Information Notice 1985-10, Posttensioned Containment Tendon Anchor Head Failure

Posttensioned Containment Tendon Anchor Head Failure

ML031180645
Person / Time
Site:	Beaver Valley, Millstone, Hatch, 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, 05000000, 05000262, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	02/06/1985
From:	Jordan E NRC/IE
To:
References
IN-85-010, NUDOCS 8502060136
Download: ML031180645 (4)

SSINS No.: 6835 IN 85-10

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, D.C. 20555 February 6, 1985 IE INFORMATION NOTICE NO. 85-10: POSTTENSIONED CONTAINMENT TENDON ANCHOR

HEAD FAILURE

Addressees

All nuclear power reactor facilities holding an operating license (OL) or a

construction permit (CP).

Purpose

This information notice is provided to alert recipients of current information

relating to a potentially significant problem regarding recent failures of

170-wire posttensioned containment tendon anchor heads at Unit 2 of the Farley

Nuclear Station. It is expected that recipients will review the information

for applicability to their facilities and consider actions, if appropriate, to

detect a similar problem at their facilities. However, suggestions contained

in this information notice do not constitute NRC requirements; therefore, no

specific action or written response is required.

NRC is continuing to obtain and evaluate pertinent information. If specific

actions are determined to be required, an additional notification will be made.

Description of Circumstances

Farley Unit 2 On January 28, 1985, while conducting a preintegrated leak rate test walkdown

of the exterior of the containment structure at the Farley Unit 2 facility, an alert utility worker noted grease leakage and a deformed vertical tendon

anchor grease cap on the top of the containment ring beam. When the grease

cap on the same tendon was inspected in the tendon access gallery, it also

revealed a deformed grease cap. Removal of the grease cap showed that the

field anchor head had broken into seven pieces. The posttensioning force

(approximately 1.5 x 10° pounds) also had been released and numerous broken

wires from the 170-wire tendon were found.

On the basis of this finding, the utility removed some additional tendon anchor

grease caps. Of the first eight anchor heads uncovered for inspection, one was

found to be cracked. Inspection was curtailed until the cracked anchor head

can be detensioned. The tendon associated with this anchor head is still

transmitting posttensioning force to the containment. The utility determined

from their records that the broken anchor head and the cracked anchor head have

the same fabrication lot control number.

8502060136

SSINS No.: 6835 IN 85-10 Additionally, the utility has sent some of the pieces of the broken anchor head

to two laboratories for a series of tests for failure analysis, including tests

on metallurgical, mechanical, chemical and other physical properties. Testing

of the corrosion inhibitor grease is under way.

Currently, the utility has personnel from the architect-engineer and the

material supplier on-site in the continuing investigation. Neither the NRC

nor the licensee has yet fully integrated the information regarding the results

of previous tendon surveillance activities at the Farley site into this infor- mation notice. Oral information from the licensee indicates the tendons at K

Farley Unit 2 were posttensioned in early 1977. The unit has been operational

since May 1981. The specific tendon whose anchor head failed and the one found

with a cracked anchor head were not included in the sample of tendons that were

subjected to surveillance activities since the plant began operation. Thus, there is no definitive information currently available on the time of occurrence

of the breakup of the one anchor head or the crack formation in the other

anchor head.

While no specific conclusions have been reached at this time regarding the

cause of the failures, the NRC believes that based on the conversations with

the supplier, INRYCO, that all material from the same fabrication lot control

number as the failed heads was utilized exclusively at Farley Unit 2.

The previous history of anchor head failures before the event at Farley Unit 2, in nuclear applications, has been confined to occurrences during the construction

phase (during or shortly after posttensioning). It is-during-this time-that

the tendon system, including the anchor head, undergoes the maximum loading

force.

As background information, previous 170-wire tendon anchor head failures during

construction at other facilities are briefly summarized below.

Bellefonte Units 1 and 2

During 1975 and 1976 a series of eight rock anchor heads, supplied by INRYCO

for the containments at Bellefonte Units 1 and 2, failed during construction

installation. In the phased construction process these 170-wire assemblies

were sealed for long periods in a highly alkaline water environment. These

anchor heads were to be coupled to the posttensioned containment vertical

tendons to serve as a direct tie between the containment and the rock foundation

material. In these instances the anchor head also broke into several pieces.

The licensee's investigations completed on these failures cited several possible

contributors. These included: (1) high anchor head stress as a result of a

1.4-inch-diameter hole in the head for grout passage, (2) inclusions in the

steel found oriented parallel to the final failure plane, (3) bending of shims J

and anchor plate, and (4) unknown environmental conditions which facilitated

stress corrosion cracking. The NRC had an independent study made that concluded

possible stress corrosion cracking as the initiator.

The resolution of the problem resulted in the removal of all the anchor heads

and replacement with new anchor heads made from a vacuum degassed (cleaner)

SSINS No.: 6835 IN 85-10 steel with the center grout hole eliminated and the anchor head coated for

temporary environmental protection. The NRC is aware of no further failures

at Bellefonte after this corrective action.

Byron Units 1 and 2 In November of 1979 two 170-wire anchor heads on horizontal tendons were reported

to have failed during construction of the Byron containments. One failure

occurred one day after stressing and seating the tendon and the other occurred

13 days after stressing and seating. By the end of January 1980, two additional

anchor heads had been reported as having failed. The supplier of the anchor

heads was INRYCO. Investigations were made by INRYCO on the material from seven

separate fabrication lots. It was found that the basic steel material used in

several of the batches had been manufactured by a process that utilized vanadium

grain refinement causing an incompatibility with the postfabrication heat

treatment. This resulted in a different steel chemistry that would have

required a higher temperature for proper heat treatment. As a result of this

conclusion all anchor heads that had received improper heat treatment for the

basic steel chemistry were removed and replaced. The NRC is not aware of any

failures at Byron since the corrective action.

Discussion

Because the integrity of the posttensioned concrete containment structure is

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

the failure of one such element in a family of tendons does not jeopardize

containment structural capability. It does, however, necessitate a determination

that a mechanism or systematic problem has not arisen under service conditions

when one such failure in a tendon is revealed. Specific tendon geometry, tendon size, containment design details, and location of individual tendons

with lost or lowered strength properties would dictate the critical number of

tendons that could be lost before containment integrity is jeopardized.

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.

rh-Eda-rd L. Jordan Director

L Division of Emergency Preparedness

and Engineering Response

Office of Inspection and Enforcement

R. Shewmaker, IE

(301)492-7432 Attachment: List of Recently Issued IE Information Notices

Attachment

IN 85-10

February 06, 1985 LIST OF RECENTLY ISSUED

IE INFORMATION NOTICES

Information Date of

Notice No. Subject Issue Issued to

85-09 Isolation Transfer Switches 1/31/85 All power reactor

And Post-Fire Shutdown facilities holding

Capability an OL or CP

85-08 Industry Experience On 1/30/85 All power reactor i

Certain Materials Used In facilities holding

Safety-Related Equipment an OL or CP

85-07 Contaminated Radiography 1/29/85 All NRC licensees

Source Shipments authorized to

possess industrial

radiography sources

85-06 Contamination of Breathing 1/23/85 All power reactor

Air Systems facilities holding

an OL or CP-

85-05 Pipe Whip Restraints 1/23/85 All power reactor

facilities holding

an OL or CP

85-04 Inadequate Management Of 1/17/85 All power reactor

Security Response Drills facilities holding

an OL or CP, & fuel

fabrication & pro- cessing -facilities

85-03 Separation Of Primary Reactor 1/15/85 All pressurized water

Coolant Pump Shaft And power reactor

Impeller facilities holding an

OL or CP

85-02 Improper Installation And 1/15/85 All power reactor

Testing Of Differential facilities holding

Pressure Transmitters an OL or CP

85-01 Continuous Supervision Of 1/10/85 All material licensees

Irradiators possessing irradiators

that are not self- shielded and contain

more than 10,000

curies of radioactive

material

OL = Operating License

CP = Construction Permit