Space dependent kinetics analysis of control rod withdrawal accident in liquid metal fast breeder reactors.

Abstract

A two-dimensional (in r-z geometry) space dependent kinetics program coupled with thermo-hydraulics for an accident analysis of a liquid metal fast breeder reactor was developed.Validation of the code was made by applying the code to the NEA CRP benchmark problem and comparing the result with those calculated at other institutions. Then, the code was applied to study the transient of a homogeneous, a tightly coupled heterogeneous and a loosely coupled heterogeneous core where a control rod was withdrawn with a reactivity insertion rate of 2 $/s and 2 ¢/s. The followings were found: (1) the order of the rapidity of the reactor power increase was the loosely coupled core, the tightly coupled core and the homogeneous core, (2) the difference from the point kinetics calculation was also larger in this order, (3) when the same reactivity insertion rate was applied for the same core, the space dependent kinetics calculation always gave larger transient power than the point kinetics calculation, and the differences were especially large for the withdrawal of the inner rod, which shows that we cannot rely on the point kinetics results even for the integral quantities such as reactor power or the reactivity in these cases.

New treatment of sodium void effect in fast reactor transient study.

“…It has been pointed out< 4 ) that the sodium void effect cannot be accurately treated with few-energy groups. The reason is twofold; (1) the slowing down component of the sodium void reactivity cannot be accurately represented by few-energy -1-Therefore, we have developed a new method to treat the sodium void reactivity during the transient properly and incorporated the method in QUASAR( 6 ), which is a two-dimensional space dependent kinetics code. The code, named as QUASAR-IT, also includes the feedbacks due to the fuel movement by the fuel expansion and fuel slumping<!).…”