Isotopic Analysis of Natural UO₂ Fuel Irradiated to 22000 MWd/MTU. Theory vs Experiment

The uranium and plutonium isotopic distributions of 45 irradiated fuel rods of natural uranium dioxide are compared to theoretical predictions made using three-dimensional P-1 neutron diffusion techniques. The calculations are different in that normalization to experimental results is made only by use of the total core energy output and measured critical rod-bank heights. This is in contrast to normalizing each individual fuel-rod burnup to the experimental value and then investigating resultant isotopic distributions in the rod. The comparison indicates good agreement but identifies the need for a spatial spectrum variation of the ²³⁸U epithermal resonance absorption cross section and improved time -dependence of the ²³⁸U and ²³⁹Pu cross sections.