Information Notice 1989-33, Potential Failure of Westinghouse Steam Generator Tube Mechanical Plugs

Potential Failure of Westinghouse Steam Generator Tube Mechanical Plugs
	ML031180754
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, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	03/23/1989
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-89-033, NUDOCS 8903230075
	Download: ML031180754 (5)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 March 23, 1989 NRC INFORMATION NOTICE NO. 89-33: POTENTIAL FAILURE OF WESTINGHOUSE STEAM

GENERATOR TUBE MECHANICAL PLUGS

Addressees

All holders of operating licenses or construction permits for pressurized-water

reactors (PWRs).

Purpose

This information notice is being provided to alert addressees to the potential

for failure of Westinghouse steam generator tube mechanical plugs. Such failures

could lead to a large primary-to-secondary leak and possible damage to adjacent

tubes. It is expected that recipients will review the information for applica- bility to their facilities and consider actions, as appropriate, to avoid similar

problems. However, suggestions contained in this information notice do not con- stitute NRC requirements; therefore, no specific action or written response is

required.

Description of Circumstances

On February 25, 1989, North Anna Unit 1 experienced a large primary-to-secondary

leak of about 70 gallons per minute (gpm) following a reactor trip from 76 percent

power. Unit response to the trip was normal. No safety injection (manual or

automatic) was initiated or required during the event, and post-trip cooldown

and depressurization were conducted in a stable manner.

Primary-to-secondary leakage in the affected steam generator (S/G) had been

negligible (< 1.0 gallon per day) with no increasing trend before the reactor

trip. I

The licensee's investigation performed after plant shutdown showed the leak was

associated with a broken plug located in the hot leg of tube R3C60. This tube

had been plugged in 1985 because a 55 percent indication had been found at the

first support plate location. The broken plug was a "mechanical" plug supplied

by Westinghouse. The top portion of the plug was completely severed from the

body of the plug, which was expanded against the tube and tubesheet. The severed

portion of the plug was apparently propelled up the length of the tube by the

primary system pressure to a location Just above the U-bend transition where

it impacted the outer curvature of the tube approximately 4 inches above the

seventh support plate.

8903230075 iZ 4 I

IN 89-33 March 23, 1989 Further investigation with a modified Welsh-Allyn video probe showed that the

impact of the broken plug piece had punctured the tube over an area approxi- mately 21 Inches long and 3/4 inches wide. The broken plug piece subsequently

impacted and dented the adjacent tube R4C60 directly above.

Discussion:

Westinghouse informed several licensees on January 17, 1989 that a few utilities

had observed dripping or wetness around tube ends plugged with Westinghouse

mechanical plugs. When some of these plugs were removed and examined, inter- granular cracks were found. Westinghouse reported that these cracks appeared

to be associated with minimal intergranular carbide precipitation, which, in

turn, may be the result of a low mill annealing temperature.

Preliminary information obtained informally from Westinghouse indicates that

plugs from two heats (numbers 3513 and 3962) may exhibit this susceptible

microstructure. The broken plug at North Anna Unit 1 was fabricated from

heat number 3962.

The licensee for North Anna Unit I is currently determining where other plugs

from the susceptible heats may be installed at Units 1 and 2 and what remedial

measures need to be taken.

During a recent inspection of steam generator tube plugs at Millstone Unit 2 (a

Combustion Engineering-designed reactor), in response to the North Anna event, the licensee removed four similar Westinghouse mechanical plugs. Current indi- cations are that these plugs were from the suspected susceptible heats. One of

the plugs severed during the removal operation as a result of a circumferential

crack.

The NRC staff is currently investigating the potential generic implications of

these plug failures.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the technical contact

listed below or the Regional Administrator of the appropriate regional office.

ha es E. Rr!l, erec tor

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contact:

E. Murphy, NRR

(301) 492-0945 Attachment: List of Recently Issued NRC Information Notices

Attachment

IN 89-33 March 23, 1989 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

89-32 Surveillance Testing 3/23/89 All holders of OLs

of Low-Temperature or CPs for PWRs.

Overpressure-Protection

Systems

89-31 Swelling and Cracking 3/22/89 All holders of OLs

of Hafnium Control Rods or CPs for PWRs with

Hafnium control rods.

89-30 High Temperature 3/15/89 All holders of OLs

Environments at or CPs for nuclear

Nuclear Power Plants power reactors.

89-29 Potential Failure of 3/15/89 All holders of OLs

ASEA Brown Boveri or CPs for nuclear

Circuit Breakers power reactors.

During Seismic Event

89-28 Weight and Center of 3/14/89 All holders of OLs

Gravity Discrepancies or CPs for nuclear

for Copes-Vulcan power reactors.

Air-Operated Valves

89-27 Limitations on the Use 3/8/89 All holders of OLs

of Waste Forms and High or CPs for nuclear

Integrity Containers for power reactors, fuel

the Disposal of Low-Level cycle licenses and

Radioactive Waste certain by-product

materials licenses.

89-26 Instrument Air Supply to 3/7/89 All holders of OLs

Safety-Related Equipment or CPs for nuclear

power reactors.

89-25 Unauthorized Transfer of 3/7/89 All U.S. NRC source, Ownership or Control of byproduct, and special

Licensed Activities nuclear material

licensees.

OL = Operati-ng License

CP = Construction Permit

IN 89-33 March 23, 1989 Further investigation with a modified Welsh-Allyn video probe showed that the

impact of the broken plug piece had punctured the tube over an area approxi- mately 2* inches long and 3/4 inches wide. The broken plug piece subsequently