Abstract: The two black line images appearing in the radiographic detection film of the lower head of the nuclear power plant reactor refueling pool and spent fuel pool cooling and processing system (PTR storage tank) were studied, and the workpiece was anatomically verified based on the characteristics of the film image, and the black line was analyzed. The cause and characteristics of the line production may provide a reference for the subsequent evaluation of the radiographic inspection film of the butt weld with a backing plate.