A Coupled Scheme for the Deterministic Safety Transient Analysis of the Atucha I Nuclear Power Plant

Abstract

Every nuclear power plant in the world has to solidly prove that its reactor safety systems are able to cope with any design-basis accident situation in a satisfactory way using sound mathematical models and computational tools. On the one hand, more accurate models are developed as new experimental results are obtained using innovative test loops. On the other hand, computer hardware and software tools are being continuously improved including remarkable breakthroughs such as massive parallelization methods or GPU-based computations. Therefore, deterministic safety analysis of nuclear power plants ought to be regularly updated using state-of-the-art techniques. This article summarizes how different branches of nuclear engineering—namely neutronics, thermal hydraulics, control systems and computational fluid-dynamics—have to be merged in order to perform coupled transient calculations considering the rather different phenomena that take place within a nuclear reactor core, together with the actuation of the associated safety systems. In particular, the work is focused on the case of a loss-of-coolant accident that requires the fast injection of a boric acid solution into the moderator tank.
This computation involves different computer codes, each solving a particular engineering problem. The space and time-dependent evolution of the boron plume is computed by a CFD code and fed into a neutron spatial kinetic code, that takes into account the thermalhydraulic conditions of the core—which are computed by another code—evaluates the instantaneous power distribution. Additionally, the plant status is monitored by a computational implementation of the reactor control and protection systems which command the actuation of the appropriate safety mechanisms that drive the plant to a safe condition.