The constrained finite element approach to coarse-mesh transport computations

Abstract

Coarse-mesh computational methods have attracted widespread interest for both diffusion theory and for higher-order transport approximations. Fine-mesh diffusion calculations for the analysis of large, neutronically loosely-coupled cores such as the BWR shown in Fig. 1 are often prohibitively expensive for routine use. Therefore, techniques that reduce the spatial grid points to a manageable number without resulting in an inordinate loss of accuracy are of considerable interest. A variety of nodal methods have been developed for the treatment of PWR cores for this reason. For the BWR core shown in Fig. 1, however, these methods are not nearly as effective, for they require that the fuel assembly cross sections be homogenized before the global calculation is carried out. But such homogenization obliterates the strong coupling of the local spectral effects due to the water gaps and control rods with the global flux variation. Neither are fine-mesh transport methods effective for LWR fuel assembly problems, such as the configuration shown in Fig. 2, without the individual fuel cells first being homogenized. In such problems, containing burnable poisons and control-rod slots, the explicit representation of the many circular fuel-coolant