Relap5 simulation of Darlington Nuclear Generating Station Loss of Flow Event

The Darlington NGS consists of four 940 MWe CANDU reactors. A detailed RELAP5 model of a Darlington NGS reactor has been created for use with RELAP5/MOD3.3. The model includes the primary heat transport system, the steam generator feedwater and main steam line supply systems., the pressure and inventory control system, and the emergency coolant injection system. The modeling of Darlington required the creation of new subroutines for RELAP5 to describe the functionality of the process control systems and emergency control systems with sufficient accuracy . The controller subroutines are standalone modules that are compiled and linked together with RELAP5 source to facilitate integration with future revision of the code. The controllers relevant to loss-of-flow assessment have been tested against benchmark controller responses and found to be excellent agreement. The November 25, 1993, loss-of-flow event at Darlington was simulated using RELAP5 model. Overall excellent agreement was obtained between the RELAP5 predictions and the station measurements. The simulation results are not sensitive to header nodalization of the three thermal-hydraulic parameters of interest to the present assessment, the header pressures and the steam generator levels compared well to station data. Assessment of core flows could not be performed due to the absence of single channel RELAP5 models. However, the overall qualitative agreement between the station measurements and the predicted system response provides confidence that core flows would likewise comare favorably if assessed.