3D modeling of passive safety condensers with CATHARE3 for a high-power pressurized water reactor

Abstract

In the wake of the Fukushima’s nuclear accident, passive safety systems have gained in appeal to improve a nuclear power plant’s resistance to accidents without requiring external power supplies. SAfety COndensers (SACO) are a promising example of these new systems. These are secondary heat exchangers, immersed in a tertiary pool, attached to the steam piping of Steam Generators (SG). In the event of a failure in the normal water supply to the SG, they take the place of emergency pumps, which require a power supply. Their purpose is to extract residual power from the core by condensation of the secondary steam produced at the SG, and return it in liquid form. Then, the secondary liquid inventory is preserved, preventing the SG from drying out.

For several years now, CEA, in collaboration with EDF, has been involved in modeling SACO of various designs (straight or “C”-shaped vertical tubes, in a calandria or a small or large pool, etc.) for new reactor concepts. In particular, the 3D modeling of immersed exchangers in a pool, using the CATHARE3 code, challenges the conventional 0D/1D modeling and shows the interest of 3D spatial discretization to better take into account the lateral feed of exchangers. As a result, several 3D SACO models, based on different experimental designs and adapted to the reactor power under consideration, are proposed. There are compared with each other on a typical secondary depressurization transient. Also, the CATHARE3 3D modeling is discussed on a typical station black-out transient for a given type of SACO design.