Solubilities of Fission Products Under Supercritical Water-Cooled Reactor Conditions

Abstract

Understanding activity transport in supercritical water-cooled reactors (SCWR) is important in both managing worker dose in keeping with the ALARA (As Low As Reasonably Achievable) principle, and predicting the consequences of fuel defects. High temperature solubility data are required to understand and predict fission product transport under SCWR chemistry conditions. The literature data on the solubilities of selected fission products in sub- and supercritical water solutions are reviewed in this paper. While the solubilities of most metal oxides and inorganic salts typically decrease rapidly as the temperature becomes supercritical, the solubilities of fuels and some fission products show quite different behavior. As an example, the solubility of uranium (IV) oxide, and probably thorium (IV) oxide, does not change as the temperature increases from sub- to supercritical. Like most metal oxides, the major dissolved species of fission products are neutral species in supercritical water, which is a concern for all direct cycle SCWR concepts as these species can be easily transported to parts of the system outside of the reactor core. Keywords: Fission products, activity transport, solubility, high temperature