Computational fluid dynamics analysis of flow/temperature distribution of moderator inside calandria and comparison of 2 different approaches

The Calandria of a Pressurized Heavy Water Reactor (PHWR) is essentially a large horizontal cylindrical vessel housing a matrix of horizontal tubes called Calandria tubes within which the pressure tubes that house several fuel bundles are contained. The Calandria is filled with heavy water moderator at a pressure slightly above the atmosphere. A large amount of heat is generated within the moderator mainly due to neutron slowing down and attenuation of gamma radiations. In the present study, two separate analyses have been carried out for predicting flow/temperature distribution inside the Calandria, using two different approaches for modeling the Calandria geometry. While in one approach, nearly full geometric details of the Calandria were incorporated in the model to achieve the flow/temperature profile, the second approach adopted is relatively simpler and computationally economic means by using the porosity based approach. The flow and temperature distribution, predicted from both the analyses show good similarity, implying that use of second approach with well-defined supporting parameters (viz. porosity, drag coefficient) would result in significant economy in computational resources. It must also be noted here that the porosity approach of modelling can easily be adopted for analyzing many other equipments of similar configuration e.g. heat exchangers, separators, steam generators, condensers and so on. (authors)