Exponential and Reactivity Experiments

Shape Perturbations in Critical Experiments. W. A. Reardon and R. C. Uoyd (GE-HAPO). When making heterogeneous critical mass measurements, several perturbations of unknown magnitude are usually presmt, such as the effect of an Irregular outer boundary. Critical approach type measurements were made with circular, elliptic, and rectangular cylinders to try to evaluate some of the effects. 

The uranium rods used in these experiments were 23.5 in. long, 0.175 in. in diameter, and enriched to 3.063 percmtt in U-235. They were encased in 0.025-in. wall Luclte tubes and were arranged in a 0.5-lnch triangular lattice the resulting HjO/U (total) volume ratio was 8.0. The assemblies were both fully reflected and moderated with HtO. 

The critical masses were calculated using the relation between the buckling and the semi-axis of ellipses given as tables br Boumia, and values ct material 

Measured and Calculated Critical Masses for 3.063% (1-235, 0.4445-cm Diameter Rods, 1.27-cm Triangular Lattice, Elliptic CyUnders, X - 6.4 cm. 

Eccentri- city Critical Semi-Major and Semi-Minor Axis No. of 59.69 cm Rods in Critical Cylinder Mc(meas.) (kg U) Mc(calc.) (kgU) B (cm ) 

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