Plutonium rock-like fuel burning in LWR

Plutonium rock-like oxide(ROX) fuel burning in LWR has been studied. To improve reactivity insertion accident(RIA) behavior of zirconia(ZrO₂) type ROX(Zr-ROX) fuel PWR, small negative Doppler reactivity coefficient of the fuel is increased with the additives such as 24mol% ThO₂ or 15mol% UO₂ in the fuel. There is also an approach of a heterogeneous core with 1/3 ROX and 2/3 UO₂ fuels. From the loss of coolant accident(LOCA) analysis of Zr-ROX fuel PWR, the importance to decrease the large power peaking is shown. The ThO₂ additive can make it easier to flatten the power distribution in the core, and improve not only the reactivity accident behavior but also the LOCA behavior. The power flattening can also be achieved by reducing the content of Gd₂O₃ mixed in ZrO₂ and adding Er₂O₃ in place.

In the case of weapons-grade plutonium burning, the plutonium transmutation rate in Zr-ROX fuel LWR is about 0.9tonne/GWe/300 days, and far larger than that of full MOX LWR. The additives of ThO₂ or UO₂ decrease the plutonium transmutation rate, yet it is still larger than that in full MOX LWR by more than 2 times. Even in 1/3 Zr-ROX fuel core, the transmutation rate is comparable with the full MOX case. Total amount of discharged plutonium becomes less than 1/4 to 1/6 in these cores.