Abstract
A midloop operation test was performed in 1992 at the BETHSY Integral Test Facility in Grenoble, France. The purpose of this experiment was to produce data that could be used to assess the performance of thermal hydraulic codes under the conditions of low pressure and decay heat. The specific scenario of the test involved the loss of the residual heat removal system in a midloop operation with manways vents open in the pressurizer and at the steam generator. In participation with the International Standard Problem #38, the RELAP5/MOD3.2 code was used to simulate the transient conducted experimentally at the BETHSY facility and assess its ability to accurately predict the observed phenomena. The overall conclusion is that the code performed quite well in terms of predicting macroscopic trends and their timing, but did not describe more specific thermal hydraulic phenomena accurately. Specific areas of disagreement included predicting water holdup cycles in the pressurizer, two-phase mixture levels in the guide tube, upper core void and temperature profiles, entrainment phenomena in the upper head bypass and mass flow ratios between the upper head bypass, pressurizer manway, and steam generator manway. The code predicted well the timing of the core uncovery and maximum core heater cladding temperature, and the integrated phasic mass flow rates at the steam generator manway. Some of these good predictions was the result of compensating errors in the prediction of component thermal hydraulic phenomena. The consequence of the poor code performance in predicting the pressurizer/pressurizer surge line phenomena was a substantial delay in the falloff of the initial system pressurization, an underestimation of the pressurizer integrated mass flow rate, and the emptying of the hot leg and upper plenum. Large mass errors were generated by the RELAP5/MOD3.2.1.1 release of this code. Typical errors were around 20% of the total system mass by the end of the transient.
Luedeke, Thomas Paul (1997). A midloop operation benchmark test of the RELAP5/MOD3.2 code. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1997 -THESIS -L868.