Effects of the Contamination by Light Water on Lattices of Natural Uranium Rods in Heavy Water

The effects of H₂O contamination on lattices of natural uranium metal in D₂O were measured in the exponential facility of the Savannah River Laboratory. The buckling changes associated with H₂O contamination were determined for two lattices with moderator-to-fuel volume ratios of 12.3 and 14.6 over a range of H₂O concentrations from 0.2 to 8.2 mol %. The agreement between calculated and experimental changes in buckling for these lattices was within ±25 × 10⁻⁶ cm⁻². Similar measurements on seven other lattices with moderator-to-fuel ratios in the range from 31 to 212 were made for a change in the H₂O concentration from 0.18 to 3.92 mol %. For these measurements the experimental change in buckling was about 15% greater than the calculated change.