Effect of Low-Energy Resonance Absorber on Positive Neutron Temperature Coefficient of Dilute Plutonium-Water Solution

The positive neutron temperature coefficient of reactivity of a dilute plutonium-water solution is discussed analytically and numerically. It is explained by the competition of the temperature sensitivity coefficients of microscopic thermal cross sections of fissile materials and absorbers. The use of ¹⁷⁶Lu, ¹⁸⁰Ta, or ¹⁶⁷Er, which have absorption resonances at low energy, in the solution makes it possible for the neutron temperature coefficient of reactivity of a dilute plutonium-water solution to be negative.