Information Notice No. 90-32: Supplement 1:Surface Crack and Subsurface Indications in the Weld of a Reactor Vessel Head
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 June 19, 1990 Information Notice No. 90-32, SUPPLEMENT 1: SURFACE CRACK AND SUBSURFACE INDICATIONS IN THE WELD OF A REACTOR VESSEL HEAD Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice supplement is intended to update the information previously provided in Information Notice No. 90-32. It is expected that recipients will review this information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: In April 1990, during the refueling outage at the James A. FitzPatrick Nuclear Power Plant, the licensee found a group of four subsurface indications in the reactor vessel head as a result of performing an ultrasonic inservice inspection from the outside of the vessel head. The preliminary sizing indicated that the subsurface indications have a total length of 12 inches, and a maximum depth of 2 inches (50 percent through wall). The licensee also observed a surface indication measuring 1 inch in length on the inside surface of the head in the general area of the subsurface indications and confirmed this observation by liquid penetrant examination (PT). The licensee reported the surface indication and subsurface indications to be located in the circular dollar plate weld at the top of the vessel head. NRC issued Information Notice No. 90-32 on May 3, 1990, to report this event. Subsequently, the licensee performed the following additional examinations to further characterize the indications: 1. Ultrasonic examination (UT) from the outside surface using automatic mode, 2. Ultrasonic sizing of the indications from both inside and outside surfaces including the use of refracted longitudinal waves, 3. Radiographic examinations from the inside of the head, 9006130247 . IN 90-32, Supplement 1 June 19, 1990 Page 2 of 2 4. Examination of radiographic films with an enhanced technique, and 5. Magnetic particle examination (MT) on the inside head surface. The results of these additional examinations indicate that the subsurface indications are not cracks, but original fabrication flaws such as slag or inclusions, and are not connected to the surface. The previously reported surface indication appears to be a very shallow surface scar that was removed during surface preparation for MT. Discussion: When performing nondestructive examinations and determining the real significance of reflector indications from within any metal, experience and knowledge in the various advanced inspection techniques used in performing surface and volumetric examinations and in flaw discrimination are important. In performing its initial assessment, the licensee interpreted the combination of the surface indication and the multiple subsurface reflections as a very large flaw. Subsequent additional examinations to better characterize the surface and subsurface indications have concluded that the multiple reflections were caused by a combination of inclusions in the material, a proximate surface scar and subsurface slag. The licensee's reactor vessel vendor, the General Electric Company (GE), has confirmed this current assessment. GE, using a test sample of equivalent material to the FitzPatrick reactor vessel head, duplicated ultrasonically the multiple reflections from inclusions in the material. The licensee has concluded that the surface indication was not a crack, but a very shallow surface scar, and that the subsurface indications are not cracks, but original fabrication flaws, such as slag and inclusions, that are not connected to the surface. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate NRR project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: William H. Koo, NRR (301) 492-0706 Robert H. Hermann, NRR (301) 492-0768 Attachment: List of Recently Issued NRC Information Notices .ENDEND
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Page Last Reviewed/Updated Tuesday, March 09, 2021