In the spent fuel storage system of pebble-bed high temperature gas-cooled reactor, several air cylinders would be employed in complex machines, such as the spent fuel charging apparatus and the spent fuel canister crane. The cylinders were designed to actuate movements smoothly in radioactive environment. In order to lock them in safe position when the compressed air source is offline by accident, an electromagnetic self-locking device was designed. When power-off, the compressive spring would push out the lock plunger to enable self-lock. When power-on, the lock plunger would be withdrawn by the magnetic force of the coil to unlock the cylinder. In order to optimize the design more efficiently, numerical simulation was performed to optimize geometry parameters of the structure surrounding the working air gap so as to improve the performance of the device. A prototype was then fabricated. Combining the simulation results with experimental test, the actuating force characteristics of the device in locking and unlocking process was analyzed. The temperature rise when the device stays unlocked with power supply was also calculated and validated. The results showed that this electromagnetic self-locking device could realize the locking and unlocking functions effectively, and the maximum temperature rise also conforms the required limit. The as-fabricated device would help guarantee the fail-safe feature of the air cylinders of complex machines in compressed air outage.

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