Device and method for disassembling and assembling main nut of reactor pressure vessel

The invention belongs to the technical field of nuclear power station reactor pressure vessel maintenance, and particularly relates to a device and method for disassembling and assembling a main nut of a reactor pressure vessel, and the device comprises a supporting sleeve, a locking ring, an insertion piece and a lifting hook claw; a plurality of lifting claws are uniformly connected along the periphery of the lower part of the supporting sleeve, the lifting claws can perform opening and closing movement relative to the supporting sleeve, and inward bosses are arranged at the bottoms of the lifting claws and are used for hooking a main nut or a main nut gasket; the bottom of the supporting sleeve is evenly connected with a plurality of inserting pieces, the inserting pieces are matched with U-shaped grooves in the main nut in shape, and the inserting pieces are used for applying torque to the main nut when the device is rotated. The locking ring is arranged on the periphery of the lifting claw in a sleeving