Analysis of ABWR FW pump performance during power ascending and verification of an operational strategy to jump pump speed across the critical region with RELAP5-3D

The fourth nuclear power plant in Taiwan is an advanced boiling water reactor (ABWR) and is scheduled to be in commercial operation in late 2009. However, it is highly suspected by the reactor vendor that the turbine-driven reactor feedwater pumps (TDRFPs) are over designed. Consequently, the critical speed of TDRFP is likely to be encountered during power ascending. Besides, the original design speed of TDRFP also has to be reduced during normal operation by using oversized TDRFPs. Therefore, the design of FW control system needs to be accordingly revised based on a proper pump speed versus demand curve. To avoid unnecessary effort during pre-operation and/or power tests, a RELAP5-3D based plant integral model covering both reactor system and BOP systems was applied to simulate and analyze the behavior of the FW system during power ascending. By using the most advanced simulation technique, the performance of TDRFPs during power ascending was calculated, and the low power interval correspondent to the range of critical speed (2400–2800 rpm) was identified. Moreover, an operational strategy proposed by plant operators to jump TDRFP across the critical speed range during power ascending was also quantitatively verified. It was found that increasing the bypass flow of either condensate pump or condensate booster pump is the most efficient and practical approach to jump the TDRFP across the critical speed interval. The successful application of the RELAP5 for the entire BOP simulation indicates that the advanced RELAP5 can extend its traditional reactor safety analysis to the entire power conversion system simulation and analysis.