Abstract: As a key component of the pressure boundary of the primary circuit in a nuclear power plant, the sealing reliability of the equipment flange of primary circuit boundary equipment is essential for ensuring the safe and stable operation of the equipment. Starting from a mechanistic analysis of flange sealing for primary circuit boundary equipment, this paper systematically carries out innovative research on the development and validation of pure graphite gaskets for flange sealing, resulting in a complete technical solution. Engineering application results show that this solution effectively addresses the challenges in developing and validating pure graphite gaskets for equipment flanges, significantly improves the sealing reliability of domestically produced pure graphite gaskets, and lays a solid foundation for the safe and stable operation of the units.