BEST-ESTIMATE TRANSIENT ANALYSIS WITH SKETCH-INS/TRAC-BF1, ASSESSMENT AGAINST OECD/NEA BWR TURBINE TRIP BENCHMARK

Incorporation of three-dimensional models of the reactor core into plant transient codes allows for a bestestimate analysis concerning the interactions between reactor core dynamics and plant systematic functions. SKETCH-INS/TRAC-BF1 is the coupled best-estimate BWR transient analysis code system, which utilizes a modern nodal method with introducing an assembly discontinuity factor for the neutron kinetics and a two-fluid six-equation model for the thermal hydraulics. Assessment on the code system for the capability to predict plant operational transients has been performed in this study against the OECD/NEA BWR turbine trip benchmark, where the following phenomena were realized with the simulation. (1) An acoustical pressure wave propagated in the main steam line, entering into the reactor pressure vessel, produced a hump in the reactor dome pressure rise. (2) The pressure wave propagated into the reactor core induced the fluctuation in core flow rates with out-of-phase, which caused void collapse in core region. (3) The reactivity insertion due to void collapse made the core power peak and the power generation shift upwards during the transient. Simulation on these phenomena demonstrated the capability of SKETCH-INS/TRAC-BF1 code system to predict the plant transients that include interactions between reactor core dynamics and plant systematic functions.