Corrosion damage to metals caused by nuclear irradiation creep
Thread Content
1. Core mechanism of action The essence of the synergistic destruction of nuclear irradiation creep and corrosion is that microscopic defects produced by irradiation accelerate creep deformation and corrosion processes at the same time, and the two amplify the damage effects of each other. The dual role of microscopic defects: Irradiation generates a large number of vacancies, self-interstitial atoms and dislocation rings, which not only induce preferential absorption of point defects through stress, promote dislocation climbing and trigger irradiation creep, but also destroy the integrity of the protective oxide film on the metal surface, providing a channel for the diffusion of corrosive media. Creep-corrosion synergistic effects: The continuous plastic deformation caused by creep will continuously tear the passivation film on the metal surface, continuously exposing the fresh matrix to the corrosive medium. ； The local thinning of materials caused by corrosion will further increase the local stress level, which in turn accelerates the creep process, forming a vicious cycle. 2. Typical damage manifestations: the overall corrosion rate increases significantly: In the pressurized water reactor water environment, the radiation creep coupling radiation effect can increase the corrosion rate of stainless steel, zirconium alloy and other materials by 1.2 to 4.4 times, and the high-temperature corrosion rate of carbon steel can even increase by 3 to 5 times. Increased risk of localized corrosion: Grain boundaries and dislocation-enriched areas where creep deformation is concentrated will become the locations where corrosion occurs preferentially, greatly increasing the probability of intergranular corrosion and radiation-assisted stress corrosion cracking (IASCC), and ultimately triggering sudden fracture failure of components. Rapid deterioration of material properties: Under the action of radiation creep, the allowable stress of materials such as austenitic stainless steel will decrease significantly. At the same time, the combined effect of corrosion and creep will accelerate the accumulation of helium bubbles and cavities at the grain boundaries, inducing helium embrittlement and further weakening the mechanical load-bearing capacity of the material.
This thread is really thorough. The synergistic damage of creep and corrosion under nuclear irradiation environment is indeed a key issue in the field of nuclear materials. The "dual role of microscopic defects" and "creep-corrosion synergistic effect" in the post are analyzed very well, especially the fact that the passivation film is constantly torn apart is very vivid, and this is indeed the case in actual service. I would like to add two points: In addition to radiation-induced segregation and dislocation loops, irradiation can also promote the redistribution of solute atoms (such as radiation-induced segregation), leading to local composition changes, thereby further aggravating corrosion behavior. This is especially obvious in austenitic stainless steels. The dominant mechanism of this synergistic effect will be different when the temperature, dose rate, and stress level are different. It is recommended to pay attention to whether there is a "critical stress" or "critical damage threshold" point between irradiation creep and corrosion, which is of great reference for engineering design. However, these are all deductions based on existing theoretical models. For specific alloys or irradiation conditions, it is recommended to consult the relevant evaluation literature of ASME BPVC or IST FA, or conduct targeted test verification. Thank you to the author for sharing such hard-core content, it is valuable!