According to “Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants” (NUREG-0800) of the U.S. Nuclear Regulatory Commission, the homogeneous and thermal equilibrium critical flow model (HEM model) is acceptable for pressure and temperature analysis of the subcompartment of the containment. However, it was not built into the RELAP5-3D code. In order to provide the blowdown boundary conditions that meet the acceptance criteria for the subcompartment pressure and temperature response analysis, Institute of Nuclear Energy Research implemented and assessed the Moody HEM model of RELAP5-3D. The assessment phase was subsequent to the implementation of the Moody HEM model of RELAP5-3D. Three experiments of Marviken critical flow tests (CFTs) were selected as the assessment cases. They were CFT 15, CFT 22, and CFT 24. The assessment input decks of RELAP5-3D had been modified from the appendixes of the references. Additional comparisons with the results of the RELAP5-3D built-in Ransom-Trapp and Henry-Fauske critical flow models were also included. The comparisons of the calculated blowdown mass flow rate with the test data assessed the newly implemented model, which gave good prediction. Moreover, the comparisons between the results of the critical flow models of RELAP5-3D and the test data provided a measure of the relative conservatism of the critical flow calculations.
