ICONE23-1008 Fast Reactor Core Concept for Preventing Re-criticality Accidents by Employing Duplex Pellets with Absorber

Abstract

In order to enhance the inherent safety features of fast reactor cores, the effect of duplex fuel, which consist of the central absorber and cylindrical fuel at the peripherals, on reactivity has been studied when the absorber is mixed at the fuel melting accident of the large sodium cooled reactor. The absorber of the duplex fuel is assumed Gadolinium oxide, and the cladding of the pin is a high temperature material such as SiC, in which the melted fuel can be kept even at the fuel melting accident. The insertion reactivity is evaluated as about -6%dk/k by the Monte Carlo Code MVP for the fuel melting condition if the fuel and the absorber are molten into a homogeneous mixture in all of the fuel pins of the core. Though the reactivity is increased to about -2% dk/k if the mixture is compressed to the theoretical density in the cladding, it remained still negative compared to that of the normal operation. This result suggests that the re-criticality problem at severe accidents can be resolved with inherent characteristics of fuel pins.