A STUDY OF FLOW AND TEMPERATURE DISTRIBUTION AROUND A SINGLE CHANNEL IN CANDU MODERATOR

Abstract

<p>A 2D computational fluid dynamics (CFD) model has been developed to calculate the moderator velocity field and temperature distribution around a single channel inside the moderator of a CANDU reactor after a postulated ballooning deformation of the pressure tube (PT) into contact with the calandria tube (CT). Following contact between the hot PT and the relatively cold CT , there is a spike ill heat flux to the moderator surrounding the CT which may lead to sustained CT dryout. This can detrimentally affect channel integrity if the CT post-dryout temperature becomes sufficiently high to result in thermal creep strain deformation. The present research is focused on establishing the limits for dryout occurrence on the CTs for the situation in which pressure tube-calandria tube contact occurs. In order to consider different flow patterns inside the calandria, both upward awl downward flow directions have been analyzed for buoyancy dominant and momentum dominant flows respectively. The standard k - ε and also k - ω turbulence models associated with logarithmic wall function are applied independently to predict the effects of turbulence and the results have been compared. The governing equations are solved by the finite element software package COMSOL. The buoyancy driven natural convection on the outer surface of a CT has been analyzed to predict the flow and temperature distribution around the single CT considering the local moderator subcooling, wall temperature and heat flux. According to the flow pattern and temperature distribution , it is predicted that stable film boiling generates in the stagnation region on the cylinder and it has been compared with the related experimental data.</p>