Information Notice 1998-27, Steam Generator Tube End Cracking

Steam Generator Tube End Cracking

ML031050119
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	07/24/1998
From:	Roe J Office of Nuclear Reactor Regulation
To:
References
IN-98-027, NUDOCS 9807240024
Download: ML031050119 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 July 24, 1998 NRC INFORMATION NOTICE 98-27: STEAM GENERATOR TUBE END CRACKING

Addressees

All holders of operating licenses for pressurized-water reactors (PWRs) 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 inform

licensees of Instances of steam generator tube-end cracking. 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 are not NRC

requirements; therefore, no specific action or written response in required.

Description of Circumstances

Entergy, the licensee for Arkansas Nuclear One, Unit I (ANO-1), conducted leak testing on

each once-through steam generator (OTSG) during the spring 1998 refueling outage to identify

the source of primary-to-secondary leakage measured during the previous operating cycle. The

leak testing revealed a small leak In one tube of each OTSG. The leak in each tube was in

flaws In the tube hardroll just below the upper tubesheet seal weld. Subsequent eddy current

inspections Identified primary-water stress-corrosion cracking (PWSCC) in each of the two

tubes. The through-wall flaws In the tubes were oriented both axially and circumferentially in

the tubes. Examinations of all upper tubesheet seal weld areas In both OTSGs revealed

possible flaws in 1896 additional tubes. For these tubes, the licensee installed an additional

hard roll in the upper tubesheet, thus redefining the reactor coolant pressure boundary.

Eddy current Inspections completed at Davis-Besse Nuclear Power Station in April 1998 Identified five tubes with "tube end anomalies" believed to be related to the flaws identified at

ANO-1. Duke Power Co. recently completed an assessment to determine If its Babcock and

Wilcox-designed, operating units, Oconee Nuclear Station, Units I and 3, were affected by

tube-end cracking. The licensee concluded that 372 indications in the Unit I OTSGs and 61 Indications in the Unit 3 OTSGs exceeded the repair criteria in the Oconee Technical

Specifications. Tube-end cracking has also been reported for the steam generators at Prairie

Island Nuclear Generating Plant.

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IN 98-27 July24, 1998 Steam generator tubes are secured into tubesheets using both mechanical expansion and

welding. In general, each tube protrudes slightly beyond the tubesheet. A seal weld provides a

leak-tight configuration. The mechanical expansion and seal welding processes introduce high

residual stresses in the ends of each tube. In addition, the high temperatures associated with

welding alter the metallurgical characteristics of the tube material in the heat-affected zone.

Although the tubes In the ANO-1 OTSGs were heat treated prior to operation (which should

have improved the material's resistance to stress-corrosion cracking), the licensee's preliminary

conclusion is that the rolling and welding processes contributed to the development of PWSCC

in the tubes at the seal weld. The licensee Is currently conducting a root-cause evaluation to

determine any future corrective measures necessary to prevent recurrence or to mitigate the

consequences of this mode of degradation.

Discussion

One of the safety functions of steam generators Is to maintain a barrier against fission product

release. Tube-to-tubesheet seal welds in steam generators minimize the potential for

primary-to-secondary leakage under normal-operating and postulated-accident conditions. The

development of PWSCC tube cracking In the vicinity of these welds may degrade the leak-tight

barrier between the primary and secondary coolant systems. Although the primary-to- secondary leakage during normal operation from a single tube-end flaw is likely to be small

relative to the limit specified in plant technical specifications, the combined leakage from tube- end flaws could become significant if a large number of tubes have through-wall cracks.

PWR technical specifications require tubes containing defects with depths that exceed the

repair criteria (typically 40 percent of nominal wall thickness) to be removed from service. The

repair criteria often require licensees to consider the entire tube in determining whether tubes

are degraded or defective. Defects located in any area of a tube are evaluated against the

repair criteria unless the area Is specifically excluded from the surveillance requirements. Upon

confirming the presence of tube-end flaws at ANO-1, the licensee utilized an industry-approved

repair method to install an additional hard roll In the upper tubesheet, thus redefining the reactor

coolant pressure boundary. The tubes In most recirculating steam generator designs are fully

expanded within the tubesheet and do not offer the option of this type of repair. While fully- expanded designs inherently provide considerable resistance to bypass leakage, licensee

technical specifications may still require licensees to consider flaws near tube-end seal welds In

dispositioning tubes as acceptable for continued service.

Steam generator tube-end cracking may not be limited to OTSGs. All PWR steam generators

contain similar welds that may be equally susceptible to the development of PWSCC in the

heat-affected zone of the tube. Due to the location of flaws associated with tube seal welds, the use of traditional Inspection techniques and analysis procedures may not be entirely

effective in detecting and characterizing this mode of degradation. The licensee for the Oconee

units found It necessary to perform supplemental eddy current Inspections on mockup test

samples to adequately address tube-end cracking.

IN 98-27- July24, 1998 This information notice requires no specific action or written response. If you have any

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

below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager.

Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Phillip J. Rush, NRR

301-415-2790

E-mail: pjrl@nrc.gov

Eric J. Benner, NRR

301-415-1171 E-mail: ejbl nrc.gov

Attachment: List of Recently Issued NRC Information Notices

Attachment

IN 98-27 July 24, 1998 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

96-48, Sup. 1 Motor-Operated Valve 7/24/98 All holders of operating licenses

Performance Issues for nuclear power reactors except

those who have permanently

ceased operation and have

certified that fuel has been

permanently removed from the

reactor vessel.

98-26 Settlement Monitoring and 7/24/98 All holders of operating licenses

Inspection of Plant Structures for nuclear power reactors; all

affected by Degradation of Porous of or applicants for licenses to

Concrete Subfoundations operate Independent Spent Fuel

Storage Installations; and

designers and fabricators of

Independent Spent Fuel Storage

Installations.

98-25 Loss of Inventory from Safety- 7/24/98 All holders of OLs for nuclear

Related, Closed-Loop Cooling power reactors; except those

Water Systems licensees who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel.

98-24 Stem Binding In Turbine 7/08/98 All holders of operating licenses

Govemor Valves In Reactor for nuclear power reactors except

Core Isolation Cooling (RCIC) those who have permanently

and Auxiliary Feedwater (AFW) ceased operation and have

Systems certified that fuel has been

permanently removed from the

reactor vessel

OL = Operating License

CP = Construction Permit

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IN 98-27 July24, 1998 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 Office of Nuclear Reactor Regulation (NRR) project manager.

[Original signed by David B. matthews]

for Jack W. Roe, Acting Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Phillip J. Rush, NRR

301-415-2790

E-mail: pjrlnrc.gov

Eric J. Benner, NRR

301-415-1171 E-mail: ejb1 @nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: A:\SG-INFO.WPD

Tech Editor reviewed and concurred on 6/29/98

• SEE PREVIOUS CONCURRENCE

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OFFICE PECB EMCB l EMCB (A)C:EMCB i

NAME EBenner* PRush* MModes* ESullivan*

lDATE 07/01/98 07/01/98 07/02/98 07/02/98 OFFICE (A)D:DE PECB C:PECBl D:DRPM

NAME GLainas* RDennig* JStoltz* JRoe*

DATE 07/09/98 07/15/98 07/20/98 07/21/98 OFFICIAL RECORD COPY

IN 98-27 July 25, 98 Page of 3 This information notice requires no specific action or written response. If u have any

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

below or the appropriate Office of Nuclear Reactor Regulation (NRR roject manager.

Jack W. Roe, A ng Director

Division of Re tor Program Management

Office of Nu ar Reactor Regulation

Technical contacts: Phillip J. Rush, NRR

301-415-2790

E-mail: pjrl @nrc.gov

Eric J. Benner, NRR

301-415-1171 E-mail: ejbl@nrc.g

Attachment: List of Recently Issued N Information Notices

DOCUMENT NAME: A: G-INFO.WPD

Tech Editor reviewed nd concurred on 6/29/98

• SEE PREVIOUS ONCURRENCE

To receive a copy of this documen Indicate Inthe box C=Copy wlo attachmenVenclosure E=Copy wit attachmentenclosure N No copy l

OFFICE PECB EMCB l EMCB l (A)C:EMCBjl

NAME { nne PRush* MModes* ESullivan*

DATE 07/01/98 07/01/98 07/02/98 07/02/98 OFFICE (A) D:DE l PECB l C:PECB l D:DRPM l

NAME GLainas* RDennig* JStoltz* JRoe*

DATE 07/09/98 07/15/98 07/20/98 07/21/98 OFFICIAL RECORD COPY

. hi -

IN

July 998 Pag of3 This information notice requires no specific action or written response. you have any

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

below or the appropriate Office of Nuclear Reactor Regulation (N ) project manager.

Jack W. Ro , Acting Director

Division of eactor Program Management

Office of ucear Reactor Regulation

Technical contacts: Phillip J. Rush, NRR

301-415-2790

E-mail: pjrl@nrc.gov

Eric J. Benner, N

301-415-1171 E-mail: ejbl@n .gov

Attachment: List of Recently lssu NRC Information Notices

DOCUMENT NAM  :%SG-INFO.WPD

Tech Editor revie ed and concurred on 6/29/98

• SEE PREVIO CONCURRENCE

To receve a copy of this d ment indicate in the box C=CoDv wio attachmentlenclosure E=Coov with attachrent/encdosure N

• No coov

OFFICE PCEMCB 6EMCB (A) C:EMCB

NAME EB.ned' rfdes!5 PRush M £Ik ESullivan

DATE 07/4d98 07/1 /98 07/2.498 07/1198 OFFICE X D:DE PECB H ;REPB D l

NAME G as RDeni4$ _ _ Foe

J__

DATE 07 /98 ____07__98 RD7_C__9P

_ECC 07/ /98 OFFICIAL RECORD COPY