Experimental investigation of fission gas release from defective fuel rods. (March 2022) - Xu, Rui
Highlights: A scaled-down experiment is performed to evaluate the fission gas release mechanism. The intensity of phase change phenomenon can significantly enhance the gas release rate. The short-term transient gas release process obeys the first-order kinetic law. The short-term release is dominated by the advection other than the diffusion. Abstract: A scale-down experiment has been performed to study the fission gas release mechanism. The experiment is focusing on the process that fission gas release from the gap to the coolant. The experimental results are presented in this paper. The geometry, flow, and phase change similarity are considered in the design of scale-down experimental apparatus. The fission gas is simulated by the oxygen. The major factors that may affect the gas release rate are evaluated, including the defect size, the loop pressure, and the loop temperature. By fitting the residual gas mass in the experimental rod, it is found that the short-term transient gas release process obeys the first-order kinetic law. The defect size and the loop temperature apparently affect the escape rate coefficient, while the loop pressure has little influence on the escape rate coefficient. From the results of the experiment, it can be deduced that the short-term transient fission gas release is an advective process with linear-flow distribution. Under such condition, the gas release rate is extremely higher than the long-term steady release, which is a diffusive process.