Assessment of RELAP5/MOD3 Against Twenty-Five Post-Dryout Experiments Performed at the Royal Institute of Technology (NUREG/IA-0094, STUDSVIK/NS–90/93)

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Publication Information

Date Published: May 1993

Prepared by:
Lars Nilsson

Swedish Nuclear Power Inspectorate
6-61182 Nykoping

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

Availability Notice


Assessment of RELAP5/MOD2 has been made against various experimental data, among others data from twenty-five post-dryout experiments conducted at the Royal Institute of Technology (RIT) in Stockholm. As the MOD3 version of RELAP5 has now been released, incorporating a different method of calculating critical heat flux compared to RELAP5/MOD2, it seemed justified to make another assessment against the same RIT-data.

The results show that the axial dryout position is generally better predicted by the MOD3 than by the MOD2 version. The prediction is, however, still nonconservative, i.e. the calculated dryout position falls in most cases downstream the actual measured point. While the pre-dryout heat transfer 'seems to be equal for MOD2 and MOD3, both versions giving slightly higher wall temperatures than the experiments, there is a considerable difference in the post-dryout heat transfer. The results of the RIT data comparison indicate that MOD3 underpredicts the post-dryout wall temperatures remarkably while MOD2 gave reasonable agreement. In this respect RELAP5/MOD3 shows no improvement over RELAP5/MOD2.

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