Abstract
The paper describes the outcomes of the experiments to study hydrogen and gaseous fission products accumulation during simulations of the wet damaged VVER-440 SNF storage in air-tight canisters with the water drained and no drying conducted. Physical and chemical processes occurring during the damaged oxide SNF storage in wet environment are discussed. The experiments were carried out in two stages: 1) preliminary soaking of fine fuel particles in water in an air-tight canister, 2) water draining and keeping the wet SNF in the air-tight canister. The experiments were conducted one after another using the same SNF canister and differing only in the SNF soaking temperature, i.e. 25 and 80 °С. The radionuclide release into the liquid phase during the SNF storage under water was studied. Uranium and cesium isotopic concentrations were found to reach steady values when the SNF is kept under water for more than a month. The kinetics of hydrogen and gaseous fission product accumulation in the gaseous phase during wet storage of the spent fuel in the air-tight canister with the water drained coincide for both experiments. The kinetics demonstrate an abrupt decrease of the hydrogen and gaseous fission product accumulation rate in 46 hours. The data obtained can be applied for development and verification of the damaged SNF behavior models during SNF storage in wet environment under radiolysis.
Highlights
Fire and explosion risk analysis is an important component of the safe handling of spent nuclear fuel and radioactive waste during all phases of the nuclear fuel cycle
Hydrogen is generated during storage of the SNF with leak-tight claddings in humid environment inside an enclosed volume only due to the radiolysis under γ-irradiation, and the hydrogen accumulation rate can be conservatively evaluated by numerical simulation
– Corrosion of the fuel induced by radiolysis products; – Other chemical interactions of accumulated radiolysis products with fission products (FP) in the fuel
Summary
Fire and explosion risk analysis is an important component of the safe handling of spent nuclear fuel and radioactive waste during all phases of the nuclear fuel cycle. The experiments demonstrated that a uranium release into the solution was much more intensive under irradiation than during leaching tests with H2O2 solutions of the same concentration without irradiation This is due to other radiolysis products participating in the UO2 oxidation (dissolution) processes under irradiation, for instance, OH· radicals (Eriksen et al 2012). With the fuel destruction still going, after a transient period concentrations of the radiolysis and leaching products (uranium, actinides, FPs) become steady in still water due to the re-precipitation of uranium UVI into the solid phase These processes govern stationary concentrations of the molecular radiolysis products and, the rate of the hydrogen and gaseous FP release into the gaseous phase. In the authors’ opinion, the above described behavior of the damaged SNF should be taken into account for the analysis of the experimental results
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