Information Notice 1991-80, Failure of Anchor Head Threads on Post-Tensioning System During Surveillance Inspection

Failure of Anchor Head Threads on Post-Tensioning System During Surveillance Inspection
	ML031190403
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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:	12/11/1991
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-91-080, NUDOCS 9112050161
	Download: ML031190403 (7)
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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C., 20555 December 11, 1991 NRC INFORMATION NOTICE 91-80: FAILURE OF ANCHOR HEAD THREADS ON POST-TENSIONING

SYSTEM-DURING SURVEILLANCE INSPECTION,

11 i , .1 , 4 Addresse Pes , :.I I I .

All holders of operating licenses or construction permits for nuclear, power

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Purpose

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

to alert addressees to problems associated with failure of internal threads on

post-tensioned containment tendon anchor heads during a tendon surveillance.

It is expected that recipients wi~llireView the information, for applicability to

their facilities and consider. actidns, las appropriate, to avoid similar prob- lems. ' However, su-*gestions,6onftained in this information notice are not NRC

requirements;' therefore, no'sJpecificaction or written response is required.

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Description of Circumstances

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On August 1, 1991, while the Duke Power Company (the licensee) was' conducting

the post-tensioning system surveillance inspections at Oconee Nuclear Station, Unit 1, as required by the technical specifications, the internal threads on

one of the tendon anchor' heads failed while the tendbn'-wa's'being lo'aded

(stressed) with a hydraulic jack (stressing ram). The stressing load was

applied to the tendon by the pull bar on the stressing ram which couples to the

internal threads on the anchor head. Whe pull bar was engaged to three-fourths

of the threads on the anchor head. When the threads on the anchor head failed, the stressing ram disengaged from the anchor head, swung free from the tendon, and posed a safety hazard to personnel performing the tendon'surveillance.

Fortunately no injuries occurred. The licensee has suspended further tendon

surveillance operations until it reviews the results of an investigation into

the cause of the anchor head thread failure.

The licensee visually examined the remaining threads on the damaged anchor head

and found that the threads had yielded before the current tendon surveillance

inspection. Duke Power also visually examined anchor heads on other tendons

and determined that the threads weretalso deformed, having been subjected to

stresses exceeding the material yield point. The licensee performed a stress

analysis of the threads on the anchor heads under application of maximum loads

applied during tendon stressing operations. This analysis disclosed that the

actual load applied to the threads during stressing operations exceeded the

anchor head material shear yield stress, which explains the'observed

9112050161 .7 m)

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<-' IN 91-80

December 11, 1991 I I iLi ;

deformations of the threads on the an'cd~fledds.!iDuke Power Company is

continuing to investigate this peoblemlAnd, i,'evdldating its effect on future

tendon surveillance inspections.

Discussion ,1.. .

Because the integrity of-the post-tensioned-concrete containment structure-e- based on a highly redundant system of several hundred elements, the failure of

one such element'in 4,affamily of tendons would not significantly'jdopardize V' '

containment structural.capability. However,-the failure-ofl-the threads as

occurred at Oconee could adversely affect occupational safety.

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This inTormation notice requires no specific action or written response. If

you have any questions aboutthe information in this notice; please contact.the"

technical contact listed below or the appropriateiOffice of.Nuclear Reactof

Regulation (NRR) project manager.

,4. ,, a , , ,7.3 43 harlesCir't E.ssi,'Direcio -.I'_)

Division of Operational Events Assessment

Office of Nuclear Reactor'Regulation I

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-- _Te-c hni cal1 Cotacf. Jo6seph J. Lenahan, RII I , ,., . X-

(404) 331-4190

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Attachmentt; List of Recently Issued NRC Ii iformation Notices

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December 11, 1991 LISTOF9RECENTLY ISSUED .!"" 'tin W1 '-f'( -!,- ; ,t, ',,

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NRCSINFORMATIONWNOTICES' 9_1," r

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Barrier Materials

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88-92,.r , Potential for Spent, 11/29/91 All-holders of -OLs -6rfCPs

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Supp. 1 . ' FueltPool Draindown' . 1for nuclear Ipower'reactors.

91-78 Status Indication of 11/28/91 All holders of OLs or CPs

Control Power for for nuclear power reactors.

Circuit Breakers Used

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90-57 Substandard, Refur-~' , ' 11/27/91 All holders of OLs or CPs

Supp. 1 bished Potter & Brum- for nuclear power reactors.

field Relays Repre- rf7 sented-as New ,,,t, 'I ,,, - . ^ . - 3,

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91i"7 ' ' Shift Staffing at 11/26/91 All holders of OLs or CPs--

Nuclear Power Plants for nuclear power reactors.

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91-76 10 CFR Parts 21 and 11/26/91 All holders of OLs or CPs

50.55(e) Final Rules and vendors for nuclear

power reactors.

91-75 Static Head Corrections 11/25/91 All holders of OLs or CPs

Mistakenly not Included for nuclear power reactors.

in Pressure Transmitter

Calibration Procedures

91-74 Changes in Pressurizer 11/25/91 All 'holders of OLs or-CPs

Safety Valve Setpoints for nuclear power reactors.

Before Installation

91-73 Loss of Shutdown Cooling 11/21/91 All holders of OLs or CPs

During Disassembly of High for nuclear power reactors-.

Pressure Safety Injection

System Check Valve

OL = Operating License

CP = Construction Permit

IN 91-80

December 11, 1991 deformations of the threads on the anchor heads. Duke Power Company is

continuing to investigate this problem and is evaluating its effect on future

tendon surveillance inspections.

Discussion

Because the integrity of the post-tensioned concrete containment structure is

based on a highly redundant system of several hundred elements, the failure of

one such element in a family of tendons would not significantly jeopardize

containment structural capability. However, the failure of the threads as

occurred at Oconee could adversely affect occupational safety.

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

you have any questions about the information in this notice, please contact the

technical contact listed below or the appropriate Office of Nuclear Reactor

Regulation (NRR) project manager.

Original Signed by

Charles E. Rossi

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contact: Joseph J. Lenahan, RII

(404) 331-4190

Attachment: List of Recently Issued NRC Information Notices

Document Name: FAILURE ANCHOR HEAD POST TENSI

SEE PREVIOUS CONCURRENCES

D *C/OGCB:DOEA:NRR

HBerlinger

/1</ 12/04/91

OGCB:DOEA:NRR *RII *RII *D/RII *RPB:ADM

NPKadambi JJLenahan Julian Gibson TechEd

11/08/91 11/08/91 12/02/91 12/02/91 11/21/91

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IN 91-XX

November xx, 1991 tions exceeded the anchor head material shear yield stress, which explains

the observed deformations of the threads on the anchor heads. Duke Power

Company is continuing their investigation of this problem and is evaluating

its effect on future tendon surveillance inspections.

Discussion

Because the integrity of the post tensioned concrete containment structure is

based on a highly redundant system of numerous elements (several hundred), the

failure of one such element in a family of tendons does not significantly

jeopardize containment structural capability. However, the failure of the

threads as occurred at Oconee raises concerns regarding occupational safety.

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

you have any questions about the information in this notice, please contact

the technical contact shown below or the appropriate Office of Nuclear Reactor

Regulation project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contact:

Joseph J. Lenahan, Region II

(404) 331-4190

Attachments:

List of Recently Issued NRC Information Notices

Document: FAILURE ANCHOR HEAD POST TENSI

fK

A90GCB:DOEA:NRR RPB:ADM C/OGCB:DOEA:NRR D/DOEA:NRR

W NPKadambi

11/ /91 JdLenahan

11/'g /91 TechEd

11/7 /91 CHBerlinger

11/ /91 CERossi

11/ /91 F-mq7 OFFICIAL RECORD COPY

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IN 91-XX

November xx, 1991 deformations of the threads on the anchor heads. Duke Power Company is