Hazard Evaluation on Geologic Disposal of High-Level Radioactive Waste

Abstract

For a long-term safety assessment of geologic disposal of high-level radioactivewaste (HLW), it is necessary to evaluate the potential hazard of radionuclides discharged into the biosphere. Therefore, the result of the safety assessement may heavily depend on this evaluation basis for the potential hazard of radionuclides. The most frequently used measure of the potential hazard is the so-called Ingestion Hazard Index based on the Maximum Permissible Concentration (MPC). Recently, however, the International Commission on Radiological Protection gave the Annual Limits of Intake for workers (ALI). The two different bases of MPC and ALI for the potential hazard bring about considerably different results concerning the safety analysis on the geologic disposal. We derived the explicit form of the solution for the migration of the 4-member decay chain through the one-dimensional sorbing media with dispersion. By applying the solution, it was revealed that in a limited condition of geologic formation, the most dangerous radionuclide in the geologic disposal may be altered by a change of the evaluation basis for the potential hazard. It was also pointed out that the importance of the waste form performance may be much increased by the alteration of the evaluation basis from MPC to ALI