Relap5 model of the Embalse Nuclear Power Plant: LOCA of 2.5% break of the reactor inlet header

As part of the life extension of Embalse Nuclear Power Plant (CNE), the ARN has developed a full thermohydraulic model with point kinetics using RELAP5 mod.3.3 Patch4, for the simulation of accidents within the design basis. This model is being used to review independently the safety analysis performed by the designer and operator. Comparisons between results of the model developed by ARN and the present state of plant were performed to verify the model and then, design changes for the life extension were implemented. After several verifications of the ARN's model response, a break of 2.5% area of an inlet header (HDR6) was simulated at 100% of full power to evaluate the plan evolution. The event was simulated considering conservative boundary and initial conditions, in agreement with a conservative methodology. The event simulation consisted, firstly, of getting a trip coverage and secondly, a long term evolution an analysis of the response of the plant, the performance of the safety systems (emergency core cooling system etc.) and the actuation of the protection system. A simulation of a hot channel is performed to evaluate that fuel and sheath temperatures are not jeopardized. This work will verify that there is, at least, one effective reactor protection signal and that the plant reaches a safe state. In addition, the accident phenomenology will be studied to know the evolution the plant throughout the transient. (authors)