United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-99: Degradation of Steel Containments

                                                            SSINS No.: 6835 
                                                            IN 86-99 

                                UNITED STATES
                           WASHINGTON, D.C.  20555

                              December 8, 1986



All nuclear power reactor facilities holding an operating license or a 
construction permit. 


This notice is to provide recipients with current information of a 
potentially significant safety problem regarding the degradation of a steel 
containment resulting from corrosion. It is expected that recipients will 
review this information for applicability to their facilities and consider 
actions, as appropriate, to promptly recognize or prevent a similar problem 
from occurring. However, suggestions contained in this notice do not 
constitute NRC requirements; therefore, no specific action or written 
response is required. 

Description of Circumstances: 

The Oyster Creek Nuclear Generating Station first discovered water in the 
gap between the boiling-water-reactor drywell and the concrete shield in 
1980 and began investigation of the cause in 1983. It appeared that the 
collection of water varied from a few drops to 2 gallons per minute, 
depending on whether the unit was in operation or an outage for refueling. 
During the spring and summer of 1986, the licensee planned work to identify 
and eliminate this water problem. The bellows at the drywell to cavity seal 
was repaired and a gasket was replaced, thus stopping the leakage. Since the 
bellows is located at the top of the drywell and the region above the 
bellows is flooded during refueling, it would explain why leakage was high 
during refueling and low during operation. 

To determine if the water in the gap had caused damaged to the steel 
containment, the licensee measured the wall thickness, using an ultrasonic 
testing (UT) technique at two elevations. The 51-ft level near the drywell 
seal was sound, but there appeared to be loss of metal on the gap side at 
the 11-ft 3-in. level immediately above the concrete floor. In this area, 
the gap is packed with sand and contains five equally spaced drain pipes 
(see attached Figure 1). A total of 143 measurements were made at this level 
and 60 indicated a reduction in thickness of more than 1/4 in. from the 
drawing thickness of 1.154 in. These readings were found throughout seven of 
the ten downcomer bays. The licensee plans to cut the steel containment and 
remove about 12 samples to confirm and evaluate the corrosion damage. 



                                                            IN 86-99 
                                                            December 8, 1986
                                                            Page 2 of 2 

The licensee plans to remove a section of the drain pipe to perform a visual
examination of the outside of the drywell. Wipe samples will be taken from 
several areas and a chemical analysis will be performed. Sand samples will 
be taken adjacent to the core holes and will be analyzed for chemicals, 
bacteria, and water composition. Some channels are being cut in the concrete 
floor that is inside the drywell to provide access for further UT 
examination of the containment-sand interface. 


The purpose of the sand is to act as a cushion and allow expansion of the 
drywell during operation. The steel containment is in contact with sand in 
those areas where corrosion has been detected. The containment material is 
ASTM A-212 Grade B carbon steel plate. The licensee stated that the outside 
surface was protected with a red lead coating from above the drywell down to
about the 10-ft. level, which means that the interface between the lead 
paint and the unprotected steel was in contact with wet sand. Red lead 
protects steel by providing a stable and impenetrable surface, but the steel 
is sacrificial with respect to the lead in dilute, acidic water conditions. 

It is possible that condensation during initial construction, moisture 
pickup through the drain line during operation, and the leaking bellows 
wetted the sand, thereby causing corrosion of the containment steel plates. 
During construction, water was seen running down the outside of containment 
into the sand. The five drain lines, as well as other penetrations in the 
concrete shield, are open during operation and would allow moist air to 
enter and rise up the gap and later cool and condense as water. Water also 
was able to enter the gap through the holes in the bellows during refueling 
until repairs were made. 

A related matter is discussed in Information Notice No. 86-35, "Fire in 
Compressible Material at Dresden Unit 3," where a large amount of water was 
used to extinguish the slowly burning fire between the drywell and the 
concrete shield. Oyster Creek uses different filler material. 

The NRC is continuing to obtain and evaluate pertinent information. If 
specific actions are required, an additional notification will be made. 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office. 

                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Paul Cortland, IE 
                    (301) 492-4175 

1.   Figure 1, Sketch of Possible Degraded Area
2.   List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015