4:30 PM - 4:45 PM
[HCG27-05] Selection of high-level radioactive waste disposal site in Japan
★Invited Papers
Keywords:High-level radioactive waste, Geological disposal, Site selection, Groundwater scenario, Volcanics, Uncertainty
I pointed out problems with the selection of high-level radioactive waste disposal site in Japan with a paper entitled “What is indispensable studies to achieve the disposal of high-level radioactive waste in Japan?” at this session of JpGU in 2018.. I said that we cannot avoid uncertainties in groundwater scenarios even though direct scenarios by fault movement, volcanic activity, uplift and erosion, and so on are cleared, so we need to find host rocks with fewer fractures as water pathways. We also need to select host rocks on which present nondestructive prospecting methods are applicable to find fractures or to develop new methods that could be used to difficult rocks. This view should have been reflected in the “Scientific Characteristic Map” published in July 2017, but this map is for the direct scenario and does not face the groundwater scenario head-on. Then, in 2020, based on the proposals from two municipalities in Hokkaido, a literature search, which is the first stage of the selection of the disposal site survey, was started. This started without any geological considerations for the groundwater scenario mentioned above, as far as I know. Although I have not directly observed the local geology, I would like to point out problems related to groundwater scenarios that would be encountered in the future from the geological literature of the area and my research experience of similar geology.
Geological sheets with a scale of 1:50000 of the two municipalities show that these areas are underlain by Miocene volcanics, such as lava and hyaloclastite intruded by volcanic dikes. The former two are generally very heterogeneous and their properties widely vary from place to place. They also have openings so that may be highly permeable. Volcanic dikes are generally permeable because of cooling joints, and their presence is not easy to detect with current nondestructive technology. These features provide conditions that make it very difficult to evaluate groundwater scenarios.
According to Japan's policy, the selection of high-level radioactive waste geological disposal sites will be carried out step by step. If the suitability as a disposal site is clearly lacking, it would be excluded from the suitable site during the investigation stage, but if it is unclear, the investigation would proceed to the next stage. If the survey is conducted on areas with complex geology and strong inhomogeneity, it is easy to assume that the suitability cannot be judged from the survey results at one stage and then proceed to the next stage. However, the local problems with the groundwater scenario mentioned above do not seem to be so easy to solve. In other words, it is necessary to keep in mind that no matter how far the investigation is conducted, it may not be possible to judge the suitability as a disposal site in a socially acceptable manner.
Geological sheets with a scale of 1:50000 of the two municipalities show that these areas are underlain by Miocene volcanics, such as lava and hyaloclastite intruded by volcanic dikes. The former two are generally very heterogeneous and their properties widely vary from place to place. They also have openings so that may be highly permeable. Volcanic dikes are generally permeable because of cooling joints, and their presence is not easy to detect with current nondestructive technology. These features provide conditions that make it very difficult to evaluate groundwater scenarios.
According to Japan's policy, the selection of high-level radioactive waste geological disposal sites will be carried out step by step. If the suitability as a disposal site is clearly lacking, it would be excluded from the suitable site during the investigation stage, but if it is unclear, the investigation would proceed to the next stage. If the survey is conducted on areas with complex geology and strong inhomogeneity, it is easy to assume that the suitability cannot be judged from the survey results at one stage and then proceed to the next stage. However, the local problems with the groundwater scenario mentioned above do not seem to be so easy to solve. In other words, it is necessary to keep in mind that no matter how far the investigation is conducted, it may not be possible to judge the suitability as a disposal site in a socially acceptable manner.