Multi-dimensional methods for back-end and decay heat calculations of BWR, PWR and WWER fuel assemblies

The SNF computer program performs spent nuclear fuel analyses using isotopic concentrations from the 2-dimensional (2-D) lattice physics codes HELIOS or CASMO-4 combined with power histories and burnups from a 3-dimensional (3-D) core simulator. The underlying method, its validation and applications are summarized in this paper. The SNF isotopic concentrations are evaluated for each axial segment (node) of the fuel assembly, based on the nodal operating history data (burnup, neutron spectrum history and power density history). With this method, the full detail and accuracy of the In-Core Fuel Management (ICFM) system is directly utilized in the decay heat and back-end analyses. Thus there are no special limitations in application of the SNF program, e.g. to heterogeneous fuel designs, as long as the fuel is adequately represented by the ICFM system. Application to WWER fuel assemblies is demonstrated and the results are compared with those of BWR and PWR fuel assemblies. (authors)