NRC NEWS

 U.S. NUCLEAR REGULATORY COMMISSION 

 Office of Public Affairs Telephone: 301/415-8200

 Washington, D.C. 20555-0001 E-mail: opa@nrc.gov 

 Web Site: http://www.nrc.gov

 

No. 07-034 March 12, 2007

 NRC ISSUES CONFIRMATORY ACTION LETTERS 

ON WELDS TO GROUP OF PWR NUCLEAR POWER PLANTS

The Nuclear Regulatory Commission is issuing Confirmatory Action Letters (CALs) to 40

nuclear power plant licensees with pressurized water reactors (PWR), confirming commitments from

those licensees to resolve concerns regarding flaws in certain welds in the reactor coolant system

(RCS) by the end of the year. 

The CALs ensure the plants will put in place more timely inspection and flaw prevention

measures, more aggressive monitoring of RCS leakage, and more conservative leak rate thresholds for

a plant to shut down to investigate a possible leak. These actions are being taken to assure continued

operational safety at these facilities. The remaining 29 PWR plants have either completed requisite

actions or do not have welds susceptible to these flaws.

 The CALs resulted from the discovery, last fall, of flaws in pressurizer welds at the Wolf

Creek reactor near Burlington, Kan. The Wolf Creek flaws were repaired and did not affect the safe

operation of the plant. The nature of the flaws identified at Wolf Creek raised further questions

regarding those welds at other PWRs.

The CAL officially documents the plant operator’s commitment to conduct volumetric (e.g.,

ultrasonic) inspections of some RCS welds containing materials known as Alloy 82 and Alloy182 or to

take action to mitigate the conditions that contribute to the flaws. These metal alloy materials have

been susceptible in the past to cracking due to their chemical makeup, residual stresses from the

welding process and PWR operating conditions. 

The first incidence of these flaws occurred in a U.S. reactor in 1993. Since 2000, additional

flaws have been documented and the NRC and the nuclear industry have progressively increased

attention to detecting, evaluating and correcting the flaws. The size and nature of the Wolf Creek flaws,

however, have led NRC staff to conclude the industry must accelerate its planned actions for the

remainder of the affected plants in the PWR fleet.

The CALs confirm commitments by the affected plant operators to complete actions by the end

of the year and implement enhanced leakage monitoring until actions are completed. Plants must be

shut down to conduct the inspections. For plants having their next planned shutdown beyond 2007,

operators have committed to shut down and resolve concerns with the welds in 2007 if additional
analyses being performed by industry do not provide the NRC with sufficient bases to support extended

schedules. Plant operators have committed to report inspection results and any corrective actions taken

within 60 days of a plant returning to operation.

Issuance of these CALs does not preclude the NRC from taking stronger actions, if warranted. 

The CALs are considered an interim measure while the American Society of Mechanical Engineers

incorporates enhanced inspection requirements into the society’s Boiler and Pressure Vessel Code. 

The NRC will review those enhanced requirements and incorporate them into agency requirements, as

appropriate.

The list of plants that will receive a CAL is attached. The CALs will be posted on the NRC

web site at:

http://www.nrc.gov/reactors/operating/ops-experience/pressure-boundary-integrity/weld-issues/.

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Attachment

Plants Receiving a Confirmatory Action Letter from NRC

Arkansas Nuclear One, Unit 1

Beaver Valley, Unit 1

Braidwood, Unit 1

Braidwood, Unit 2

Byron, Unit 2

Callaway

Calvert Cliffs, Unit 2

Catawba, Unit 2

Comanche Peak, Unit 1

Comanche Peak, Unit 2

Crystal River, Unit 3

Davis-Besse

Diablo Canyon, Unit 2

Farley, Unit 1 & Unit 2

McGuire, Unit 1

Millstone, Unit 3

North Anna, Unit 1 & Unit 2

Oconee, Unit 2 & Unit 3

Palisades

Palo Verde, Unit 1& Unit 3

Palo Verde, Unit 2

Prairie Island, Unit 2

San Onofre, Unit 2 & Unit 3

Seabrook

Sequoyah, Unit 1

Shearon Harris

South Texas Project, Unit 1

South Texas Project, Unit 2

St. Lucie, Unit 2

Summer

Three Mile Island, Unit 1

Vogtle, Unit 1

Vogtle, Unit 2

Waterford, Unit 3

Watts Bar, Unit 1