Development of advanced in situ techniques for chemistry monitoring and corrosion mitigation in SCWO environments. 1997 annual progress report

'This report evaluates the first year''s results of the research on the development of advanced electrochemical sensors for use in high subcritical and supercritical aqueous environments. The work has emphasized the designing of an advanced reference electrode, and the development of high-temperature pH and redox sensors for characterizing the fundamental properties of supercritical aqueous solutions. Also, electrochemical noise sensors have been designed for characterizing metal/water interactions, including corrosion processes. A test loop has been designed and constructed to meet the expected operation conditions. The authors have also developed an approach to define a practical pH scale for use with supercritical aqueous systems and an operational electrochemical thermocell was tested for pH measurements in HCl + NaCl aqueous solutions. The potentials of the thermocell for several HCl(aq) solutions of different concentrations have been measured over wide ranges of temperature from 25 to 400 C and for flow rates from 0.1 to 1.5 cm min{sup -1} . The corresponding pH differences ({Delta}pH) for two HCl(aq) concentrations in 0.1 NaCl(aq) solution have been experimentally derived and thermodynamically analyzed. Their first experimental measurements, and subsequent theoretical analysis, clearly demonstrate the viability of pH measurements in high subcritical and supercritical aqueous solutions with a high accuracy of \2610.02 to 0.05 units.