The Correlation of Integral Experiments and High Energy Cross Sections

The status of integral experiments on factors important to the neutron economy of reactors is reviewed. Integral experiments on the fast effect in isolated uranium rods are found to be in agreement for normal rod sizes but in disagreement for very thick rods. Relatively low inelastic cross sections for U²³⁸ are indicated by the analysis of recent Snell experiments. The value of 1.075 ± 0.020 for the fast multiplication factor of beryllium is confirmed by a preliminary survey of beryllium moderated critical experiments. The revised Hellstrand formula for the resonance integral of U²³⁸ is in agreement with old U.S. data, except for thick rods. The accuracy of recent calculations based on the modern theory of resonance absorption requires a similar increase in the accuracy of measurements of resonance integrals in reactor lattices. Discrepancies in direct measurements of the intermediate energy variation of eta for U²³⁸ could be resolved by accurate critical experiments on simple, undermoderated U²³⁸ fuelled assemblies.