The OCP signal was also relatively constant with small spikes correlated with the spikes in the X-ray signal during the first four hours. The coincidence between OCP and X-ray signals point to a global electrostatic disturbance in the solution due to the liberation of foil pieces. Large peaks in the OCP measurements after about 5 hours are due to the corrosion of the W electrode. We confirmed this conclusion by observing a XANES signal corresponding to W 3+ after the hour five.