ML113010322

Summary of Conference Call Regarding 2011 Steam Generator Tube Inspections

ML113010322
Person / Time
Site:	Byron
Issue date:	11/07/2011
From:	Nicholas Difrancesco Plant Licensing Branch III
To:	Pacilio M Exelon Nuclear
DiFrancesco N, NRR/DORL/LPL3-2, 415-1115
References
TAC ME7191
Download: ML113010322 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001

. November 7, 2011 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NO.2 -

SUMMARY

OF CONFERENCE CALL REGARDING 2011 STEAM GENERATOR TUBE INSPECTIONS (TAC NO. ME7191)

Dear Mr. Pacilio:

On September 29, 2011, the U.S. Nuclear Regulatory Commission (NRC) staff participated in a conference call with Exelon Generation Company, LLC (the licensee) regarding their ongoing steam generator tube inspection activities at Byron Station, Unit No.2. Enclosed is a summary of the conference call. This completes the NRC staff efforts for TAC No. ME7191.

If you have any questions regarding this matter, please contact me at (301) 415-1115.

Nicholas J. DiFrancesco, Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-455

Enclosures:

Conference call summary List of Participates cc w/encl: Distribution via Listserv

SUMMARY

OF CONFERENCE CALL WITH BYRON STATION UNIT NO.2 REGARDING THE 2011 STEAM GENERATOR TUBE INSPECTION RESULTS DOCKET NO. 50-455 On September 29, 2011, the NRC staff of the Steam Generator Tube Integrity and Chemical Engineering Branch (ESGB) of the Division of Engineering participated in a conference call with representatives of Exelon Generation Company, LLC (the licensee) regarding their ongoing steam generator (SG) tube inspection activities at Byron Station Unit NO.2. A summary of the conference call is enclosed. Information provided by the licensee includes email dated September 26, 2011 (Agencywide Documents Access Management System (ADAMS)

Accession No. ML11286A024), and September 28, 2011 (ADAMS Accession No. ML11286A026).

Byron Unit No.2 has four Westinghouse Model 05 SGs, each containing 4,570 thermally treated Alloy 600 tubes. The tubes have a nominal outside diameter of 0.750 inches and a nominal wall thickness of 0.043 inches. The tubes were hydraulically expanded at both ends for the full length of the tubesheet and are supported by a number of stainless steel tube supports with quatrefoil-shaped holes. The pre-heater tube support baffle plates are also fabricated from stainless steel, but have drilled hole tube openings. The U-bend region of the tubes in rows 1 through 9 was thermally stress relieved after bending.

Information provided by the licensee during the phone call, not included in the prior emails.is summarized below.

The SGs have been in service for approximately 21 effective full-power years. The hot-leg operating temperature is 611°F.

There are 54 new dents in SG B, all of low voltage (2-5 volts), and all located at the bottom edge of the 03C baffle plate on the cold-leg side. There is also one newly reported dent in the freespan region of the tube located at row 48, column 37, in SG B. This dent signal was present in previous inspections but was below the 2-volt reporting threshold. When viewed from above, the 54 new dents have a symmetrical pattern across the baffle plate that is somewhat crescent shaped.

A similar pattern of denting occurred in between the 2001 and 2002 inspections, when approximately 100 dents were found in the same 03C baffle plate location. This historical event also resulted in the same crescent shaped pattern of denting, with dents measuring from 2 - 15 volts. To date, only nine of these historical dents have changed size greater than the eddy current measurement uncertainty.

Enclosure 1

-2 A 25 percent sample size of both new and old dents was performed this outage, using a 3-coil rotating pancake coil (RPC) with the 80 millimeter coil modified to be a non-surface riding coil, to determine the length and width of the dents. All tubes were also inspected by bobbin coil.

When measuring the dents with the RPC coil, an attempt was made at determining the shape and orientation of the dents. With the RPC coil inserted in a dented tube, first a bobbin coil and then a strong rare earth magnet, was placed in the adjacent guide tube, which is in the tube diagonally across from the target tube in a square pitch tube pattern, in an attempt to determine the shape and orientation of the dents. These attempts were unsuccessful due to the eddy current probe not detecting the reference magnet signal and the orientation and shape of the dents are unknown.

The circumferential extent of most of the dents. was 80 OF and most tubes were dented on just one side. A few tubes had two dents, with the dents separated circumferentially by approximately 160 OF. The tubes with two dents had larger bobbin signals. There was no evidence of deposits, anomalies (burrs or high spots on the baffle plate holes), or damage to the 03C baffle plate.

The suction strainers of the three main feed pumps that can supply SG B were inspected and the strainers were found to be intact and contained few loose parts (gasket material and wires).

These strainers have a strainer wire size of 32 mils (0.032 inches) and openings of 68 mils (0.068 inches).

Westinghouse performed a review of the tube support plate/baffle plate system in the Byron Unit No.2 SGs and concluded that the system is robust. Westinghouse also performed a historical review and has no information on this type of denting phenomenon occurring in other plants. The licensee also performed an informal industry survey and did not find any occurrences of a similar denting phenomenon.

An operating data review for water hammer and other flow or pressure transients revealed no events that could be correlated to the denting. A similar operating data review also showed no loose part alarms. Additionally, there was no evidence of reduced tube-to-tube spacing.

The licensee has concluded that these dents were not created by the traditional denting process of baffle plate corrosion products within the drilled baffle plate holes building up and denting the tubes. The licensee also concluded that the dents were not caused by foreign objects.

The next planned inspection is two operating cycles from this inspection.

LIST OF PARTICIPATES REGARDING BYRON STATION UNIT NO.2 2011 STEAM GENERATOR TUBE INSPECTION RESULTS CONFERENCE CALL Andrew Johnson, NRR Jay Smith, Exelon Ken Karwoski, NRR Patrick Simpson, Exelon Tom Bilk, R-III Steve Queen, Exelon Mel Helmberg, R-1I1 Jack Feimster, Exelon Jim Nancy, R-1I1 Gary Contrady, Exelon John Robbins, R-I\I Greg Gerzen, Exelon David Hill, R-III Joe Langan, Exelon Emmett Murphy, NRR Scott Swanson, Exelon Araceli Billoch, NRR Lisa Simpson, Exelon Mike Mahoney, NRR Nick DiFrancesco, NRR Rick Mauer, Westinghouse Bill Cullen, Westinghouse Don Siska, Westinghouse Enclosure 2

November 7,2011 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BYRON STATION, UNIT NO.2 -

SUMMARY

OF CONFERENCE CALL REGARDING 2011 STEAM GENERATOR TUBE INSPECTIONS (TAC NO.

ME7191)

Dear Mr. Pacilio:

On September 29, 2011, the U.S. Nuclear Regulatory Commission (NRC) staff participated in a conference call with Exelon Generation Company, LLC (the licensee) regarding their ongoing steam generator tube inspection activities at Byron Station, Unit NO.2. Enclosed is a summary of the conference call. This completes the NRC staff efforts for TAC No. ME7191.

If you have any questions regarding this matter, please contact me at (301) 415-1115.

Sincerely, IRA!

Nicholas J. DiFrancesco, Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. STN 50-455

Enclosures:

Conference call summary List of Participates cc w/encl: Distribution via Listserv DISTRIBUTION:

PUBLIC RidsAcrsAcnw_MaitCTR Resource AJohnson LPL3-2 RtF RidsNrrLASRohrer Resource RidsNrrDeEsgb Resource RidsNrrPMByron Resource RidsRgn3MailCenter Resource RidsOgcRp Resource RidsNrrDorlLpl3-2 Resource KKarwoski RidsNrrDorlDpr Resource ADAMS Accession No ML113010322 NRC-001 OFFICE LPL3-2/PM LPL3-2/LA DE/ESGB/BC LPL3-21 BC NAME NDiFrancesco SRohrer VCusumano JZimmerman DATE 11/01/11 11/01/11 10/20/11 11/07/11 OFFICIAL RECORD COpy