RELAP/MOD2 Calculations of OECD-LOFT Test LP-SB-01 (NUREG/IA-0012)

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Publication Information

Date Published: January 1990

Prepared by:
P.C. Hall, G. Brown

Central Electricity Generating Board
Barnwood, Gloucester
United Kingdom

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
under the International Thermal-Hydraulic Code Assessment
and Application Program (ICAP)

Published by:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555

Availability Notice


To assist CEGB in assessing the capabilities and status of RELAP5/MOD2, the code has been used to simulate SBLOCA test LP-SB-O1 carried out in the LOFT experimental reactor under the OECD LOFT programme. This test simulated a 1.0% hot leg break in a PWR, withi.early tripping of the primary coolant circulating pumps. This report compares the results of the RELAP5/MOD2 analysis with experimental measurements.

Comparison of the present calculation with earlier RELAP5/MOD1 calculations shows that significant improvements have been made. Most notably, the horizontal stratification model in MOD2 was found to enable improved calculation of fluid density close to the break in this test. In addition mass conservation errors, numerical stability and the computer run time were all greatly improved, compared with an earlier CEGB analysis using MODi.

The major difference between the RELAP5/MOD2 results and the experimental data is in the critical discharge flow rate. It is concluded that!-the error arises from thermal disequilibrium effects in thei discharge nozzle which are not modelled in the code. However, the discrepancies are not considered unduly significant for safety analysis of small break loss of coolant accidents in nuclear power plants, since in this application such effects would normally be allowed for by performing sensitivity studies to break size, orientation, etc.

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