KINGLET Critical Assembly: An Experiment with Flowing Fissile Solution

A critical assembly with circulating enriched uranium solution was operated for brief periods at power up to 2 MW corresponding to a core temperature differential of 13°C. Although delayed neutron precursors were swept out of the critical region, contributing little to control, power followed excess reactivity satisfactorily. At excess reactivity of 0.2 dollar, power oscillations began to appear, and above ∼0.5 dollar they diverged. The 1-s period appears to be associated with vibration of unconstrained piping. Reactivity quench coefficients are greater than those measured without flow. The difference is attributed to macroscopic release of radiolytic gas.