TRACG ANALYSIS OF THE OECD/NEA OSKARSHAMN-2 BWR STABILITY BENCHMARK BASED ON FEBRUARY 25, 1999 FEEDWATER TRANSIENT EVENT

摘要

On February 25, 1999, the Oskarshamn-2 (OKG2) Boiling Water Reactor (BWR) experienced an instability event that culminated in an unstable high power to flow operating region with diverging power oscillations having a decay ratio (or growth rate) of approximately 1.4. An international benchmark was organized where the plant data collected from the OKG2 instability event was made available to participants. The best-estimate system code TRACG, the GE Hitachi Nuclear Energy proprietary version of the Transient Reactor Analysis Code (TRAC), is used to model the OKG2 reactor vessel, fuel channels and piping of the plant as well as the thermal-hydraulic conditions of the reactor prior to and during the instability event. TRACG includes a multi-dimensional, two-fluid representation of two-phase flow for the reactor thermal-hydraulics and has the capability to model three-dimensional reactor kinetics. The operating plant data is used to validate the steady state OKG2 TRACG system model. This paper will compare the TRACG event analysis simulation with the OKG2 plant data and provide results of the sensitivity studies performed using benchmark-defined boundary and initial conditions for the event.