Use of Secondary Ions Mass Spectrometry (SIMS) for Cladding Materials Post- Irradiation Examination (PIE)

Zirconium-based alloys are widely used in the field of nuclear industry as cladding for nuclear fuel in power plants. In a pressurized water reactor (PWR), boric acid is added in the coolant for reactivity control. Lithium hydroxide is added to render the coolant slightly alkaline, which helps to inhibit corrosion product deposition on the fuel cladding and reduces the corrosion rate of structural materials. On the other hand, out-of-pile experiments demonstrated that lithium increases Zircaloy corrosion rates above a certain concentration level [1]. Moreover, the corrosion phenomenon is accompanied by the release of hydrogen gas according to the redox reaction, Zr + 2 H2O ZrO2 + 2 H2. The released hydrogen gas partly diffuses into the alloy and forms zirconium hydrides. According to the local temperature, hydrides precipitates are formed when the solubility limit of hydrogen in Zircaloy is exceeded. Their formation leads to cladding blistering and cracking: the hydrogen embrittlement. Both corrosion and H-uptake are key phenomena which reduce the cladding life time under irradiation. Postirradiation examination of irradiated cladding tubes is consequently of great interest for the understanding of the corrosion behavior. Local information (micrometer range) is required like lithium and boron concentration level (ppm range) in the oxide layer or hydrides distribution through the cladding ring. Both are data that Electron Probe Micro Analysis (EPMA) cannot provide, as these elements are too light.