Application of modified explicit higher-order perturbation (MHP) method to PWR core analysis

A PWR core analysis was performed by using the Modified Explicit Higher-Order Perturbation (MHP) method. A new perturbation calculation code with two energy groups in a two-dimensional x-y geometry based on the MHP method TWOPEC was developed to evaluate the change both in the neutron flux distribution and the reactivity caused by a perturbation. The results were compared with those by the direct eigenvalue calculations to examine the capability of the MHP method. It was demonstrated that both the neutron flux distribution and the reactivity can be accurately evaluated by the MHP method for a string and local perturbation caused by the control rod insertion when one uses large numbers of expansion modes and perturbation orders. The MHP method was applied to the pseudo burnup calculations that regarded the change in cross sections caused by the fuel burnup as the perturbation. It was found that one can also obtain satisfactory results not only for the burnup reactivity but also for the control rod worth at each burnup step.