Gamma and neutron dose rates on the outer surface of the nuclear waste disposal canisters

摘要

Gamma and neutron dose rates on the outer surface of the new versions of the canisters designed for the final disposal of the Finnish spent nuclear fuel have been calculated with the MCNP4A code based on the Monte Carlo technique and with the MARMER code, which applies the standard pointkernel method. The gamma dose rates calculated by the programs are in a satisfactory agreement. Two canister types, one for hexagonal VVER-440 fuel assemblies from the Loviisa nuclear power plant (IVO canister) and the other for square BWR fuel bundles from the Olkiluoto nuclear power plant (TVO canister) have been studied. The canister types are quite similar. The maximum gamma dose rate on the outer surface of the IVO canister designed to contain 11 VVER-440 fuel assemblies is about 250 mSv/h, when the discharge burnup of the spent fuel is 42 MWd/kgU and the cooling time 20 years. For the TVO canister loaded with 11 BWR fuel bundles having the discharge burnup of 45 MWd/kgU and having cooled for 20 years, the corresponding value is about 150 mSv/h. In both cases the average dose rates are about one half of the maximum values. The neutron dose rates around the canisters are much lower than the gamma dose rates, typically less than 10 mSv/h. (orig.) (17 refs.). (Atomindex citation 28:038097)