Initial Conversion Ratios and Fast Fission Factors in Heavy-Water Natural-Uranium Lattices Using 19-Element UO₂ Fuel Rods

A previously described experimental method of determining initial conversion ratios in reactor lattices has been improved. Measurements have been made on D₂O-cooled, 19-element UO₂, heavy-water lattices at pitches of 18, 21, 24, 28, and 36 cm. The initial conversion ratios obtained were 0.9547 ± 0.0086, 0.8578 ± 0.077, 0.7671 ± 0.0069, 0.7416 ± 0.0067, and 0.6853 ± 0.0062 and the resonance escape probabilities derived are 0.8226, 0.8656, 0.9104, 0.9228, and 0.9511, respectively. The fast fission factors obtained for the 18, 24, 28, and 36 cm lattice pitches were 1.0283, 1.0265, 1.0253, and 1.0247.