NUCLEAR DESIGN OF A SUBCRITICAL ASSEMBLY DRIVEN BY ISOTOPIC NEUTRON SOURCES

A feasibility study of a conceptual nuclear design of a facility capable of producing high thermal neutron fluxes using isotopic neutron sources in a multiplying medium was carried out. The one-dimensional multigroup neutron diffusion equation was solved using the finite difference technique. A computer code SUNDES was written in FORTRAN 77 programming language and used to study the effect of reflectors, shielding materials and strength of isotopic neutron sources on the production levels of neutron fluxes. The neutronic calculations showed that with a homogeneous mixture of 20% enriched U02 and Be as multiplying medium, BeO as reflector, Al as cladding and concrete as shield, thermal neutron 7 2 fluxes as high as 1x10 n/cm -s could be produced. Simultaneous irradiation of samples in two different regions at different fluxes is possible in the assembly. The analysis also revealed that different orders of thermal neutron fluxes could be produced depending on the strength of the driving isotopic neutron sources.