A model for predicting coolant activity behaviour for fuel-failure monitoring analysis

A mathematical treatment has been developed to predict the release of volatile fission products from operating defective nuclear fuel elements. The activity in both the fuel-to-clad gap and coolant as a function of time can be predicted during all reactor operations including steady operation as well as reactor shutdown, startup and bundle-shifting maneuvers. The model has been implemented as the STAR (Steady-state and Transient Activity Release) code based on a finite-element solution of the mass transport equations. The model parameters are derived from in-reactor experiments conducted with defective fuel elements containing natural and artificial failures at the Chalk River Laboratories. The STAR code has also been successfully validated against an analytical solution and benchmarked against several defect occurrences in a commercial reactor.