Projected Predictor-Corrector Method for Lattice Physics Burnup Calculations

A new burnup calculation method, called the projected predictor-corrector (PPC) method, is proposed. In comparison with the conventional predictor-corrector (PC) method, a larger time-step size can be used in burnup calculation without losing calculational accuracy. The PPC method is especially useful for Gd-bearing fuel assemblies, for which a fine time step size is necessary in burnup calculations. The PPC method utilizes a correlation between the number density and the reaction rate in each burnable nuclide and improves the accuracy of the microscopic reaction rate in the corrector step by estimating the "projected" reaction rate. The additional computation time for the PPC method is negligible. Verification calculations are performed for 17 x 17 pressurized water reactor fuel assemblies with 16 Gd-bearing fuel rods. The content of Gd in Gd-bearing fuel rods is set to be 2 to 10 wt%. The calculation results indicate that the PPC method shows comparable accuracy to conventional PC methods whose step time size is about half; i.e., the number of burnup steps in the PPC method can be reduced to about half of that in the conventional PC method.