Space Dependent Kinetics Analysis of Control Rod Withdrawal Accident in Liquid Metal Fast Breeder Reactors

抄録

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of a homogeneous, a tightly coupled heterogeneous and a loosely coupled heterogeneous core where a control rod was withdrawn with a reactivity insertion rate of 2 $/s and 2 ¢/s. The followings were found : (1) the order of the rapidity of the reactor power increase was the loosely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.