No 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of a homogeneous, a tightly coupled heterogeneous and a loosely coupled heterogeneous core where a control rod was withdrawn with a reactivity insertion rate of 2 $/s and 2 ¢/s. The followings were found: (1) the order of the rapidity of the reactor power increase was the loosely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.

No abstract

Simplified BWRs are characterized as an adoption of a passive ECCS and a passive containment cooling system (PCCS). While a passive ECCS has a short term core cooling function, a PCCS has a long-term decay heat removal function. As a PCCS, several concepts, differing in cooling location and method employed, have been considered. From the containment thermalhydraulic response analysis viewpoint, simplified BWRs are essentially different from the current BWRs. For evaluating and comparing the performance of several PCCSs over full break spectra, the new containment safety evaluation code TOSP AC was developed as a preliminary design tool for PCCS. This paper summarizes the thermal-hydraulic modelings of the TOSP AC code and the validity evaluation of the TOSPAC code, compared with TRAC-BF1 calculation. From the validity evaluation concerning a main steam line break (MSLB) accident analysis for an isolation condenser (1/C) as a PCCS, it was found that the TOSP AC calculation result shows reasonable agreement with that for TRAC, even though the TOSPAC consists of simpler modelings.