Abstract
Recently, several advanced computational tools for simulating reactor system behavior during real and hypothetical transient scenarios were developed. The TRAC/RELAP Advanced Computational Engine (TRACE) is the latest in a series of advanced, best-estimate reactor system codes developed by the United States Nuclear Regulatory Commission (US NRC). Nevertheless, the RELAP5/MOD3.3 computer code will be maintained in the next years. The purpose of the present study was to assess how the accuracy of Bethsy 9.1b test calculation depends on the US NRC RELAP5 code version used. Bethsy 9.1b test (International Standard Problem no. 27) was 5.08 cm equivalent diameter cold leg break without high-pressure safety injection and with delayed ultimate procedure. Seven different RELAP5 code versions were used and as much as possible the same input model. The obtained results indicate that the results obtained by the oldest and latest RELAP5 versions are in general comparable for Bethsy 9.1b test. This is very important for the validity of the results, obtained in the past with older RELAP5 versions. Due to the fact that observation was restricted to Bethsy 9.1b posttest, with its own physical phenomena, this conclusion could be generalized only for scenarios having similar range of the considered Bethsy transient conditions.
Highlights
Several advanced computational tools for simulating reactor system behavior during real and hypothetical transient scenarios were developed
The results showed that qualitatively all RELAP5 versions in general produce similar results in spite of some differences in the boundary conditions and the nodalization details
The Bethsy 9.1b test, which is 5.08 cm equivalent diameter cold leg break without high-pressure safety injection and with delayed ultimate procedure, was simulated by different RELAP5 code versions using input models, originating from the same RELAP/MOD2 posttest input model developed at Jozef Stefan Institute
Summary
Several advanced computational tools for simulating reactor system behavior during real and hypothetical transient scenarios were developed. Since the release of RELAP5/MOD2 in 1985 the code was continuously improved and extended. The Jozef Stefan Institute (JSI) activities in the area of RELAP5 analyses have been aimed to extend the experiences in simulations of small break loss of coolant accidents (LOCAs) and two-phase natural circulation cooling. Its own RELAP5 input model of Bethsy facility [2] has been developed. The Bethsy-experiences-based improved modeling methods have been used in simulations of real plant transients and evaluation of plant accident management procedures [3,4,5]. The aim of this study was to perform calculations with to JSI available RELAP5 versions using as much as possible the same input model in order to see the differences between the code versions. In the past, typical comparisons were done between new and old versions, while this comparison covers the last 25 years of US NRC RELAP5 development
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