Information Notice 2010-05, 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) | |
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 IN 2010-05