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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 June 29, 1990 Information Notice No. 89-79, SUPPLEMENT 1: DEGRADED COATINGS AND CORROSION OF STEEL CONTAINMENT VESSELS Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice supplement is intended to alert addressees to additional information concerning the corrosion of containment vessels. It is expected that recipients will review the 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: Information Notice No. 89-79 described the discovery of significant coating damage and base metal corrosion on the outer surface of the steel shells of the ice condenser containments of the William B. McGuire Nuclear Station, Units 1 and 2, and the Catawba Nuclear Station, Units 1 and 2. On April 18, 1990, the Duke Power Company reported that during the current refueling outage of McGuire Unit 1, it inspected the containment vessel and identified additional areas of degradation of the steel containment. The degradation consists of general coating failures and localized pits having a depth of up to 45 mils. In some areas, the localized pits range from 0.25 inch to 1 inch in diameter and in other areas they may be up to 1 inch wide and 2 inches long. The corrosion is located on the inside surface at the floor level between the upper and the lower containment compartments, in the vicinity of the ice condenser. The corrosion occurs in a 2-inch floor gap filled with cork that interfaces with the coated steel containment. The cork contains moisture originating most likely from the ice condenser or from condensation or both. General surface corrosion, which is presently of no significance, appears throughout the areas accessible for inspection. Duke Power has indicated that a large portion of the areas in question are inaccessible because of the presence of other structures or equipment. According to Duke Power, the ultrasonic examination of the containment shell with sound coating on both sides indicated an average thickness of 0.78 inch. The average thickness of the general corrosion area was 9006250072 . IN 89-79, Supplement 1 June 29, 1990 Page 2 of 2 0.760 inch. The minimum thickness of the worst pitted area was 0.730 inch, which is greater than the minimum thickness required by the ASME Code, Section III. Duke Power Company has submitted to the staff a proposed resolution of the problem. The actions include performing a more detailed inspection, developing corrective actions and acceptance criteria for expansion joint material and coating, removing the cork material and failed coatings, recoating and coating the containment shell area susceptible to corrosion, and preventing water and acid from penetrating the expansion joint. Discussion: Even though corrosion of the containment shell at the cork interface of the floor expansion joint has been discovered only at McGuire Unit 1, it is expected that such corrosion most likely will occur at other plants with the same design details for the floor expansion joint. Although cork has not been used at the foundation level at McGuire, there are indications that cork may have been used in expansion joints at the foundation level in other plants. The additional corrosion in McGuire Unit 1 has occurred at locations considered not susceptible to corrosion and inaccessible for inspection and maintenance. The detection of corroded steel plate material in the drywells and wet wells of BWR plants and corroded steel containments of PWR plants has resulted in the concern that degradation caused by corrosion may be generic to all types of containments. 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: Chen P. Tan, NRR (301) 492-3315 Keith R. Wichman, NRR (301) 492-0757 Attachment: List of Recently Issued NRC Information Notices .
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