Heterogeneous discontinuity factor treatment in Variational Nodal Method

Abstract To handle the control rod cusping effect in Pressurized Water Reactor (PWR) core calculation, the heterogeneous Variational Nodal Method (VNM) employed by the fuel management calculation code system NECP-Bamboo has been enhanced to treat heterogeneous discontinuity factor (DF) appearing on nodal interface. To solve the neutron-diffusion equations with heterogeneous DF, firstly, the functional in VNM is modified to contain the discontinuity of neutron flux in the surface integral term. Secondly, other than volumetric flux and surface partial currents, cross sections and surface DF are also expanded into the sum of orthogonal piece-wise polynomials to construct the nodal response matrixes. Four test problems in this paper including the CISE, Henry-Worley, HAFAS benchmark problems and the BEAVRS problems were employed to verify the method in treating heterogeneous DF. It has been demonstrated that the control rod cusping effect can be fully eliminated by the heterogeneous VNM with heterogeneous DF in terms of control rod differential worth and three-dimensional pin-power profile.