Characterization of oxide films formed on Alloy 600 and Alloy 690 in simulated PWR primary water by using hard X-ray photoelectron spectroscopy

Abstract

Oxide films on Alloy 600 and Alloy 690 formed during exposure to the simulated primary side water of a pressurized water reactor were characterized using hard X-ray photoelectron spectroscopy. The specimens were immersed in a solution containing 500 ppm B + 2 ppm Li with or without dissolved hydrogen at 320 or 360 °C for 24 h. Photoelectrons generated in the oxide films with thickness up to 25 nm and in the substrate alloy underneath the oxide films could be observed simultaneously without any destructive techniques such as sputtering. The oxide films were composed of an inner oxide layer of mainly Cr and a covering hydroxide layer of Ni and Cr, with needle-like oxides distributed on the outermost surface. In addition, alloyed Cr was depleted from the substrate alloy directly underneath the oxide layer. Even though the Ni-based alloys examined were mainly composed of Ni, almost no Ni oxide was present in the oxide films formed in solution with dissolved hydrogen. Most of Ni was incorporated as hydroxide. However, Cr was incorporated both in the hydroxide and the inner oxide layers.