This paper is to present a fluid transient analysis for the safety valve vent stack which is an open discharge system using the AREVA in-house thermal hydraulic code S-RELAP5. S-RELAP5 was developed by AREVA to perform thermal hydraulic analyses. It is a RELAP5-based thermal-hydraulic system code which incorporates features of the NRC RELAP5/MOD2 and RELAP5/MOD3 as well as other improvements. S-RELAP5 deals with one-dimensional two-phase, two-fluid, non-equilibrium hydrodynamic model with a non-condensable gas field.

ASME B31.1-2010 Non-mandatory Appendix II provides formulas for hand calculation of blow down forces at elbow exit and vent pipe. In general, this approach generates only steady state forces. To more accurately calculate forcing functions, S-RELAP5 is a good tool to achieve this task. The purpose of this S-RELAP5 application is to show that the usage of BRANCH and other components in the S-RELAP5 code can effectively simulate the safety valve open system discharge. This is a first-of-a-kind application of the code. Furthermore, this method provides an alternative to the ASME Appendix II hand calculation. In this paper a sample problem from ASME Appendix II is utilized to generate the time history forcing functions to demonstrate the versatility of S-RELAP5. These forcing functions can then be used for the subsequent piping dynamic analysis.

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