This study aims at providing quantitative data concerning the oxygen and hydrogen diffusion through the oxide scale formed on alloy 600 in PWR primary medium conditions (325 degrees C) using D-2 and O-18 isotopes as markers. The diffusion coefficients were calculated according to a short-circuit diffusion of the tracers along the oxide grain boundaries (so-called "C-regime"). The values obtained are respectively D-sc = 4.6+/-0.9 x 10(-17) cm(2)/s for O-18, and D-sc = 5.2 +/-1.2x 10(-17) cm(2)/s for D-2. These experiments confirm that the transport mechanism of hydrogen through the oxide scale as hydroxide ions on the anionic sublattice is highly probable. The effect of hydrogen subsequent absorption by the alloy substrate, notably in stress corrosion cracking phenomenon is discussed. (c) 2012 Published by Elsevier B.V.