Science Tokyo demonstrates high corrosion resistance and self-healing functions in ADS structural material

A research group, including Associate Professor Masatoshi Kondo of the Laboratory for Zero-Carbon Energy, Institute of Integrated Research at the Institute of Science Tokyo, and Assistant Principal Researchers Shigeru Saito and Hironari Obayashi of the J-PARC Center at the Japan Atomic Energy Agency (JAEA), announced on March 3 that they have confirmed that FeCrAl alloy (ferritic stainless steel), a candidate structural material for accelerator-driven subcritical systems (ADS), exhibits extremely high corrosion resistance and self-healing functions under the flow environment of liquid lead-bismuth eutectic (LBE), which simulates the neutron generation components of an ADS. This was discovered through corrosion tests conducted at 723 K over a period of 4000 hours. These results are expected to be applied to ADS, which can utilize high-level radioactive waste for energy. The results were published in Corrosion Science.

ADS is expected to be realized as an innovative nuclear technology capable of providing a stable supply of zero-carbon electricity while effectively utilizing the world's ever-increasing supplies of high-level radioactive waste as energy.

This technology irradiates liquid lead-bismuth eutectic (LBE) with protons accelerated by a high-intensity proton accelerator. Using neutrons generated through the spallation reaction of the liquid LBE, the fuel core is operated in a subcritical state to obtain thermal energy while converting high-level radioactive waste into short-lived nuclides. However, liquid LBE tends to corrode structural materials.

The alloy FeCrAl, a candidate structural material, shows excellent oxidation resistance at high temperatures due to the formation of an oxide film, but the effects of liquid LBE and prolonged exposure to high heat in a reactor remained unknown.

Therefore, the research group conducted corrosion tests that reproduced the operating environment of ADS. The tests were carried out using "OLLOCHI," a non-isothermal high-temperature liquid metal flow loop and material evaluation device built at JAEA's Nuclear Science Research Institute, which can replicate actual ADS environments. The device, which is roughly the size of a basketball court, was reportedly named after its shape.

In the corrosion test, specimens of FeCrAl with abraded surfaces and specimens with oxide films (α-Al₂O₃) pre-formed on their surfaces were placed in the "OLLOCHI" test section and immersed in liquid LBE for 2000 hours to simulate the ADS operating environment. Analyses were conducted using scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX).

The results showed that on the surface of abraded specimens, an oxide film rich in Cr and Fe formed on the outermost layer, and an Al-rich oxide film formed continuously directly beneath it. This self-forming multilayered oxide film was found to suppress the leaching of metallic components from the material.

For specimens with pre-formed oxide films, it was confirmed that the films possessed high barrier properties, blocking the flow of LBE and others. It appears that pre-forming the oxide film leads to higher performance, and micro-scratch tests also confirmed that this film has excellent adhesion. Furthermore, a portion of the specimens with multilayered oxide films were artificially removed before subjecting them to another 2000 hours of immersion.

As a result, the removed sections did not corrode, and a protective film rapidly re-formed. FeCrAl alloy is intended for use in ADS components that reach particularly high temperatures. Its high durability has now been confirmed.

Kondo stated, "Moving forward, we are considering the design evaluation of materials, including whether components such as heating elements, cores, and pumps made of FeCrAl alloy will function correctly.

Unlike the material slices used in this study, full-scale components are costly. To advance our research and development, we established Lead accel Co., Ltd. (Institute of Science Tokyo Certified Venture No. 20) last year.

By continuing our research, we hope to contribute to strengthening the foundational technology for the realization of ADS."

Journal Information
Publication: Corrosion Science
Title: Reformation of protective oxide layers on artificially abraded surfaces of FeCrAl alloy during 4000 h exposure in flowing lead-bismuth eutectic
DOI: 10.1016/j.corsci.2026.113646