Theoretical Study of Deuterium Isotope Effects on Acidity at Ambient and Hydrothermal Conditions
Hart Plommer, 1,2 Yulia Egorova, 1,3 Nelaine Mora-Diez1*
1Thompson Rivers University, Department of Chemistry, Kamloops, Canada
2Memorial University of Newfoundland, Department of Chemistry, St. John’s, Canada
3University of British Columbia, Department of Earth and Ocean Sciences, Vancouver, Canada
Email: nmora@tru.ca
Heavy water (D2O) plays an important role as a neutron moderator and coolant in CANDU (Canada Deuterium Uranium) nuclear reactors, allowing unenriched uranium to be used as a fuel. The lifetime of these reactors is compromised by corrosion of the D2O-carrying pipes because acidic species present are chemically altered by deuterium isotope exchange. Established corrosion mitigation techniques are insufficient to deal with this problem as they are based on data generated from light water since very little data (i.e., pKa values) is available for heavy water under hydrothermal conditions. Our research involved the computational determination of pKa values of 74 weak organic and inorganic acids in both H2O and D2O at ambient (25o C, 101.3 kPa) and hydrothermal (250o C, 20.0 MPa) conditions using DFT and continuum solvation methods. The calculated difference of pKa between D2O and H2O at ambient conditions for the studied acids is in very good agreement with experimental values, which provides confidence in the calculated pKa difference at hydrothermal conditions, for which little experimental data is available. In addition, both pKa differences follow a very interesting pattern depending on temperature and pressure which is further investigated.