CFD Simulation of Fission Gas Release Under Fuel Defects Condition in Pressurized Water Reactor

During normal pressurized water reactor (PWR) operation, the fuel cladding is inevitably defective. It is important to develop a model to evaluate the fission gas (FG) release from the fuel-cladding gap into the coolant, which benefits the fuel failure monitoring and improves the reactor safety. The objective of this paper is to give an overview of three-dimensional two-phase transient CFD simulation based on the Volume of Fluid (VOF) method to evaluate the fission gas migrating inside the gap and escaping through the defects. The topics of this paper include the behavior and release rate of FG in the fuel-cladding gap when the fuel cladding is defective. An analysis is presented on the suitability of the CFD simulation and it is shown that three-dimensional two-phase transient CFD simulation can be utilized in evaluating the FG release process. The results show that water enters the gap immediately after an abrupt cladding defect. The entering water flashes and causes pressure pulsation, which induces the transient FG release.