Prediction at Moderator Temperature Distribution Inside CANDU Calandrla and Its Effect on Criticality and Safety

Abstract

A numerical study for the prediction of the moderator flow and temperature distribution inside a CmU reactor vessel is carried-out. The porous medium concept which is usually used to account for the effect of the calandria tubes matrix on the flow pattern is avoided. Instead, the tubes matrix are simulated by blocking the cells containing the tubes in the finite difference mesh. A jet momentum dominated flow pattern is predicted with two main hot spots regions. The calculated moderator temperature distribution are used to cridet the moderator as an ultimate heat sink and to study the effects of the changes in the moderator temperature on reactor criticality. The multiplication factor is calculated using a refined version of the four-factor formula at different moderator temperatures. Consequently the temperature coefficient of reactivity is calculated.