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<p>Fast reactors play a vital role in addressing India’s growing energy demands. The reactor’s core components are fabricated from nuclear-grade AISI 316&#xa0;L austenitic stainless steel, valued for its superior corrosion resistance, high-temperature creep strength, and impact durability. However, certain components, such as the control rod sheath, experience continuous rotational and translational motion during reactor operation. This movement, combined with prolonged exposure to high-temperature liquid sodium, leads to severe wear and surface sticking (self-welding), compromising reactor efficiency and safety. The control rod sheath functions as a protective housing, facilitating control rod movement to regulate reactor power. To enhance wear resistance and prevent self-welding, a cobalt-based Stellite 6 hardfacing layer is applied using the Gas Tungsten Arc Welding (GTAW) process. This study investigates the microstructure and microhardness of the deposited layer to improve the mechanical integrity of the sheath. The results indicate that a 2.5–3&#xa0;mm Stellite 6 coating achieves optimal hardness (450–500 HV) with strong metallurgical bonding, significantly reducing wear-related failures. Furthermore, finite element thermal analysis was conducted to determine the outer surface temperature of the base metal required to achieve the necessary inner temperature for proper weld deposition without defects. Additionally, immersed ultrasonic testing (UT) was conducted to evaluate the presence of cracks or debonding, and the results confirmed that the defects were within acceptable limits, ensuring structural integrity and long-term durability. These findings establish that Stellite 6 hardfacing provides a durable, reliable, and sustainable solution, enhancing the lifespan of fast reactor components and ensuring long-term reactor performance in extreme operating conditions. This method is recommended for critical components exposed to severe wear in nuclear environments, with broader implications for improving safety, reliability, and maintenance intervals in advanced reactor systems.</p> Graphical Abstract <p></p>

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Development of Cobalt Alloy-Based Hardfacing Procedure for Fast Reactor Control Rod Sheath Using Conventional Gas Tungsten Arc Welding Process and Solid Wire ER CoCr – B

  • 期刊论文

  • 发表日期：

    2025年12月3日

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  • N. Arunkumar,
  • R. Adithyaa,
  • B. Hariharan,
  • Aniket Shingewad,
  • M. Siva

摘要

Fast reactors play a vital role in addressing India’s growing energy demands. The reactor’s core components are fabricated from nuclear-grade AISI 316 L austenitic stainless steel, valued for its superior corrosion resistance, high-temperature creep strength, and impact durability. However, certain components, such as the control rod sheath, experience continuous rotational and translational motion during reactor operation. This movement, combined with prolonged exposure to high-temperature liquid sodium, leads to severe wear and surface sticking (self-welding), compromising reactor efficiency and safety. The control rod sheath functions as a protective housing, facilitating control rod movement to regulate reactor power. To enhance wear resistance and prevent self-welding, a cobalt-based Stellite 6 hardfacing layer is applied using the Gas Tungsten Arc Welding (GTAW) process. This study investigates the microstructure and microhardness of the deposited layer to improve the mechanical integrity of the sheath. The results indicate that a 2.5–3 mm Stellite 6 coating achieves optimal hardness (450–500 HV) with strong metallurgical bonding, significantly reducing wear-related failures. Furthermore, finite element thermal analysis was conducted to determine the outer surface temperature of the base metal required to achieve the necessary inner temperature for proper weld deposition without defects. Additionally, immersed ultrasonic testing (UT) was conducted to evaluate the presence of cracks or debonding, and the results confirmed that the defects were within acceptable limits, ensuring structural integrity and long-term durability. These findings establish that Stellite 6 hardfacing provides a durable, reliable, and sustainable solution, enhancing the lifespan of fast reactor components and ensuring long-term reactor performance in extreme operating conditions. This method is recommended for critical components exposed to severe wear in nuclear environments, with broader implications for improving safety, reliability, and maintenance intervals in advanced reactor systems.

Graphical Abstract