Neutron Penetrations Through Thick Sodium

Neutron reaction rates were measured by activation foils and thermoluminescent detectors through 180-cm-thick sodium shields and also through the layers of a 6-cm-thick iron plate and the sodium shields. A tightly coupled source shield configuration was constructed with the fast neutron reactor YAYOI as a source. Analysis of the experiments was made by using the DOT 3.5 code with 13-group neutron cross sections from the ENDF/B-IV library. Bondarenko-type self-shielding factors were included. The source condition for the analysis was determined by an iteration method from the experimental result at the reactor-shield interface and the initial estimate that was obtained from the core criticality calculation. The calculated neutron distributions in the shields agree with the experiments within ∼25% for the penetration through 180-cm-thick sodium. The shapes of the spatial distributions of the reaction rates in the shields show rather good agreement with the experiment.