Evaluating the BN-800 as a Reactor-Based Option for Plutonium Disposition

In 2000, Russia and the United States concluded the Plutonium Management and Disposition Agreement to dispose an amount of 34 tons excess weapon plutonium. Over the last decades, different options to render this plutonium unusable for weapons were discussed. Currently, both states plan to use the plutonium as mixed oxide fuel (MOX) in commercial nuclear reactors. Russia foresees to use it in its sodium cooled fast reactors BN-600 and BN-800, the latter currently still under construction. Both reactors were originally designed as breeder reactors. During the disposition of pluto- nium, production of fresh plutonium is undesirable. It would take place at least in blankets of depleted or natural uranium. The agreement states that the BN-800 should be operated with a breeding ratio of less than one. We calculate the depletion effects of weapon-grade MOX fuel in the BN-800 for different configurations, with and without breeding blankets. All reactor config- urations shift the isotopic composition of spent fuel from core regions to higher Pu isotopes and make the material less weapon-usable, with a Pu-239 content of less than 90 wt%. We analyze the breeding ratios of different configurations and present the resulting spent fuel composition, as well as an estimate of the possible fissile material throughput in the BN-800. All calculations have been carried out using MCMATH, an iterative depletion calculation routine using MCNP and Mathematica. The software has been developed and validated to accommodate many different reactor types and is capable of calculating time-dependent breeding and conversion ratios.