Butt welding process method for large-thickness plate with U-shaped structure

The invention discloses a butt welding process method for a large-thickness plate of a U-shaped structure. The large-thickness plate of the U-shaped structure is used for manufacturing a fusion reactor shell and comprises two side plates and a middle section for connecting the two side plates. The method comprises the following steps: (1) firstly welding side plates to form welding seams on two sides; (2) dividing the middle section into an inner side and an outer side so as to weld the middle section twice; firstly welding the inner side of the middle section to form an inner welding seam; wherein the inner side welding seam takes the shape of an arch, the bottom edge of the inner side of the middle section is used as a string of the arch, and the other edge of the arch is a circular arc;(3) setting the ends, close to the middle section, of welding seams on two sides to be arc ending positions; polishing or machining the arc ending positions of the inner and outer welding seams to enable the arc ending posit