Yuanzineng kexue jishu (Jun 2023)
Numerical Simulation on Effect of Cr Coating on Blistering Behavior of Plate-type Fuel Element
Abstract
Blistering usually occurs in plate-type fuels because of the absence of the gap between the cladding and the fuel meat. It can narrow coolant channels and deteriorate the local heat transfer, resulting in the increase of cladding temperature and plastic deformation, which threatens the integrity of fuel elements. Much research work mainly focuses on the causes of blistering and its effect on fuel elements, while few measures to reduce blistering were proposed. In view of the effect that Cr coating can effectively reduce the ballooning of fuel rod cladding during loss of coolant accident (LOCA), a design to apply Cr coating to plate-type fuels to restrain their blistering was proposed. In order to study the effect of Cr coating on the blistering of plate-type fuel elements, the simulation of a blistering test was conducted based on the MOOSE framework. The material properties of Zr and Cr were added, and the thermal creep, as well as plastic behavior after irradiation hardening was considered according to the characteristics of blistering. In addition, the effect of temperature and thickness of Cr coating on blistering were also analyzed and some important results were obtained. The simulation of the blistering test indicates that the reduction of blistering for the plate-type fuel cladding by Cr coating is not as significant as that of ballooning for the fuel rod cladding. The reason for the difference and the difference between the two phenomena were analyzed. The results also show that due to its low yield stress, Cr coating is likely to enter the plastic stage when the cladding blisters, which cannot effectively prevent the occurrence of blistering. However, owing to the low creep rate of Cr even at a relatively high temperature, the height of blistering can be reduced, and the higher the temperature, the more obvious the reduction effect. Under the premise of keeping the overall thickness of the cladding and the coating unchanged, even if the presence of Cr coating will reduce the thickness of cladding and thus reduce its mechanical strength, it can still effectively reduce the blistering height at high temperatures, and the thicker the coating, the more obvious the reduction effect. Nevertheless, adding Cr coating to the cladding of the original thickness has the most significant effect. From the results above, the main conclusion can be drawn: The thin coating can hardly affect the overall mechanical properties of the cladding, but it can effectively inhibit the creep, thereby reducing the blistering height.
