RELAP5/MOD2 Calculations of OECD LOFT Test LP-SB-2 (NUREG/IA-0021)
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Date Published: April 1990
Central Electricity Generating Board
Generation Development & Construction Division
Barnwood, Gloucester GL4 7RS
Prepared as part of:
The Agreement on Research Participation and Technical Exchange
under the International Thermal-Hydraulic Code Assessment
and Application Program (ICAP)
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555
To help in assessing the capabilities of RELAP5/MOD2 for PWR Fault Analysis, the code is being used by CEGB to simulate several small LOCA and pressurised transient experiments in the LOFT experimental reactor. The present report describes an analysis of small LOCA test LP-SB-02, which simulated a 1% hot leg break LOCA in a PWR; with delayed tripping of the primary coolant pumps. This test was carried out under the OECD LOFT Programme.
An important deficiency identified in the code is inadequate modelling of the quality of the fluid discharged from the hot leg into the break pipework. This gives rise to large errors in the calculated system mass inventory. The effect of using an improved model for vapour pull-through into the break is described.
A second significant code deficiency identified is the failure to predict the occurrence of stratified flow in the hot leg at the correct time in the test. It is believed that this error contributed to gross errors in the loop flow conditions after about 1300s.
Additional separate effects data necessary to resolve the code deficiencies encountered are identified.