Study On Improved Semi-Predictor-Corrector For Coupling Schemes Of Monte Carlo Transport-Burnup Calculation

The management of reactor core fuel is closely related to the economy and safety of the reactor.The reactor fuel consumption calculation is an important part of reactor design and analysis.Reactor burnup calculation requires an iterative calculation of particle transport calculation and point-burnup calculation.The steady-state neutronics parameters of the core can be obtained by solving the Boltzmann equation through transport calculation,and the variation of the core nuclide density over time can be obtained by solving the Bateman equations through the point-burnup calculation.In the depletion process,the microscopic reaction rate is closely related to the material nuclide density.In the traditional method,the forced decoupling through setting burnup steps of depletion will bring deviation of calculation.Therefore,in the Monte Carlo(MC)transport-burnup coupling calculation process,it is necessary to accurately consider the impact of microscopic reaction rate changes during the nuclide depletion procedure,in order to achieve the purpose of improving calculation efficiency and ensuring calculation accuracy.The traditional MC transport-burnup coupling schemes need to set short time-step size to ensure the calculation accuracy.This processing method will increase the number of burnup steps and reduce the calculation efficiency.Based on Super Multi-functional Calculation Program for Nuclear Design and Safety Evaluation(SuperMC),this paper carries out a study on the improved semi-predictor-corrector(semi-PC)method of Monte Carlo transport-burnup calculation coupling schemes.Firstly,based on semi-PC method,the projected predictor-corrector(PPC)method is used which assumed of PPC a correlation between the microscopic reaction rate and the density for each nuclide.According to the assumption,the microscopic reaction rate at the beginning-of-step is modified to avoid gradual accumulation of calculation error.Secondly,the improved semi-PC method also combines with the idea of substep algorithm.This algorithm divides a time-step to several substeps,obtaining the microscopic reaction rate of each substep by polynomial fitting method,performing the burnup calculation at each substep.Thus,it is possible to use a longer time-step size to perform calculations on the premise of ensuring the same calculation accuracy,thereby improving the calculation efficiency.In order to verify the correctness and efficiency of the improved semi-PC method,this study selected the TAKAHAMA-3 PWR benchmark and the IAEA BN-600 model for comprehensive testing.The test results showed that,compared with traditional coupling scheme,the improved semi-PC method could make the time-step size 8 times longer with the same precise.