Hydrodynamic Loads Calculation of Pressurizer Safety Valve Discharge Piping Using RELAP5/MOD3.1 Computer Code

An assessment was performed with RELAP5/MOD3.1 computer code for EPRI/CE Test No. 917 which was a simulation of a hot water loop seal discharge followed by steam discharge through a pressurizer safety valve. In the RELAP5/MOD3.1 calculation, the input data such as valve opening characteristics, initial fluid conditions, system nodalizations, and system component modeling, were modeled to be identical to those in the RELAP5/MOD1 calculation performed by EPRI. In addition, the input data such as options applied to volumes and junctions, heat transfer to the pipe walls, and pipe orientations, were modeled in accordance with the modeling guidelines suggested in NUREG/IA-0093 which was a RELAP5/MOD3/5m5 code assessment for EPRI/CE Test No. 917. The calculation results were compared with the experimental data as well as the RELAP5/MOD1 calculation to assess the applicability of the RELAP5/MOD3.1 for the hydrodynamic loads calculation. It was demonstrated from the comparisons that the RELAP5/MOD3.1 computer code yielded very similar hydrodynamic loads to the experimental data as well as the RELAP5/MOD1 calculation results, even though minor discrepancies were also identified. Therefore, it is concluded from the assessment that the RELAP5/MOD3.1 computer code can be used as a suitable design tool to calculate the hydrodynamic loads for the hot water loop seal discharge followed by steam discharge transient.