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The simulation of a 1-inch break loss-of-coolant accident at the ROSA-IV/AP600 test facility using RELAP5/AP600 test facility using RELAP5/MOD3.2
Abstract
During certification of the Advanced Passive 600 MWe Nuclear Reactor (AP600), the Nuclear Regulatory Commission (NRC) contracted with the Japan Atomic Energy Research Institute (JAERI) to conduct a series of confirmatory experiments at the Rig of Safety Assessment (ROSA-IV) Test Facility. The data from these experiments would provide: the response of the new AP600's passive safety systems and the data necessary to assess the ability of RELAP5/MOD3.2 thermal-hydraulic computer code to simulate the AP600 behavior during a small break loss-of-coolant accident. An experiment to simulate a I-inch break at the bottom of Loop B Cold Leg (APCL-03) was conducted. During the test thermal stratifications of 184' K and 123' K in Loop A and B Cold Legs, respectively, were observed. RELAP5/MOD3.2 is a one dimensional code is incapable of simulating this thermal stratification. To present this threedimensional phenomenon using RELAP5/MOD3.2 thermal-hydraulic code, a multi-stack noding approach was adopted. Two different nodalization techniques, split cold leg with cross-flow and split without cross-flow junctions, were performed. The nodalization patterns had little difference in calculating the temperatures in the cold legs. Split cold leg without cross-flow junctions nodalization was chosen for further study. The code predictions with the two-regions nodes produced thermal stratifications in Loop A and Loop B Cold Legs of 132' K and 74' K, respectively. This is approximately 50' K less than the maximum seen in AP-CL-03 measurement. This is due to only two regions being used. When the thermal interfaces do not lie along the centerline of the pipe, then an average of the temperatures above and below the interface are calculated. The most important information is the influence of the thermal stratification on the core collapsed liquid level. The nominal case showed a minimum value of 53% of the core covered, while with the other case a minimum value of 52% was obtained. With less than 1% difference, the splitting of the cold leg into a multi-stack nodes does not cause any significant deviations in estimating the collapsed liquid level of the core.
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Citation
Piper, Robert Beverly (1995). The simulation of a 1-inch break loss-of-coolant accident at the ROSA-IV/AP600 test facility using RELAP5/AP600 test facility using RELAP5/MOD3.2. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -P56.
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