Improvements of RELAP5/Mod3.3 heat transfer capabilities for simulation of in-pool passive power removal systems

Despite system thermal–hydraulic codes were extensively validated for transient simulations of LWR, several activities highlighted limited capabilities these tools to model heat transfer within in-pool passive power removal system. Discrepancies with experimental results related the underestimate pool boiling and film condensation coefficients. Thus, DIAEE “Sapienza” University Rome developed a modified version RELAP5/Mod3.3, able handle fundamental exchange phenomena involved in safety systems. A primary validation procedure has been performed separated integral effects. Dealing nucleate boiling, Root Mean Squared Relative Error (RMSRE) wall superheat reduced from 1.290 0.182. Concerning condensation, temperature RMSRE 0.192 0.058. The effect assessment an test PERSEO facility. qualitative comparison between experiments calculations significant improvements RELAP5/Mod3.3.