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Micro-Tensile Testing of Chromium Coated Zirconium Cladding

After the Fukushima accident there has been a large push globally for accident tolerant fuels (ATF) to increase the grace period during an accident, that is, the time during which operators may be able to avoid major consequences by undertaking mitigating actions. At Fukushima, the oxidation of the Zircaloy cladding produced hydrogen gas, that contributed to the failure of the primary containment. A concept for ATF is to coat zirconium-based cladding with chromium to inhibit the oxidation of the cladding and reduce hydrogen production. 

Product Number: ED22-17270-SG
Author: David Frazer, Cameron Howard, Yachun Wang, Daniel Murray, Fei Teng, Colin Judge, Jorie Walters, Benjamin Maier, Allan Jaworski, Jonathan Wright, Luke Olson
Publication Date: 2022
$20.00
$20.00
$20.00

After the Fukushima nuclear accident, there has been a push worldwide for accident tolerant cladding concepts. During the accident, the oxidation of the Zirconium based cladding led to hydrogen production that contributed to the primary containment failure. One of these concepts is to coat the zirconium cladding rods with a material that inhibits oxidation and prevents hydrogen gas formation. This led to coating the zirconium with chromium as the protective layer. An important parameter when coating a material is the adhesion strength of the coating to the substrate material, which can be difficult to measure on thin coatings on the order of 10s of micrometers in thickness. Small scale testing like micro-tensile testing can be used to evaluate the deformation and the adhesion of the coating. In this work, micro-tensile testing was performed at room temperature and near PWR prototypic temperature at 300 ºC on chromium coated zirconium cladding material. A total of 3 different coating methods were used: 2 cold spray variants and physical vapor deposition (PVD). It was observed that the micro-tensile specimens for all 3 coatings mostly failed in the zirconium substrate material at elevated temperature in a plastic fashion. This demonstrates excellent adherence of the coatings to the zirconium substrate, especially at reactor operation temperature. For the cold spray specimens tested at room temperature, a few brittle fractures were observed in the chromium coatings due to manufacturing defects. In the testing of these early stage developmental coatings, only 4 out of 51 total micro-tensile bars failed at their interface, demonstrating excellent future promise.


After the Fukushima nuclear accident, there has been a push worldwide for accident tolerant cladding concepts. During the accident, the oxidation of the Zirconium based cladding led to hydrogen production that contributed to the primary containment failure. One of these concepts is to coat the zirconium cladding rods with a material that inhibits oxidation and prevents hydrogen gas formation. This led to coating the zirconium with chromium as the protective layer. An important parameter when coating a material is the adhesion strength of the coating to the substrate material, which can be difficult to measure on thin coatings on the order of 10s of micrometers in thickness. Small scale testing like micro-tensile testing can be used to evaluate the deformation and the adhesion of the coating. In this work, micro-tensile testing was performed at room temperature and near PWR prototypic temperature at 300 ºC on chromium coated zirconium cladding material. A total of 3 different coating methods were used: 2 cold spray variants and physical vapor deposition (PVD). It was observed that the micro-tensile specimens for all 3 coatings mostly failed in the zirconium substrate material at elevated temperature in a plastic fashion. This demonstrates excellent adherence of the coatings to the zirconium substrate, especially at reactor operation temperature. For the cold spray specimens tested at room temperature, a few brittle fractures were observed in the chromium coatings due to manufacturing defects. In the testing of these early stage developmental coatings, only 4 out of 51 total micro-tensile bars failed at their interface, demonstrating excellent future promise.