Vol.4 No.4 2012

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Research paper : Safety assessment of high-level nuclear waste disposal in Japan from the standpoint of geology (T. Yamamoto )−204−Synthesiology - English edition Vol.4 No.4 (2012) the area where the disposal facility will be built is stable for a long period. The Specified Radioactive Waste Final Disposal Act requires the disposal site candidates that “there is no record of significant changes in the strata by natural phenomena such as earthquake, volcanic eruption, uplift, erosion, and others” and that “it is expected that significant change in the strata is not likely to occur due to such natural phenomena in the future”. In geological disposal, it is important that the HLR waste is isolated in a stable geological environment where the effects of natural phenomena such as earthquakes will not extend. To do so, it is required to conduct a comprehensive and quantitative assessment on what kind of external impact there will be on the geological disposal system, through the long-term changes in the geological environment over a hundred thousand years. At the Research Core for Deep Geological Environments (formerly Research Center for Deep Geological Environments), AIST organized the knowledge necessary to investigate the safety regulations pertaining to the geological disposal, at the Waste Safety Subcommittee that was set under the Nuclear and Industrial Safety Subcommittee, Advisory Committee on Energy and Natural Resources, which is an advisory panel for the Minister of Economy, Trade and Industry.Figure 2 shows the correlation diagram that identifies the phenomena that may affect the geological disposal system as external disturbances in Japan, based on the international FEP list for geological disposal created by the Nuclear Energy Agency, Organisation for Economic Co-operation and Development (OECD/NEA)[4]. The FEP is categorized into those with the geology-related FEPs that arise from the internal energy of earth “F1.2.01 Tectonic movement and orogeny”, and the climate-related FEPs caused by the solar incident energy “F1.3.01 Climate change, global”. In Fig. 2, these are arranged on the left and right, and the disposal system domain is shown in the lowest part. The whole process is seen as a series of phenomena (scenario) where one event undergoes a process to cause the next event (as shown by the arrows), and this in turn causes the next process and event. The FEPs in parenthesis that are not joined by the cause-effect arrows are eliminated from the investigation since their effects can be ignored in Japan.The Research Center for Deep Geological Environments investigated the geological and climatic phenomena that may affect the aforementioned disposal system, and in 2007 publicized the “Technical Report on the Features for Preliminary Field Investigations of HLW Geological Disposals” (http://www.gsj.jp/GDB/openfile/files/no0459/0459index.html)[5]. This indicates the assessment items and investigation methods necessary for the security of the closed disposal site, in the investigations (various Fig. 2 Geological and climatic processes in Japan Islands using international FEPs database of OECD/NEAArrows indicate the effecting direction. FEPs in [ ] means ignorable ones in Japan Islands. After Yamamoto and Kodama[4]F1.2.07 Erosion and sedimentationF1.2.05 MetamorphismF1.2.03 SeismicityF1.2.04 Volcanic and magmatic activityF1.2.02 Deformation, elastic, plastic or brittle[F1.2.09 Salt diapirism and dissolution][F1.3.06 Warm climate effects]F1.3.02 Climate change, regional and localF1.3.01 Climate change, globalF1.2.01 Tectonic movements and orogenyMantle circulation and ascending plumeInternal energy of the earthIncoming solar energy[F1.3.05 Glacial ice sheet effects,local][F1.3.04 Periglacial effects]F1.2.06 Hydrothermal activityF1.3.03 Sea level changeF1.2.10 Hydrological/hydrogeological response to geological changesF1.2.10 Hydrological/hydrogeological response to geological changesDisposal system domainF1.3.07 Hydrological/hydrogeological response to climate changesF1.2.08 Diagenesis

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