We propose the use of a proton accelerator to run a slightly subcritical fast breeder and incinerator of minor actinides. By injecting medium-energy protons into a subcritical assembly and by providing external neutrons produced by spallation and by high-energy fission reactions, the reactor can be operated in a safer condition than a reactor operated in a critical condition. The safety problems associated with super-criticality, which might be created by factors such as a positive Na void coefficient and fuel bowing, can be alleviated.

The metal-fueled fast breeder has small decrement in reactivity of power and burn-up, but by mixing the MA of 237Np with the oxide-fueled reactor, this decrement of reactivity can be reduced substantially. Thus, these reactors can be operated at a sub-criticality of k=0.99 with small beam proton power of 15 mA and 1 GeV energy (15 MW). This slightly subcritical condition produces a power distribution that is more or less flat, which is important from the point of view of reactor safety. The cost of the multi-stage cyclotron and linear accelerator and the proton energy for neutron yield is discussed.