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Assessment of the reactor pressure vessel integrity in PTS conditions. Thermal hydraulic study of a safety injection in a three loop PWR plant with the finite element code N3S

Abstract:

This paper explains the Research and Development program started at E.D.F about the cooling phenomena of a PWR vessel after a Pressure Thermal Shock. The numerical results are obtained with the thermal hydraulic Finite Element (FE) code N3S coupled with the thermal-solid code SYRTHES to take into account the conjugate heat transfer on the cooling of the vessel. The geometry used represents a three loop PWR plant which is the more common running plant in the world. In this calculation, the simulated finite element mesh takes into account as much as possible the exact geometry of the lower plenum such as guide tubes and tie plates of core bottom instrumentation. The configuration investigated is related to the injection of cold water in the vessel during a severe operating transients and its impact on the solid part formed by cladding and base metal. Numerical results are given in terms of temperature field in the cold legs and in the downcomer.