Study of a loss of coolant accident with an EPR simulator

This thesis has been developed in the framework of an Internship in Electricté de France (EDF). In a world where competitiveness between low carbon electricity providers is at its fiercest and the stakes given the ecological transition are highest, EDF aims to strengthen its position as one of the world leaders in the field. To achieve this goal, the company wishes to preserve as well as develop its expertise and its capacity to manage potential accidents as maintaining high levels of safety remains its top priority. In particular, the National Emergency Response Center’ understanding of the impact of the safety injection system’s availability during accidental transients, such as the Loss Of Coolant Accident (LOCA), is essential. The study was conducted using EDF’s simulator of the Evolutionary Power Reactor (EPR), TREFLE. It involves the analysis of a non-penalised and a penalised LOCA, the first one in fully operational conditions and the second one where 50% of the safety injection system is considered non-operational. The analysis reveals that, even if the safety criteria remain satisfied despite the unavailability of 50% of the safety injection system, the penalised scenario implies a change in the reactor’s accidental operation and a notable deterioration of the safety margins related to functional states and the safety criteria of the reactor. The results shed lights on the importance of redundancy in the safety of nuclear power plants. Indeed, while 2 independent trains are enough to satisfy the safety criteria in case of a LOCA with an intermediate size break, having 4 independent trains provides greater flexibility during the mitigation of the accident and the ability to react in case of a cumulative faults.