Neutron Beams from Split-Core Light-Water-Moderated Reactors

These studies were performed for the purpose of determining whether simple fuel alteration could lead to improved performance of neutron beam experiments at light-water-moderated reactors of the Bulk Shielding Facility (BSF) type. Thermal-neutron beams from split cores and a standard BSF core were characterized. Data were normalized to the standard core. For a split core with a 4-in. gap, the ratio of thermal neutrons-to-fast neutrons was improved by a factor of 6.6 ± 0.3 over that in a standard core; the ratio of thermal neutrons-to-gamma rays was improved by a factor of 2.9 ± 0.1 over that in a standard core. The thermal-neutron beam intensity was 67% of the value obtained from the standard core. Reactivity characteristics of split cores with a 4-in. gap were also investigated as a function of size. In an assembly with a built-in excess k of > 2.5%, it was found that one section of the core could be taken critical independent of the position of control rods in the other section.