Corrosion control and anti-hydrogen-absorption of fuel cladding by surface modification technology, Fresh Green

We invent a surface modification technology, Fresh Green, to oxidize and carbonize a zirconium surface in the same process. XRD and XPS analyses indicated that a modified layer on zirconium surface is carbon-doped zirconium dioxide, in which some of oxygen atoms in monoclinic zirconium dioxide are replaced by carbon. The Fresh Green surface modification is applied for zircaloy-2 fuel cladding tubes at three different temperatures (500degC, 580degC and 660degC). Three autoclave experiments are conducted at three representative conditions: uniform corrosion, nodular corrosion, critical water corrosion. The Fresh Green surface modification at 500degC for 1h and 580degC for 1h reduce both corrosion rate and hydrogen-pickup to a half of that with untreated base material. This is because the Fresh Green layer is closely packed and adhered closely to the base material. Hydrides were found in the base material, through they were scarcely observed in the treated specimen at 500degC. Since the operating temperature of the Fresh Green process is lower than the final annealing temperature in a manufacturing process, the process does not affect the material property and crystal structure. The Fresh Green process, which can be operated at slightly higher pressure than ambient, can be introduced in the conventional manufacturing process without complicity. (author)