Experimental data on criticality of uranium-zirconium hydride systems with 21 and 36% enriched uranium-235

The critical facility ''Crystal'' of the Joint Institute for Power and Nuclear Research-Sosny of the National Academy of Science of Belarus was used investigate the characteristics of four critical assemblies configurations, representing non-uniform multiple zones heterogeneous uranium-zirconium hydride lattices comprising hexagonal fuel assemblies with cylindrical fuel rods, boron absorbing plates, boron and europium absorbing rods, zirconium hydride and steel side and end reflectors. The critical assemblies represented the cores collected from three types of fuel assemblies with different structure, surrounded by assemblies and units of a side reflector. The core included channels for the regulating, compensating and emergency protection rods. The moderator - ZrH_1.89. The fuel composition - UO₂ with 21 and 36 uranium-235 enrichment. The absorber in plates - B with 85 % boron-10 enrichment. The absorber in rods - B₄C and Eu₂O₃. We measured the critical configurations, the reactivity margin, the efficiency of the absorber rods and the dependence of the efficiency of the absorber rods on their depth of insertion in a core. Different methods for measuring the reactivity, the reactivity margin and the efficiency of the absorber rods we used. The presentation provides the description of the structure and the composition of the investigated critical assembly configurations and the associated experimental results. (author)