Critical Experiments on Light Water Lattices of UO₂ and Gd₂O₃ Rods

The physical behavior of the mockup burnable poison rods, containing 0.5, 1.0, and 2.0 wt% Gd₂O₃ in natural uranium oxide pellets, has been studied in critical experiments. Specifically, the reactivity effects, thermal-neutron density distributions, and overall temperature coefficient of reactivity were of interest when related to the poison effect. It was shown that the poison reactivity effect did not change greatly when the Gd₂O₃ content of the fuel pellets was >0.5 wt%. The poison also made the temperature coefficient of reactivity more negative. Some analytical methods are given, and the calculated and experimental results are compared.