Paul Scherrer Institute uses novel X-ray imaging technique to detect internal corrosion in nuclear fuel cladding

Researchers at the Paul Scherrer Institute (PSI) have employed a novel X-ray imaging technique to conduct three-dimensional inspection of internal corrosion in nuclear fuel rod cladding material, successfully identifying pores as small as 80 nanometers. The study examined whether the protective layer surrounding fuel rods remains effective after years of exposure to cooling water and radiation. The team used cladding tube samples from nuclear power plant operations, mapping their internal structure using PSI's Swiss Light Source. Results showed the tubes remained sealed during service, and measurements indicated the protective oxide layer continued to perform its function.

These findings help assess fuel rod safety and determine whether conventional laboratory corrosion tests accurately reflect material behavior under reactor conditions. The announcement did not specify when the experiments were conducted.

Corrosion inspection of cladding material

Fuel rod cladding must remain sealed during reactor operation, even though environmental conditions can cause corrosion. Researchers therefore need to understand the rate of corrosion layer formation and its porosity. These cladding tubes typically contain more than 98% zirconium, with small amounts of other metals added to improve performance. The cladding wraps stacked uranium dioxide fuel pellets, forming fuel rods for nuclear reactors. The study brought together three research centers within PSI, covering nuclear engineering, photon science, and neutron and muon science. In the institute's hot laboratory, staff used a precision saw inside a shielded hot cell to cut wafer-thin slices of used fuel rod cladding, then used a focused ion beam to machine the material into cylinders.

The samples came from the zirconium oxide layer that forms on the cladding surface during operation.

Lead author Okan Yeti̇k said: "Ultimately, our small zirconium oxide cylinders measured just 20 micrometers in diameter, barely visible to the naked eye. A human hair is three to four times thicker." These small samples kept radiation emissions low enough for examination outside a dedicated shielded hot cell. The team examined the cylinders using ptychographic X-ray computed tomography (PXCT), developed at PSI's Swiss Light Source.

The X-ray beam scanned the sample point by point from different angles, generating high-resolution three-dimensional images of its internal structure. Co-author Andreas Menzel noted: "We were even able to identify pores as small as 80 nanometers." Measurements also showed the oxide layer retained its protective function after prolonged use. PSI researcher Liliana Duarte said: "Measurements at the SLS showed the protective oxide layer on the cladding tubes remained intact and continued to perform its role after years of use."

Application potential of the new technology

Researchers compared used material with unirradiated cladding samples exposed to water in an autoclave under high pressure and temperature. The density of the reactor-used samples was nearly identical to that of the autoclaved material, supporting the value of standard corrosion tests. This means researchers do not necessarily need used cladding for investigations. The findings can also help operators improve reactor water chemistry and help manufacturers optimize alloys and heat treatments. The technology opens possibilities for similar detailed inspections of small modular reactors and fusion reactors.

The researchers have published their findings in the journal Advanced Engineering Materials.

Impact of novel X-ray technology on nuclear safety

Using novel X-ray imaging technology to inspect corrosion in nuclear fuel cladding is crucial for nuclear safety. This research not only confirms the effectiveness of cladding material but also provides a new method for assessing nuclear fuel rod safety. As nuclear energy demand grows, ensuring safe reactor operation becomes increasingly important. The results show conventional corrosion tests may be insufficient to reflect actual conditions, prompting the industry to reconsider material inspection standards. Moreover, the technology's application potential extends beyond existing reactors to small modular reactors and fusion reactors, paving the way for future nuclear energy development.