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 )−205−Synthesiology - English edition Vol.4 No.4 (2012) investigations from the land surface in the PIA selection phase) as designated by the Specified Radioactive Waste Final Disposal Act. The following items are extracted:(1) Erosion, deposition, and sea level change•It is necessary to avoid areas where the estimated erosion may become greater than the depth of burial, because the disposed material may become exposed to the surface.•It is necessary to consider the effects of relative sea level change in the areas where the flow or quality of underground water may change and may affect the containment function of the radioactive materials in the future, due to the changes in relative sea level by uplift, subsidence, or glacial sea level change.•It is necessary to consider the future stability of the tectonics that may affect the uplift and subsidence.(2) Seismicity•It is necessary to avoid the range to which the effect of the faulting may extend in areas that are found to have faults that were active in the Quaternary period, because the disposed material may be directly damaged due to the rupture along the fault.•It is necessary to consider the range to which the effect of the rupture may extend if there is a large fault on the surface or underground, even if there was no activity in the Quaternary period, because there may be possibilities of reactivation and induced dislocation of the fault.•It is necessary to consider the effect of the seismicity in areas where the seismicity may cause changes in the flow or quality of the groundwater that may affect the containment of the radioactive materials.•It is necessary to consider the future stability for the tectonics that may affect the seismicity.(3) Volcanic and magmatic activities•It is necessary to avoid the areas that were found to have Quaternary volcanoes, because there are possibilities that the disposed materials may become directly damaged or pushed up to the surface by eruptions.•It is necessary to avoid the areas where new volcanoes may emerge even if there are no Quaternary volcanoes, because there are possibilities that the disposed materials may become directly damaged or pushed up to the surface by eruptions.•It is necessary to consider the effect of volcanic and magmatic activities in the areas around the Quaternary volcanoes or in the range with possibilities of large-scale eruptions, where there may be changes in the ground temperature or in the flow or water of the underground water that may affect the containment function of the radioactive substances in the future.•It is necessary to consider the future stability of the tectonics that may affect the volcanic and magmatic activities.(4) Crustal fluid•It is necessary to consider the effect of the crustal fluid activities in the areas where there may be changes in the flow or quality of the underground water that may affect the containment function of the radioactive substances in the future, due to the activities of the crustal fluid.•It is necessary to consider the future stability of the tectonics that may affect the crustal fluid activities.(5) Mud volcano•It is necessary to avoid the areas where there are mud volcanoes that were active in the Quaternary period, because there are possibilities that the disposed materials may become directly damaged or be pushed up to the surface by eruptions. (Mud volcano: phenomenon where the mud with abnormally high pressure gushes out to the surface with groundwater, gas, or sometimes oil.)(6) Mass movement•It is necessary to avoid the areas in which the effect of creep and ruptures may extend and where the signs of large-scale mass movement become apparent in the investigation, because the disposed materials may become directly damaged by the creep and fault ruptures due to slope movement. (Mass movement: general term for the movement of materials on the ground surface, and it includes landslides and debris flow.) 4 Methodology for long-term forecast4.1 Basic thinkingAs mentioned earlier, in the safety assessment of geological disposal, it is necessary to make forecasts of the geological and climatic phenomena for several hundred thousand years into the future. For example, the assessment of seismicity is divided into short-term (immediately before~about one year) and long term (about 1~100 years) according to the time scale in question, and following this categorization, the time span for the forecast for geological disposal must be called super long-term. The methodology for seismicity assessment differs by the assessment period. The main methods for short-term assessment are geophysical, geodetic, geochemical, and hydrological observations. On the other hand, the main method for long-term assessment is the statistical inference from past history. In Japan, the long-term assessment of earthquakes was done actively since the South Hyogo Prefecture Earthquake (Great Hanshin Earthquake) in 1995, and the earthquakes at the plate boundary and along the major active faults can be assessed by the recurrent rate (Headquarters for Earthquake Research Promotion, http://www.jishin.go.jp/main/p_hyoka02.htm). However, as the 2011 Earthquake off the Pacific Coast of Tohoku (M9.0) was an “unexpected phenomenon”, it cannot be said that this long-term assessment functioned sufficiently in preventing the disaster. Moreover, if the current long-term forecast is extrapolated to super long-term, the uncertainty of whether the initial

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