Epithermal and Thermal Spectrum Indices in Heavy Water Lattices

Spectral indices have been measured by foil activation technique in a number of different D2O-moderated lattices in the Swedish zero power reactor R0 and the pressurized exponential assembly TZ. In most cases the fuel was in the form of single rods, distributed uniformly in the lattice. Parameters in these cases were lattice pitch and fuel composition. A 31-rod cluster lattice was also investigated, with the moderator temperature varying up to 210 deg C. On the basis of these measurements, as well as measurements on cluster lattices, reported by other investigators, it has been possible to derive simple correlations for the spectral indices, which seem to be of fairly general validity for D2O lattices. The experimental results have also been compared to calculations with the multigroup collision probability program FLEF