Information Notice 2010-05, Management of Steam Generator Loose Parts and Automated Eddy Current Data Analysis

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Management of Steam Generator Loose Parts and Automated Eddy Current Data Analysis
ML093640691
Person / Time
Issue date: 02/03/2010
Revision: 0
From: McGinty T J
Division of Policy and Rulemaking
To:
Beaulieu, D P, NRR/DPR, 415-3243
References
IN-10-005
Download: ML093640691 (5)
v • d • e


ML093640691 February 3, 2010 NRC INFORMATION NOTICE 2010-05: MANAGEMENT OF STEAM GENERATOR LOOSE PARTS AND AUTOMATED EDDY CURRENT DATA ANALYSIS

ADDRESSEES

All holders of an operating license or construction permit for a nuclear power pressurized-water reactor issued under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, "Domestic Licensing of Production and Utilization Facilities," except those who have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vesse

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform addressees of recent operating experience with (1) loose parts (foreign objects) in steam generators and (2) the use of automatic steam generator eddy current data analysis system The NRC expects recipients to review the information for applicability to their facilities and to consider actions, as appropriate, to avoid similar problem However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is require

DESCRIPTION OF CIRCUMSTANCES

At the Braidwood Station, Unit 1, in 2009, the licensee, Exelon Generation Company, LLC, inspected steam generator tubes using eddy current technique As is common practice, the licensee used two independent teams (i.e., primary and secondary teams) to evaluate the dat Each of the two teams used an automated data screening system to evaluate the bobbin coil eddy current dat Human analysts reviewed the results of each of the automated data screening systems to accept, reject, or modify the classification of the signals identified through the automatic data analysi During the 2009 inspections, one of the automated data analysis systems identified a distorted signal from the bobbin coil eddy current data slightly above both the expansion transition and the tubesheet on the hot-leg side of the steam generato The human analyst accepted this signal for further investigatio To resolve the nature of this indication, the licensee used a rotating eddy current probe to inspect the location with the distortio Based on the result of this subsequent examination, the licensee concluded that mechanical wear between the tube and a foreign object caused the indicatio The depth of the wear indication was estimated from the rotating probe as 73 percent through the tube wal Because of its size, the indication was in situ pressure tested to confirm that it did not significantly compromise the integrity of the tub The licensee did not observe any leakage during the in situ pressure test and confirmed the tube had adequate integrit Following the in situ pressure test, the licensee stabilized and plugged the tub The plant technical specifications require the licensee to plug any tubes with flaws equal to or exceeding 40 percent of the wall thicknes This tube had been inspected during prior outage Upon review of the historical eddy current data, the licensee concluded that an indication had existed at this location since 200 The indication in 2006 was smaller than that observed in 2009, whereas the indication in 2007 was similar in size to the indication observed in 200 As a result, the licensee concluded that the tube should have been plugged in 200 As was the case for the 2009 steam generator tube inspections, two independent automated data analysis systems were employed during the 2006 and 2007 inspections at Braidwood Station, Unit During all three inspections, the primary automated data analysis system identified a distorted signal at the location where the flaw was observed in 200 Because the human analyst rejected these signals in both 2006 and 2007, no further investigation into the nature of the signal was performe The secondary automated data analysis system did not identify this location as having a distorted signal in the 2006, 2007, or 2009 inspections, although a signal attributed to a potential loose part was initially identified in 2006 and was subsequently rejected by the human analyst during that inspectio During the 2009 outage, no foreign object was found near the tube with the 73 percent through- wall wear indicatio However, the affected tube was located near a cluster of tubes that the licensee had plugged in 2003 because of a foreign object that was identified but could not be remove During the 2007 outage, the licensee could not locate this foreign object and now postulates that it moved from its original location and caused the 73 percent through-wall wear indicatio The licensee also postulates that the foreign object may have broken into smaller pieces that were removed by the blowdown system or during the removal of sludge from the top of the tubesheet (i.e., sludge lancing). The licensee assessed the cause of this event and determined that it was a historic human performance issue related to the amount of technical rigor applied during the review of the distorted eddy current data that the automated data analysis system identified during the 2006 and 2007 inspection A contributing cause was that one of the automated data analysis systems did not identify the distorted indicatio The licensee took the following corrective actions:

  • It revised the guidelines for the eddy current data analysis to emphasize the requirement to manually review available frequencies associated with distorted top of the tubesheet indications before determining whether an indication requires additional testing and/or analysi
  • It incorporated the lessons learned from this issue in its site-specific performance demonstration training and testing program to ensure that all data analysts and computer screening systems can properly identify the signal as requiring additional eddy current inspectio
  • It reevaluated the logic parameters in the automated data analysis system that the secondary data analysis team use
  • It determined and implemented changes to ensure that foreign object wear indications are correctly identified at the top of the tubesheet regio The licensee also assessed the eddy current method that it had chosen to size the wear indication identified in 2009 (i.e., the rotating eddy current probe). Different sizing methods exist for differently shaped wear scars (e.g., football-shaped and tapered-hole wear scars) and for volumetric indications, like wear, in the free spa For at least one of these techniques (e.g., sizing with a pancake coil), the resultant size would have been much smaller than 73 percent, thereby resulting in a flaw that would not require in situ pressure testin The licensee used a sizing method that conservatively estimated the flaw size and verified that the integrity of the tube was not compromised through in situ pressure testin

BACKGROUND

Related Generic Communications Previous related generic communications include the following:

DISCUSSION

In addition to reinforcing the information in NRC IN 2004-10 and NRC IN 2004-17, the recent operating experience at Braidwood, Unit 1 illustrates several important points relative to the management and detection of loose parts and the use of automatic data analysis system The loose part that may have caused the wear scar identified in 2009 was first identified in adjacent tubes during a refueling outage in 200 The licensee stabilized and plugged the tubes surrounding the original location of the loose part because it was unable to remove the loose part; however, the loose part eventually migrated from its original locatio Monitoring the location of loose parts that are left in the steam generator may help licensees detect tubes potentially affected by loose part For example, if a loose part is left in the steam generator, the licensee can perform secondary side visual inspections during subsequent outages to verify that the loose part has not move If the loose part has moved, additional secondary side visual inspections could be performed to locate the loose part, and primary side inspections could be performed on active tubes surrounding the original location of the loose part to determine whether the loose part has affected these tube If visual examination of the loose part's original location is not possible, primary side inspections of the active tubes surrounding the original location could determine whether the loose part has moved and whether additional tubes have been damage This process may lead to the more timely detection of wear caused by loose part At Braidwood, Unit 1 only one of the automated data analysis systems identified the distorted signal attributed to the wear scar estimated as being 73 percent through the tube wal The qualification of an automated data analysis system is important for ensuring that all relevant flaw signals are identifie Ensuring that an automated data analysis tool can detect the various types of flaws that may occur along the entire length of the tube is important for ensuring tube integrity, and plant technical specifications require licensees to perform inspections with the objective of detecting flaws of any type that may satisfy the applicable tube repair criteri Most plants with thermally treated Alloy 690 tubing, such as Braidwood, Unit 1 have very little degradation, and the forms of degradation that are observed at these plants tend to be easily detectabl Because many of the signals identified during the automated data analysis screening may not be flaws, it is important that eddy current data analysts do not inadvertently dismiss relevant signal The experience at Braidwood, Unit 1 highlights the importance of ensuring that human data analysts effectively review eddy current dat A licensee can monitor the performance of a human analyst by inserting a known flaw signal from a "Judas" (or "Cobra") tube into the data stream that is being reviewed, as discussed in NRC IN 2003-0 Choosing the appropriate method to size an indication is important for verifying tube integrit In instances where multiple techniques exist for sizing a flaw, it is important to select the most appropriate techniqu If the licensee cannot determine an appropriate technique, a conservative approach should be used to ensure that tube integrity is being maintained as required by the plant technical specification At Braidwood, Unit 1 the licensee used a sizing method that conservatively estimated the flaw size and in situ pressure tested the flaw to verify that tube integrity was maintaine

CONTACT

This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or to the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ Timothy J. McGinty, Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation

Technical Contact:

Kenneth J. Karwoski, NRR 301-415-2752 E-mail: kenneth.karwoski@nrc.gov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collection whether additional tubes have been damage This process may lead to the more timely detection of wear caused by loose part At Braidwood, Unit 1 only one of the automated data analysis systems identified the distorted signal attributed to the wear scar estimated as being 73 percent through the tube wal The qualification of an automated data analysis system is important for ensuring that all relevant flaw signals are identifie Ensuring that an automated data analysis tool can detect the various types of flaws that may occur along the entire length of the tube is important for ensuring tube integrity, and plant technical specifications require licensees to perform inspections with the objective of detecting flaws of any type that may satisfy the applicable tube repair criteri Most plants with thermally treated Alloy 690 tubing, such as Braidwood, Unit 1 have very little degradation, and the forms of degradation that are observed at these plants tend to be easily detectabl Because many of the signals identified during the automated data analysis screening may not be flaws, it is important that eddy current data analysts do not inadvertently dismiss relevant signal The experience at Braidwood, Unit 1 highlights the importance of ensuring that human data analysts effectively review eddy current dat A licensee can monitor the performance of a human analyst by inserting a known flaw signal from a "Judas" (or "Cobra") tube into the data stream that is being reviewed, as discussed in NRC IN 2003-0 Choosing the appropriate method to size an indication is important for verifying tube integrit In instances where multiple techniques exist for sizing a flaw, it is important to select the most appropriate techniqu If the licensee cannot determine an appropriate technique, a conservative approach should be used to ensure that tube integrity is being maintained as required by the plant technical specification At Braidwood, Unit 1 the licensee used a sizing method that conservatively estimated the flaw size and in situ pressure tested the flaw to verify that tube integrity was maintaine

CONTACT

This IN requires no specific action or written respons Please direct any questions about this matter to the technical contact listed below or to the appropriate Office of Nuclear Reactor Regulation (NRR) project manage /RA/ Timothy J. McGinty, Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation

Technical Contact:

Kenneth J. Karwoski, NRR 301-415-2752 E-mail: kenneth.karwoski@nrc.gov Note: NRC generic communications may be found on the NRC public Web site, http://www.nrc.gov, under Electronic Reading Room/Document Collections. ADAMS Accession Number: ML093640691 TAC ME2900 OFFICE DCI Tech Editor BC:CSGB:DCI D:DCI NAME KKarwoski KAzariah-Kribbs RTaylor MEvans DATE 01/19/10 01/04/10 e-mail 01/22/10 01/27/10 OFFICE LA:PGCB:NRR PM:PGCB:NRR BC:PGCB:NRR D:DPR:NRR NAME CHawes DBeaulieu MMurphy TMcGinty OFFICE 01/28/10 01/27/10 02/02/10 02/03/10 OFFICIAL RECORD COPY


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