RELAP5/MOD3 Assessment Using the Semiscale 50% Feed Line Break Test S–FS–11 (NUREG/IA-0104)

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Publication Information

Date Published: June 1993

Prepared by:
E. J. Lee, B. D. Chung, H. J. Kim

Korea Institute of Nuclear Safety
P. O. Box 16, Daeduk–Danji
Daejon, Korea 305-353

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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The RELAP5/MOD3 5m5 code was assessed using the 1/1705 volume scaled Semiscale 50 % Feed Line Break (FLB) test S-FS-11. Test S-FS-11 was designed in three different phases:(a) blowdown phase, (b) stabilization phase, and (c) refill phase. The first objective was to assess the code applicability to 50 % FLB situation, the second was to evaluate FSAR conservatisms regarding SG heat transfer degradation, steam line check valve failure, break flow state, and peak primary system pressure, and the third was to validate the EOP effectiveness. The code was able to simulate the major T/H parameters except for the two-phase break flow and the secondary convective heat transfer rate. The two-phase break flow had still deficiencies. Correlations for the current boiling heat transfer coefficient were developed from the data for flow inside a heated tube, not for flow around heated tubes in a tube bundle. Results indicated that the assumption of 100 % heat transfer up to the liquid inventory depletion was not conservative, the failed affected steam generator main steam line check valve assumption was not conservative. The measured break flow experienced all types of flow conditions. The relative value to the 110 % design pressure limit was conservative. The automatic actions during the blowdown phase were effective in mitigating the consequences. The stabilization operation performed by operator actions was effective permiting natural circulation cooldown and depressurization. The voided secondary refill operations also verified the effectiveness of the operations while recovering the inventory in a voided steam generator.

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