A self-consistent nuclear energy system (SCNES) can be a promising option as a future nuclear energy source. An SCNES should fulfill (a) efficient energy generation, (b) fuel production or breeding, (c) burning minor actinides with incinerating fission products, and (d) system safety. We focus on the system safety and present a simple evaluation model for the inherent and passive power stabilization capability of intact fast reactor cores under the conditions of an anticipated transient without scram (ATWS), i.e., self-controllability.

The simple evaluation model is referred to as the "reactivity correlation model." The model assesses self-controllability of a core based on the capabilities of reactivity feedbacks to stabilize transient power and maintain temperatures within predefined safety limits. Here the safety limits are "no fuel failure" and "nonboiling of coolant."

The reactivity correlation model was used to survey the self-controllability for metallic-fueled fast reactor cores. The survey was performed by selecting the core volume fractions of fuel, coolant, and structure; the arrangement of material compositions; and core configuration. A variety of reactor cores were examined, ranging from a standard 100-cm height to a flat 40-cm height. The effect of additions of sodium plena and channels, increased/decreased fuel volume fraction (Vf), loading 0 to 10 wt% minor actinides, and installing fission product-burning assemblies was also examined. The core performances were evaluated relative to tolerances against typical ATWSs, i.e., unprotected transient overpower and unprotected loss of flow. An optimum fast reactor core with the self-controllability as well as well-balanced tolerance against ATWSs resulted. The performance of this optimal core was examined for the other three prerequisites of a self-consistent nuclear energy system.