Hierarchical Holographic Modeling for Risk Identification in Complex Radioactive Waste Disposal Systems, 20-R9567

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Principal Investigators
Olufemi Osidele
Osvaldo Pensado
Jude McMurry
Sitakanta Mohanty

Inclusive Dates:  10/03/05 – 05/03/07

Background -  Risk analysis models for radioactive waste disposal systems generally offer limited flexibility to accommodate changes in regulations, design, and scientific knowledge. One reason for this limitation is the prior screening of risk factors whereby plausible risk scenarios are excluded because their likelihood of occurrence or perceived consequences are low. In addition, several alternative conceptual models are often considered in integrating the complex physical and chemical processes associated with radioactive waste disposal systems. Thus, whenever regulatory or technical criteria change, model revision takes considerable effort in reassessing the risk scenarios and conceptual models. Moreover, the utility of the revised risk analysis models — especially for prioritizing subsequent regulatory and technical activities — may not be determined until revisions are complete and extensive analyses are conducted.

Approach - The goal of this project was to develop a capability for identifying the important technical aspects of risk analysis models at the conceptual stages. This would potentially reduce efforts expended in revising risk analysis models and provide information to support prioritization of regulatory and technical program activities. In this project, a decision-analysis framework was developed, implemented, and tested in the MATLAB® computing environment. The framework integrates three aspects of safety assessments for radioactive waste disposal systems — technical issues, risk factors, and conceptual models. Technical issues are focal topics for the design, implementation, and regulation of the system. Priorities for decisionmaking are set in terms of the technical issues. Conceptual models include the features, events, and processes believed to govern the long-term behavior of the disposal system and are assumed to include all related technical evidence. Derived from expert judgment and stakeholder opinions, risk factors represent multiple perspectives on the external threats and internal vulnerabilities that create the perception of risk. In essence, therefore, the decision-analysis framework integrates risk perception with technical evidence.

Accomplishments - Numerical experiments were conducted to test the effectiveness of the decision-analysis framework on a conceptual nuclear waste repository situated in geologic and climatic conditions similar to northern America and Europe. Matrix configurations were designed and analyzed to study the relative dominance of the conceptual model and the risk factors in ranking the importance of the technical issues. Comparison of rankings from multiple expert inputs identified fundamental differences of opinions about risk that could influence priorities for subsequent program activities. Overall, the experiments successfully demonstrated that the framework effectively integrates risk perception (via the risk factors) with technical evidence (via the conceptual model) in judging the importance of technical issues that are considered in risk assessments for radioactive waste disposal systems. This research has led to presentations at two international conferences, an invitation for publication in the international journal Integrated Assessment, and another internal research project now in progress to explore data fusion methods for threat detection in nuclear materials transportation.

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