Radionuclide migration from the geological repository of the RBMK-1500 spent nuclear fuel in crystalline rocks 1. The concept of repository

The international consensus has it that spent nuclear fuel (SNF) and long-lived high level radioactive wastes are best disposed of in geological repositories, using a system of engineered and natural barriers. Due to the danger of exposure arising from long-lived radionuclides to humans and the environment, SNF is not allowed to be disposed of in near-surface repositories. Performing the assessment of radionuclide migration (an integrated part of repository safety assessment) a description of the disposal system is required. The generic repository concept for RBMK-1500 SNF disposal in crystalline rocks in Lithuania is presented in this paper. The proposed repository concept is based on the KBS-3 concept developed by SKB for the disposal of PWR and BWR spent nuclear fuel in Sweden. The generic repository concept for SNF disposal in crystalline rocks in Lithuania foresees the SNF disposal in the parallel horizontal emplacement tunnels with a diameter of 1.85 m and length of 250 m at a depth of 300-500 m. Based on thermal calculations, in case of the distance of 1.2 m between the canisters and the distance of 40 m between the tunnels, the repository would cover an area of appr. 0.4 km2. The preliminary data on the copper canister for RBMK-1500 SNF are 1050 mm in diameter and 4070 mm in length, and it could hold 32 RBMK- 1500 SNF half-assemblies. For the disposal of spent nuclear fuel from the Ignalina Nuclear Power Plant, 1400 canisters would be required. For the isolation of the canisters, bentonite with a thickness of 0.35 m is proposed. For the backfilling of the main tunnels, shafts and ramp, a mixture of crushed rock and bentonite is selected. (author)