Development of a multicell methodology to account for heterogeneous core effects in the core-analysis diffusion code

In CANDU R reactor calculations, the lattice-cell cross sections are calculated with WIMS-AECL, and the three-dimensional core neutron-flux and power distributions are calculated with RFSP-IST. The lattice-cell cross sections employed in RFSP-IST and in many other commercial core-analysis diffusion codes are usually based on the use of single-lattice-cell calculations, without considering the effects of the environment. This approximation is not sufficiently accurate for heterogeneous core configurations in the ACR-1000TM. A multicell correction method is therefore developed in RFSP-IST to account for heterogeneous core effects in the design and analysis of ACR-1000. The calculation results show that the multicell methodology developed in RFSP-IST is effective, generic, and it works well for ACR core analysis. (authors)