Inherent Shutdown Capabilities of Metal-Fueled Liquid-Metal-Cooled Reactors during Unscrammed Loss-of-Flow and Loss-of-Heat-Sink Incidents

Abstract

The longer term response of oxide- and metal-fueled liquid-metal-cooled reactors to unscrammed loss-of-flow and loss-of-heat-sink failures is investigated. The investigation consists of a review of numerical transient calculations performed by the Argonne National Laboratory Reactor Analysis and Safety Division, and of analytical analyses of semiasymptotic states. The emphasis is on the identification and evaluation of an inherent shutdown state for metal fuel, with its high heat conductivity, as an alternative to the familiar low-power asymptotic critical state. Design implications for retaining the inherently effected shutdown for a sufficiently long period are discussed and quantitatively evaluated. In addition, the effect of uncertainties of reactivity coefficients on predictions for such unscrammed transients is investigated. It is shown how measurements during a preoperational safety demonstration phase can validate and possibly correct those predictions.