Modelling of liquid leakage with ASTEC in a severe accident of a PWR

Sammanfattning: In a nuclear reactor, in case of a severe accident occurs, backup circuits are usedlike SIS and CSS, flooding the reactor with water. This might lead to many liquidleakages outside the reactor containment building. These leakages contain a lot offission products and especially iodine that is dangerous in terms of radiotoxicity oncereleased into the environment. Therefore, it is necessary to model correctly the liquidleakage in a reactor to size their impact properly. Their re-injection with a newpump implemented as part of the safety review for the extension lifetime of reactorsbeyond 40 years constitutes also a safety improvement to reduce the source term inthe environment.Modelling the transfer of fission products through liquid leakage and the re-injectionof said leakages is performed at IRSN with the ASTEC code. This thesis focuses onthe optimization of this model, and the consequences of modification in the code forfission products. Indeed, the model of pump used for leakages and re-injection hadsome issues that had to be circumvented.Also, the efficiency of re-injection will be tested with the new model, knowing thatthis implementation has already been proven to be effective in reducing releases tothe environment. Besides, this thesis studies the failure of the reinjection of liquidleaks that can lead to an accumulation of fission products in the auxiliary safeguardingbuilding. Other pH sensitivities in different areas are also studied.