BWR Fuel Thermomechanical Evaluation for Preconditioning Procedures With FEMAXI-V Available to Purchase

Burnup limitations are normally set to limit stresses in the fuel assembly components. The defined limits provide guidance to the fuel designer to minimize fuel failure during steady sate operation, and also prevent against some thermal and mechanical phenomena that could occur during overpower transients. In particular, a LHGR limit value is set to take into account physical phenomena that could lead to pellet-cladding interaction. This limit value directly relates to a PCI limit, which may be set based on experimental ramp tests. Thus, to avoid violating the PCI limit, fuel conditioning procedures are still required for both barrier and non-barrier fuel. Simulation of the power ramp procedures to be performed by the reactor operator during startup or power increase maneuvers is advisable as a preventive measure of possible overpower consequences on the fuel thermomechanical behavior. In this paper, the thermomechanical behavior of two different kinds of BWR fuel rods is analyzed for fuel preconditioning procedures. Five different preconditioning computations were performed, each with three different ascending linear power rate ramps. The starting point of the ramps was taken from data of the Cycle 8 of the Unit 1 of the Laguna Verde Nuclear Power Plant, located in MEXICO. The top limit of the ramps was the threshold linear power at which failure by PCI could occur, as a function of burnup. The analysis was performed with the FEMAXI-V code.