Fusion reactors, which aim to provide a sustainable energy source, rely on liquid metal coolants like lithium or lithium-lead to transfer heat and breed tritium. However, these coolants can corrode structural materials, threatening reactor longevity. LiPb, in particular, poses significant challenges due to its high lithium content, which reacts aggressively with structural alloys.
The research team, led by Associate Professor Masatoshi Kondo in collaboration with Yokohama National University, Nippon Nuclear Fuel Development, and the National Institute for Fusion Science, explored the performance of protective oxide layers formed on ODS FeCrAl alloys under prolonged exposure to flowing LiPb at elevated temperatures. Their findings, published in 'Corrosion Science' on September 17, 2024, highlight the potential of these alloys for use in demanding high-temperature environments.
Using two alloy types, SP10 and NF12, the researchers conducted corrosion tests under static and stirred-flow conditions at 873 K to replicate operational conditions in fusion reactors. Advanced analysis techniques, such as scanning transmission electron microscopy and electron energy loss spectroscopy, were used to assess the composition and durability of oxide layers formed on the alloy surfaces.
Initial results revealed that pre-formed aluminum oxide (a-Al2O3) layers effectively mitigated early-stage corrosion but partially transformed into lithium-aluminum oxide (a/?-LiAlO2) due to lithium adsorption. Remarkably, even without pre-oxidation, the alloys developed a self-forming ?-LiAlO2 layer in situ, providing robust protection. Both a-Al2O3 and ?-LiAlO2 layers exhibited strong adhesion and resistance to exfoliation, even under significant mechanical and thermal stress caused by LiPb solidification.
"The lithium-aluminum oxide layer's durability shows that these alloys could last longer in high-temperature, high-stress settings. This layer serves as a sustainable shield that continues protecting reactor components even after initial wear," said Kondo.
Microstructural analysis revealed that lithium penetration into the oxide layers caused chemical transformation but did not significantly compromise their structural integrity. Micro-scratch tests confirmed the strong adhesion of the oxide layers, suggesting they are capable of withstanding operational stresses in fusion reactor systems.
"Our findings show that ODS FeCrAl alloys, with their ability to form durable protective layers, could play a vital role in the future of fusion reactors and other high-temperature power systems," added Kondo.
These insights mark a significant advancement toward creating durable materials for sustainable energy technologies. The ability of ODS alloys to self-form protective layers under extreme conditions could improve the longevity and safety of future fusion reactors.
Research Report:Chemical and structural durability of a-Al2O3 and ?-LiAlO2 layers formed on ODS FeCrAl alloys in liquid lithium lead stirred flow
