LONG-TERM SAFETY ASSESSMENT OF "RADON" TYPE FACILITY

Up till now multi-barrier systems are accepted as a basic approach for long-term radioactive waste isolation in near-surface and deep repositories. Performance assessment of the natural and hand-made (engineered) barriers on time is one of the main difficulties to evaluate reliability of the waste insulation due to the large number of possible scenarios and uncertainties to be considered. The International Atomic Energy Agency (IAEA) had launched the Coordinated Research Program on Improvement of Safety Assessment Methodologies for NearSurface Radioactive Waste Disposal Facilities (ISAM) at the end of 1997 with the purpose to provide a critical evaluation of the approaches and tools that are currently used in the long-term safety assessment of near -surface radioactive waste disposal facilities. This paper describes an application of the ISAM methodology to safety assessment of Russian near-surface disposal facilities of low - and intermediate-level radioactive waste (“Radon” facilities) ISAM PROGRAM: SCIENT IFIC SCOPE AND PROPOSED PROGRAM GOALS In practice low - and intermediate-level radioactive waste (LILW) are frequently disposed at near -surface repositories, such as vaults, trenches, pits, mounds, boreholes, so on. For any storage/disposal activity it is important to be sure that the activity is safe enough for the public and the Environment. Therefore, it is necessary to perform a safety assessment of the disposal facilities at each stage of their life cycle, which includes site selection, construction wor ks, operation, closure and post-closure periods. At present there are many methods and approaches to evaluate safety of radioactive hazardous facilities. The methods are used in different ways, for different purposes and conditions and may have a differen t level of confidence. An initial attempt to develop an improved confidence in safety assessment approaches was the IAEA Co-ordinated Research Program (CRP), which is called the Near-Surface Radioactive Waste Disposal Safety Assessment Reliability Study (N SARS) that was implemented from 1991 to 1995 [1]. NSARS focused on developing confidence in physical process models by conducting comparative studies of approaches for specific test cases that represented typical safety assessment problems. The new program, Implementation of Safety Assessment Methodologies (ISAM), is built on NSARS experience but places special emphasis on the implementation of safety assessment methodologies. The scope of the program includes the scientific and technical aspects related to long-term safety assessment of near-surface disposal facilities.