Neutron Streaming through Narrow and Long Annulus

Neutron streaming in a very narrow and long stainless steel annulus which was 3 mm wide and 2,480 mm long, was measured by TLDs and a neutron dose rate meter at the fast neutron source reactor YAYOI. The attenuation was very strong near the entrance and became very weak beyond 900 mm. The weak attenuation was due to the streaming of neutrons through the annulus. The two-dimensional discrete ordinates transport calculation with a forward biased S418 quadrature set failed to predict the attenuation beyond the point where the most-forward ray from the entrance intersected the wall of the annulus. It was practically impossible to analyze the streaming problem by the Sn code with more detailed Sn quadratures. The analytic expression describing the direct component agreed fairly well with the experiment far from the entrance of the annulus.