Radioactive waste is classified and disposed of in a repository, which is developed at suitable depth depending on its character. Radionuclides in the radioactive waste disposed of in the repository migrate with groundwater and reach the biosphere. Therefore, the disposal facility should be developed in a geologic formation where the flow rate of the groundwater is slow or where there is little or no groundwater. In addition, to restrain leakage of radionuclides from the waste, the waste should be surrounded with an artificial barrier.
Safety assessments should be conducted for appropriate periods depending on the half-lives of the radionuclides in the waste. Waste for geologic disposal contains radionuclides with very long half-lives. Therefore, it is possible that the safety assessment for geologic disposal should be conducted for several hundred thousand years. Chemical conditions are considered for the assessment. If necessary, a change in the groundwater system during the period of assessment is also considered. The safety assessments support decision making form the core of a safety case in demonstrating safety to relevant stakeholders.
To support discussion of safety provision between members, the Integration Group for the Safety Case (IGSC) was established in 2000 by the NEA Radioactive Waste Management Committee (RWMC). The IGSC is the main technical advisory body to the RWMC on deep geological disposal, especially for long-lived and high-level radioactive waste. A safety case is a collection of safety evidence and arguments that demonstrate the safety of a management process or a facility throughout its lifetime. The expertise, approach and strategies required for the development of assessment scenarios, the management of uncertainties and the associated risk evaluations in compiling and presenting safety cases for different disposal facilities share some commonalities. The IGSC has three subgroups – Clay Club, Salt Club and Crystalline Club – to discuss the safety cases for each geologic formation. In addition, the Expert Group on Operational Safety (EGOS) was established to discuss the safety cases during the operational phase of a disposal facility.
