Experimental studies of neutron diffusion in the presence of absorbers and voids
Boundary conditions at the surface of a control absorber were investigated for thermal and epithermal neutron groups. Experimental measurements were obtained from a graphite moderated exponential assembly according to the established method, and compared with theoretical predictions of the same valu...
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Imperial College London
1963
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| Online Access: | https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.622107 |
| Summary: | Boundary conditions at the surface of a control absorber were investigated for thermal and epithermal neutron groups. Experimental measurements were obtained from a graphite moderated exponential assembly according to the established method, and compared with theoretical predictions of the same values. Thermal neutron boundary conditions for black cylindrical absorbers were investigated in purely diffusing assemblies, and it was concluded that homogenization of a medium with large holes leads to an overestimate of thermal neutron absorption in the absorber. An approximate correction was calculated to bring the theory into better agreement with experiments. The effective epithermal group extrapolation length was deduced from experiments on two multiplying lattices with different diffusion coefficients using both the uncorrected and corrected thermal group values from the previous work. These were then compared with a theoretical epithermal group extrapolation length obtained from an approximate solution for the neutron slowing down density at the surface of the control absorber from fission energy to the thermal group boundary. Variation of the effective epithermal group extrapolation length with reactor supercell radius has been predicted by means of the approximate averaging technique. |
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