Comparison of Turbulent Models for CANDU® Moderator Following a Pressure Tube To Calandria Tube Contact

Abstract

In this paper, the CANDU moderator flow and temperature distribution have been studied by developing a Computational Fluid Dynamics (CFD) model. The model predicts the fluid velocity and temperature distribution around a channel in normal operation and also after a postulated ballooning deformation of the pressure tube (PT) into contact with its calandria tube (CT). The present research is focused on establishing the limits for dryout occurrence on the CTs after PT/CT contact. CT dryout may occur due to the large spike of heat flux to the moderator after contact. The CT post-dryout temperature may become sufficiently high to result the thermal creep strain deformation and affect the channel integrity. In this study two different turbulent models, standard and , have been used and compared in order to consider turbulence in moderator flow. Governing equations have been solved by the finite element software package COMSOL. The buoyancy driven natural convection, the local moderator subcooling, fluid velocity, wall temperature and heat flux has been analyzed in the model. The flow pattern and temperature distribution predicted by both turbulent models indicate a greater tendency for film boiling to occur at low subcoolings and at the top or bottom of the CT.