ML12128A365

Cycle 17 180-Day Steam Generator Inspection Report

ML12128A365
Person / Time
Site:	Sequoyah
Issue date:	05/07/2012
From:	Siva Lingam Plant Licensing Branch II
To:	Mackaman C Tennessee Valley Authority
References
TAC ME7705
Download: ML12128A365 (3)

Text

1 NRR-PMDAPEm Resource From: Lingam, Siva Sent: Monday, May 07, 2012 11:48 AM To: Mackaman, Clyde Douglas Cc: Broaddus, Doug; Kulesa, Gloria; Ka rwoski, Kenneth; Johnson, Andrew

Subject:

Sequoyah Nuclear Plant, Unit 2 - Cycle 17 180-Day Steam Generator Inspection Report (TAC NO. ME7705)Please note the following official RAIs for the subject report, and provide your responses within 45 days:

By letters dated September 16, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML112660570), and December 13, 2011 (ADAMS Accession No. ML113500496), Tennessee Valley Authority, the licensee, submitted information summarizing the results of the 2011 steam generator (SG) tube inspections at Sequoyah Nuclear Plant (SQN), Unit 2. In addition to these reports, the U.S. Nuclear

Regulatory Commission (NRC) staff summarized additional information concerning the 2011 SG tube inspections at SQN, Unit 2 in a letter dated August 16, 2011 (ADAMS Accession No. ML11208C216).

In order to complete its review, the NRC staff requests responses to the following questions.

1. Please discuss the scope and results of any secondary side inspections that were performed in the steam drum or upper bundle. 2. In your application of the in-situ screening criteria for several degradation mechanisms (e.g., axially oriented outside diameter stress corrosion cracking (ODSCC) in the freespan), you had several indications that exceeded the 0.5 volt "quick screen" criterion. In these cases, it appears that you determined that in-situ pressure testing was not needed since the flaw did not have a voltage of 0.4 volts for all the data points in any 0.6-inch portion of the flaw. Is this interpretation correct? If so, it appears to be non-conservative since you could have a 0.6-inch flaw where all but one data point is 10 volts (or higher) and one data point is less than 0.4 volts and therefore would not need to be in-situ pressure tested. Please clarify.

3. In Section 4.6 of the September 16, 2011, letter, an assessment of the negative growth rates observed for axially oriented ODSCC in the tubes at the tube support plate elevations during the 2011 inspections were provided. In this discussion, it was indicated that a different frequency generator and a probe designed (and possibly manufactured) by a different vendor was used during the 2011 steam generator tube inspections. The negative growth rates were attributed to the difference in probe design.

The voltage-based alternate repair criteria for axially oriented ODSCC relies, in part, on representative/repeatable voltages being obtained for the flaws (at all plants and for the laboratory specimens). During the development of the repair criteria studies were performed to assess probes from different vendors. In addition, limits were placed on the design of the bobbin probe.

a. Please discuss whether the bobbin probes used during application of the voltage-based repair criteria since implementation at SQN, Unit 2 are equivalent to what was used during the development of the criteria. For example, were the data in the databases obtained with Zetec designed probes similar to what was used in 2011 or the Westinghouse designed probes used during the three prior outages?

2b. Please discuss how the Westinghouse and Zetec designed bobbin probes were qualified for use during application of the voltage based repair criteria.

c. In the condition monitoring and operational assessment for axially oriented ODSCC in the portion of the tube passing through the tube support plates, the measured voltages from the Zetec designed probe were used. Since the previous operational assessment used voltages obtained from a Westinghouse designed probe (that gave higher voltages for similar flaws), it is not clear that it is appropriate to compare the previous operational assessment results with the current condition monitoring results. It would appear that some adjustment to the voltages would be needed to ensure that the 2011 results were consistent with expectations from the 2009 operational assessment. Please clarify.

d. The Westinghouse designed probe appeared to detect more degradation than the Zetec designed probe. As a result, one may postulate that there were more undetected flaws during the 2011 inspections than in the 2009 inspections (since the Zetec designed probe was used during the 2011 inspections and the Westinghouse designed probe was used during the 2009 inspections). If previous operational assessments with a 0.6 probability of detection resulted in non-conservative or marginally conservative results for the number of indications detected, it is not clear that using a 0.6 probability of detection for the operational assessment following the 2011 inspections is appropriate (since if a Westinghouse designed probe were used during the 2011 outage, more flaws would have been detected in the 2011 outage and this larger number of flaws would have resulted in even more flaws being predicted because of the 0.6 probability of detection). Please discuss why it is not appropriate to account for the potentially higher number of undetected flaws as a result of using a probe which appears to be less sensitive to degradation.

e. The results presented for the voltage based repair criteria potentially have generic implications. It appears that two bobbin probes that have been identically calibrated can give different voltage readings for the same flaw. This would appear to draw into question any voltage-based sizing technique unless qualification was specific to the probe designer. What actions were taken to ensure appropriate sizing methods were applied during the 2011 inspections (i.e., the probe used to size degradation was equivalent to probe used during the development of the qualified technique). f. Please discuss the basis for concluding that the frequency generator was not the cause of the negative growth rates.

Siva P. Lingam U.S. Nuclear Regulatory Commission Project Manager (NRR/DORL/LPL2-2) Sequoyah Nuclear Plant Crystal River Nuclear plant (EPU)

Location: O8-D5; Mail Stop: O8-G9a Telephone: 301-415-1564; Fax: 301-415-1222 E-mail address: siva.lingam@nrc.gov

Hearing Identifier: NRR_PMDA Email Number: 368 Mail Envelope Properties (Siva.Lingam@nrc.gov20120507114800)

Subject:

Sequoyah Nuclear Plant, Unit 2 - Cycle 17 180-Day Steam Generator Inspection Report (TAC NO. ME7705) Sent Date: 5/7/2012 11:48:15 AM Received Date: 5/7/2012 11:48:00 AM From: Lingam, Siva Created By: Siva.Lingam@nrc.gov Recipients: "Broaddus, Doug" <Doug.Broaddus@nrc.gov> Tracking Status: None "Kulesa, Gloria" <Gloria.Kulesa@nrc.gov> Tracking Status: None "Karwoski, Kenneth" <Kenneth.Karwoski@nrc.gov>

Tracking Status: None "Johnson, Andrew" <Andrew.Johnson@nrc.gov> Tracking Status: None "Mackaman, Clyde Douglas" <cdmackaman@tva.gov> Tracking Status: None Post Office: Files Size Date & Time MESSAGE 6120 5/7/2012 11:48:00 AM

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