Effects of inter-assembly spectral interaction in MOX cores analyzed by CASMO-3M/AFEN

The assembly homogenization code CASMO-3 that is currently in wide use assumes zero net current boundary condition for the fuel assembly. This assumption is not strictly valid in actual reactors. The zero net current boundary condition isolates a fuel assembly from the rest of the assemblies in the core. Thus, it precludes the consideration of the inter-assembly spectral interaction. This paper describes a homogenization method that can treat any actual boundary condition, i.e., non-zero net current boundary condition, by modifying CASMO-3. The method is applied to a benchmark problem with MOX fuel assemblies. The results indicate that the effects of the non-zero net current boundary condition are significant