Information Notice 1994-05, Potential Failure of Steam Generator Tubes with Kinetically Welded Sleeves

Potential Failure of Steam Generator Tubes with Kinetically Welded Sleeves

ML031070052
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:	01/19/1994
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-94-005, NUDOCS 9401130075
Download: ML031070052 (5)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 January 19, 1994 NRC INFORMATION NOTICE 94-05: POTENTIAL FAILURE OF STEAM GENERATOR TUBES

WITH KINETICALLY WELDED SLEEVES

Addrq ,sees

All holders of operating licenses or construction permits for pressurized

water reactors (PWRs).

Purpose

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

notice (IN)to alert addressees to the potential failure of steam generator

tubes sleeved with kinetically (explosively) welded sleeves supplied by B&W

Nuclear Service Company (BWNS). 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 is required.

Background

For certain types of defects, a steam generator tube may be repaired using an

approved sleeving method as an alternative to plugging the tube and removing

it from service. In this process, the sleeve is positioned inside the steam

generator tube so that it bridges the defect. The sleeve is then joined to

the parent tube on both sides of the defect to serve as a new primary coolant

interface and allow the tube to be returned to service. The sleeve can be

Joined to the tube wall by a mechanical seal or a weld. In the case of the

kinetic welding process used by BWNS, an explosive charge expands a narrow

band of the sleeve, fusing the outer sleeve wall to the inner tube wall. The

process leaves residual stresses in the parent tube in the vicinity of the

seal or weld which necessitates a post-weld heat treatment to relieve the

stresses. The heat treatment is necessary in the parent tube because the tube

is constructed of nickel Alloy 600 which is susceptible to stress corrosion

cracking. Heat treatment is not necessary for the repair sleeve because it is

made of nickel Alloy 690 which is more resistant to stress corrosion cracking.

Description of Circumstances

of the McGuire I Incident

On August 22, 1993, operators at Unit 1 of the William B. McGuire Nuclear

Station (McGuire) shut down the reactor because of a primary-to-secondary leak

of about 760 liters [200 gallons] a day in steam generator A. This amount of

leakage was within the technical specification limits but exceeded the

administrative limit. Duke Power Company, the licensee, determined that a

tube containing a BWNS kinetically welded sleeve was the source of the leak.

9401130075 Et gE Niot'cx 5 F 9L-O

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'--ON 94-05 January 19, 1993 crack

The licensee removed the tube and the sleeve and found a circumferential and the

that joined the tube

in the parent tube just above the upper weld reinspected in

sleeve. The sleeve had been installed in 1991 and had beenused a rotating eddy

April 1993 with no indications of cracking. The licensee

and found an indication of a

current probe to examine the tube in situ examination of

120-degree to 180-degree circumferential defect. Destructive

crack extending 270 degrees

the tube found a through-wall circumferential

around the tube. The remaining 90 degrees of the tube was initiatedcracked

wall. The crack had from the

appr:ximately 50 percent through the primary water

inner surface (primary coolant side) and was characteristic of

side stress corrosion cracking (PWSCC). This type of stress corrosion

The

cracking is a well-known failure mechanism in steam generator tubes. notices

mechanism is discussed in greater detail in the NRC information

referenced at the end of this notice.

tube was

Another tube that had been sleeved at the same time as the leaking same area as

also removed because an eddy current indication was found in the to be the

in the failed tube. The indication was not a defect but was found examination of

result of a variation in the surface geometry. Metallographic A review of

the sleeve and parent tube also showed no signs of cracking. relief

process records showed that both tubes had received the same stress tubes had

temperature and time. Hardness measurements confirmed that both

been stress relieved after the kinetic welding.

removed

Physical and chemical tests performed on the two tubes that were

showed significant differences in the yield strength, carbon content, Tests

microstructure, and PWSCC susceptibility of the tube material.Board, and

sponsored jointly by Studsvik Power, the Swedish State Power the carbon

AB Sandvick Steel show that a strong correlation exists between to PWSCC.

content and yield strength of the material and its susceptibility cracking for

to

Results of accelerated corrosion tests indicate that the time with

reverse U-bend tubes is shorter for tubes constructed of materials

strength of

elevated yield strengths and carbon content. Based on a yield heat of

51.7 MPa (72.5 ksi) and a 0.05-percent carbon content, the material to PWSCC in

the leaking tube would be ranked as one of the most susceptible that it

the plant. Metallographic examination of the tube material confirmed

had a susceptible microstructure.

qualified for

The BWNS kinetic sleeve stress-relieving process was originally

a range of material corrosion susceptibilities. The stress relief

temperatures were selected for what was believed to be the worst-case tube that

material. As evidenced by the destructive examination of the

leaked, material properties of steam generator tubes can be significantly

Report

different than the properties listed in a Certified Material Test tube should have

(CMTR). Based on the CMTR, the yield strength of the leaking

yield strength was 51.7 MPa

been 44.1 MPa (64 ksi), whereas the actual be

data, BWNS will

(72.5 ksi). As a result of this and other industry cycles for

evaluating the appropriateness of using alternate stress relief

tubing of higher yield strengths.

that the

The destructive examination of the sleeved tube at McGuire indicates the parent

susceptibility of

root cause of the parent tube leak was the high

V IN 94-05 January 19, 1994 tube material to stress corrosion cracking. Since 1990, approximately 4500

sleeves manufactured by BWNS have been installed worldwide using the kinetic

weld process. According to BWNS, the defective tube sleeve at McGuire is the

first confirmed case of cracking in a sleeved tube that had received the

post-weld stress relief treatment required in the process qualification. A

kinetically sleeved tube cracked and leaked at the Trojan Nuclear Plant in

1992 but that tube had not received the required post-weld stress relief

treatment.

Discuss~nn

In September 1993, B&W Nuclear Technologies contacted affected domestic

licensees to inform them that the destructive examination of the sleeved tube

at McGuire indicated that the root cause of the leak in the parent tube was a

high susceptibility of the parent tube material to stress corrosion cracking.

Five domestic nuclear units have installed tube sleeves using the BWNS process

and a number of others are licensed to install them.

After the incident at McGuire 1, B&W Nuclear Technologies made recommendations

to licensees with BWNS kinetically welded sleeves concerning (1)the

identification of highly susceptible parent tube material, (2)procedures for

dealing with primary-to-secondary leakage, and (3)operator readiness to

respond to a tube leak such as the one that occurred at McGuire. Duke Power

Company implemented these recommendations at McGuire 1 and for preventive

purposes plugged sleeved tubes that were not axially restrained (peripheral

tubes not completely surrounded by other tubes).

This failure mechanism has the potential for introducing difficult-to-detect

circumferential stress corrosion cracks in steam generator tubes which could

lead to rapidly increasing primary-to-secondary leakage. The NRC staff has

contacted all affected licensees concerning the implications of these findings

and is continuing to monitor this issue.

Related Generic Communications

1. NRC IN 92-80, "Operation With Steam Generator Tubes Seriously Degraded,"

December 7, 1992.

2. NRC IN 91-43, "Recent Incidents Involving Rapid Increases in

Primary-to-Secondary Leak Rate," July 5, 1991.

3. NRC IN 90-49, "Stress Corrosion Cracking in PWR Steam Generator Tubes,"

August 6, 1990.

4. NRC IN 88-99, "Detection and Monitoring of Sudden and/or Rapidly

Increasing Primary-to-Secondary Leakage," December 20, 1988.

IN 94-05 January 19, 1994 No specific action or written response is required by this information notice.

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

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

manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contact: H. Conrad, NRR

(301) 504-2703 Attachment:

List of Recently Issued NRC Information Notices

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Attachment

IN 94-05 January 19, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

94-04 Digital Integrated 01/14/94 All NRC licensees except

Circuit Sockets with licensed operators.

Intermittent Contact

94-03 Deficiencies Identified 01/11/94 All holders of OLs or CPs

during Service Water System for nuclear power reactors.

Operational Performance

Inspections

94-02 Inoperability of General 01/07/94 All holders of OLs or CPs

Electric Magne-Blast for nuclear power reactors.

Breaker Because of Mis- alignment of Close-Latch

Spring

94-01 Turbine Blade Failures 01/07/94 All holders of OLs or CPs

Caused by Torsional for nuclear power reactors.

Excitation from Electrical

System Disturbance

93-101 Jet Pump Hold-Down Beam 12/17/93 All holders of OLs or CPs

Failure for boiling-water reactors.93-100 Reporting Requirements 12/22/93 All U.S. Nuclear Regulatory

for Bankruptcy Commission licensees.

91-29, Potential Deficiencies 12/22/93 All holders of OLs or CPs

Supp. 2 Found During Electrical for nuclear power reactors.

Distribution System

Functional Inspections

93-99 Undervoltage Relay and 12/21/93 All holders of OLs and CPs

Thermal Overload Setpoint for nuclear power reactors.

Problems

93-98 Motor Brakes on Valve 12/20/93 All holders of OLs and CPs

Actuator Motors for nuclear power reactors.

93-97 Failures of Yokes 12/17/93 All holders of OLs or CPs

Installed on Walworth for nuclear power reactors.

Gate and Globe Valves

OL - Operating License

CP - Construction Permit