To apply fast and accurate simulation techniques to Taiwanese nuclear power plants, the Chinshan plant analyzer was developed based on the Brookhaven National Laboratory boiling water reactor (BWR) plant analyzer. The Chinshan plant analyzer provides user-friendly, on-line, interactive simulation capability with graphics display and is suitable for control system analysis. During the generator load rejection (GLR) test at the Chinshan BWR power station located in northern Taiwan, the reactor feedwater pump (RFP) tripped because of a high downcomer level (level 8). Feedwater control was then lost because of the RFP trip. By the end of the transient, a huge amount of water had accumulated in the reactor pressure vessel. The margin to main steamline flooding was decreased. An optimization module was developed and added to the Chinshan plant analyzer. With the optimized feedwater controller settings, the maximum downcomer level is below level 8, and the RFP does not trip during the GLR transient. The margin to main steamline flooding is increased. These techniques will be applied for improving plant performance in the near future.