TRACG TRANSIENT ANALYSIS CODE - 3-DIMENSIONAL KINETICS MODEL IMPLEMENTATION AND APPLICABILITY FOR SPACE-DEPENDENT ANALYSIS

Space- and time-dependent phenomena, mostly related to neutron flux os cillations, have been observed in several boiling water reactor plants . A time-dependent three-dimensional transient analysis code is indisp ensable for simulating such phenomena. In a joint effort between the G eneral Electric Company and the Toshiba Corporation, a three-dimension al neutron kinetics model has been implemented into the best-estimate thermal-hydraulics code, TRACG. A neutronics model implementation and the applicability of the modified TRACG code for analyzing space-depen dent phenomena are discussed. To verify the code, startup tests with s elected rod insertions, where control rods are locally inserted, are s imulated. Both corewide, spatially in-phase neutron flux oscillations and regional, spatially out-of-phase oscillations are modeled. The res ults show that the modified TRACG code has sufficient capability to si mulate space-dependent transients and is also a useful tool for invest igating the fundamental mechanisms behind such transients.