Technical Bases for Yucca Mountain Standards (1995) / Chapter Skim
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CHAPTER 2 - PROTECTING HUMAN HEALTH
CHAPTER 2 - PROTECTING HUMAN HEALTH
Pages 33-66
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From page 33... ...
assuming that policy makers ant! the public are prepared to accept that very low radiation doses pose a negligible risk.
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From page 34... ...
Most of what is known about effects of radiation on human health comes from studying people exposed to large doses of radiation. The empirical relationship between cancer induction and radiation dose appears linear at the high doses received by the atomic bomb survivors.
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From page 35... ...
Radiation ciamage to genes, chromosomes, or other vital organelles can be lethal to affected cells, especially dividing cells, which are highly radiosensitive as a class. The survival of dividing cells, measured in terms of their capacity to grow and divide, tencis to decrease exponentially with increasing close, 1-2 Sv generally sufficing to recluce the surviving cell population by about 50% (NRC, ~ 990a)
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From page 36... ...
Although the risks of certain cancers have been significantly elevated in some cohorts of radiation workers, especially those employed in the era preceding modern safety standards, no definite or consistent evidence of carcinogenic effects has been observed in workers exposed within present maximum permissible dose limits or in populations residing in areas of high natural background radiation. Hence, assessment of any cancer risks attributable to irradiation in such populations must be based on extrapolation from observations of the effects of exposure at higher dose levels.
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From page 37... ...
The lifetime risk of developing a fatal cancer from irradiation is estimated to be 5 x 10~2/Sv for a member of the general population. Nonfatal cancers, although projected to be pro~iucect more frequently than fatal cancers, were judged to contribute less to the overall health impact of irradiation because of their lesser severity in affecter!
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From page 38... ...
(°/0) Natural Radons 2.0 55 Cosmic 0.27 Terrestrial 0.28 Internal 0.39 ~ ~ Total Natural 3.0 82 Anthropogenic Medical X-ray diagnosis 0.39 Nuclear medicine 0.14 Consumer products 0.10 Occupational ~ 0.01 Nuclear fuel cycle ~ 0.01 Nuclear fallout < 0.01 Miscellaneous ~ 0.01 Total anthropogenic Total Natural ant} Anthropogenic 11 <0.3 0.63 < 0.03 < 0.03 < 0.03 18 3.6 100 a From NRC (199Oa)
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From page 39... ...
of cases per 100 per Svb Fatal cancers Nonfatal cancers Severe heredity disorders Total 5.0 1.0 1.3 7.3 a From ICRP (1 99 1 ~ b Numbers of cases, weighted for severity of their impacts on affected individuals over their lifetimes, attributable to low-level Radiation of a population of all ages. DEVELOPMENT OF RADIATION PROTECTION STANDARDS There is a worIc~wide interest in the development of radiation protection standards, including those for the disposal of high-level radioactive waste, and a consiclerable belly of analysis anti informer} judgment exists from which to draw in formulating a standard for the proposed Yucca Mountain repository.
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From page 40... ...
effective close for continuous or frequent exposure from radiation sources other than medical exposures. Countries that have considered national radiation protection standards in this area have endorsed the ICRP recommendation of 1 mSv per year radiation dose limit above natural background radiation for
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From page 41... ...
States, DOE, in Order 5400.5, and USNRC, in 10 CFR 20, have set the close stanciarc! for public exposure to ionizing radiation at 1 mSv per year above natural background]
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From page 42... ...
it is essential to define specifically how to calculate this risk, however, for otherwise it will not be clear what number to use to compare with the risk limit established in the standards. From the scientific perspective, the calculation of health risks should take into account all of the uncertainties involved in analyzing repository performance over very long time periods.
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From page 43... ...
IAEA ICRP Also includes . Safety Series 99 Publication 46 qualitative .
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From page 44... ...
inflow" limiting Includes other Individual risk releases to qualitative < 10~6/yr biosphere, based criteria (disruptive on inflow of events) natural alpha radionuclides SPAIN Individual dose Further Statement by <0.1 mSv/yr development Nuclear Safety Individual risk under study Council, 1987 |
From page 45... ...
PROTECTING HUMAN HEALTH UNITED No specific No time-frame ALARA to be KINGDOMC criteria for for quantitative used to the HEW but likely assessment extent practical application of specified and reasonable principles similar to existing objectives for L/ILW:< 1 0~6/yr target for individual risk from a single facility U.S. EPA Limits on Individual dose 1985 EPA 40 CFR 191 projected (over 1000 standard was (1985)
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From page 46... ...
Secretariat, based on national presentations made at a Joint Radioactive Waste Management Committee and Committee on Radiation Protection and Public Health
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From page 47... ...
value of the lifetime dose that an individual receives, calculated from a probabilistic distribution of close, is lxl 0~4 Sv, then that person's lifetime risk of a fatal cancer is Sxl o-6 (lxl 0~4 Sv x SxT o-2 fatal cancers per Sv)
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From page 48... ...
Thus, within the aquifer, there would be a plume of contaminated ground water stretching away from the vicinity of the repository. Near Yucca Mountain, there is no flowing surface water that might serve as a source in preference to ground water.
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From page 49... ...
nuclear regulations, as shown in Table 2-4. In acidition, the risk equivalent of the dose limits set by authorities outside the Uniter!
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From page 50... ...
d Annualized Individual R;ska 4x10-4 lXlo-6 3x10-4 1 .25xl As 11 1x10-5 lxlO-5 lxlO-s 7.5x10-6 Sxlo-6 2x1 o-6 2xlo-6 1 o-6 to 1 o-8e 3x 10-4 a Assumes a lifetime risk of Sxl o-2 per Sievert (Sxl 0~4 per rem)
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From page 51... ...
b Neglects consideration of ALARA radiation protection measures; actual doses to members of the public from all pathways are generally far below the dose limit. c These levels of the standard are consistent with EPA's ground water protection strategy.
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From page 52... ...
In the case of Yucca Mountain, these individuals presumably would live in the near vicinity of the site and would! potentially be exposed to radiation through the use of contaminated ground water.
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From page 53... ...
Based on cautious, but reasonable, assumptions, the group would include the persons expected to be at highest risk, would be homogeneous in risks, and would be relatively small. The critical-group risk calculates} for purposes of comparison with the risk limit established in the stanciarc!
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From page 54... ...
In the present anti near future, these persons are real; that is, they are the persons now living in the near vicinity of the repository that lies in the direction of the flow of the ground water plume of raclionuclicles that would occur far in the future. The expected containment capability of an undisturbed]
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From page 55... ...
We recommend in Chapter 3 that compliance assessment be conducteci for the time when the greatest risk occurs, within the limits imposed by long-term preclictability of both the geologic environment and the distribution of local and global populations. IndeecI, the 10,000-year limitation might be inconsistent with protection of public health.
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From page 56... ...
Although current generations are assumer} to have benefited from activities, such as electricity production or national defense programs that have causer] radioactive wastes to accumulate, far future generations will not benefit clirectly, but might be exposed to risks when any radioactive materials eventually escape the proposed repository.
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From page 57... ...
The question posed by Congress is important because limiting individual dose or risk lions not automatically guarantee that adequate protection is provider] to the general public for all possible repository sites or for the Yucca Mountain site in particular.
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From page 58... ...
states that: Finally, it must be recognized that derivation of risk estimates for low doses and dose rates through the use of any type of risk mode] involves assumptions that remain to be validated.
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From page 59... ...
Thus the possibility that there may be no risks from exposures comparable to external natural background radiation cannot be ruled out. At such low doses and dose rates, it must be acknowledged that the lower limit of the range of uncertainty in the risk estimates extends to zero.8 59 The doses to global populations involved in gaseous release from Yucca Mountain are likely to be well below the mSv range noted in BEIR V
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From page 60... ...
We suggest the risk equivalent of the negligible incremental dose recommended by the NCRP as a reasonable starting point for cleveloping consensus in a rulemaking process. For example, the average dose to a member of the global population from exposure to i4C from the repository 9 Where authors use "negligible dose" or "negligible risk" the teens should be understood as increments to the unavoidable background radiation.
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From page 61... ...
It should be feasible to determine a spatial distribution of potential concentrations in ground water or air and a spatial distribution of individual doses ant! risks, employing the same types of exposure assumptions used for calculating doses ant} risks to members of a critical group (see Chapter 3~.
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From page 62... ...
inclividual-risk protection scheme. Spatial Gradient in Risk -An alternative approach that does have a technical basis is consideration of the spatial distribution of individual risks near the critical group, at the distant future time when the critical-group risk is highest.
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From page 63... ...
For the simpler task of adequately characterizing the exposure scenarios leacling to calculation of risks to a critical group, we have concluded that a feasible procedure can be developed using known distributions of physical and chemical parameters ant! defensible assumptions on lifestyles; in other worcis, there is a reasonable technical basis for a critical-group calculation.
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From page 64... ...
Therefore, a population standard alone is insufficient to protect the population most at risk and, probably for this reason, 40 CFR 191 contains a parallel individual standard. Also, as discussed earlier in this chapter, assessing compliance with a standard designed to protect the global population involves highly uncertain calculations because of the extremely low incremental doses to which large numbers of persons may be exposed.
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From page 65... ...
We define risk as the expected value of the probabilistic distribution of health effects. The distribution of health effects is derived from a distribution of dose and the expected health effects per unit dose.
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