Honeycomb structure found in oxide scale on lead-based small reactor materials

Recently, the research team led by Jiang Zhizhong, from the Hefei Institutes of Physical Sciences (HFIPS) of the Chinese Academy of Sciences (CAS), found a honeycomb structure in localized regions at the top of the magnetite layer on martensitic steel and analyzed its reason and process of formation.

Small nuclear reactors have good application prospects in marine energy, regional power supply, seawater desalination and other fields. The lead-cooled fast reactor with an eutectic lead-bismuth alloy (LBE) as the main coolant has unique miniaturization advantages: compact core, high nuclear heat transfer efficiency and simple auxiliary system. However, homogeneous oxidation corrosion or solution corrosion may occur in steel materials, and LBE infiltration and pitting corrosion may also occur in local areas, due to the high solubility of Fe, Cr and Ni in the high temperature LBE. Pitting corrosion is one of the most destructive forms of corrosion, which will seriously affect the long-term safe service of lead-cooled small fast reactor.

“We found that the honeycomb structure was composed of many oxygen-poor pores and surrounding net-like branches,” said Luo Lin, one of the key staff members of the research team. “Low oxygen concentrations favored the formation of honeycomb structures in a shorter time and more domains.”

In addition, the pore size and surface areas of oxygen-poor regions increased with corrosion time. By 2000 h, the oxygen-poor regions had extended to the magnetite and spinel layers below the pores, resulting in numerous oxygen vacancies in the upper layers.

“The honeycomb structure can become a nucleation point of pitting corrosion and promote the development of pitting corrosion,” Luo concluded.

This study showed that the presence of a honeycomb structure meant that the low dissolved oxygen concentration in the LBE was low and the design of the oxygen control system needed to be optimized.

– This press release was originally posted on the website of the Hefei Institutes of Physical Sciences of the Chinese Academy of Sciences

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