Study on Pin-by-pin Neutron Kinetics Calculation based on EFEN-SP3 Method

To provide the hottest pin power for safety analysis without introducing the assembly homogenization and pin-power reconstruction, a three-dimensional pin-by-pin neutron kinetics calculation method was researched. The time-variable of the multi-group time-dependent neutron kinetics equations was discretized by using the fully-implicit backward finite difference method. The EFEN-SP₃ (exponential function expansion nodal-SP₃) method was employed to solve the multi-group neutron fixed source equations containing fission medium. To eliminate the inconsistency between neutron source distribution and precursor solution distribution, the EFEN-SP₃ method was improved with high-order source expansion technique. To enhance the computing efficiency, acceleration technologies including Ks factor, LW extrapolation and coarse-mesh rebalancing were adopted. Numerical results based on three-dimensional pin-by-pin neutron kinetics calculation show that pin-by-pin neutron kinetics calculation can directly provide the pin-by-pin power distribution. The high-order source expansion can suppress the deviation increasing in terms of time steps effectively. A speedup of 134.9 times can be provided by the acceleration technologies.