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Classical molecular dynamics simulations using simple point charge water potential were performed to obtain high temperature diffusion coefficients for pure water, and for O 2 , H 2 , and OH radical in an infinitely dilute aqueous solution. The simulations were carried out at temperatures ranging from ambient to 973 K and system densities from 0.1 to 1.0 g cm −3 . A logarithmic density expansion of a hard sphere collision model was used to formulate a polynomial fit to the diffusion data and four sets of fitting coefficients are presented. Fourteen coefficients were sufficient to accurately reproduce mass transport coefficients in water at high temperatures and at supercritical conditions. Our parametric fits can be used to estimate diffusion coefficients for these species in a wide range of thermodynamic states, including those relevant to the GEN IV supercritical water cooled nuclear reactor.

Hydrogen is a clean burning energy source and an essential oxygen scavenger used in corrosion control chemistry for nuclear power plants. Here, we report on the combustion rate of hydrogen in supercritical water. The reaction of hydrogen oxidation by oxygen is studied in a flow-through reactor operating under continuous steady state conditions in terms of surface oxidation. Hydrogen released in situ from the metal oxide reactor surface is accounted for in the overall reaction kinetics. Rate constants are presented for 500, 550, and 650 °C at 25 MPa. The activation energy for the homogeneous oxidation reaction is estimated to be 96.4 kJ mol −1 . This value is comparable with the activation energies obtained for other small fuel molecules.

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