Decay heat analysis of MNSR reactor core using ORIGEN-2 code

Abstract

The knowledge of the decay heat of nuclear fuel is necessary for performing the reactor safety analysis, determining the heating load in fuel pools, shielding requirements on fuel discharge and transport routes when irradiated reactor fuel is transferred from the reactor, via some intermediate storage location, to the final disposal or the chemical reprocessing plant. In this study, analysis of the decay heat parameters of the Miniature Neutron Source Reactor (MNSR) including radioactivity, decay heat and the isotopic mass variation with time since reactor shutdown for the potential Low Enriched Uranium (LEU) (UO2-Zircaloy and U3Si-Al) and the standard Highly Enriched Uranium (HEU) (HEU-Al4) cores has been performed using the ORIGEN-2 code. For this purpose, a new one-group cross-section data base of the ORlGEN-2 computer code for the MNSR with LEU and HEU fuels has been developed using the MCNP-4C code. The variation of fission products, actinides and daughters and activation products with post shutdown time for the standard core and the potential LEU cores have been considered in the analysis of the decay heat power resources. It was found that, all the three types of MNSR fuels show close agreement in the total decay heat, which is mainly due to the fission products. This behavior continued for about 1.0E05 days. After this time, the fission products decay heat became comparable with the corresponding actinides decay heat in which the standard HEU UAl4-Al fuel showed the smallest decay heat values while the potential LEU-UO2 fuel had the highest decay heat followed by the LEU-U3Si fuel. The time variation of the total radioactivity followed the same behavior as the corresponding total decay heat. Finally, the relative decay heat as a function of reactor shutdown time has been also computed by various analytical functions and the results compared with the ORIGEN-2 code for the three types of fuels.