A study on recriticality characteristics of fast reactors in pursuit of recriticality-accident-free concepts

Recriticality of the fast reactor core loaded with mixed oxide fuels is discussed based on the steady-state neutronics calculations where simplified axial compaction of the molten core materials is assumed to take place within fixed core boundaries. A diffusion code was used to analyze the influences of variations in the core materials composition, reactor power and core diameter/height ratio on keff. It was shown that a steel component in the core compaction played a dominant role in overall reactivity behaviors. The calculations implied that a reactor core had less recriticality potentials with higher fuel volume fraction and, if designed properly, also with higher core diameter/height ratio and increasing reactor power while keeping the power density constant.