Investigation of Effect of Ballooned Fuel Pins on Quenching Behavior: Design of Experiment and Preliminary Analysis

Heat transfer characteristics of intact fuel pins under reflood conditions have been extensively studied to understand the quench behavior of a typical pressurized water reactor (PWR). Overheating of fuel pins due to loss of nucleate boiling under exposed conditions causes the clad to balloon over large portions of the fuel pin length (up to 60%). The reflood behavior of ballooned fuel pins has been studied experimentally for ballooned heater pin configurations with an up to 15% ballooned length of the total length. Substantial changes in the reflood behavior are observed for a higher extent of the ballooned region. An experimental setup is thus being developed to study the effect of the large extent of the ballooned region (up to 60% of the total length) on the reflood behavior. The experimental setup employs a 5×5 matrix of indirectly heated fuel pins surrounded by 32 dummy fuel pins. The scaling analysis carried out for the design of the experimental setup is presented here. The nondimensional π terms pertaining to the quench phenomena have been conserved as compared to the typical PWR values. The evolution of some of the nondimensional π terms under reflood conditions has been discussed for simulations done with RELAP5 for ballooned as well as nonballooned test cases. Delayed quenching is observed in the extended ballooned fuel pins due to poor heat transfer in the ballooned region.