant impacts on the program at Yucca Mountain. First, they have sparked renewed efforts to understand the properties of and the processes that operate in the geological system. The geological barrier is an essential feature of any repository. These findings have also prompted the redesign of the engineered barriers in the repository to reduce the potential for radionuclide migration from the near-field environment—similar in many respects to the strategy being used by the Swedish program. Thus, the new findings have led to an increased effort to understand the geology as well as add protection through engineered barriers.

This example illustrates the importance of having a good understanding of the geological media if it is to be relied on to provide a barrier to radionuclide migration. The Yucca Mountain program was used to make this point because site-specific scientific investigations are at an advanced state compared to most other programs. All national programs must emphasize sound, objective scientific research throughout their site-specific investigations and must maintain the flexibility to respond to unexpected results. These programs must have specific, focused research on identification of the appropriate conceptual models for their sites.

Image: jpg
~ enlarge ~
Figure 6.2 Engineered barrier system.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 97

PERFORMANCE ASSESSMENT METHODOLOGY

Based on the extensive research summarized above, it has been possible, despite the open questions remaining, for interdisciplinary teams of safety assessors—including representatives from the fields of engineering, physics, chemistry, earth sciences, and mathematics—to develop over the past 20 years a safety assessment methodology capable of providing an important part of the decision basis required before implementation of geological repositories.

Basically, this methodology can be used to make quantified estimates, or “predictions,” of the possible future behavior of repositories and to also quantify the uncertainties in these predictions. This is called performance assessment (PA) (see Sidebar 6.3 ). The methodology is well documented and has been widely applied in many national programs (NEA, 1991a, 1997a, and 2000d). It has also been judged by the technical community as a sufficiently reliable tool for input to decision making (NEA, 1991b).

However, a direct demonstration of the reliability of the performance assessment methodology, including a rigorous and complete proof that the models used are correct, is not possible. Accordingly, the acceptability of project decisions based, at least in part, upon the results of safety assessments will depend on the level of confidence placed in the methodology by the technical experts within the implementer and regulator organizations, political decision makers, and the public. The following sections expand on the principles, technical approaches, and confidence-building measures that have been developed for analyzing the safety of geological repositories.

A typical PA includes the following two main elements:

    1. The central element is an analysis of the most likely behavior (often called “normal evolution”) of the repository. If the repository site is chosen properly and the repository design is appropriate, then the PA should show that it is most likely that nothing harmful will ever happen and that the waste will be confined in the repository, or in its immediate vicinity, for the length of time in question. The length of time over which such an analysis is made may be specified by a regulation (e.g., 10,000 years) or may be unbounded. If the length of time is not bounded, then the analysis is made until the time when all radionuclides have decayed to levels that would result in radiation exposures near the natural background. Many PAs in different countries have predicted high levels of safety for normal evolution scenarios (NEA, 1991a).

    2. Equally important is an analysis of the probability, and thereafter the consequences, of natural developments that might lead to loss of confinement of the waste. This can be caused by an adverse evolution of the geological setting of the site (e.g., faulting or volcanism), adverse evolu-

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 98

    tion of the environment (e.g., climate change, glaciation, accelerated erosion), unanticipated early weakening of some of the components of the natural or engineered barrier system because the site does not behave exactly as expected (e.g., early corrosion of the waste package, enhanced leaching rate and solubility, faster groundwater flow), or the existence in the system of unexpected negative features that may jeopardize the confinement (e.g., undetected manufacturing defects in a canister, an undetected geological fault). The probability of such a loss of confinement should be small for a suitable site. Proper site selection is therefore an important aspect of repository design, but it can only reduce the probability of release, not eliminate it.

In all cases, the occurrence of a release, even in the distant future, must be evaluated in terms of the potential harm it can cause. One therefore has to estimate the effect of the radionuclides released by a repository on humans and the environment. Current practice is to make such estimates by assuming that the living habits of humans in the future will be identical to those observed today.

In this respect the PA must also include an entirely different class of human-induced events—most importantly, the accidental “intrusion” of humans into the repository at some time in the future by drilling, underground excavation, or other means. Current practice is to assume that the PA includes only those events that could take place if the existence of the repository is forgotten (NEA, 1995b; NRC, 1995). An intentional intrusion into a known repository is considered to be outside the current generation's responsibility. In practice, such inadvertent intrusion scenarios must be highly “stylized” in that they are simplified and approximated, since it is impossible to try to analyze what the future society's technology will look like. The likelihood (or probability) of such intrusion scenarios depends on the properties of the site (e.g., existence of natural resources) and is sometimes quantified as a function of the present rate of drilling in the area.

Sidebar 6.3: Performance Assessment

Performance assessment is a formal quantitative methodology for estimating the long-term behavior of a candidate repository system, including the site. PA should be used iteratively throughout repository development, particularly once a candidate site has been selected and studied in detail. The results of this analysis are used in an application to the regulating authority for licenses to construct, open, fill, and close the repository. The important steps in the PA methodology are listed below:

    1. Characterize the waste to be disposed and its near-field environment, both the present properties and the way in which these properties may change in the future.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 99

2. Characterize the repository design including the engineered barriers, both for its present-day properties and for its potential evolution.

3. Characterize the selected site, both for its present-day properties and for its potential evolution.

4. List all the features, events, and processes (feps) that will act on and within the repository. Internationally agreed-to lists of feps can be used as checklists for this task (NEA, 2000a).

5. Screen all of the relevant feps that apply to the selected site and planned repository.

6. Assess the probability of occurrence of the selected feps.

7. Construct models of repository behavior for each selected fep and for all the couplings of feps that may occur. Verify these models and validate them against observations that have not also been used for establishing the model.

8. Estimate (or measure) the uncertainty of each of the parameters needed for each model. Determine if alternative sets of models (with their relevant parameters) could be used to assess conceptual model uncertainty.

9. Group those feps into a number of “scenarios”:

  • those that are certain to occur within the repository, as it evolves with time;

  • those natural feps that may occur with a low probability; the time of occurrence of these external feps may be random, and

  • the human-induced feps, i.e., the various human intrusion scenarios.

    10. In some countries, regulations prescribe the feps that have to be studied, both natural and human induced. This clearly simplifies the task of those carrying out the PA, but it does not guarantee that the choice is more realistic or complete and may even decrease confidence in the result. To avoid such a decrease in confidence, the prescribed feps should be considered by the PA analyst as the minimum set required.

    11. The consequences of each scenario are calculated with the models. In most countries, the consequence of a scenario is a dose or risk to a human in a well-defined population known as the critical group (NEA, 1997b). The risk here is defined as the probability of occurrence of a scenario, times the dose received, times the probability of harm from that dose. The outcome of a consequence calculation has to be compared with a predetermined criterion, which is defined by the safety authority (acceptable release, acceptable dose, and acceptable risk). The proposed repository design and siting will not be acceptable if the criterion is not met.

    12. A sensitivity analysis of the results of the PA to the uncertainty in the parameters of the models, to the uncertainty of the conceptual models, and finally to the scenario uncertainty is generally made to demonstrate robustness. If some uncertain parameters are found to change the outcome of the PA significantly, these parameters should receive more attention through additional research and experiments or through modification of the repository design before the PA is finalized.

    13. The decision of the safety authority is not based solely on a single criterion being met—for example, an acceptable release within a prescribed time period—or even on a series of such numerical criteria, but on an overall judgment of whether the site is safe, the various calculations performed by the applicant being the only elements for making the decision.

    14. The final judgment of the safety authority has to be acceptable to both the political authorities and also to the public for a positive decision to be possible. In most countries, no such decision can be taken without a democratic process (see Chapter 5 ).

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 100

DISCUSSION: UNCERTAINTY AND CONFIDENCE BUILDING

The preceding discussion in this chapter has described performance assessment, the approach developed by the waste management community to try to understand and quantify the risks associated with geological disposal. The questions are whether scientists judge this to be an effective way of evaluating the suitability of the repository option and whether other people will be convinced that it is a well-grounded and feasible approach. The most fundamental technical problem in applying performance assessment concepts, which were originally developed for nuclear reactor safety studies, to repositories concerns the geological part of the system (see Sidebar 6.1 ). This is why many designs try to compensate for these difficulties by including a robust engineered system to reduce the consequences of geological uncertainties.

In attempting to model a geological system the basic question is: Have we used the correct conceptual models (see Sidebar 6.1) representing the geological and other processes, to make the assessment? This uncertainty, which cannot be easily quantified, can be reduced by using alternative conceptual models and should always be kept in mind. There is a danger that a legalistic, prescriptive regulatory environment or a project forced to meet deadlines can induce scientists charged with developing a performance assessment to assume that they have no uncertainty in their conceptual models (see Sidebar 6.1, Sidebar 6.2).

The purpose of PA is to quantify the probability and the consequences of repository failure. The aim is to compare predicted repository performance against a regulatory, as well as a common-sense, standard of risk. Adjustments can be made to the design of a repository if a PA shows that these are needed to align estimates based on assessment of possible repository performance with acceptable levels of risk. However, a repository can never be proved in advance to be absolutely safe over the entire period of its operation. Neither a 100 percent level of safety nor 100 percent confidence in the reliability of the assessments is possible. This is a fact that is true also for every other comparable technical undertaking, and it is important to assure that unique, unattainable requirements to the contrary are not placed on HLW disposal. Some probability of future failure will always exist. The PA analysis must compare the uncertainty that remains in this estimation against an acceptable level of uncertainty.

Either PA can contribute to convincing observers of the adequacy of a repository proposal, or it can have the converse effect of discouraging confidence. Interested parties may challenge the PA methodology and assumptions or question the adequacy of design adjustments. Furthermore, there are differing perceptions in society of what constitutes acceptable risk and of how much uncertainty in analysis is tolerable. Indeed these terms are loaded with many meanings. At the present time, probably a

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 101

relatively small segment of the public and of political decision makers agrees on the definitions of acceptable risk and uncertainty developed by the waste community in its professional and scientific practice. In the opinion of the committee, these notions will require extensive discussion and debate among the various stakeholders over the coming years before any broad consensus can be obtained (see Chapter 5). Furthermore, these residual risks and uncertainties must be compared with those for alternative management options—for example, surface storage—for any given period of time. 1

The following sections, based on analysis by the committee of what has happened in the past in national programs, review some of the steps that may be required of the scientific analysis of a repository in order to bridge the gap between those doing the analysis and the rest of the community. The goal should be that all parties involved in the decision-making process have a consistent and accurate perception of what PA can and cannot do, so that they do not make sub-optimal or irresponsible decisions based on incorrect or biased perceptions.

All of the decisions within the PA process can be taken only if there is sufficient confidence in the procedures and in the results of the assessments. Building confidence in the safety of geological disposal requires a range of measures (NEA, 2000b). One important measure concerns the technical issue of building confidence in safety assessment methods. A common approach to this task is comparison of calculated results with experimental values obtained in the laboratory or the field. The fact that feasible measurement times are always much shorter than the time scales of relevance for disposal systems is obviously a great limitation here. Nevertheless, agreement between calculation and experiments under a range of relevant conditions can enhance confidence in understanding the mechanisms involved and can also provide a database for extrapolation. Extensive laboratory programs, as briefly referred to elsewhere in this chapter, have studied the behaviors of all materials in the repository system (waste matrices, container materials, cements, rock types). In the field or in URLs, large experiments have simulated key aspects of rock mechanics, hydrogeology, and hydrochemistry, increasing confidence in the ability to model key transport processes in groundwater. The combination of short-term, exact experiments and observations with long-term analogue studies can also contribute to elimination of unsuitable models and to increase confidence in the models retained for the final safety assessments.


1 The use of risk numbers for comparison among alternatives (“relative risk”) rather than for assurance of adequate safety (“absolute risk”) has been emphasized in many reports on nuclear safety. See, for example, Lewis et al. (1978).

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 102

There remains, of course, a large element of human judgment in this methodology, as in most other technical assessments. It is important to explore ways to inform this judgment such that the quality of the technical work and reliability of products used in a repository can be judged appropriately. Natural analogues may be useful in this regard if they are understandable and reassuring to a wide public despite the inherent difficulties of quantification. Other common approaches to inform judgments include the use of open and objective reviews of technical work, and impartial and unbiased elicitation of expert opinion on issues where human judgment remains of key importance.

Efforts to raise public confidence have also been widely undertaken by the scientific and technical community. In their 1991 collective opinion on safety assessment methodology (NEA, 1991b), representatives of the Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development (OECD), the International Atomic Energy Agency (IAEA), and the European Commission (EC) expressed their belief that adequate (although not perfect) methods were available for assessment of the safety of a waste repository. However, this opinion, formulated by experts within the waste community, continues to be challenged at the broad level by nuclear opponents and many members of the public. At the detailed technical level, a debate on the validity of specific models continues within the technical community. It is therefore not surprising that decision makers and the public reserve judgment or are led to “choose sides.”

At the technical level there must be increased recognition that perfect solutions are not possible on repository-relevant time scales, nor indeed are they required for justifiable project decisions. It is more important that scientists concentrate on understanding the effects of uncertainties in current models and data and on providing reasonable assurance that these current approaches will not underestimate potential releases of radioactive materials from repositories.

At the wider level, it is crucial that safety assessment experts communicate their belief that their calculated results, although imperfect, provide sufficiently reliable input for decision makers. To this end, presentation of results is very important. The non-expert looking at typical results from PAs will be confused by complex, probabilistically expressed results. The specialist, if confronted by simple scenarios, treated purely deterministically, will quickly ask for the associated probabilities. No one outside the radiation protection field will fully grasp the meaning of extremely low-dose predictions if a perspective on their health effects is not provided. Numerical results of analyses extending to geological times, if presented without sufficient discussion of their significance, lead understandably to accusations of over-optimism, hubris, or even irrationality. To the extent that there is uncertainty in conceptual models, this must be made clear.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 103

When waste management specialists are considering how to reach out to other communities to achieve a common understanding of key issues, it is useful to start asking the questions: “Who are the stakeholders; in which order, and in what way should they become involved?” (See also Sidebar 1.5 ). The committee has identified four general groups of stakeholders for this analysis. These include the general scientific and technical community, regulators, elected officials, and concerned citizens. How science and scientists interact with each of these groups is discussed below.

The Scientific and Technical Community

It seems clear that HLW disposal in any country cannot occur if the scientific and technical community does not support it. This community includes (1) scientists and engineers directly involved in the project who prepare the technical material that goes into the tools and models used in PA; (2) scientists and engineers involved in various review groups, at the local, national, or international level; and (3) members of the scientific and technical community not involved in the project, who may have some knowledge of the issue, or who have acquired the esteem and respect of their colleagues and the public because of the quality of their work. How does this scientific community arrive at its judgment?

As in any field of science, the first step is that the scientists actually working on the project have the stature and reputation that brings respect for their work from colleagues. Agencies involved in the preparation of a repository project should be aware of this requirement, applying not just at the top scientific levels, but at all levels. Evaluation of the feasibility of HLW disposal is a scientific challenge, and the highest-quality and most up-to-date science needs to be used. Independent expertise, including international expertise, should be used to complement the work of inhouse staff. The findings of the scientific staff need to be published regularly in the open scientific literature. This should not be considered by the agency as a secondary aim, but as a major requirement of the work.

Scientists involved in the programs must also have some opportunities for launching new studies in order to verify and develop new concepts. For instance, the examples concerning transport processes in Sidebar 6.1 and Sidebar 6.2 should motivate the examination of processes and mechanisms that were not anticipated when many national programs started one or two decades ago. It is necessary that new ideas be examined, which implies that scientists inside and outside the project can submit proposals and receive funding for performing work designed to disprove the prevailing conceptual model or to collect data that may support an alternative conceptual model. Of course, there must be a limit to the work that deserves to be funded; that decision, however, should not de-

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 104

pend on the responsible agency alone, but also on external agencies experienced in funding scientific research.

Scientists with expertise relevant to a project must be able to express their views on the safety of the project to their peers, before the project enters the licensing phase. The National Research Council report on the Waste Isolation Pilot Plant (NRC, 1998), which came out about a month before the Department of Energy (DOE) applied to the Environmental Protection Agency (EPA) for compliance certification, was an excellent example of such an activity.

Scientists will be more easily convinced by a formal argument (the “safety case”) that an engineered system is safe if the design of the system is robust. The concept of robustness can be applied to repository systems as follows (McCombie et al., 1991):

  • A robust repository system has (1) simple geology, physics, chemistry, and design; (2) large safety factors; and (3) some degree of redundancy.

  • A robust performance assessment is characterized by (1) being based either on well-validated, realistic models or else on clearly conservative models and data; (2) assuring that all potentially negative processes are analyzed; and (3) being relatively insensitive to parameter and conceptual model changes.

For example, the robustness of the assertion that an engineered barrier is long-lived can be sought from archaeological evidence or from physical principles and short-term measurements. This approach led the Swedes and the Finns to select copper as the canister material (see Figure 4.1 ). Copper is known to be stable in reducing environments, both from the existence of native copper and from archaeological artifacts. Corrosion can also be estimated using the basic principles of metal corrosion thermodynamics. Both approaches provide confidence that this material will last for millions of years in favorable environments. The role of the geological barrier is then to maintain this favorable environment.

The Regulators' Dilemma

The first role of a regulator is to decide the rules for demonstrating compliance that the implementing agencies should obey; then the regulator has to establish for the remaining stakeholders the credibility of its decisions by making clear why these rules are necessary and sufficient to convince the regulator of repository safety. The regulator's second role is to decide if the license application, which is made by the implementing agency, meets these requirements. Both roles require that the regulator has scientific credibility and that the same rules as those described above for science at the implementing agencies apply also to regulators. This

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 105

includes the need for scientists at the highest levels, sufficient scientific staff, publications, room and funding for independent research, and expression of independent scientific views.

In comparison to communicating with general scientists and the public, the interaction of regulators with implementers should be a more straightforward, technical task. This is not to say that the role of regulators is unimportant. Rather, experience shows that regulators should be in constant interaction with the implementing agencies. Regulators directly or indirectly interact with implementers with respect to the methods they should use to show compliance, the data they should collect, and the nature of the evidence they should provide. Furthermore, regulators have to understand the PA methodology very well. Only if regulators are convinced that the science behind the PA is good, and if the PA estimates of performance meet regulator-established requirements both quantitatively (i.e., meeting the numerical requirements in the regulations) and qualitatively (i.e., demonstrating in nonnumerical terms that the repository will be safe, using, for example, a convincing safety case), will regulators endorse and approve the licensing application.

The ultimate application of the safety assessment methodology is in the preparation of a full safety case for licensing a repository. There are three categories of requirements:

    1. The repository system itself must be based on a robust disposal concept, good engineering and technology, and a suitable site.

    2. The safety analysis requires a convincing safety case (robust models based on sound data), proper regulatory framework, and transparent presentation at all levels.

    3. The regulatory process depends on having a competent implementing body, a competent regulatory body, and proper communication among all stakeholders.

Today, particularly with respect to nuclear activities, there is insufficient public and political trust to permit unquestioned acceptance of projects worked out only among technical experts in the implementer and the regulatory agencies. As in all highly technical initiatives, trust and confidence must be engendered in wider circles, and this requires that all experts be answerable to a wider audience. The special challenges of involving the public in nuclear and radioactive waste issues are dealt with in detail in Chapter 5 and Chapter 8 .

Although no deep geological repository for long-lived wastes has yet been licensed through a standard procedure, 2 regulators and implementers are relatively confident that workable procedures have been, or can be,


2 The WIPP is a special case, certified by the EPA for limited types of DOE waste (see Sidebar 4.1 ).

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 106

developed. This is not to imply that there are no open issues. The following list provides some of the topics currently being discussed among regulators (NEA, 1997b):

  • Time perspective—there are no scientific reasons for specific cutoff times such as 10,000 years—but are there policy reasons (NRC, 1995)?

  • How can the safety of geological disposal be evaluated using the established regulatory concept of “reasonable assurance”?

  • Should regulators require investigation of alternatives to geological disposal?

  • What is the role of the regulator in site selection and choice of disposal method?

  • Legal and regulatory issues—what are the roles of government agencies and regulators?

  • What should the regulatory attitude be toward retrievability?

  • How should human intrusion be treated when the future actions of society are unpredictable?

  • How should the first 100-year-period risks (such as proliferation, transportation, and worker health) be weighted relative to the 10,000-year risks or to the maximum risks at any time?

  • How can a reasonable decision be arrived at—setting up a decision process, participation, and a stepwise implementation process?

The last item leads to the heart of the “regulator's dilemma”—how to organize a regulatory approach to enable solid and accepted regulatory decisions to be made in light of the uncertainties, some of which are in fact not resolvable. Sidebar 6.4 provides a summary of the committee's views on regulatory issues related to geological disposal.

Sidebar 6.4: Summary of Committee Views on Regulatory Issues Related to Geological Disposal

The following points summarize the committee's views of regulatory issues connected with geological disposal.

    1. A “phased approach” to regulation of a deep geological repository, as expounded 10 years ago in the Board on Radioactive Waste Management's Rethinking High-Level Radioactive Waste Disposal (NRC, 1990), remains excellent advice. A key corollary is that the regulator must strive to avoid over-prescriptive rules too early in the overall multi-decade process of regulatory approval. A second corollary is that, in general, a “compliance” attitude and philosophy is an inappropriate way for the regulator to approach the major yes-or-no decision; the regulatory yes-or-no decision for a geological repository will always require a good deal of judgment, not merely a cookbook compliance-type finding. At some very fundamental level, the implementer is always responsible for showing that the site

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 107

    is safe. Programs should be careful that a prescriptive regulatory approach does not induce a compliance attitude rather than a “safety” attitude.

    2. Public involvement is essential in the process whereby the regulator arrives at the rules and regulations to be used in project approval. Public involvement should begin at the earliest phases of the rule-making process and continue throughout. This implies a fully open process, in which the public can challenge and comment on the approaches to be used by the regulatory body.

    3. As stated explicitly in regulatory documents from many countries (USNRC, 1998; EPA, 1999), “proof” that the proposed geological repository meets any specific set of regulatory standards cannot be had in the ordinary sense of that word. This is because of the very long time frames involved, including but not limited to our inability to understand changes in human behavior over such a long period.

    4. Even when a particular country's legal system requires quite prescriptive regulations for a deep geological repository, there is substantial room for flexibility at the level of detailed regulatory guidance, decision making, and inspection programs.

    5. The regulatory body's ability to adopt and utilize a less prescriptive system that involves relatively more judgment is very much tied up with how much trust that body enjoys with the bread public. The more trust, the more deference is afforded the regulatory body to exercise judgment instead of relying on prescriptive yes-or-no findings, and the more likely is acceptance by the public of the regulator's decisions.

    6. The corollary is that if a regulatory body has engendered mistrust and hostility among key sectors of the broad public, then it is typically forced into both more prescriptive and less flexible regulatory decision-making situations, and more conservative rules and decision criteria. This is because the political repercussions of any decision, where broad trust is absent, can become so uncomfortable for the regulatory body that it finds itself needing much more regulatory “margin” to make any decision.

    7. There is inevitably a lot of uncertainty in any analysis of future repository performance, no matter how well it is done. This is true even of those parts of the analysis, such as the geological, hydrological, metallurgical, and chemical aspects, that ought to be more “science based.” This has led to suggestions that the key regulatory yes-or-no decision should in general be based on more than a single numerical figure of merit. The approach of relying on a single figure of merit could be supplemented by use of one or more quite different figures, including an overall judgmental criterion, namely, Does the safety case make good technical sense?

    8. It is important to emphasize the value to every country of the principles incorporated in the Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management (IAEA, 1997a). Internationally agreed-upon principles for radioactive waste management are discussed in Chapter 9 (see Sidebar 9.1 ).

    9. Both the repository developer and the regulatory body should take a systems view of the analysis of future repository performance. Insights gained from a systems view are not just the sum of the insights from analysis of the details: understanding the “forest” is more than just a sum of understanding various individual “trees.”

    10. How far into the future the specific regulatory compliance period should extend is primarily a public policy issue, not a technical issue that science can address.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 108

    11. The job of regulating a first-of-a-kind repository is intrinsically one of gradual learning and refinement. Nobody should expect that a regulatory body could put into place in 2000 a set of regulations that would govern for, say, 100 years. The phased approach also allows regulations to develop and to take account of new knowledge gained during the lengthy phases leading ultimately to closed and sealed repositories.

    12. It is broadly agreed that while a regulator should require the developer to put into place a monitoring system to measure various relevant repository performance parameters, it is an incorrect regulatory approach to make such monitoring an essential feature of assuring safety (IAEA, 1997b; ANDRA 1998). Regulators do not believe that such monitoring could be relied on for long enough—centuries or millennia—to identify flaws in the repository's safety case, which will likely emerge (if at all) only centuries or millennia in the future. This is not to say that monitoring that does in fact detect a repository failure or surprising behavior should be ignored.

    13. Finally, it is important to consider how the regulator can structure a program for communicating effectively with the public.

The Link Between Scientific and Societal Responsibility

In the past few years, more attention has been paid to the issue of increasing public involvement in the process leading to final disposal. In essence, there is pressure to structure a process that assures accessibility of all relevant information, gives adequate opportunity for public input and questions, retains options for as long as possible, and remains reversible should new evidence show that better options have become available. The most conspicuous result of these developments has been an intensive debate on monitoring repositories, on phased or stepwise implementation programs, and on measures needed to guarantee reversibility of steps—including retrieval of emplaced wastes.

The technical community accepted the validity of these points rather grudgingly. Originally, it was often pointed out that no scientifically meaningful monitoring programs could be proposed and that retrieval was a scenario that could be excluded by proper planning and execution of disposal projects. Now it is widely accepted that “confidence monitoring” to address public concerns is a legitimate exercise, even if scientific considerations indicate that the probability of detecting a malfunction is negligible even for centuries or millennia. It is also accepted that retrievability, or more generally reversibility, which was always feasible in principle, can be made more straightforward (“enhanced”) without unacceptable negative impacts on repository safety (IAEA, 1997b). In short, there has been an increase in the readiness of insider “experts” to listen to public concerns and to work toward allaying them. This very fact should

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 109

contribute to enhancing the public's involvement in geological disposal decisions.

Both the scientifically based performance assessment and the public processes associated with making choices about nuclear waste are complex and inherently uncertain. Those on both the technical and the public sides of this issue may wish that the other side were certain, but neither scientific understanding nor societal decision making are completely predictable. Importantly, there is a large potential for negative interaction between these two uncertainties. Scientists may wish to treat technical uncertainty through the calculation of risk. However, scientific uncertainty, or even the perception of scientific uncertainty, can easily cause public entities to fight a project. Public opposition can elicit a “bunker mentality” on the part of the implementer. The net result is a lack of true dialogue and the potential for suboptimal or even irrational decisions. Stirling (1999) refers to the tension between narrow notions of “sound science” and the “precautionary principle” 3 as a “dichotomy trap,” in which productive and creative “solution-oriented” thinking is impossible.

Both public interest organizations and technical implementers should be enjoined to act responsibly. It is not responsible to obfuscate the potential risks of a geological repository when communicating with the public. Nor is it responsible to take irreversible action when the risk cannot be sufficiently quantified. On the other hand, it is not responsible to block any action designed to reduce significantly the risk to society, merely because some risk remains. Invoking the precautionary principle in this regard can cause great harm by preventing appropriate waste management. There is no path forward that is risk-free, including taking no action. It is important that society make wise choices concerning the wastes that already exist and require management.

Rather than seeing the public need to be cautious as being in contradiction with a science-based management process, it is possible to view this caution as entirely consistent with sound scientific practice. In responding to intractable problems in risk assessment such as “ignorance” (“we don't know what we don't know”) and “incommensurability” (“we have to compare apples and oranges”), the role of precaution then becomes the same as the adoption of a stepwise approach in which difficult or irreversible decisions are taken only when commensurate with understanding. It is nearly impossible to quantify risk when we are also uncertain of the appropriate conceptual model underlying the phenomena of interest. The issues involved in gaining public acceptance under conceptual uncertainty include acknowledging the importance of ignorance and

3 The precautionary principle as a concept is a matter of intense debate in the risk community as well as in the international legal community. A recent summary describes its various formulations (Foster et al., 2000).

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 110

the subjectivity of the trade-offs and “framing assumptions” that necessarily condition any analysis. A rational response both to ignorance and to the implicit element of uncertainty in analysis is to broaden out the appraisal process systematically in such a way as to consider a wide array of different issues and options, contingencies, and possibilities and forms of effect, and to include a diverse range of disciplines and stakeholder groups, to provide for careful long-term monitoring, and to place the burden of persuasion on the developers rather than the regulators.

These choices make sense from a technical perspective, and they also allow a constructive dialogue with the public. In a measured and incremental application of an approach, Stirling recommends that “science should be on tap, not on top” (Stirling, 1999, p. 29). There can be no simple analytical, instrumental, or institutional “fixes” for the complexities encountered in the management of technological risks. Policy making must obviously be based on available scientific information, but science on its own is not enough. In this way, it is possible to integrate technical and socioeconomic factors in the management of risk by examining different technological options and evaluating their flexibility, resilience, and diversity. The recognition and active accommodation of dissenting voices in the societal debate is simply an extension of that crucial principle of quality in the scientific process: organized skepticism. Transparency is an essential means to the end of full public engagement. Inter- and intradisciplinary scientific conflicts should not be concealed. The full implications of uncertainties should be acknowledged. Alternative assumptions and value judgments should be explored fully.

Such an incremental approach, which makes sense from the technical standpoint, also offers a way to provide for the open-ended societal learning that is an essential quality of the successful waste management program. In this regard, there is a distinct difference between processes for deciding what to do and the process for doing what's decided. The two should not be confused. Societal acceptance will be more likely if the government's role is to facilitate the first process and not anticipate the result by sponsoring particular solutions. As the societal appraisal process illuminates the consequences of adopting different framing assumptions in interpreting the available science, then it becomes the role of the government to make incremental decisions and to be accountable transparently for the inevitable political and value-laden elements in such decisions.

In addition, a stepwise program is scientifically beneficial since it allows decisions at each step to be commensurate with the status of the science base at that time. Moreover, the reduced pace of development that these interactive processes and deliberately phased schedules imply for implementation programs affords more time for building public and political participation in the decision. These gains are to be set against the unavoidable increases in time and resources needed to carry out reposi-

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 111

tory projects. Further aspects of the interaction with the public are discussed in Chapter 5 and Chapter 8.

CONCLUSIONS

The challenge of safely managing HLW and SNF is not only a scientific issue. Indeed, the key areas in which problems have arisen, and new approaches may be needed, are more concerned with societal issues. Scientists and technologists involved in waste management have recognized this increasingly in past years and have shown a readiness to become involved more directly in these issues. Nevertheless, scientists have a prime, continuing responsibility to try to identify, understand, and communicate to the public the technical issues that influence the general debate. The corresponding conclusions widely agreed to by the committee and, it believes, also by the scientific and technical communities, are summarized below.

Science, Technology, and Performance Assessment

Based on the preceding discussions, the following can be concluded:

  • The necessity of modeling the long-term performance of a repository is universally recognized. Quantitative results from assessments provide a necessary input for decisions throughout disposal system development. The calculated results do not, however, provide hard criteria that obviate the need for human judgment. Safety assessments alone are not the only considerations governing the acceptability of any disposal facility.

  • The feasibility of performing assessments of sufficient quality is accepted by technical experts within the waste management community. A somewhat lower level of confidence exists in wider scientific circles, and in limited segments of the public severe reservations are still expressed. Some of the remaining differences in views could be narrowed if assessors made clearer that their aim is not to analyze the future exactly, but rather to scope the range of potential future behaviors of the repository system and the consequences of the remaining uncertainties.

  • Specific parts of the modeling chain for geological repositories will continue to be developed and refined. In particular, there is a critical need to focus explicitly on the conceptual models that underlie the calculations. It is these studies that will illuminate the physical and chemical principles that dominate the behavior of the repository. It is fundamentally necessary to identify the appropriate conceptual models before we define the appropriate parameters characterizing the site and then try to understand the statistical variability associated with these parameters. The common time scales for implementation of HLW repositories leave many years for potential improvements. These developments may ease the difficulties in

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 112

    future licensing procedures; nevertheless, they will not result in perfect models that produce unquestionably accurate results. The requirements for human judgment and expert opinion will remain.
  • The critical issue with respect to safety assessment is the required or achievable level of confidence in the results of the analyses. Neither a 100 percent level of safety nor 100 percent confidence in the reliability of the assessments is possible. This is a fact that is true also for every other comparable technical undertaking, and it is important to assure that unique, unattainable requirements to the contrary are not placed on radioactive waste disposal.

  • The extensive technical efforts that are being put into specific, technical validation programs, centered around comparisons of calculations, experiments, and observations of analogue objects, should be complemented increasingly by further confidence-building measures. These include peer review, more formalized quality assurance, transparent documentation, large-scale demonstration experiments, and—of great importance—development of processes assuring open discussion among all involved parties.

Confidence and Trust

  • Confidence of the experts within the waste management community in the feasibility of safe geological disposal is documented in, for example, the collective opinions prepared by the OECD-NEA (NEA, 1991b). This confidence is not shared by sufficiently many members of the public and decision makers to allow rapid development of geological disposal projects.

  • Performance assessments alone do not engender sufficient confidence in safety. Demonstration of sound scientific work (e.g., by transparency, peer review) and admission of indirect evidence (e.g., from natural or man-made analogues) are also necessary.

  • The technical community now acknowledges the necessity of devising concepts and procedures explicitly aimed at raising public confidence. These include concepts for monitoring and retrieval of emplaced wastes and procedures for implementing repositories in a phased or stepwise manner. Maintaining a capability for reversibility of steps during the long processes leading to a closed and sealed repository is a major factor in enhancing public confidence.

General Conclusions

  • A phased or stepwise approach to implementation of repositories can offer a proper compromise between minimizing future burdens and maximizing future choice. Properly designed and sited repositories can

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×

Page 113

    have a long period of monitored controls and enhanced retrievability before being converted into their final closed state.
  • Adequately safe geological repositories can be implemented with various combinations of carefully selected host rocks, sites, and engineered barriers as long as decisions are taken commensurate with understanding. It will never be possible to demonstrate that any one site is the “safest” choice. Factors other than long-term safety will also determine or even dominate siting choices.

Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 85
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 86
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 87
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 88
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 89
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 90
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 91
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 92
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 93
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 94
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 95
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 96
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 97
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 98
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 99
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 100
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 101
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 102
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 103
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 104
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 105
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 106
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 107
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 108
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 109
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 110
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 111
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 112
Suggested Citation:" 6 Scientific and Technical Issues in Radioactive Waste Management ." National Research Council. 2001. Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges. Washington, DC: The National Academies Press. doi: 10.17226/10119.
×
Page 113
Next: 7 Alternatives to Geological Disposition »
Disposition of High-Level Waste and Spent Nuclear Fuel: The Continuing Societal and Technical Challenges Get This Book
×
Buy Paperback | $44.00 Buy Ebook | $35.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

Focused attention by world leaders is needed to address the substantial challenges posed by disposal of spent nuclear fuel from reactors and high-level radioactive waste from processing such fuel. The biggest challenges in achieving safe and secure storage and permanent waste disposal are societal, although technical challenges remain.

Disposition of radioactive wastes in a deep geological repository is a sound approach as long as it progresses through a stepwise decision-making process that takes advantage of technical advances, public participation, and international cooperation. Written for concerned citizens as well as policymakers, this book was sponsored by the U.S. Department of Energy, U.S. Nuclear Regulatory Commission, and waste management organizations in eight other countries.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!