Lattice-Parameter Measurements for Solid and Concentric Tubes of Uranium Fuel in Graphite Lattices

Lattice parameters have been measured for natural uranium concentric tubes and solid fuel elements of 2.5 inches outside diameter in the Physical Constants Testing Reactor (PCTR). The primary quantities measured are the mass of copper required to reduce k_∞ to one, copper activations throughout the lattice, and cadmium ratios for U²³⁸ capture, U²³⁵ and U²³⁸ fission, copper, gold, and lutetium. The results derived from these measurements are k_∞, ε, and the effective neutron temperature for the concentric tube in a 10.5-inch graphite lattice with both water and air in the coolant channels; k_∞ and for the concentric tube in an 8.375-inch lattice, water cooled only; and k_∞, , and for the solid fuel in a 10.5-inch graphite lattice, water and air cooled. The effective fraction of the internal surfaces for resonance capture was determined to be 0.50. The average value of η for natural uranium in these lattices was found to be 1.30.