Electrochemical and direct build up measurements of oxide deposition in accelerated flow

CRUD deposition is known to occur at high temperature in high purity hydrogenated water such as that typically used in a primary circuit of a pressurized water reactor (PWR), and is more severe in regions of accelerated flow. The deposition mechanism is debated, however electrokinetic effects are believed to induce a polarisation across the solution/metal interface and support a Faradaic deposition process. To verify this mechanism, a miniature cell was built to evaluate the effects of water chemistry and flow rate on CRUD deposition, and to determine whether it is possible to detect currents associated with the formation of CRUD. The investigations were carried out by monitoring the potential of different sections of the flow cell as a function of the flow rate and water chemistry. A series of electrochemical measurements were carried out by galvanically coupling different sections of the flow cell and autoclave flow loop, to identify the streaming current as well as the current distribution that can be responsible for the CRUD deposition. The net currents associated with CRUD build up were shown to be cathodic overall in the flow orifice, but it is also clear that this could allow for anodic and cathodic regions to coexist on a sample. Furthermore, the current component was found to be anodic in high purity water and cathodic in lithiated and hydrogenated water. The effects of water chemistry and flow conditions on the current distribution in the region of accelerated and decelerated flow are also discussed.