REACTOR PRESSURE VESSEL

PURPOSE:To need no support and easily perform site installation, repair and inspection by making a lower mirror of a reactor pressure vessel (RPV) and a housing tube of a control rod drive mechanism (CRD) enlarge upper diameter rather than lower diameter. CONSTITUTION:A CRD housing tube 1 is inserted in a CRD hosing flange penetrating through hole 4 from the inner part of a RPV lower mirror 3, and the upper faces of the tube 1 and the through hole 4 are welded. After the tube 1 is inserted from the mirror 3, the CRD housing flange 2 is screwed on the male screw cut on the tube 1 and its lower part is welded to mount. Further, since the diameter of their upper part is larger than that of their lower part in regard to the through hole 4 and tube 1, the CRD housing cannot be dropped even if the welding part of the through hole 4 and the tube 1 is damaged. Therefore, site workload for installing a support is reduced and site installation, repair and inspection can easily be performed.