385. 大型高速炉炉心の核的ディカップリング特性

Abstract

It was made clear by critical experiments (called JUPITER) that nuclear characteristics of large-sized fast reactor cores were quite different from those of small-sized cores. For instance, radial neutron flux distributions are significantly changed by perturbations, control rod reactivity interaction effects are large, etc. These phenomena are interpreted to be commonly caused by the spatial neutronic decoupling of large core. The changeability and instability of flux distribution, which might cause a power peaking and a flux tilting, is a new problem for the development of large core. The paper shows measured results of static decoupling characteristics, interprets them physically, and considers a reactor physics system of large core. The paper also investigates a nuclear core design method, in which the decoupling characteristics are taken into account. A neutronic stability is a new requirement for the nuclear design of large core, which the design policy is to promote and secure together with the performance and the safety. The more tightly coupled the core, i.e., the smaller the degree of decoupling, the better the neutronic stability.