Structural Analysis of the Pressurizer Relief Valve Discharge Piping of NPP Angra I

摘要

The pressurizer relief and safety valve system provides the reactor coolant system overpressure protection and,therefore, it is fundamental for the security of a nuclear plant. This paper suggests some modifications to the original pipingconfiguration of the pressurizer relief and safety valve system, in accordance with the recommendations of NUREG-0578(TMI-2 Lessons Learned Task Force Status Report and Short -Term Recommendations). These modifications were proposedin order to reduce the high stress levels induced by the thermal-hydrodynamic loads caused by the discharge of the subcooledwater during the relief valve opening. The thermal-hydrodynamic loads were calculated using the computer codesRELAP5/MOD2, PREPREF and REFORC. Several thermal-hydraulics models were tested considering the influence of theseal water heating and the simultaneous opening of the valves to reduce these loads. The piping structural analysis wasperformed using the computer program system KWUROHR.