Application of a Comprehensive Sensitivity Analysis Method on the Safety Assessment of TRU Waste Disposal in JAPAN
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0985-NN03-21
Application of a Comprehensive Sensitivity Analysis Method on the Safety Assessment of TRU Waste Disposal in JAPAN Takao Ohi1, Hiroyasu Takase2, Manabu Inagaki1, Kiyoshi Oyamada3, Tomoyuki Sone1, Morihiro Mihara1, Takeshi Ebashi1, and Kunihiko Nakajima4 1 JAEA, 4-33 Muramatsu, Tokai-mura, Ibaraki-ken, 319-1194, Japan 2 Quintessa K. K, Queen's Tower A 7-707, 2-3-1 Minatomirai Nishi-ku, Yokohama, Kanagawaken, 220-6007, Japan 3 JGC Corporation, 2-3-1 Minatomirai Nishi-ku, Yokohama, Kanagawa-ken, 220-6001, Japan 4 NESI Inc., 4-33 Muramatsu, Tokai-mura, Ibaraki-ken, 319-1112, Japan
ABSTRACT A comprehensive sensitivity analysis method has been developed with the aim of providing quantitative information in an efficient manner. This methodology is composed of the following two components: (1) a statistical method with random sampling of independent parameters, which identifies important parameters and extracts threshold values of parameters and/or combinations yielding a ‘successful condition’ where maximum dose does not exceed a target value, (2) A nuclide migration model that as far as possible incorporates a comprehensive set of phenomena occurring within the repository. This approach was applied as part of a safety assessment of the geological disposal of transuranic (TRU) waste in Japan (TRU-2). It was shown that the concept of TRU waste disposal is robust from the point of view of safety. INTRODUCTION Organisation for Economic Co-operation and Development / Nuclear Energy Agency (OECD/NEA) have set out the activities that are necessary to obtain an adequate evaluation of the safety of a radioactive waste repository [1]. These include verification and validation of models, quality assurance, critical reviews and international cooperation. However, this report did not give specific consideration about how to present and explain the results of safety assessments in a clear and comprehensive way to decision-makers and the public. OECD/NEA have emphasized the importance of building a safety case for the development of confidence and stated that “an important aspect of strategy is management of uncertainties”[2]. Uncertainties can be evaluated deterministically by changing parameter values. In past assessments the influence of them has been evaluated by, for example, comparing results of a reference case with results of alternative cases [3, 4]. In such evaluations of uncertainty, the logic of parameter selection and the adequacy of combinations need to be explained and justified to provide confidence in the assessment. To complement such deterministic evaluations, statistical approaches have been adapted using probability density functions to represent possible parameter variations and combinations [4]. However, in such statistical approach, in addition to probabilistic estimates, there is a need to identify key safety parameters and to extract quantitative conditions to further enhance the understanding of disposal safety.
Such an approach, the Strategic Partitioning of Assessment Ranges and Consequence
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