United States Nuclear Regulatory Commission - Protecting People and the Environment

RELAP5/MOD2 Analysis of LOFT Experiment L9–4 (NUREG/IA-0066, GD/PE–N/721)

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Publication Information

Date Published: April 1992

Prepared by:
M. B. Keevill

National Power Nuclear
Barnett Way
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)

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Summary

As part of a programme to validate RELAP5/MOD2 for use in the analysis of certain fault transients in the Sizewell B PWR, the code has been used to simulate experiment L9-4 carried out in the Loss-Of-Fluid Test (LOFT) facility. Experiment L9-4 simulated a Loss-Of-Offsite-Power Anticipated Transient Without Trip (LOOP ATWT) in which power is lost to the primary coolant pumps and main feed is lost to the steam generators but the control rods fail to insert in the reactor core.

RELAP5/MOD2 generally predicted the transient well, although there were some differences compared to the test data. These differences are largely due to the use of power and flow as boundary conditions and because of uncertainties in the power and flow experimental data. The most noticeable difference was that the steam generator was predicted to boil down too fast. This is believed to be partly due to errors in the RELAP5 interphase drag model. The RELAP5 calculation also showed the primary pressure to be very sensitive to the primary flow rate, making the exact simulation of primary side relief valve movements difficult to reproduce.

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