In a nuclear power plant, safety isn’t just “important,” it’s “the only thing.” The consequences of a radioactive leak are unimaginable. And you might not realize that a cable passing through a wall or a pipe running through a floor—these seemingly insignificant “small holes”—are actually one of the most critical “Achilles’ heel” in the nuclear safety system.

Why? Because the sealing of a nuclear power plant must not only be fireproof, waterproof, and explosion-proof, but also radiation-resistant, high-temperature resistant, earthquake-resistant, and age-resistant for 60 years! Traditional methods of “sealing holes” with fire-retardant putty and rubber rings simply cannot withstand the extreme environment of the nuclear island for more than a few years. So what do modern nuclear power plants rely on? The answer is—TST SEAL nuclear-grade safety sealing module solutions.

The “Hellish” Challenge of Nuclear-Grade Sealing

The operating conditions of a nuclear power plant are considered the industry’s “extreme testing ground”: High temperature and high pressure: Primary circuit water temperature 350℃, pressure 15.5MPa, ordinary materials directly “soften.”

High Radiation: Fast neutron flux exceeding 10²¹ n/cm² will cause rubber to pulverize and metals to become embrittled.

Boric Acid Corrosion: Cooling water containing 1800 ppm boric acid induces stress corrosion cracking.

Seismic Load: SSE (Safe Shutdown Earthquake) acceleration reaches 0.3g; seals must be “vibration-resistant and crack-resistant.”

Design Life of 60 Years: Unlike ordinary factories where “replace when it breaks,” seals must be reliable from the start, ensuring lifelong reliability.

In this environment, seal failure equals safety failure. Therefore, nuclear power plant seals are not “components,” but core components of the safety system.

TST SEAL Nuclear-Grade Sealing Module’s “Triple Defense” Philosophy: Modern nuclear power plants employ a “defense-in-depth” concept, with seals consisting of three layers:

First Layer: Metal Seal—A Radiation-Resistant “Steel Fortress”: Made with nuclear-grade alloys such as Inconel 718 and 316LN stainless steel, C-rings and O-rings are high-temperature resistant, radiation-resistant, and high-strength. For example, reactor pressure vessel flanges achieve “zero leakage” thanks to double Inconel C-rings.

The second layer: Graphite sealing – an emergency “self-healing shield.” This uses materials such as boronized graphite and pyrolytic graphite. In a LOCA (Loss-of-Water Accident), high-temperature steam causes the graphite to form a borosilicate glass layer, actively “healing” cracks and maintaining a seal.

The third layer: Intelligent monitoring – 15-year advance warning. Embedding FBG fiber optic sensors or neutron damage monitoring chips at critical sealing points allows for real-time monitoring of stress, temperature, and radiation damage, with a lifespan prediction error of <5%, achieving “predictive maintenance.”

Real-world example: The “pressurized sealing” miracle at Haiyang Nuclear Power Plant. In 2023, the compressed air system at the Haiyang Nuclear Power Plant in Shandong Province experienced a sudden pipeline leak. However, the unit was operating at full power and could not be shut down for isolation. What to do?

Engineers employed pressurized sealing technology:

A custom-designed clamp was fitted over the leak point;

Nuclear-grade sealant (radiation- and pressure-resistant) was injected;

The seal was completed within 3 hours without shutting down the reactor or reducing power, preventing an unplanned shutdown and saving over ten million yuan in economic losses.

This success was built upon meticulous control over sealing materials, processes, and procedures.

Cable Penetration Sealing: The Nuclear Island’s “Neural Firewall”

Tens of thousands of cables pass through the containment vessel in nuclear power plants, each a potential risk point. The solution was:

Modular Fireproof Sealing System: Utilizing nuclear-grade fireproof modules with expanded graphite, ceramic fiber, and a stainless steel frame, providing 3 hours of fire resistance and protection against LOCA accidents.

Dual Protection: Electromagnetic Shielding and Airtightness: Preventing external electromagnetic interference from affecting the instrumentation and control system while ensuring the airtight integrity of the containment vessel (leakage rate ≤1×10⁻⁹ m³/s).

Seismic Design: Passing ASME QME-1 seismic testing, with sealing performance fluctuations of <10% after vibration.

Industry Trends: From “Passive Protection” to “Active Sensing”

The Rise of Intelligent Sealing: Integrated sensors enable real-time monitoring of sealing status, and digital twin systems simulate sealing integrity under earthquake conditions.

Breakthroughs in New Materials: Such as self-healing metal seals (microencapsulated low-melting-point alloys that automatically seal cracks at 62℃), and CVD-densified graphite (porosity <0.1%).

Accelerated Domestic Production: Previously reliant on imports, TST has achieved independent development of nuclear-grade sealing components, breaking through the “bottleneck” problem.

In nuclear power plants, there are no “small parts,” only “great responsibilities.” Every TST SEAL sealing module is the cornerstone of 60 years of safe operation. Though hidden within walls and buried underground, they silently withstand the tests of high temperature, high pressure, and strong radiation, safeguarding the safety of millions.

In the future, as Hualong One and Guohe One go global, China’s nuclear-grade sealing technology is moving from “following” to “leading.” These “sealed fortresses,” only a few centimeters in diameter, are not only the culmination of technology but also the source of China’s confidence in “going global” with its nuclear power industry.