Manufacture method of large-caliber medium-and-thick-wall seamless steel tube for nuclear power plant

The invention provides a manufacture method of a large-caliber medium-and-thick-wall seamless steel tube for a nuclear power plant. The manufacture method includes the following steps: heating a round steel billet; using a cone mill to punch holes on the round steel billet to form a tubular billet; using a 508mm-diameter Pilger cycle pipe mill group to produce the tubular billet into a tube billet, ensuring that the full-length wall thickness deviation of the tube billet is controlled to be +/-8% and the section wall thickness range of the tube billet is no larger than 80% of the full-length wall thickness deviation of the tube billet; heating the tube billet to be at 1000-1100 DEG C and using a drawing-type pipe expander to expand the diameter of the tube billet; performing softening heat treatment for the diameter expanded tube billet; performing integral coping for the inner surface and the outer surface of the diameter expanded tube billet and controlling the coping amount to be 1.0-1.8mm; and using a precise hydraulic drawing machine to perform drawing for the integrally coped tube billet to manufacture the large-caliber medium-and-thick-wall seamless steel tube for the nuclear power plant. The manufacture method has the advantages of being low in production cost, high in production efficiency, high in product geometric dimensioning accuracy, good in product surface quality and the like.