Fasteners Use for Nuclear Power Plants

Nuclear-grade fasteners are specialized fastening components designed to meet the stringent requirements of nuclear power plants. These fasteners must withstand extreme temperatures, high pressure, radiation, and corrosive environments while maintaining their structural integrity and functionality. Materials such as A453 Grade 660 and B637 UNS N07718 are often used in manufacturing these fasteners due to their high-performance properties, such as excellent corrosion resistance, high tensile strength, and resistance to hydrogen embrittlement.

Nuclear power plants operate under harsh conditions that involve high temperatures, high pressure, and a corrosive environment. Such an environment is prone to precipitate corrosion and attendant degradation of components, thereby compromising their performance and endangering the overall safety and integrity of the plant. To ensure the reliability and longevity of components, selecting appropriate fasteners designed for these environments is crucial.

The corrosive environment in a nuclear power plant primarily stems from the presence of coolant be it water or sodium, which is used to transfer heat from the reactor core to the heat exchanger. In addition, the incidence of radiation can cause radiolysis of water, resulting in the formation of corrosive species, such as hydrogen peroxide, oxygen, and hydrogen. These factors contribute to various forms of corrosion, including stress corrosion cracking, pitting corrosion, and intergranular corrosion.

Nuclear-grade fasteners are designed to withstand these harsh conditions. Materials such as A453 Grade 660, an iron-based superalloy quality, and B637 UNS N07718, also known as Inconel 718, are ubiquitously employed in the manufacturing process of nuclear-grade fasteners. These materials exhibit excellent corrosion resistance, high mechanical strength, and resistance to hydrogen embrittlement, making them suitable for nuclear power plant applications.

Hydrogen embrittlement represents a phenomenon in which metals become brittle and susceptible to cracking due to the ingress and permeation of hydrogen into the material's microstructure. This can lead to premature failure of components, posing a risk to the plant's safety and reliability. Within nuclear power plants, hydrogen embrittlement can occur due to the existence of hydrogen in the environment, and due to the radiolysis of water, giving rise to hydrogen as a secondary product.

Using high-performance materials: As mentioned earlier, materials such as A453 Grade 660 and B637 UNS N07718 are commonly exploited in manufacturing nuclear-grade fasteners. These materials feature high corrosion resistance, augmented tensile strength, and strong resistance to hydrogen embrittlement, qualifying them for use in nuclear power plants.

Surface treatment of fasteners: A diverse array of surface treatments can be applied to fasteners to enhance their resistance to hydrogen embrittlement and corrosion. These treatments may include electroplating, anodizing, or the application of coatings such as zinc, cadmium, or phosphate. These treatments erect a barricade between the fastener's surface and the corrosive environment, reducing the likelihood of hydrogen ingress and subsequent embrittlement.

An engineering case that vividly exemplifies the cruciality of adopting nuclear-grade fasteners is the replacement of the reactor coolant pump (RCP) fasteners within a pressurized water reactor (PWR) nuclear power facility. The original fasteners, made of A193 B7 material, were found to have suffered from stress corrosion cracking, which could have led to catastrophic failure of the RCPs. The fasteners were replaced with A453 Grade 660 fasteners, which can furnish enhanced corrosion resistance and improved resistance to hydrogen embrittlement, ensuring the safety and reliability of the reactor coolant pumps.

Another example can be found in the construction of advanced boiling water reactors (ABWRs). B637 UNS N07718 fasteners were crucial in addressing concerns related to stress corrosion cracking in the reactor pressure vessel and associated components.  These high-performance fasteners not only improved the safety and reliability of the reactor but also extended the service life of the components, reducing maintenance costs and minimizing downtime.

In conclusion, using the appropriate nuclear-grade fasteners is essential for ensuring the safety, reliability, and longevity of components in a nuclear power plant. By utilizing high-performance materials such as A453 Grade 660 and B637 UNS N07718 and employing appropriate surface treatments, nuclear-grade fasteners can effectively withstand the harsh environments present in nuclear power plants, reducing the risk of hydrogen embrittlement and other forms of corrosion.

Understanding the unique challenges presented by the corrosive environment in a nuclear power plant is crucial for selecting the most suitable fasteners for each application. Integrating engineering case studies and adopting optimal practices in the design, material selection, and surface treatment of fasteners enable engineers and plant operators to ensure critical facilities operate continuously, safely, and efficiently. Nuclear-grade fasteners play a vital role in maintaining the structural integrity of components under extreme conditions, and their proper selection, design, and installation are essential for the safe and reliable operation of nuclear power plants. By employing high-performance materials and surface treatments, nuclear-grade fasteners can effectively mitigate the risks associated with hydrogen embrittlement and other forms of corrosion, ensuring that these essential facilities can maintain long-term performance and safety.

Nuclear-grade fasteners are commonly made from A453 Grade 660, an iron-based superalloy, and from B637 UNS N07718, also known as Inconel 718. Both combine high tensile strength with corrosion resistance and resistance to hydrogen embrittlement, which is what allows the fasteners to keep their structural integrity in a reactor environment.

Standard items can be supplied from one piece. Special grades, non-standard lengths and custom coatings are quoted per drawing, so the minimum is set by the specification you send.

Normal production is completed within 30 days as a rule. The actual schedule depends on quantity, material grade and surface treatment, and stock items can go out immediately.

We accept common international terms including T/T and L/C. The final arrangement is agreed together with the quotation for each order.