Passivity breakdown and pitting on pure copper has been studied in simulated repository ground water (x M NaCl + 2 x 10(-4) M Na2S, pH = 9.0 +/- 0.2 at 40 degrees C, as established by 0.2 M boric acid/ sodium hydroxide buffer, with x = 0.05 to 5), at elevated temperatures (22. C to 82 degrees C) by means of potentiodynamic polarization, cyclic voltammetry, and potentiostatic polarization, as well as by using SEM/EDS to explore the elemental composition of the film. By assuming that the potential breakdown sites are normally distributed with respect to the cation vacancy diffusivity, a near normal distribution in breakdown potential is predicted by the Point Defect Model (PDM) and is found experimentally at different temperatures (42-82 degrees C). From the potential sweep-rate dependence of the breakdown voltage, the critical, areal cation vacancy concentration,., leading to passivity breakdown on copper is in the range of 9.15 x 1014(-1).01 x 1015 cm(-2). These values are in excellent agreement with that estimated structurally (1014-1015 cm(-2)), assuming vacancy condensation on either the copper substrate or upon the cation sublattice of the barrier layer (Cu2S). (C) 2016 The Electrochemical Society.