UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

April 27, 2004

NRC INFORMATION NOTICE 2004-09: CORROSION OF STEEL CONTAINMENT AND

CONTAINMENT LINER 

Addressees:

All holders of operating licenses for nuclear power reactors except those who have permanently

ceased operation and have certified that fuel has been permanently removed from the reactor

vessel.

Purpose:

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert

addressees to recent occurrences of corrosion in freestanding metallic containments and in

liner plates of reinforced and pre-stressed concrete containments. It is expected that recipients

will review this information for applicability to their facilities and consider actions, as appropriate. 

However, the suggestions in this information notice are not NRC requirements; therefore, no

specific action or written response is required. 

Background:

As discussed in Information Notice 97-10, “Liner Plate Corrosion in Concrete Containments,”

the containment liners have safety factors well above the theoretically calculated strains. Any

corrosion (metal thinning) of the liner plate or freestanding metallic containment could change

the failure threshold of the containment under a challenging environmental or accident

condition. Thinning changes the geometry of the containment shell or liner plate, which may

reduce the design margin of safety against postulated accident and environmental loads. 

Recent experience has shown that the integrity of the moisture barrier seal at the floor-to-liner

or floor-to-containment junction is important in avoiding conditions favorable to corrosion and

thinning of the containment liner plate material.

Description of Circumstances:

Inspections of containment at the floor level, as well as at higher elevations, have identified

various degrees of corrosion and containment plate thinning. This is a partial listing of such

occurrences.

ML041170030
IN 2004-09

Page 2 of 5

Corrosion of freestanding metallic containment

 In July of 2002, at the Davis-Besse Nuclear Power Station, the NRC identified corrosion

where the containment meets the floor. The licensee subsequently performed ultrasonic

examinations to confirm that the freestanding metal containment had not been corroded

below the minimum design thickness. The licensee subsequently installed a moisture

barrier at the containment-to-floor junction to prevent moisture intrusion (NRC Inspection

Report 50-346/02-09, ADAMS Accession No. ML022560237).

 In May of 2002, at the Sequoyah Nuclear Plant, Unit 2, the NRC identified areas of the

steel containment vessel (SCV) with degraded coatings and rust (NRC Inspection

Report 50-328/02-02, ADAMS Accession No. ML022070149). One of the floor drains

was clogged in the annulus area (1.5 m [5 feet] wide) between the SCV and the

reinforced concrete shield building. Localized water ponding at the clogged drain had

come in contact with a section of the SCV, causing deterioration of the SCV coatings

and rusting of the SCV. This SCV is restricted for access due to the close proximity

between the SCV and the emergency gas treatment system (EGTS) duct work. After

reviewing NRC Information Notice 89-79, the licensee had identified the problem in

1990, but the corrective action was inadequate. Since the identification in 2002,

additional corrective actions have been implemented by the licensee. These actions

consist of the removal of the EGTS duct work on both Unit 1 and Unit 2 to allow the SCV

area behind the EGTS duct work to be cleaned and recoated. Also the licensee has

identified this SCV area behind the EGTS duct work for periodic visual examination.

 In November of 2001, at the Dresden Unit 2 Nuclear Power Station, the licensee

identified an area of missing coating and primer encircling the drywell shell adjacent to

the basement floor. The area was 5-10 cm (2-4 inches) wide. In this area, the base

metal of the drywell shell was found to be corroded. However, based on ultrasonic and

visual examinations, the degraded area was found to be within the corrosion allowance

for the drywell shell. The shell coating was repaired in this area to prevent further

degradation (Inservice Inspection Summary Report, Fall 2001 Inspection Period,

ADAMS Accession No. ML020450608).

Corrosion of containment liner plate

 In March of 2001, at the D. C. Cook Nuclear Power Plant, the licensee discovered a

through-wall hole in the containment liner plate. Surface preparation for further

inspection of a weld repair of the liner plate dislodged the repair material, leaving a hole. 

The hole was repaired. However, further examination of the repair area indicated

corrosion of the liner from the embedded side of the liner. The cause of this corrosion

was found to be a wire brush handle lodged in the concrete at the interface with the

liner. The licensee replaced an area about 30 cm (12 inches) square in the liner plate

and performed a local leak rate test as part of the corrective action (AEP:NRC:2612-01:

"Response to NRC Request for Additional Information Regarding License Amendment

Request for One-Time Extension of Containment Integrated Leakage Rate Test

Interval," November 11, 2002, ADAMS Accession No. ML023170524). 
_______________________

*These documents are available in the NRC Legacy Library. The legacy documents are

stored on microfiche in the NRC Public Documents Room. Copies may be made for a fee.

IN 2004-09

Page 3 of 5

• In February and March of 1998, at the D. C. Cook Nuclear Power Plant, the licensee

identified corrosion (pitting) of the containment liner at the moisture barrier seal areas of

both units. At Unit 1, the licensee identified more than 60 areas in which the thickness

(1 cm [3/8 inch] nominally) of the steel liner plate had been reduced below the minimum

design thickness value of (0.6 cm [0.25 inch]). The licensee subsequently installed a

new liner-to-floor moisture barrier seal (Licensee Event Report 50-315/98011-02,

NUDOCS Accession No. 9809040123* and NRC Inspection Report 50-315/99026,

ADAMS Accession No. ML003677533).

 In fall 2003, at the Surry Power Station, Unit 2, NRC inspectors found degraded

coatings and rust on the containment liner at the junction of the metal liner and interior

concrete floor. The inspectors also discovered that the moisture barrier at the junction

between the metal liner plate and interior concrete floor was degraded. Review of the

records of previous inspections performed by licensee personnel in 2000, 2002, and

2003 revealed that the licensee had not identified the degraded moisture barrier

(caulking), but had identified the degraded coatings. (NRC Inspection Report

50-281/2003-05, ADAMS Accession No. ML040280056).

 In October of 1999, at the Palisades Plant, the licensee discovered that a floor-to-liner

moisture barrier seal had never been installed and used a thin metal blade as a probe,

confirming the presence of moisture in the crevice. Subsequently, the licensee used a

borescope to identify areas of liner corrosion. The licensee determined that the

corrosion had not yet appreciably degraded the liner in this area and installed a new

liner-to-floor moisture barrier seal.

 In May of 1999, at the Brunswick Steam Electric Plant, Unit 2, the licensee identified

three areas in the drywell liner where corrosion had penetrated the liner. These areas

were at the 5.5, 16, and 21 m (18, 52, and 70 feet) elevations. At the 16 m elevation,

the wall had corroded from the outside to the inside surface. At the 21 m elevation, the

wall had corroded from the inside to the outside surface. At the 5.5 m elevation, the

direction of the through-wall corrosion could not be determined. The liner corrosion was

a result of foreign materials embedded in the concrete containment adjacent to the liner. 

One hole in the liner was adjacent to a leather work glove found buried in the concrete,

while the other two hole locations were adjacent to wood found buried in the concrete

(NRC Inspection Report 50-324/99-03, NUDOCS No. 9906170114*).

 In December, 1996, at the H.B. Robinson Steam Electric Plant, Unit 2, an NRC

inspector identified degraded caulking and insulation sheathing panels during a

containment walkdown. The vertical portion of the containment liner at Robinson is

protected by Vinylcel insulation, a polyvinyl chloride material, and a metal sheathing

material. The licensee determined that a portion of this insulation sheathing material

was loose and that some of the caulking between the sheathing panels was 
_______________________

*These documents are available in the NRC Legacy Library. The legacy documents are

stored on microfiche in the NRC Public Documents Room. Copies may be made for a fee.

IN 2004-09

Page 4 of 5

deteriorated. After examination during subsequent refueling outages, the licensee

determined that the protective coating for the containment liner was degraded and that

while some corrosion of the containment liner had occurred, the liner met design

requirements. The licensee restored the coating and insulation panels (NRC Inspection

Reports 50-261/96-14, NUDOCS Accession No 9702110115* and 50-261/98-02,

NUDOCS Accession No. 9805050171*).

Discussion:

An amendment to Section 50.55a of Title 10 of the Code of Federal Regulations (10 CFR

50.55a) (61 FR 41303) became effective September 9, 1996. This amendment requires the

use of Subsections IWE and IWL of Section XI of the ASME Boiler and Pressure Vessel Code

to perform inservice inspections of containment components. These subsections provide

detailed requirements for inservice inspection of Class MC pressure-retaining components and

their integral attachments and of metallic shells and penetration liners of Class CC pressureretaining components and their integral attachments. Inspection of concrete containment shell

and steel liner plate in accordance with 10 CFR 50.55a involves consideration of potential

corrosion areas. Such inspection includes examination, evaluation, repair, and replacement of

corroded areas of the liner plate. 

As a result of these required containment inservice inspections, licensees have found that over

time, the existing floor-to-containment seal can degrade, allowing moisture into the crevice

between the containment liner plate and floor. Small amounts of stagnant water behind the

floor seal area promote pitting corrosion. To identify corrosion in this area, licensees have had

to remove the original floor seal and either excavate the concrete or do a visual inspection

aided by fiber optics. Licensee corrective actions for this condition have typically included

inspections to determine the extent of corrosion, evaluations of containment integrity, and

installation of new floor-to-containment moisture seal barriers.

In some instances, corrosion has been found at higher elevations of the liner plates. Generally,

the instances of such corrosion have been associated with foreign objects (wooden pieces,

workers’ gloves, wire brush handles, etc.) lodged between the liner plate and the concrete. As

the corrosion is initiated in the areas not visible during visual examinations, such instances of

corrosion were found when corrosion had penetrated through the liner thickness. Some

licensees have performed ultrasonic examination of the suspect areas (areas of obvious

bulging, hollow sound, etc.) to detect such corroded areas.
IN 2004-09

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Related Generic Communications:

NRC Information Notice 97-29, “Containment Inspection Rule”

NRC Information Notice 89-79, “Degraded Coatings and Corrosion of Steel Containment

Vessels

This information notice requires no specific action or written response. If you have any

questions about information in this notice, please contact one of the technical contacts listed

below or the appropriate NRR project manager. 

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contacts: Melvin Holmberg, RIII Dr. C. Vernon Hodge, NRR

(630) 829-9748 (301) 415-1861

E-mail: msh@nrc.gov E-mail: cvh@nrc.gov

Joseph Lenahan, RII Hans Ashar, NRR

(404) 562-4625 (301) 415-2851

E-mail: jjl3@nrc.gov E-mail: hga@nrc.gov

Attachment: List of Recently Issued NRC Information Notices
LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2004-08 Reactor Coolant Pressure

Boundary Leakage Attributable

to Propagation of Cracking in

Reactor Vessel Nozzle Welds

04/22/2004 All holders of operating licensees

for nuclear power boiling-water

reactors (BWRs), except those

who have permanently ceased

operations and have certified that

fuel has been permanently

removed from the reactor vessel.

2004-07 Plugging of Safety Injection

Pump Lubrication Oil Coolers

with Lakeweed

04/07/2004 All holders of operating licenses

or construction permits for

nuclear power reactors, except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel.

2004-06 Loss of Feedwater Isokinetic

Sampling Probes at Dresden

Units 2 and 3

03/26/2004 All holders of operating licensees

for nuclear power reactors except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel.

2004-05 Spent Fuel Pool Leakage to

Onsite Groundwater

03/03/2004 All holders of operating licensees

for nuclear power reactors (except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel) and for research

and test reactors, and all holders

of fuel storage licenses and

construction permits.

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