Burn up extension in a PBMR-400 full core using weapon grade plutonium fuel mixed with thorium

In this study, the time dependent criticality and burn up analyses for a full core model of Pebble Bed Modular Reactors, such as PBMR-400, are performed using weapon grade plutonium mixed with thorium as an alternative to enriched UO2 fuel. Neutronic calculations are performed with the MCNP and MONTEBURNS 2.0 using ENDF/B-V nuclear data library. 9.6% enriched UO2 gives an effective multiplication factor of keff ∼ 1.2395, which can be achieved by 18% weapon grade plutonium +82% ThO2 fuel mixture. Thorium mixed fuel with 18% weapon grade plutonium fuel would allow reactor operation periods ∝ 7 years without fuel change with burn up levels of 205 000 MW.D/t, for end of life keff set equal to 1.02. (orig.)