United States Nuclear Regulatory Commission - Protecting People and the Environment

RELAP5/MOD2 Calculations of OECD LOFT Test LP-SB-2 (NUREG/IA-0021)

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Publication Information

Date Published: April 1990

Prepared by:
P.C. Hall

Central Electricity Generating Board
Generation Development & Construction Division
Barnwood, Gloucester GL4 7RS
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

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Abstract

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.

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