Validation of an improved reflooding model in ICARE-CATHARE code: QUENCH 11 test calculation

In case of the loss of coolant accident (LOCA) the prime accident management procedure consists in injecting water in the reactor core, by means of various safety injection devices. Nevertheless, the success of a core reflood is not guaranteed because of possible negative effects. The success of a core reflood depends mainly on the core state (geometry and temperature), the primary pressure and the injection rate. The description of the reflooding phase, for any core configuration, is one of the objectives of ICARE/CATHARE V2 code. A new reflooding model has been implemented in the ICARE-CATHARE V2 code, improving significantly the tracking of quench front and the accuracy of heat transfer calculation in the transition boiling zone. This new model has been qualified on QUENCH 11 test showing that the model is also valid for very high temperature of claddings and when rods are slightly damaged. The new model changes the thermalhydraulic behaviour and results in a better prediction of hydrogen production. It confirms that the understanding of thermal-hydraulic phenomena is a key point in the safety management, as important as the kinetic of oxidation. At high temperature, kinetic rate is so fast that the reaction is limited by steam availability. The impact of the injection on the hydrogen production has been studied. The conclusion is that injecting water during a severe accident is not an obvious procedure. If the flow rate is too low, the hydrogen production may increase significantly