The corrosion rates of alloys that will be present in spent fuel waste packages are being measured to
represent the generation rates of H2 in a breached package under a range of Eh-pH conditions. The H2
concentration is a crucial parameter in repository performance analyses because the presence of even
small amounts of H2 in a breached waste container can significantly decrease the oxidative-dissolution
rate of directly-disposed spent UO2 fuel. Potentiostatic tests are being conducted in pH 4, 7, and 10 buffer
solutions spiked with NaCl at several potentials that span the ranges of redox and chemical conditions
that could occur in a breached waste package. The corrosion currents are monitored as the alloys corrode
and changes in the electrical properties of the metal surfaces are measured using electrochemical
impedance spectroscopy. Results of tests with 316L stainless steel, Zircaloy-4, and 4320 low alloy carbon
steel conducted at several voltages in pH 10 solutions with added NaCl are presented as examples. The
dependencies of alloy corrosion rates on these variables and the sensitivity of the fuel dissolution rate
are discussed.