Post-shutdown decay power and radionuclide inventories in the discharged fuels of HEU and potential LEU miniature neutron source reactors

Assessment of fission product and actinide content along with the time variation of decay power of discharged fuels of both HEU and LEU cores of MNSRs have been carried out for once-through cycle using the ORIGEN2 computer code. The results for the LEU core have been compared with the corresponding values for the current HEU core of MNSRs. For the HEU and the potential LEU UO2, U-9Mo discharged fuels, the ORIGEN2 computed isotopic and total activity values have been found in good agreement with the corresponding results obtained by using the WIMSD4 code. All three MNSR fuels show fission product dominated activity behavior for post-shutdown periods up to about 103 years during which, the total activity decreases by as much as 106 times. The residual actinide activity shows smaller variations as the three discharged fuels decay thru 106 years. The time variation of the decay power follows the same behavior as the corresponding total activity values during the fission product dominated period. A decrease from initial values of 154.76, 162.6,160.39 W to the final values 9.35 × 10−5, 2.1 × 10−3, 1.7 × 10−3 W has been found for the standard HEU, and potential UO2, U-9Mo LEU fuels correspondingly during this time. The standard HEU fuel shows smallest decay power values while the UO2 and U-9Mo LEU fuels have comparable values for time spans from 103 to about 106 years.