United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-79, Supplement 1: Degraded Coatings and Corrosion of Steel Containment Vessels

                                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 




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                                                  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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