Reconstruction of pin power in fuel assemblies from nodal calculations in hexagonal geometry

A new formulation based on maximum entropy and minimum cross-entropy methods has been worked out for pin power reconstruction in hexagonal fuel assemblies. These methods help in estimation of boundary fluxes at the surfaces of an assembly using the values from nodal calculations. Representing the heterogeneities in the assembly using fine meshes, the diffusion equation in it is solved using finite difference (FD) technique. The results of a numerical problem formulated for the purpose have been compared with those obtained from (i) detailed fine-mesh (FD) estimations for the core as a whole and (ii) the imbedded estimations applied for the box. The boundary fluxes in the imbedded method are obtained using cubic splines at the surfaces of the assembly. Numerical difficulties encountered while imposing neutron currents as additional constraints in the entropy methods are also discussed.