Reactivity Measurements in a Thorium Critical Assembly

Measurement of the reactivity effect due to substitution of metallic thorium for the core elements in a critical assembly has been made as part of the preliminary experiment for an intermediate reactor by using the multiregion critical core. The results of criticality calculations have been in good agreement with experiments in the case of the core without thorium, although the calculated neutron multiplication factor has been ∼2% larger than the experimental value for the core with thorium.