A Review of Circulating Voids and Gaseous Fission Product Behavior in Molten Salt Reactors

Abstract

Molten salt reactors (MSRs) are a family of advanced, generation-IV, nuclear reactors that use a circulating molten alkali fluoride fuel salt as both a primary working fluid and a fuel matrix. Since the fuel salt is liquid, gases become entrained in the fuel salt flow, and these entrained gases are called circulating voids. This paper reviews some aspects of circulating voids on reactor behavior. A formal definition of the circulating void fraction is given. A time-line of Oak Ridge reports on circulating void behavior is presented. Methods to measure the circulating void fraction are described. Foam induced by gas entrained in the fuel salt is discussed. The discovery of circulating voids in the molten salt reactor experiment (MSRE) is detailed. Aspects related to bubble size and interfacial area are reviewed. The Laplace pressure is examined. The void and pressure coefficients of reactivity are examined. Some requirements for a bubble model for xenon behavior analysis are proposed. The effects of bubble surface mobility are examined. Finally, sources of gas production in the fuel salt are investigated.