Aqueous Chemistry of Fission Products under Supercritical Water Reactor Coolant Conditions

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This proposal seeks funding for the second phase of a collaborative project that uses state-of-the-art instruments to determine chemical equilibrium constants for simple acids, bases, dissolved metals, and metal complexes under the extreme conditions that will be encountered in the proposed Generation IV supercritical-water-cooled nuclear reactor ("SCWR"). The instrumental methods include Raman and UV-visible spectroscopy; AC conductance; and visualization techniques; supported by ab initio computations. These are extremely specialized pieces of high-precision equipment, with capabilities shared by few other laboratories in North America, constructed for the specific purpose of making quantitative measurements under SCWR operating conditions. The first phase of the project included the construction of high-pressure cells and novel instruments for operation in the supercritical region. Theoretical and Raman studies on copper, nickel and cobalt complexes, and novel conductivity studies on strontium ion pairing up to 350 °C were completed. The second phase will extend these studies to more fission-product species; to uranyl complexes; and to temperatures above the critical point (T > 373 °C). Semi-empirical equations will be developed to predict the behaviour of these and other aqueous species under the extreme conditions relevant to Gen IV steam generator chemistry. The ions to be studied include cesium, strontium, a trivalent lanthanide fission-product ion (Pr3+, Y3+ or Ce3+) , iodide, pertechnetate (as its surrogate stable isotope, perrhenate); and their reaction products with contaminant species and possible pH control agents.