Investigation of Neutron Diffusion Parameters in Liquid Moderators and Liquid Moderated Multiplying Assemblies

Abstract

The effect of voids on neutron multiplication in a natural uranium/water moderated subcritical assembly has been investigated. Voids were introduced by bubbling compressed air through the core and covered the range O% to about 10% void fraction. A 150 Kev S.A.M.E.S. accelerator provided D-D source neutrons to the subcritical assembly and neutron flux measurement was by Indium foil activation with subsequent β-counting on a plastic scintillation counter. The results of the measurement have shown that the system has a positive void coefficient of reactivity, at least, for the size of void fractions used. Good agreement was found with theory and there was also good agreement with the results of other workers, notably Kouts et.al (18) . Fluctuations were also induced in the assembly with the view of predicting the onset of local fluctuations of neutron population in reactors. For this aspect of the work a 3 Curie-Am—Be neutron source was used. instead of the S.A.M.E.S accelerator and neutron counting was by means of a Li6 loaded glass scintillation counter. Results have shown that the onset of fluctuations in a reactor is easily predictable and it is suggested that an on-line computer could be used to monitor this.