Geological Disposal of High Level Radioactive Wastes in Japan and Earth Science

Abstract

About one fourth of the total production of electricity in Japan was generated in nuclear power plants in 1985. Now, the disposal of radioactive wastes is a major environmental problem. The Japanese islands locate in the tectonically active zone around the Pacific Ocean. Four major lithospheric plates collide or scratch each other in or near Japan. Major earthquakes often shake the Japanese islands where active faults distribute densely. Eruption of volcanoes and hot springs indicate high geothermal activity.However, many observations indicate that shocks of earthquakes are much milder at the depth of some hundred meters than at the ground surface. Some areas even in Japan have been free from volcanic activities during the last tens of millions years.High density of fractures in rocks due to past tectonic disturbances are more serious problems for the isolation of radioactive wastes, as some of fractures might provide pathways for hazardous contaminated water. Major efforts should be paid to develop precise techniques which allow us three dimensional mapping of underground fractures with no hurt to rock body which provides the natural barrier against the migration of radionuclides.The long-term performance of the waste isolation system should be estimated adequately. The knowledge of recent tectonic activities (Quaternary tectonics) and the study of natural analogues provide a basis for long-term prediction of the stability of the burial site.