Analysis of producing 238Pu as a byproduct in an MSFR

Abstract 238Pu can be used as the heat source in radioisotope thermoelectric generators for deep space exploration, while it is currently in shortage because of the suspension of 238Pu production in the USA and Russia for many years. Two possible scenarios for the production of 238Pu as a byproduct in a molten salt fast reactor (MSFR) are assessed in this work. For the first scenario, the MSFR is started with low-enriched uranium (LEU), and neptunium is extracted from the fuel salt and then fed into the fertile salt of thorium for high-purity 238Pu production. For the second scenario, the ignition material for the MSFR is 233U, and highly purified 238Pu is produced by directly extracting plutonium from the fuel salt. The simulated results indicate that on average 15.48 kg 238Pu with the quality (ratio of 238Pu mass to total mass of Pu isotopes) larger than 98.6% can be produced per year during a 60-year operation for scenario I. In parallel, 8.31 kg 238Pu with the quality larger than 91.9% can be produced annually for scenario II. The 238Pu production has a small impact on the neutronic performance of the core for the two scenarios except that bred 238U is reduced by 922 kg for scenario I and by 261 kg for scenario II during the 60-year lifetime. The 238Pu production has a very tiny effect on the radiotoxicity of discharged nuclear fuel for scenario I, while it can reduce the total radiotoxicity of discharged nuclear fuel by three times for scenario II.