Power distribution skewing effects on fuel temperature during TOP in a large commercial-base fast reactor

Kawashima, Katsuyuki; Okubo, Tsutomu; Mizuno, Tomoyasu

As part of the FaCT Project, the study is focusing on to evaluate the effects of power distribution skewing on the fuel temperature at the TOP state in the large commercial-base Fast Reactor (JSFR), in order to help streamline the safety evaluation methods of the JSFR. It is shown that the considerations of the power distribution skewing increase the average fuel temperature rise, leading to more negative reactivity feedback which decreases the rate of hot pin temperature rise during TOP, and the peak linear power is significantly mitigated by local feedback reactivities due to temperature rise in the fuel assemblies adjacent to the withdrawn control rod. A conventional calculation model which neither considers the power distribution skewing effect nor the local feedback reactivities effect gives the conservative results of the peak linear power in the TOP event.