Thread Content
Combined with the previously introduced formation mechanism of dent corrosion in steam generator heat transfer tubes and the background of typical cases, its impact on the safe operation of the unit can be divided into multiple levels.: Direct damage to the pressure barrier dent corrosion will squeeze the heat transfer tube and cause plastic deformation of the tube wall, destroying the integrity of the pressure boundary between the primary and secondary circuits. In severe cases, it will directly cause creep rupture of the heat transfer tube, bringing the risk of containment bypass. Radioactive materials can bypass the containment and be released directly to the environment. Inducing the risk of secondary failure, the dent area will generate extremely high local stress, which will greatly increase the probability of primary/secondary intergranular stress corrosion cracking of the heat transfer tube. It will also significantly increase the sensitivity of the U-shaped elbow area to high cycle fatigue, accelerating the damage process of the heat transfer tube. After obvious dent corrosion interferes with the normal operation of the unit, the power plant needs to increase pipe plugging operations. When the number of blocked pipes reaches the limit, the unit must be shut down for maintenance in advance, which greatly shortens the design service life of the steam generator and greatly increases the probability of unplanned shutdown of the unit. If it escalates to a serious accident, if the heat transfer tube ruptures due to dent corrosion (SGTR accident), this accident is one of the rare accidents with the highest frequency in nuclear power plants. If not handled in time, it may cause the two radioactive safety barriers to fail at the same time. In extreme cases, it may even bring about the risk of a meltdown. Overall, dent corrosion is an important hidden danger that threatens the long-term safe operation of pressurized water reactor units. In severe cases, it can directly trigger high-level accidents related to nuclear safety.