DOSE TO CEMENTITIOUS MATERIAL FOR MODERATOR EXCLUSION IN A SPENT NUCLEAR FUEL CANISTER DURING A REPOSITORY TIMEFRAME

摘要

One of the concerns regarding direct disposal of spentnuclear fuel (SNF) dual-purpose canisters (DPCs)currently in dry storage is criticality during disposal timeframes (e.g., 10,000 years or more). Preconditioning DPCswith appropriate filler materials (e.g., cementitiousmaterials, low-melting metals) before disposal couldprevent post-closure criticality by means of moderatordisplacement. However, potential radiolysis of the fillermaterial by ionizing radiation and release of reactivechemical species over repository time frames maynegatively impact the mechanical and chemical propertiesof the filler materials. Evaluation of the energy depositedin candidate filler materials by SNF radiation is essentialfor the calculation of radiolytic species. This paperprovides an evaluation of the total energy deposited bygamma and neutron radiation in a candidate filler materialover 10,000 years for a representative pressurized waterreactor SNF DPC. The canister is assumed to containidentical SNF assemblies with a burnup value of 55GWd/MTU, which is the bounding burnup value for morethan 95% of the SNF inventory discharged from 1968 to2013. The evaluated energy deposited per unit volume offiller material between 10 years and 10,000 years after fueldischarge is approximately 9.3E+23 eV/cm3. Gasproduction from radiolysis was not evaluated and may berevisited in future work. Radiolysis may be the principalgas generation mechanism for a cementitious system.