The gas gate of nuclear power plant runs through the inner and outer containment of reactor. Because of its complex structure, strong logic and relevance of mechanism movement, high requirements of pressure seal, it is a large-scale complex electromechanical integrated equipment with frequent faults. The mechanical transmission mechanism of airlock door is mainly composed of the locking mechanism of airlock door latch, the interlock and pressure balance mechanism of internal and external airlock doors, the intermediate transmission box, the transmission connecting shaft and other main parts. Among them, the output torque of the intermediate transmission box is driven by gears to realize the expansion and contraction of the latch in the locking transmission mechanism of the latch, so as to carry out the opening and closing operation of the seal door.

This paper studies the failure mechanism of the thin-walled gears used in the mechanical transmission mechanism of the airlock gate of a nuclear power plant in service in China, analyzes the root cause of the gear tooth fracture, and puts forward the optimization and improvement measures, so as to ensure the safety and reliability of the on-site operation of the mechanical transmission mechanism of the airlock gate during the short, medium and long-term operation of the nuclear power plant.

The main function of mechanical transmission mechanism of airlock door is to realize the normal opening and closing operation of airlock door. The load of mechanical transmission mechanism can be realized by hand wheel manual operation and electric operation (motor driven) of intermediate transmission box, and the two operation modes can be switched freely. In the whole mechanical transmission system, the latch locking mechanism of the sealed door mainly realizes the operation of latch up and latch down, so as to realize the closing and opening of the sealed door. The interlock and pressure balance mechanism of the sealing door mainly realizes the related operation of the inner and outer sealing doors, prevents the double opening of the inner and outer sealing doors during the operation of the nuclear power plant, and realizes the pressure balance on both sides of the sealing doors. The intermediate transmission box is used to open and close the inner and outer sealing doors in the airlock chamber by manual and electric means.

This set of in-service nuclear power plant airlock and its mechanical transmission system are designed and supplied by company of the United States. During the operation of nuclear power plant in service, thin-walled gears for latch locking mechanism of 4 sets of airlocks of 2 sets of nuclear motor sets have broken teeth several times, and the thin-walled gears with broken teeth are of the same specification (irregular displacement gears with 12 teeth). The tooth fracture of thin-walled gear occurred in the process of refueling outage in nuclear power plant, which occupied the critical path of refueling outage, and had a great impact on the short-term, medium-term and long-term operation of the units in service.