ML19231A208

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Response to Request for Information Regarding Unit 2 Cycle 22 - 180-Day Steam Generator Tube Inspection Report
ML19231A208
Person / Time
Site: Sequoyah Tennessee Valley Authority icon.png
Issue date: 08/19/2019
From: Rasmussen M
Tennessee Valley Authority
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML19231A208 (13)
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Text

Tennessee Valley Authority, Sequoyah Nuclear Plant, P.O. Box 2000, Soddy Daisy, Tennessee 37384 August 19, 2019 10CFR50.4 ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Unit 2 Renewed Facility Operating License No. DPR-79 NRC Docket No. 50-328

Subject:

Response to Request for Information Regarding Unit 2 Cycle 22 - 180-Day Steam Generator Tube Inspection Report

Reference:

TVA letter to NRC, "Unit 2 Cycle 22 - 180-Day Steam Generator Tube Inspection Report," dated April 25, 2019 This letter provides response to an NRC request for information received on June 26, 2019, via email. In the request, NRC noted that two paragraphs of the steam generator report of the Referenced Letter contained typographical errors and desired clarification of this matter.

TVA confirms that the two paragraphs in Section 2.0 g, "The Results of Condition Monitoring, ,

Including the Results of Tube Pulls and In-Situ Testing," did contain typographical errors. This condition was entered into the corrective action program. A revised report is enclosed. The revised report corrects the typographical errors and adds additional specific information regarding observed foreign object wear indications.

printed on recycled paper

U.S. Nuclear Regulatory Commission Page 2 August 19, 2019 There are no new regulatory commitments contained in this letter. If you have any questions concerning this report, please contact Mr. Jonathan Johnson, Site Licensing Manager, at (423)843-8129.

Respectfully, Matthew Rasmussen Site Vice President Sequoyah Nuclear Plant

Enclosure:

Unit 2 Cycle 22 - 180-Day Steam Generator Tube Inspection Report - Revision 1 cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector- Sequoyah Nuclear Plant

ENCLOSURE TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT UNIT 2 CYCLE 22 180-DAY STEAM GENERATOR TUBE INSPECTION REPORT REVISION 1

Westinghouse Non-Proprietary Class 3 SG-SGMP-18-22 July 2019 Revision 1 Sequoyah U2R22 180 Day Steam Generator Tube Inspection Report

'This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

WESTINGHOUSE NON-PROPRIETARY CLASS 3 SG-SGMP-18-22 Revision 1 Sequoyah U2R22 180 Day Steam Generator Tube Inspection Report Prepared for:

Tennessee Valley Authority Author's Name: Signature / Date For Pages Bradley T. Carpenter *Electronkallv Approved All Component Design & Management Programs Verifier's Name: Signature / Date For Pages Inessa E. Berman *Electronically Approved AU Component Design & Management Programs Manager's Name: Signature / Date For Pages Michael E. Bradley, Manager *Electronically Approved All ComponentDesign & Management Programs Reviewer's Name: Signature / Date For Pages Jeremy W. Mayo V/.f _AH TVA SG Program Manager Reviewer's Name: Signature / Date For Pages Daniel P. Folsom "S^X, \L^ 7/W/9 AU TVA NDE Level III ^^ ' y

  • Electronically Approved Records arc Aatbenticatcdin the Electronic Document Management System

©2019 Westinghouse Electric Company LLC All Rights Reserved SG-SGMP-18-22 J-J^

Revlslonl Page 2of 10

" This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

Record of Revisions Revision Date Description December Oa 2018 Preliminary draft for Tennessee Valley Authority review and comment.

January 2019 Final incorporating review comments from the Tennessee Valley Authority.

July Revised to correct two typos inSection g ofthe report. Also, a list ofthe foreign 2019 object wear indications observed is added to Section d of the report in new Table 2-

6. Revisions are shown by a bar in the left-hand margin.

SG-SGMP-18-22 July 2019 Revision 1 Page 3 of 10

' This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

Table of Contents 1.0 Introduction 5 2.0 180 Day Steam Generator Tube Inspection Report 6

a. The Scope of the Inspections Performed on Each SG 6
b. Active Degradation Mechanisms Found 6
c. Nondestructive Examination Techniques Utilized for Each Degradation Mechanism 7
d. Location, Orientation (if Linear), andMeasured Sizes (if Available) of Service Induced Indications.. 7
e. Number of Tubes Plugged During the Inspection Outage for Each Active Degradation Mechanism... 8
f. Total Number and Percentage of Tubes Plugged to Date 8
g. The Results ofCondition Monitoring, Including the Results ofTube Pulls and In-Situ Testing 9
h. TheEffective Plugging Percentage forAll Plugging in Each SG 10 List of Tables and Figures Figure 1-1: Tube Support Arrangement for Sequoyah Unit 2 Model 57AG+ Replacement Steam Generators... 5 Table 2-1: Sequoyah U2R22 Steam Generator Eddy Current Inspection Scope 6 Table 2-2: Number of Indications Detected for Each Degradation Mechanism 7 Table 2-3: NDE Techniques forEach Existing or Potential Degradation Mechanism 7 Table 2-4: Sequoyah U2R22 U-bend Support Structure Wear Indications 7 Table 2-5: Sequoyah U2R22 Horizontal Tube Support Grid Wear Indications 8 Table 2-6: Sequoyah U2R22 Foreign Object Wear Indications 8 Table 2-7: Number of Tubes Plugged for Each Degradation Mechanism 8 SG-SGMP-18-22 July 2019 Revision 1 Page 4of10
      • This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

1.0 Introduction This report documents the "Sequoyah U2R22 180-Day Steam Generator Tube Inspection Report" as required by the SQN2 Technical Specifications. Inspections of the replacement steam generators (RSGs) were performed during the Sequoyah Unit 2 (SQN2) fall 2018 refueling outage designated as (U2R22).

These inspections included eddy current testing of the SG tubing as well as primary and secondary side cleanings and visual inspections. The original SGs at SQN2 were replaced in 2012 with Westinghouse Model 57AG" SGs which have thermally treated Alloy 690 tubing. The Sequoyah U2R22 outage was conducted after cumulative SG service equivalent toapproximately 5.40 effective full power years (EFPY).

The service time from the previous SG eddy current inspections during U2R19 was 4.09 EFPY. No tube leakage has been reported during this operating interval. Figure 1-1 below provides the arrangement and location designation of the tube support structures for the SQN2 SGs.

Figure 1-1: Tube Support Arrangement for Sequoyah Unit 2 Model 57AG+ Replacement Steam Generators Notes: VS = Vertical Strap. DS = Diagonal Strap. HTS/CTS = Hot/Cold Tubesheet (designates top of tubesheet).

HTE/CTE = Hot/Cold Tube End. Horizontal supports are a lattice grid design SG-SGMP-18-22 July 2019 Revision 1 Page 5 of 10 1This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

2.0 180 Day Steam Generator Tube Inspection Report In accordance with SQN2 Technical Specification Section 5.5.7, "Steam Generator Program," and Technical Specification Section 5.6.6, "Steam Generator Tube Inspection Report," this report documents the scope and results of the U2R22 SG inspections. There are eight specific reporting requirements associated withthe Technical Specification. Each lettered reporting requirement listed below is followed withthe associated information based on the inspections performed during U2R22.

a. The Scope of the Inspections Performed on Each SG The U2R22 outage included a 100% bobbin inspection of the full length of all in-service tubes.

The combination bobbin and array probe was used to inspect the top of tubesheet intersections of tubes along the tube bundle periphery and center tubelane a minimum of three tubes deep on both the hot leg (HL) and cold leg(CL) side. As a result, the inspection included all tubes with prior indications of degradation and all tubes not inspected during the previous SG in-service inspection. Array and rotating pancake coil (RPC) probes were used for special interest testing and resolution of bobbin indications when necessary. Table 2-1 below summarizes the number andtype of eddy current examinations performed during U2R22.

Table 2-1: Sequoyah U2R22 Steam Generator Eddy Current Inspection Scope Scope # Eddy Current Exam Type SGI SG2 SG3 SG4 Total 1 0.610 Full Length Bobbin' 2,380 4,247 3,685 3,495 13,807 2 0.610 HL Bobbin VS3-HTE1 2,115 248 810 1,000 4,173 3 0.610 CL Bobbin VS3-CTE1 2,115 248 810 1,000 4,173 4 0.610 HL Array Rows 1-9 H01-HTE 787 787 787 7562 3,117 5 0.610 CL Array Rows 1-9 C01-CTE 787 787 787 787 3,148 6 0.610 Array HL&CL Special Interest 18 16 13 93 140 7 0.610 HL RPC Special Interest 0 0 0 9 9 Notel: Eith er the full length was inspected in one complet i test or eac h half of the ; tube was te sted in two s enarate tests Also, combination bobbin and array probe tests used tocapture the tube bundle periphery inspection scope are counted under these programs.

Note 2: The remaining array probe tests were captured in scopes one through three where combination bobbin and array probes were used.

In addition to the eddy current inspections, visual inspections were also performed on both the primary and secondary sides. Primary side visual inspections included the channel head bowl cladding and the divider plate. There were no previously installed tube plugs to inspect from the primary side. Secondary side visual inspections were performed at the top of the tubesheet for the detection of foreign objects, assessment of hard deposit buildup in the tube bundle interior

'kidney region' and for determining the effectiveness ofthe tubesheet cleaning performed in all four SGs.

b. Active Degradation Mechanisms Found Volumetric wear was the only degradation mechanism detected during the U2R22 inspection.

The support structure wear indications detected were located at the U-bend or horizontal tube supports. There were also foreign object wear indications located near the first support on the hot leg side (H01) in SG 4. Table 2-2 below shows the number of indications reported during the U2R22 inspection.

SG-SGMP-18-22 July 2019 Revision 1 Page 6 of 10 "This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

Table 2-2: Number of Indications Detected for Each Degradation Mechanism Degradation Mechanism SGI SG2 SG3 SG4 Total U-Bend Support Structure Wear 3 5 1 1 10 Horizontal Tube Support Grid Wear 5 1 3 6 15 Foreign Object Wear 0 0 0 4 4

c. Nondestructive Examination Techniques Utilized for Each Degradation Mechanism Table 2-3 below provides the nondestructive examination (NDE) techniques that were used for the detection of each degradation mechanism that was considered as existing or potential forthe U2R22 inspection.

Table 2-3: NDE Techniques for Each Existingor Potential Degradation Mechanism Eddy Current EPRIETSS Degradation Mechanism Probe Type Detection Technique U-Bend Bobbin 96004.1, Revision 13 Array 11956.1, Revision 3 Support Structure Wear Array 11956.2, Revision 2 Horizontal Bobbin 96004.1, Revision 13 Array 11956.1, Revision 3 Tube Support Grid Wear Array 11956.2, Revision 2 Bobbin 27091.2, Revision 2 Array 1790X.1, Revision 01 Foreign Object Wear Array 1790X.3, Revision 01 RPC 2790X.11 Tube-to-Tube Bobbin 13091.1, Revision 0 Array 13902.1, Revision 0 Contact Wear RPC 13901.1, Revision 1 Note 1: The applicable ETSSs are numbered2790X.1 where X is variable between 1 and 7. For ETSS 1790X.1 and 1790X.3 techniques X is variable between 1 and 6 and all are Revision0.

Techniques and corresponding uncertainty used for sizing of foreign object wear is dependent on foreign objectwear indication geometry.

d. Location, Orientation (if Linear), and Measured Sizes (if Available) of Service Induced Indications Table 2-4, Table 2-5 and Table 2-6 below provide a listing of all service-induced indications reported during the U2R22 inspection including the estimated percent through-wall (%TW) depths from the qualified eddy current sizing technique.

Table 2-4: Sequoyah U2R22 U-bend Support Structure Wear Indications SG Row Col Locn Inch Ind %TW Characterization 1 69 95 DS4 0.93 PCT 18 U-bend Support Wear 1 92 62 VS3 0.79 PCT 18 U-bend Support Wear 1 97 61 VS2 0.89 PCT 19 U-bend Support Wear 2 89 59 VS2 -0.96 PCT 15 U-bend Support Wear 2 93 59 VS2 -1.07 PCT 23 U-bend Support Wear 2 93 59 VS3 0.73 PCT 13 U-bend Support Wear 2 95 63 VS3 0.35 PCT 17 U-bend Support Wear 2 98 64 DS3 -0.77 PCT 16 U-bend Support Wear 3 82 78 VS2 -0.57 PCT 24 U-bend Support Wear 4 67 67 DS4 -0.7 PCT 15 U-bend Support Wear SG-SGMP-18-22 July 2019 Revision 1 Page 7 of 10

'This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

Table 2-5: Sequoyah U2R22 Horizontal Tube Support Grid Wear Indications SG Row Col Locn Inch Ind %TW Characterization 3 1 C04 -1 PCT 20 Horizontal Tube Support Grid Wear 3 1 C05 -0.98 PCT 17 Horizontal Tube Support Grid Wear 3 91 C04 -0.92 PCT 17 Horizontal Tube Support Grid Wear 3 91 C05 0.66 PCT 22 Horizontal Tube Support Grid Wear 6 60 H03 0.05 PCT 16 Horizontal Tube Support Grid Wear 2 3 85 C05 0.64 PCT 21 Horizontal Tube Support Grid Wear 3 14 122 C05 -0.99 PCT 17 Horizontal Tube Support Grid Wear 3 22 54 H04 -1.11 PCT 22 Horizontal Tube Support Grid Wear 3 43 119 C05 -1.04 PCT 21 Horizontal Tube Support Grid Wear 4 1 93 C06 -0.95 PCT 18 Horizontal Tube Support Grid Wear 4 3 39 C04 -0.94 PCT 15 Horizontal Tube Support Grid Wear 4 3 93 C06 -0.97 PCT 15 Horizontal Tube Support Grid Wear 4 4 102 C05 0.73 PCT 16 Horizontal Tube Support Grid Wear 4 5 33 C06 0.71 PCT 15 Horizontal Tube Support Grid Wear 4 5 33 C07 -0.99 PCT 17 Horizontal Tube Support Grid Wear Table 2-6: Sequoyah U2R22 Foreign Object Wear Indications SG Row Col Locn Inch Ind %TW Characterization 4 98 76 H01 -1.08 VOL 21 Foreign Object Wear 4 99 75 H01 -1.15 VOL 8 Foreign Object Wear 4 97 75 H01 -1.15 VOL 23 Foreign Object Wear 4 96 74 H01 -1.32 VOL 9 Foreign Object Wear Number ofTubes Plugged During the Inspection Outage for Each Active Degradation Mechanism Table 2-7 below provides the numbers of tubes plugged for each degradation mechanism detected. As shown inthe table, there were no tubes plugged prior to U2R22 and there were no tubes plugged during U2R22. Therefore, there are currently no tubes plugged in any SG at Sequoyah Unit 2.

Table 2-7: Number of Tubes Plugged for Each Degradation Mechanism SGI SG2 SG3 SG4 Total Plugged Tubes Prior to U2R22 0 0 0 0 0 Tubes Plugged During U2R22 0 0 0 0 0 Total Plugged to Date 0 0 0 0 0 Percentage Plugged to Date 0.00% 0.00% 0.00% 0.00% 0.00%

f. Total Number and Percentage of Tubes Plugged to Date Table 2-7 in the previous section provides the number and percentage oftubes plugged to date.

SG-SGMP-18-22 July 2019 Revision 1 Page 8 of 10

>This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

g. The Results of Condition Monitoring, Including the Results of Tube Pulls and In-Situ Testing Tube Integrity A condition monitoring (CM) assessment was performed as required by the SQN2 steam generator program. The tube degradation detected during the U2R22 inspection included wear at the U-bend and horizontal grid tube support structures and wear due to foreign objects. The CM results for each of these mechanisms are as follows:
  • The deepest U-bend tube support structure wear indication had a measured depth of 24%TW from the bobbin coil exam and was located at a vertical strap. Conservatively assuming anenveloping flaw length greater than the width ofthe support (2.5 inches), the CM limit for U-bend support structure wear is 45%TW.
  • The deepest horizontal grid support tube wear indication had a measured depth of22%TW from the bobbin coil exam. Conservatively assuming an enveloping flaw length equal to the full width ofthe support (2.0 inches), the CM limit for horizontal grid support structure wear is 46%TW.
  • The deepest foreign object wear indication had ameasured depth of23%TW from the array coil exam and was located justbelow the bottom edge of Tube Support HOI near the tube bundle periphery. The array coil ETSS technique 17905.1 corresponding toflat volumetric wear was applied to size the foreign object wear indications. Conservatively assuming an enveloping flaw length of 1.5 inches, the CM limit for foreign object wear is 47%TW.

These CM limits include uncertainties for material properties, NDE depth sizing, and the burst pressure relationship. Since the deepest flaw has an estimated depth less than the corresponding CM limit, the structural integrity performance criterion was met for the operating interval prior to U2R22. Since volumetric wear indications will leak and burst atessentially the same pressure, accident-induced leakage integrity at a much lower accident pressure differential isalso satisfied.

Operational leakage integrity was demonstrated by the absence of any detectable primary-to-secondary leakage during the inspection interval from U2R19 to U2R22. Since tube integrity was demonstrated analytically, in-situ pressure testing was not required nor performed during the U2R22 outage. No tube pulls were planned or performed during U2R22.

Visual Inspection Results Visual inspections were also performed on both the primary and secondary sides during U2R22.

Primary side inspections included visual inspections ofthe channel head bowl cladding and the divider plate. Satisfactory inspection results were observed in all SGs with no indications of cladding surface degradation or observable change in the known existing bowl clad surface discolorations.

Prior to the secondary side foreign object search and retrieval (FOSAR) inspections, sludge, scale, foreign objects, and other deposit accumulations atthe top ofthe tubesheet were removed as part ofthe top oftubesheet water lancing process. The secondary side FOSAR inspections performed inall four SGs included visual examination oftube bundle periphery tubes from the hot leg and cold leg annulus and center tubelane. A total of24 foreign objects were identified during FOSAR inspections, 18 ofwhich were removed from the top ofthe tubesheet region while 6objects remain on the secondary side among the four SGs. The foreign objects remaining are three small bristles, a small piece ofwire mesh and two sludge rocks. Any foreign objects not able to be retrieved were characterized and an analysis performed to demonstrate acceptability ofcontinued operation without exceeding the performance criteria. A limited top oftubesheet SG-SGMP-18-22 July 2019 Revision 1 Page 9of10

      • This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)

in-bundle visual inspection was also performed in each SG for the purpose of assessing and trending the level of hardened deposit buildup in the kidney region. Finally, a special interest secondary side visual inspection was performed in SG 4 viewing upwards from the tubesheet at the tube intersections with Tube Support HOI toview the tube locations with new foreign object wear detected by eddy current. This inspection verified that no foreign object was still present at the HOI elevation for the tubes affected by foreign objectwear.

h. The Effective Plugging Percentage for All Plugging in Each SG There are no sleeves installed in the SQN2 replacement SGs. Therefore, the effective plugging percentage is the same as the plugging percentage shown in Table 2-7.

SG-SGMP-18-22 July 2019 Revisionl Page 10 of10

      • This record was final approved on 7/23/2019 7:17:56 AM. (This statement was added by the PRIME system upon its validation)
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