On Void Reactivity Limitation for the Core Loaded with Mixed Nitride Fuels

Abstract

Self-controllability and self-terminability are strongly required as passive safety features in future liquid-metal FBR (LMFBR) commercialization. In this study, the self-terminability of the MN-fueled core was focused on. The FBR cores including the MN-fueled core should be designed to eliminate severe recriticality leading to energetics during core disruptive accidents (CDAs) because the cores are not designed to operate in an optimum configuration from a reactivity point of view. In addition, in the case of the MN-fueled core, the nitrogen gas N 2 generated by the thermal dissociation, one of the unique phenomena of the nitride fuel, would give another cause of reactor vessel failure. Such a mechanical effect would strongly depend on the magnitude of the void reactivity. In this study, the allowable maximum void reactivity of the MN-fueled core to maintain the mechanical integrity of the reactor vessel was evaluated against an Unprotected Loss-of-Flow (ULOF) accident by using ARGO taking into account the equation-of-state of the MN fuel. By considering the partial-pressure-dependent thermal dissociation process, the design limit of the core void reactivity (positive sum) was estimated to be 6.2 $.

Study of the Self-Controllability for the Fast Reactor Core with High-Thermal-Conductivity Fuel

“…3) The self-terminability is a capability to exclude superprompt criticality conditions leading to the energetics during CDA. 4,5) Ninokata et al 3) proposed the evaluation procedure for the self-controllability based on the effective reactivity concept by describing a safety map. Much effort has been paid to describe the safety maps for mixed oxide (MOX)-, metallic-, and mixed nitride (MN)-fueled cores.…”