UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

May 4, 2004

NRC INFORMATION NOTICE 2004-10: LOOSE PARTS IN STEAM GENERATORS 

Addressees:

All holders of operating licenses for pressurized-water reactors (PWRs), except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor.

Purpose:

The U.S. Nuclear Regulatory Commission is issuing this information notice to inform

addressees about loose parts found in steam generators. This notice discusses only a few

illustrative examples of loose parts found in steam generators. The NRC anticipates that

recipients will review the information for applicability to their facilities and consider taking

actions, as appropriate, to avoid similar issues. However, no specific action or written response

is required.

Description of Circumstances:

In its fall 2003 inspection, Exelon Generation Company found several loose parts in its

Braidwood Unit 2 steam generators. For example, an object 3.18 cm (1.25 inch) long and

1.91 cm (0.75 inch) in diameter was discovered during a secondary-side visual inspection of

one steam generator. Exelon then reviewed the eddy current data for the tubes surrounding

the part and in hindsight identified tube wear in one tube and a possible loose part signal in

three tubes. The tube wear caused by the loose part measured 38 percent through-wall as

determined by a +PointTM coil. The indication of tube wear was present in prior cycles, but was

not reported because the indication was distorted due to its location (i.e., near an expanded

preheater baffle plate support).

In another steam generator, Exelon identified a piece of weld slag measuring 2.86 cm (1.125

inches) by 2.54 cm (1 inch) by 0.89 cm (0.35 inch) on the top of the cold-leg tubesheet. The

weld slag was originally identified during a foreign object search-and-retrieval inspection in

2002, but could not be retrieved. No tube wear was associated with this object. Four tubes

surrounding this object were plugged and stabilized in 2003. In addition, Exelon found two

manufacturing fitup bars (also referred to as backing bars) measuring 2.54 cm (1 inch) by

2.54 cm (1 inch) by 7.62 cm (3 inches) on top of a preheater baffle plate. These bars were

used to assist in the assembly of the steam generator and were welded on the bottom of

another preheater baffle plate. These fitup bars serve no structural or operational function. 

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After visually identifying the presence of these fitup bars, the licensee could ascertain from

eddy current data that one of these bars had been present on the top of the preheater baffle

plate since the spring of 1990 and the other since the fall of 1994. These bars resulted in tube

wear.

 

One bar caused two wear scars (with maximum depths of 28 percent and 21 percent

through-wall) in one tube and the other bar caused one wear scar (maximum depth of 5 percent

through-wall). After visually identifying these fitup bars in 2003, Exelon attributed a 39-percent

through-wall volumetric indication detected in a neighboring tube in 1994 and plugged in 1997

to wear associated with the fitup bar. These two backing bars could not be removed from the

steam generator, so Exelon plugged and stabilized all of the tubes surrounding them. As part

of its evaluation, Exelon also assessed the potential for other fitup bars to cause tube damage

(refer to NRC Letter to Exelon Nuclear, Subject: Summary of Conference Call With Exelon

Nuclear Regarding the 2003 Steam Generator Inspections at Braidwood Unit 2, January 15,

2004, ADAMS Accession No. ML033580377).

In its fall 2003 inspection, Nuclear Management Company (NMC) reported several potential

loose part indications on the tubes in the hot leg top of the tubesheet region in the Prairie Island

Unit 2 steam generators. These potential loose part indications were present in previous

inspections and have not resulted in any tube wear. NMC typically performs visual inspection of

the top of the tubesheet and a search for loose parts in the annulus region of one steam

generator during each outage regardless of indications of possible loose parts. Before

resuming plant operation, NMC evaluates and resolves possible loose part indications which

include an inspection of these indications with a rotating probe. (NRC Letter to NMC, Subject:

Prairie Island Nuclear Generating Plant, Unit 2 - Summary of Conference Call With Nuclear

Management Company, LLC Regarding the 2003 Steam Generator Inspections, November 26,

2003, ADAMS Accession No. ML033210569). 

On June 22, 2002, Exelon shut down its Byron Unit 2 plant when the steam generator primaryto-secondary leak rate reached a level of 284 liters (75 gallons) to 303 liters (80 gallons) per

day. A subsequent investigation into the source of the leak identified one leaking tube. In this

leaking tube, a volumetric flaw was identified above a cold-leg tube support near the feedwater

inlet. Inspections performed around the leaking tube resulted in the identification of several

other flaws. Given the nature (volumetric) and location of the signals (periphery near feedwater

inlet), the flaws were attributed to wear from a loose part; however no loose parts were

observed during the eddy current inspection. The leaking tube and other degraded tubes were

plugged and stabilized. In its September 2002 refueling outage inspection, Exelon performed

sludge lancing and foreign object search-and-retrieval inspections and confirmed the presence

of loose parts in the Byron Unit 2 steam generators, including the parts believed to have

resulted in the leaking tube (NRC Letter to Exelon, Subject: Byron Station, Unit 2, Summary of

Conference Calls with Exelon Generation Company Regarding Its 2002 Steam Generator Tube

Inspection Results, November 8, 2002, ADAMS Accession No. ML022950043).

On May 10, 2002, Wolf Creek Nuclear Operating Corporation detected indications of an

unusual noise coming from steam generator D followed by an alarm in the plant’s loose parts

monitoring system (NRC Memorandum, Subject: Response to Request for Information on

Loose Parts Found In the Steam Generator at Wolf Creek Generating Station, August 27, 2002,

ADAMS Accession No. ML022340708). After a detailed evaluation of available information,
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plant management directed the shutdown of Wolf Creek on May 13, 2002, in order to identify

the source of the noise. During its inspections, the licensee retrieved two loose parts, a guide

tube support pin nut, and a locking device from the primary side of steam generator D. There 

were no indications within the steam generator of serious damage to the tubes, tubesheet,

welds, or divider plate. The loose parts did not result in any primary-to-secondary tube leakage.

In the subsequent refueling outage (fall 2003), detailed inspections of steam generator D

resulted in repairs to the tube sheet and a mechanical plug. An additional loose part from the

split pin was identified to be lodged in one of the steam generator tubes which resulted in the

plugging of that tube. Additionally, all guide tube split pins were replaced with stainless steel

split pins. 

Discussion:

Loose parts have been found in steam generators for a number of years (refer to NRC

Information Notice 83-24, “Loose Parts In the Secondary Side of Steam Generators at

Pressurized Water Reactors,” dated April 28, 1983). These parts may be introduced into the

steam generators from maintenance activities or degradation in primary- or secondary-system 

components. Some of these parts have resulted in degradation of the steam generator tubes,

and in some cases have led to tube leaks. Tube degradation may be the result of the

mechanical interaction between the loose part and the tube or may be the result of chemical

impurities (e.g., lead, chlorides) introduced into the steam generator by the part. Licensees

have found that to ensure that loose parts do not impair tube integrity, it is important to take

measures to limit their introduction into the steam generator. In addition, it is important to have

programs for detecting and monitoring loose parts in case loose parts are introduced into steam

generators. Recent operating experience of most plants indicates that loose parts have not

significantly affected tube integrity; however, they have resulted in tube degradation. Since

many licensees are beginning to extend the operating interval between tube inspections

(especially at plants with advanced tube materials), it is important to ensure that programs

continue to effectively limit the introduction of loose parts, promptly detect loose parts that do

enter, and implement appropriate corrective action upon identification of loose parts in steam

generators.

Licensees can take actions to prevent the introduction of loose parts into the steam generators. 

By preventing the introduction of loose parts into the primary and secondary system, damage

from loose parts will be avoided. Procedures for precluding the introduction of loose parts into

the primary and secondary system typically include (a) detailed accountability for all tools and

equipment used during a maintenance operation, (b) appropriate controls on foreign objects

such as eyeglasses and film badges including barriers to keep material from dropping into a

system (e.g., feedwater), (c) cleanliness requirements, (d) accountability procedures for

components and parts removed from major components (e.g., reassembly of cut and removed

components), and (e) post-maintenance inspections.

Actions taken in response to the detection of a loose part in a steam generator vary depending

on the nature and location of the part and its effect on tube integrity. In many cases, parts are

removed from a steam generator upon detection. However, retrieval of a loose part is not

always practical or possible. In these cases, an engineering evaluation will determine whether

the part will impair tube integrity if it is left in service. This evaluation may result in preventive 
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tube plugging and stabilization of the affected and surrounding tubes or may result in other

corrective actions such as insertion of additional access points in the steam generator shell to

provide access for removing the part.

The above examples and other operating experience illustrate several important points with

respect to managing steam generator loose parts. For example, verifying the integrity of

primary- and secondary-system components (such as support pins and fitup bars) may prevent

the introduction of loose parts into the steam generator from these sources. Operating

experience also indicates that loose part monitoring systems may provide an early indication

that a part is in a steam generator, permitting prompt corrective action to be taken before any

significant tube damage occurs. The importance of supplementing the steam generator tube

eddy current examinations with secondary side visual inspections is also supported by recent 

operating experience indicating that some loose parts may not be detected during the eddy

current examination. In addition, operating experience indicates that tube damage from minor

loose parts may not always be detectable due to the presence of interfering signals.

This information notice does not require any specific action or written response. If you have

any questions about the information in this notice, please contact one of the technical contacts

listed below or the appropriate project manager in the NRC’s Office of Nuclear Reactor

Regulation (NRR).

/RA/

William D. Beckner, Chief

Reactor Operations Branch

Division of Inspection Program Management

Office of Nuclear Reactor Regulation

Technical Contact: John Tsao, NRR Kenneth Karwoski, NRR

301-415-2702 301-415-2752

E-mail: jct@nrc.gov E-mail: kjk1@nrc.gov

Attachment: List of Recently Issued NRC Information Notices
____________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment

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LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2004-09 Corrosion of Steel

Containment and Containment

Liner

04/27/2004 All holders of operating licenses

for nuclear power reactors except

those who have permanently

ceased operation and have

certified that fuel has been

permanently removed from the

reactor vessel.

2004-08 Reactor Coolant Pressure

Boundary Leakage Attributable

to Propagation of Cracking in

Reactor Vessel Nozzle Welds

04/22/2004 All holders of operating licensees

for nuclear power boiling-water

reactors (BWRs), except those

who have permanently ceased

operations and have certified that

fuel has been permanently

removed from the reactor vessel.

2004-07 Plugging of Safety Injection

Pump Lubrication Oil Coolers

with Lakeweed

04/07/2004 All holders of operating licenses

or construction permits for

nuclear power reactors, except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel.

2004-06 Loss of Feedwater Isokinetic

Sampling Probes at Dresden

Units 2 and 3

03/26/2004 All holders of operating licensees

for nuclear power reactors except

those who have permanently

ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel.

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