Analysis of Interaction of Calandria Tubes with the End Shields in Advanced Heavy Water Reactor (AHWR)

Abstract

Advanced Heavy Water Reactor (AHWR) is a 300 MWe vertical pressure tube type, boiling light water cooled and heavy water moderated reactor. It consists of 452 coolant channels wherein the heat of nuclear reaction is used to boil the light water coolant to generate steam. Typical coolant channel assembly of AHWR consists of a pressure tube of cold worked Zr- 2.5Nb alloy extended by stainless steel end-fittings, attached at its ends. A Calandria tube of annealed Zircaloy-4 alloy separates the hot pressure tube from the cold heavy water moderator. The Calandria tube is attached at its ends to the Calandria side tube-sheets of both the bottom and top end shields. Thermal expansion, irradiation enhanced axial creep and growth of Calandria tubes cause them to elongate. These elongations induce compressive stresses in Calandria tubes and also load the tube-sheets of the end shields. Stresses also get induced in the annular plate, main-shell and sub-shells of the Calandria vessel. Nature of interaction and types of stresses induced in these components will depend upon the support conditions of both the end shields, creep and growth rates of Calandria tubes. This has been studied for different combinations of fixed and floating types of support conditions of both the top and the bottom end shields. It has been observed that compared to the fixed support condition of both the end shields, stresses induced in the different components reduce to half when either of the end shields support condition is kept floating or on some flexible support.