Computational Fluid Dynamics Simulation of the Atucha II Nuclear Power Plant Reactor

Abstract

A Computational Fluid Dynamics (CFD) simulation of the Heavy Water Pressure Reactor (PHWR) of the Atucha II nuclear power plant was developed. A 3-dimensional (3D) detailed model was employed to simulate the upper and lower plenums, the down comer and the hot-legs and cold-legs. The control rods and the coolant channel walls were also included to account for their influence on flow mixing. The behavior of the coolant channels was modeled by imposing the nominal mass flow at mass and momentum sinks and sources at the location of the inlet and outlet coolant channel ports, respectively. The hydraulic zone distribution was also considered, applying different mass flow rates according to the local coolant channel location. In this preliminary work, the nominal mass flow rate was imposed to the channels to know the steady state reactor behavior. Latterly the mass flow rate through each one of the coolant channels was calculated based on the local pressure at the channel ends at the lower and upper plenums. Simulations allowed a deep understanding of the complex thermo-hydraulic phenomena inside the reactor plenums. The temperature profile and the velocity field inside the upper plenum could be visualized. This computational model is the first step for developing a real time dynamic model, which will be capable to simulate unsteady conditions and some typical operational problems like control rod stepping caused by thermal stratification in the hot-legs or hot-leg streaming.