Exponential Measurements of Natural Uranium Rods in Heavy Water and Comparisons with Critical Experiments

Buckling measurements of 42 lattices of natural uranium 1-in. rods in heavy water have been made in an exponential facility at two moderator purities. The fuel assemblies were single rods and clusters of 3, 7, and 19 rods. Lattice pitches varied from 3.00 to 21.59 in. A comparison was made between the bucklings that were measured in the exponential facility and those that were obtained from critical measurements. On the basis of a constant radial buckling for the exponential, systematic differences between the exponential and critical measurements were noted. Possible causes of these differences are discussed. Experimental curves for changes in buckling produced by changes in moderator purity are also given.