Other Reflector Geometries

The optimum light collection geometry for chemiluminescent solutions uses an ellipsoidal reflector with the light source at one focus and a cooled phototube photocathode at the other. Individual colored glass filters are placed near the face of the phototube and the emission spectrum is determined by the differences in filter transmissions. With this idealized system the authors report a sensitivity such that their noise equivalent signal at 500 nm and a bandwidth of 30 nm is (Inaba et at., 1979)... 

Calculations performed assuming the same contents in all tanks indicate that the reactivity of the tank next to the concrete reflector exceeds that of the other tanks. This is due to enhanced reflection of epithermal neutrons by the concrete. Solutions of U, which are more reactive in slab geometry than solutions of Pu or U, will only be placed into the new tanks located away from the concrete wall. (This prevents contamination of other tanks by radioactive decay daughters.) Calculations assuming that the two tanks closest to the wall are filled with Pu(N03)4 and that the two outer tanks are filled with U02(N03)2, yield keff = 0.8S8 0.006. This is about the same as when all tanks are Filled with Pu solution, and indicates that the reactivity of a polyethylene-reflected tank of solution docs not exceed the reactivity of a conciete-refleeted tank of Pu solution. Additional calculations show that the subcriticality of the four-tank grouping is not jeopardized by off-normal construction well beyond that to which control is readily achievable. 

Before discussing the analogous treatment of other geometries, some of the physical consequences of the addition of the reflector will be considered. The results which follow are developed for the special case of the sphere, but similar relations can be obtained for the cylinder and the rectangular-block reactors. We begin with a study of the reflected-sphere system in which the extrapolated thickness (Ri — Ro) of the reflector is small compared to both the core radius Rq and the diffusion length in the reflector Lr, (Admittedly the diffusion theory postulated... 

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