Study with the Neptune CFD software of the pressurisation of a water injection safety system in a water reactor

Since the major nuclear accidents, one of the main focus in the safety nuclear field has been on passive safety systems. These systems perform the same functions as active systems, but without the use of energy or human intervention. The SESI/LEMS laboratory, in the field of research, analysis and modelling of passive systems, proposes a new configuration for the Automatic Depressurisation System (ADS) already present in the AP1000 reactor. In particular, the new configuration involves the addition of a tank called LPWT (Low Pressure Water Tank) into which is injected the steam produced in the primary circuit in the event of an Loss of Coolant accident. The purpose of this tank is to pressurise itself so that water can be injected into the reactor at an intermediate pressure. This work concerns a CFD analysis to study the steam injection in the tank and the pressure evolution through the Neptune software. Two studies have been conducted: the first calculation aims to evaluate the CFD results in comparison with the experiment of steam injection into a small tank and evaluates the behaviour for different injection diameters. The second study was carried out by varying the injection direction. The results indicate a connection between tank pressurisation and the amount of condensed mass: its shows a more rapid pressure increase evolution with smaller diameters in relation to the fact that there is more condensation by direct contact due to the higher velocity of the incoming steam. Furthermore, the second study demonstrates that a lateral injection limits condensation and shows a higher tank pressurisation.