Theoretical and experimental investigation of the temperature effect of heterogeneous assemblies with a heavily blocked absorber

Techniques for measuring and calculating the temperature dependence of reactivity of regular heterogeneous uranium-water critical assemblies are shortly described. The experiments were conducted in the temperature range from 20 to 240 deg C with three types of the critical assemblies differing in the number of fuel elements, structural materials and neutron absorbers (gadolinium or cadmium oxides). Two experimental techniques were used: measuring the drho/dT=f(T) dependence with subsequent integration and measuring reactivity of the system in a subcritical reactor by the pulse α method (α-damping decrement of prompt neutron flux). The calculations were performed in a two-group diffusion approximation using the Ssub(n) method to determine thermal neutron constants. It is concluded that the calculated and experimental techniques proposed are adequate to study the regular assemblies with heavily blocked neutron absorbers