Application of subcriticality measuring methods for studying the temperature effect of the reactivity of uranium-water lattice assemblies

This paper presents some results of investigations of the temperature dependence of the reactivity of the MATR-1 stand of the Physics Power Institute; two techniques were used: a pulsed neutron source and an expelled source. The proposed scheme of the investigations was checked in uranium-water assemblies in which a reflector is important for the reactivity balance. The kinetic parameters were assumed for U 235 in both the experiments and calculations. The calculations were made in the two-group diffusion approximation in two dimensional geometry with the FACTOR and DNESTR programs. The constnats of the thermal neutron group were determined taking into account the heterogeneous core structure by averaging over the space-energy distribution of the neutron flux in modeled Wigner-Seitz cells. Results show that the systematic application of subcriticality measuring methods allows the direct determination of the importance of the core and reflector shapes i nthe development of the temperature dependence of the reactivity.