Risk and Decisions About Disposition of Transuranic and High-Level Radioactive Waste (2005) / Chapter Skim
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4 A Risk-Informed Approach: Procedures and Criteria for Risk Assessment to Support an Exemption Process
4 A Risk-Informed Approach: Procedures and Criteria for Risk Assessment to Support an Exemption Process
Pages 87-112
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From page 87... ...
4.1 USING RISK ASSESSMENT The general methods of risk assessment for environmental concerns are well established in numerous earlier publications. These include a series of reports on risk assessment methods and processes by the National Research Council (NRC, 1983, 1994a, 1996)
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From page 88... ...
risk characterization. The definition includes quantitative risk assessment, which emphasizes reliance on numerical expressions of risk, qualitative expressions of risk, and characterization of the attendant uncertainties (see Appendix A for a more detailed definition from the NRC, 1983)
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From page 89... ...
When alternative conceptual models are considered, data collection and analysis may also be targeted to allow evaluation of which model or models are most supported by the data. If more than one model provides a similar quality of fit to the observations, risk estimates should be made from the multiple models.
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From page 90... ...
Specifically, the risk analysis conducted in support of an exemption application must be as follows: 1The term "stakeholder" here includes the interested and affected public.
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From page 91... ...
The methods used in each step must be consistent with current scientific knowledge and practices. If the state of science has competing theories, the risk analysis must consider appropriate alternative approaches, rather than choosing one, unless it can be demonstrated that such a simplification would
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From page 92... ...
complete removal of all HLW for disposal in a deep geologic repository, and (2) a specific plan for how much of tank residuals may be left in a tank and any associated form of stabilization (e.g., grouting)
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From page 93... ...
At the same time, the complexity can be a barrier to gaining confidence and trust in any recommendations that may purportedly be justified by the risk analysis. The approach described here embraces the principle that analytical detail and complexity should be limited to the minimum necessary to distinguish the best option or options.2 If the relative risks and trade-offs can be established with a relatively simple analysis that is nonetheless grounded in empirical data, then this simpler analysis will be easier to explain and easier for non-analysts to understand.
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From page 94... ...
Also, considerable technical sophistication is needed to produce even a "simple" analysis that can effectively guide the addition of detail. The critical point is that the quantitative analysis be initiated with minimal complexity and that the complexity be increased gradually, as the need for it is determined and as all participants gain understanding of the key elements of the analysis that are driving its risk estimates.3 It is also possible that the forms of complexity resulting from this iterative process will be quite different from the forms of complexity that would have been added if analysts were to strive to incorporate a final degree of complexity from the outset.
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From page 95... ...
developed in ad vance of any analysis, · risk computations performed at the minimal level of complexity necessary to separate options according to the decision criteria, · risk computations performed simulating competing views of the physical processes and using ranges of parameter values that re flect the state of science, and · uncertainties explicitly explored and retained unless they are demonstrated not to affect the relative ranking of the disposition options.
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From page 96... ...
This capability can enable modelers and non-modelers alike to gain hands-on familiarity with how the risk model responds to 5A recent example where a decision support system was integrated into an iterative and participative public decision process like the risk analysis process described in this chapter can be found in Passell et al.
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From page 97... ...
A decision support system is not essential for a good iterative and participatory process, but it can be a valuable supplement if it is created with a proper understanding of its role and limitations, and if appropriate software development resources are allocated. its elements are familiar and that the whole process is compatible with CERCLA.6 However, the following steps were devised specifically to illustrate a process for the transuranic and high-level waste disposition decisions that DOE may wish to have considered in an exemption application.
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From page 98... ...
If DOE attempts to suggest that risks are "acceptable" for an alternative, it puts itself in the impossible position of having to prove that its risk calculations are precise and that uncertainties are not large. Under a comparative approach, DOE and stakeholders need only come to a consensus about which alternative, if any, presents a distinct improvement over the others in terms of the overall balance among decision criteria.
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From page 99... ...
What are the general types of alternative disposition options? These questions must be considered in advance, and those seeking the exemption must be prepared to discuss them with stakeholders before initi ating any analyses or defining a single specific alternative that it wishes to have considered as an exemption.
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From page 100... ...
In New Mexico, DOE funds supported the Environmental Evaluation Group, which provided technical oversight of the Waste Isolation Pilot Plant. To enable states and American Indian tribes that are affected by the federal high-level radioactive waste disposal program to participate in the activities prescribed by the Nuclear Waste Policy Act of 1982, including review and oversight, the act requires that DOE grant funds to the affected governments.
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From page 101... ...
Having access to experts, designated representatives who can dedicate time to following DOE's environmental management of a site, and even the funds to hold public meetings makes for more meaningful participation by the affected parties. Meaningful participation makes a participatory, risk-informed decision process, such as is recommended here, more effective.
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From page 102... ...
However, the process is a gradual one, and the next step involves only a relatively simple set of risk calculations, which can be characterized as a scoping analysis, before consultation occurs again.
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From page 103... ...
Sorption on these colloids facilitates transport rather than inhibiting it. Contami nant transport in solution using K for retardation and colloidal d transport represent competing models of the dominant physical processes that affect risk estimates from groundwater pathways.
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From page 104... ...
· Perform scoping risk assessment and sensitivity studies to identify critical parameters requiring the greatest attention. The risk calculations at this stage may be simpler, principle based analyses with less detail than may ultimately be required, and their main purpose is to identify the most important needs for additional data development and additional model complex ity.
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From page 105... ...
Review here need not be in fault values has the drawback of obscuring rather than highlighting the importance of the data gap to obtaining a sound risk estimate. At this scoping stage, the goal is to identify information to collect for the risk assessment, not to produce an actual risk estimate.
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From page 106... ...
When presenting results of this scoping analysis, all of the data gaps must be listed, along with the range of possible values explored and a summary of how much the risk estimates under each disposition alternative were altered as a result of varying the input over that range of values. The impact on results of using competing representation of physical processes must also be presented.
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From page 107... ...
As with all the steps, an external review of the output of this step would build confidence before moving to the next step, which is to use these new data in revised risk calculations. In such a review, experts would be en gaged to comment on the quality of the new data, and whether they sufficiently meet the objectives that were established in the scoping step.
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From page 108... ...
In fact, it may be most illuminating to continue to produce separate results using alternative conceptual models, if this model uncertainty could not be resolved as a result of the additional data collection. With regard to remaining uncertainties in the parameters, best es timates must now be developed, and sensitivity analysis per formed again.
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From page 109... ...
Often a given uncertain parameter will affect risk estimates for each of the alternatives under con sideration in a similar manner. It is important that the summary of uncertainties be done in a comparative manner, indicating how they affect the differences in risks estimated for the disposition alternatives.
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From page 110... ...
Step 6. Finalize Decision Risk estimates will never be completely free of uncertainty or even controversy.
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From page 111... ...
will tend to cause resistance and unintended consequences of an exemption process. Any meaningful decision process that involves stakeholders such as the risk-informed process recommended here, will require finding ways to implement an exemption process in the least disruptive manner possible with regard to existing laws, regulations, and agreements.
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From page 112... ...
112 RISK AND DECISIONS ABOUT TRU AND HLW tively the risk-informed approach recommended here. Specifically, they should provide for a formal, well-structured exemption process, institute technical review of the risk analysis independent of the agency producing the analysis, give decision-making authority to an agency outside DOE, and ensure that sufficient resources are reliably available for regulators, tribal nations, and stakeholders to participate meaningfully in the process.
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