NPP transient caused by stuck-open pressurized spray valve

This paper reports that the RELAP5/MOD2 code was used to perform analysis of the transient which occurred with a stuck-open pressurizer spray valve. The primary system and part of the secondary system including the complete control systems of the Krsko Nuclear Power Plant were modeled. Models used for the calculations were tested using start-up test data. The results from simulation of the pressurizer spray valve malfunction show very good agreement with the data measured in the plant. The analyses further confirmed that the most important parameters from a safety perspective only reached values well below allowable margins