Accidental Criticality of a Fusion-Fission Hybrid Blanket Design

Whenever a fissionable blanket is added to a controlled thermonuclear reactor, an investigation of the potential for accidental criticality is necessary to ensure the safety of this hybrid device. The neutronic effects of blanket meltdown and the ingress of steam into the blanket, studied for one such fusion-fission hybrid reactor, indicate that accidental criticality will be achieved only for very long blanket residence times or highly improbable accident sequences. Even though only one hybrid device was investigated, the results indicate that it is possible to design a reactor that will remain subcritical even under certain incredible circumstances.