Method for machining omega weld joint groove in lower portion of CRDM of nuclear power plant and cutter

The invention discloses a method for machining an omega weld joint groove in the lower portion of a CRDM of a nuclear power plant and a cutter. The method and the cutter are used for solving the technical problems that the size of the machined omega weld joint groove in the lower portion of the CRDM of the nuclear power plant in the prior art is difficult to guarantee, reliability is low, welding quality is affected, and a construction period is prolonged. The cutter comprises a first machining blade, a second machining blade and a third machining blade. The method for machining the groove includes the steps that firstly, adjustment is performed, so that the concentricity of a cutter drive device is identical to that of a pipe connection seat and the initial position of the cutter is set; secondly, the cutter is driven to rotate around the axis of the pipe connection seat and driven to move downwards simultaneously, so that weld joint residues on the inner side, the upper portion and the outer side of the lip edge of the pipe connection seat are cut off through the first machining blade, the second machining blade and the third machining blade respectively; and thirdly, after the cutter reaches the preset position, the cutter is controlled to stop moving downwards, and the cutter moves upwards to be away from the lip edge of the pipe connection seat. By the adoption of the method and the cutter, the machining accuracy of the size of the lip edge of the pipe connection seat of a top cover of a pressure container is improved, the welding quality of a weld joint at the lower portion of the CRDM is guaranteed, and reliability is high.