Optimization study on nuclear-grade heat exchanger metal C-type gasket seal

Abstract In a specific nuclear power plant, the metal C-type sealing ring is utilized to seal the tube side of the normal residual heat discharge heat exchanger. The original design specified silver as the outer layer material; however, silver undergoes activation under neutron irradiation, leading to increased personnel radiation exposure and extended maintenance periods. Following an in-depth investigation, it was proposed to replace the outer layer with pure nickel (N6). Given the unique structure of this sealing ring, altering the sealing layer material poses significant challenges to its sealing performance. Moreover, there has been a lack of systematic studies on sealing performance after material replacement within China, making this a critical area for domestic technological advancement. This study employs a scaled-down metal C-type sealing ring with an outer diameter of 318 mm, featuring a double-layer structure: the inner layer consists of Inconel X750 spring, the middle layer is made of Inconel 600 alloy, and the outer layer is coated with N6 pure nickel. Six types of tests were conducted on the scaled component, including sealing characteristic curve testing, overload testing, large temperature gradient thermal cycling, fatigue testing, stress relaxation testing, and hydrostatic testing. The results indicate that both the total rebound amount and the effective rebound amount meet the required standards. The sealing ring demonstrates excellent sealing and mechanical properties under extreme conditions such as overload, large temperature gradient thermal cycling, and fatigue. The stress relaxation rate satisfies the criteria, and no leakage occurred during the hydrostatic test under various conditions. These findings suggest that replacing the sealing layer of the metal C-type sealing ring with N6 pure nickel maintains its superior sealing performance. Additionally, this study establishes a systematic research methodology for evaluating the sealing ring, providing detailed and reliable data.