Effective homogenization method for control rod channels

A cell calculation method has been developed for accurately treating neutron transport and heterogeneity effects of control rods (CRs) within the bounds of homogeneous neutron diffusion theory. In this method, CR cell-averaged homogeneous neutron cross sections are calculated by a heterogeneous neutron transport calculation with an annular supercell model, in which a CR assembly is surrounded by a homogeneous fuel region. Then, a neutron diffusion calculation is carried out using the homogeneous neutron cross sections in the same supercell, and the CR cell-averaged radial neutron diffusion coefficients are modified in an iterative manner such that the CR cell-interface neutron current which is obtained by the heterogeneous transport calculation can be reproduced by the homogeneous diffusion calculation. In the case of a 1,000-MWe-class FBR, the center CR worth, which was calculated by an RZ diffusion calculation using the cross sections obtained by the above method, agreed within 1% with that obtained by a heterogeneous transport calculation, proving the validity of the method. (author)