PSI Researchers Map Nuclear Fuel Rod Corrosion in 3D at Nanoscale Resolution

Researchers at Switzerland's Paul Scherrer Institute (PSI) have applied a three-dimensional imaging method to examine corrosion on nuclear fuel rod cladding tubes at nanometer resolution, according to a report by TechXplore (https://techxplore.com/news/2026-10-3d-imaging-technique-nuclear-fuel.html). The findings, published in the journal Advanced Engineering Materials, provide direct structural measurements of cladding materials retrieved after years of active service in a nuclear power plant.

Fuel rod cladding tubes must remain leak-tight despite prolonged radiation exposure and corrosive contact with cooling water. To inspect how corrosion layers evolve, a cross-disciplinary team spanning PSI's Center for Nuclear Engineering and Sciences, Center for Photon Science, and Center for Neutron and Muon Sciences prepared microscopic samples inside PSI's Hot Laboratory. Technicians used precision saws within shielded hot cells and a focused ion beam to machine zirconium oxide surface layers into cylinders measuring just 20 micrometers in diameter—roughly one-third the thickness of a human hair.

Reducing the specimen volume significantly lowered its ionizing radiation output below the regulatory threshold requiring shielded containment. That reduction allowed the team to transfer the sample to PSI's Swiss Light Source (SLS) synchrotron for analysis using ptychographic X-ray computed tomography (PXCT). The technique scans specimens point by point from multiple angles using an X-ray beam to build three-dimensional structural reconstructions, resolving internal pores as small as 80 nanometers.

The imaging demonstrated that protective zirconium oxide layers remained intact and functional after years of reactor operation. The researchers also scanned non-irradiated control cladding prepared in autoclaves—pressurized vessels simulating reactor temperature, pressure, and water conditions—and found that the material density of spent reactor cladding was practically identical to that of the autoclaved samples.

This density match confirms that standard non-radioactive autoclave testing provides an accurate proxy for in-reactor material degradation, reducing the need to extract and analyze spent radioactive cladding for routine assessments. PSI researchers noted that the diagnostic method can assist operators in optimizing cooling water chemistry and guide fuel manufacturers in tailoring alloy compositions, while offering a framework to evaluate structural materials for future small modular reactors and fusion systems.