Combination of finite-difference and finite-volume techniques in global reactor calculations

The paper addresses the problems encountered in reconstructing, based on the nodal coarsemesh solution, the interior of pin values which are needed in local safety margin analysis. Finite-difference techniques are applied to find flux corner values using the results of the nodal diffusion calculation. The advantage of this new approach is that it can be used for an arbitrary number of neutron energy groups and in any geometry. As examples, corner formulae for Cartesian and hexagonal geometry are derived and analysed with respect to computational expenditure and atainable accuracy. Its shown that the fine-mesh flux distribution in a node can be directly reconstructed by successive use of higher-order standard and rotated finite-difference formulae. In this way an approximation to the discrete solution is computed up to an error comparable to the truncation error of a much more expensive standard finite-difference calculation. (orig./HP)