Tank Waste Retrieval, Processing, and On-site Disposal at Three Department of Energy Sites Final Report (2006) / Chapter Skim
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X Illustrative Example of the Recommended Decision-Making Process
X Illustrative Example of the Recommended Decision-Making Process
Pages 112-120
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From page 112... ...
The Illustrative Tank and Its Hypothetical Risk Profile EXAMPLE OF HOW TO STRUCTURE DECISIONS Risks associated with future release of radionuclides in ABOUT WHETHER A TANK IS SUFFICIENTLY CLEAN the tank heels vary over time and space, which is called the TO GROUT AND CLOSE "risk profile" to distinguish it from the narrower concept of The following is an example of a risk-informed, transpar- risks at a single "point of compliance," as required for estab lishing whether performance objectives have been met.1 ent decision-making framework for tank closure. This example illustrates how a single, consistent approach to Figure X-1 summarizes the illustrative example's risk prothinking about both waste removal to the maximum extent file for grouting and closing a tank that already has some soil practical and tank closure can lead to very different choices contamination around it, which will start to be cleaned up as from site to site and even from tank to tank within a single soon as the tank has been closed.
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From page 113... ...
where transport through the vadose zone flow is assumed to Location 3 is intended in this example to be the desig- be approximately vertical and flow in the saturated zone is nated "point of compliance." The associated figure for Loca- assumed to be approximately horizontal. Although these tion 3 shows that radionuclides released from the closed tank assumptions are not inconsistent with groundwater flow at would not reach that location until almost 400 years from the Savannah River Site, they are not representative of the now.
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From page 114... ...
The assumption is that the tank is still connected to 4Other potential or perceived drawbacks of using oxalic acid, such as the criticality concerns and downstream problems described in Chapter III, are 3For example, staff at Idaho National Laboratory indicated that they feel not considered in this example. 5Once a specific technology has been identified as the one worth waiting urgency to close their emptied high-level waste tanks because they cannot start to clean up very high dose rate soil contamination from earlier transfer for, a more specific set of risks can be added to the list that follows and pipe leaks until the tanks are closed.
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From page 115... ...
With some probability p, create some trade-offs between higher risks in the near term, however, there would be a release from the tank at the time and potentially lower risks in the long term, which is the of the washing, and this will increase potential exposures at time that is the focus of the performance objectives. These each location much earlier than in the case of immediate trade-offs can be assessed only by considering the full temgrouting.
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From page 116... ...
Since Illustration of Impact of Alternative Tank Options on the performance objectives are met at Location 3 (the desigRisk Profiles nated point of compliance) even under Option A, a compari To illustrate how the decision tree in Figure X-2 can actu- son of risks based solely on the ability to meet performance ally be used to provide a risk-based evaluation of the three objectives does not demonstrate a convincing case to stakealternatives, specific numerical assumptions have to be holders for the extra residual waste reduction with oxalic introduced in addition to those that generated the initial risk acid washing unless the risk-benefits trade-offs required by profile shown in Figure X-1.
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From page 117... ...
tree such as has been highlighted here. Of the three illustrative tank examples, Tank Z might be viewed as relatively more like the situation with Idaho National Laboratory's liquid high-level waste or sodiumDifferent Decisions Will Be Warranted for Different Tanks bearing waste tanks.
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From page 118... ...
NOTE: P.O. = performance objective.
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From page 119... ...
(Note that all three of these hypothetical tanks would cleanout, there may be unacceptable levels of risk at some meet the performance objectives with Option A -- immediate locations unless institutional controls are assumed to be closure -- if the point of compliance is Location 3.) Table X-3 effective for hundreds of years.
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From page 120... ...
Different end points for An example discussed in this chapter shows how waste removal and final tank closure can emerge for differ ent types of tank, sites, and waste types.
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