An option of power flattening for SHERHAN code

A new option of power flattening over reactor core has been developed and included into SHERHAN code [1]. The latter was designed for 3D burn-up simulation on the basis of the advanced method of heterogeneous reactor theory. The previous procedure of power flattening used a parametric approach with the application of Golden Section algorithm in an iterative procedure for the choice of optimal positions of some pairs of control rods (CR), or groups of control rods. The present approach is based on the application of linear programming (LP) simplex-method, with the reactivities of all control rods estimated for their displacements from current positions upward and downward. The corresponding influence functions, defined as the differences between (strongly) perturbed and basic solutions are used to form a matrix for linear programming problem in some ''dangerous'' points (fuel assemblies) of the core. The reactivities of CRs are used as independent variables to be determined in LP solution under the constraint that the total perturbation of reactivity is zero. The obtained reactivities are used for the determination of CR positions at the next step leading to the new optimised solution for power distribution after some correction of general position of all the CRs bringing the reactor to critical state. The new option has shown some advantages in the effectiveness of power flattening over the previous procedure. (orig.)