Neutronics of Minor-Actinide Burning Accelerator-Driven Systems with Ceramic Fuel

We have investigated neutronic properties of lead-bismuth-cooled accelerator-driven systems with different minor-actinide-based ceramic fuels (two composite oxides and one solid-solution nitride). Adopting a transuranic composition with 40% plutonium in the initial load, transmutation rates of higher actinides (americium and curium) equal to 265 to 285 kg/GW(thermal)yr are obtained. The smallest reactivity swing is provided by the magnesium oxide-based cercer fuel. The cercer cores, however, exhibit large coolant void worths, which is of concern in the case of gas bubble introduction into the core. Nitride and cermet cores are more stable with respect to void formation. The poorer neutron economy of the molybdenum-based cermet makes it difficult, however, to accommodate an inert matrix volume fraction exceeding 50%, a lower limit for fabricability. Higher plutonium fraction is thus required for the cermet, which would lead to lower actinide burning rates. The nitride core yields high actinide burning rates, low void worths, and acceptable reactivity losses.