Effect of Water Gaps on Various Nuclear Parameters of a Light-Water Reactor

Neutron density and importance distributions, β_eff/Λ and moderator temperature coefficients have been experimentally studied in connection with a central water gap of a light-water reactor having a water to UO₂ volume ratio of 1.5. Thermal importance functions are determined from the reactivity weighting function, while the fast importance functions are measured by a ²⁵²Cf source introduction method. Values of β_eff/Λ measured by pulsed-neutron experiments decrease from 202 sec⁻¹ in the uniform core to 185 sec^−1- for the core with a water gap of 6.7 cm effective radius. It is also shown that the water gap influences the moderator temperature coefficient to a considerable extent.