Assessing the PRISM reactor as a disposition option for the British plutonium stockpile

Abstract The United Kingdom considered using the PRISM sodium-cooled fast reactor as a disposition option for its civilian plutonium from reprocessed MAGNOX and Advanced Gas-cooled Reactor spent fuel. This article assesses the plutonium disposition capabilities of the PRISM reactor for the U.K. stockpile. The article first describes how the stockpile was created. It then provides a simulation of reactor burn-up, the resultant isotopic compositions of PRISM spent fuel are simulated and the dose rates of that fuel. Dose rates greater than 1 Sv/h at 1 meter from the fuel were assumed to establish “proliferation resistance” and would constitute a radiation barrier to proliferators. Results suggest that the U.K. stockpile could be irradiated to that proliferation resistance target in 31.3 years, using two 840 MWth PRISM cores operating at a 30 MWd/kgHM burnup rate. By the time all the U.K. plutonium has been irradiated, however a fraction of the PRISM spent fuel will have decayed below the proliferation resistance target. Thus, even though in 2019 PRISM was removed from consideration by the U.K. government because it is not expected to be available for that use for another 20 years, this paper concludes that should PRISM become available earlier it would still be a poor choice for plutonium disposition.