Fundamental design activity of fast reactor with inherent safety characteristics for effective transmutation of minor actinide

Abstract

In order to reduce Minor Actinides (MA), the transmutation of MA in a fast reactor has been studied in Japan. In the transmutation in the fast reactor, MAs are mixed in the ordinary MOX fuel and they are burned up. For the design of a fast reactor with inherent safety characteristics, it is necessary to secure negative void reactivity and cooling via a natural convection under the situation of the severe accident. Therefore, this study aims to fundamentally design the fast reactor for the MA transmutation with inherent safety characteristics. First, in order to clarify the design range of the core design parameter, the parametric study was conducted using four design parameters determining the core configuration. As the result of this parametric study, the feasible combination of each four parameters satisfying the negative void reactivity was clarified. Among parameters satisfying the negative void reactivity, the condition that results in the maximum reduction of MA amount was obtained. Secondly, the CFD simulation focused on the sodium coolant channel between fuel pins was conducted. In this CFD simulation, as the first step for the design activity, the confirmation of the occurrence condition of a natural convection due to the decay heat after shifting to the transient situation was confirmed. Temperature and velocity distribution were evaluated. And the heat transfer efficiency was summarized using Ra number and Nu number.