Deformation and rupture of pressurized and transiently heated zircaloy tube

A creep deformation model is developed which enables the diametral strain and rupture temperature of transiently heated Zircaloy tubes to be predicted as a function of the differential pressure across the tube wall. The validity of the analysis is established by comparing the model predictions with the observed deformation and rupture response of ductile tubes subjected to a constant differential pressure. The model is subsequently used to calculate the deformation behaviour of Zircaloy tubes subjected to transient pressure conditions which are typical of those pertaining during the early stages of a loss-of-coolant accident in a pressurized water cooled reactor. It is predicted that rupture temperatures will be appreciably higher than those calculated for otherwise identical tubes deforming under the influence of a constant differential pressure. This conclusion is significant since fuel tube ductility is enhanced when rupture occurs at the elevated temperatures defined by the model. Such enhancement may increase the extent of fuel assembly blockage following a postulated loss-of-coolant accident and thus modify the heat transfer effectiveness of the emergency coolant supply. In view of the safety analysis implications, experimental verification of the predicted deformation response of tubes subjected to a progressively increasing differential pressure is clearly indicated. (author)