ML17269A030

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End of Cycle 24 Steam Generator Tube Inspection Report
ML17269A030
Person / Time
Site: Millstone Dominion icon.png
Issue date: 09/18/2017
From: Daugherty J
Dominion Nuclear Connecticut
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
17-353
Download: ML17269A030 (13)
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Text

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Dominion Nuclear Connecticut, Inc.

Rope Ferry Rd., Warerford, CT 06385 SEP 1 8 2017 Mailing Address: P.O. Box 128 Warerford, CT 06385 dam.com U.S. Nuclear Regulatory Commission Serial No.17-353 Attention: Document Control Desk NSS&L/MLC RO Washington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 END OF CYCLE 24 STEAM GENERATOR TUBE INSPECTION REPORT In accordance with Millstone Power Station Unit 2 (MPS2) Technical Specification (TS) 6.9.1.9, Dominion Nuclear Connecticut, Inc. hereby submits the End of Cycle 24 Steam Generator Tube Inspection Report. The report is submitted within 180 days after initial entry into Mode 4 following completion of an inspection performed in accordance with TS 6.26, Steam Generator (SG) Program.

The report includes the following:

a. The scope of inspections performed on each SG,
b. Degradation mechanisms found,
c. Nondestructive examination techniques utilized for each degradation mechanism,
d. Location, orientation (if linear), and measured sizes (if available) of service induced indications,
e. Number of tubes plugged during the inspection outage for each degradation mechanism,
f. The number and percentage of tubes plugged to date, and the effective plugging percentage in each steam generator,
g. The results of condition monitoring, including the results of tube pulls and in-situ testing.
  • If you have any questions or require additional information, please contact Mr. Jeffry A.

Langan at 860-444-5544.

Sincerely, J1.~

Site Vice President - Millstone Power Station

Serial No.17-353 Docket No. 50-336 Page 2 of 2

Enclosures:

(1)

Commitments made in this letter: None.

cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd. Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08-C2 11555 Rockville Pike Rockville, MD 20852-2738 NRG Senior Resident Inspector Millstone Power Station

Serial No.17-353 Docket No. 50-336 ENCLOSURE END OF CYCLE 24 STEAM GENERATOR TUBE INSPECTION REPORT MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC.

Serial No.17-353 Docket No. 50-336 Enclosure, Page 1 of 8 End of Cycle 24 Steam Generator Tube Inspection Report The acronyms used in the tables are defined in Attachment 1 of this enclosure.

In accordance with Millstone Power Station Unit 2 (MPS2) Technical Specification (TS) 6.9.1.9, Dominion Nuclear Connecticut, Inc. (DNC) is submitting this 180-day report which describes the results of the End of Cycle (EOC) 24 steam generator (SG) examinations which were performed during the MPS2 Refueling Outage 24 (2R24 ). Based upon entry into Mode 4 on May 1, 2017, this report is required to be submitted by October 28, 2017.

Background:

MPS2 is a two loop Combustion Engineering pressurized water reactor (PWR) with Babcock and Wilcox replacement SGs. Each SG is designed to contain 8523 Li-bend thermally-treated lnconel 690 tubes. The tubing is nominally 0.750 inch outside diameter with a 0.0445 inch nominal wall thickness.

Secondary side tube support structures include seven lattice grid supports on the vertical section of the tubes and 12 fan bar assemblies in the Li-bend section of the tubes. All lattice grid supports are full supports. All tube supports were fabricated with 410-series stainless steel.

The MPS2 SGs were replaced during 2R11 (1992). The SGs have accrued approximately 17.8 Effective Full Power Years (EFPYs) of operation as of the EOC 24 (April 2017). Since the first sequential period begins after the first inservice inspection, programmatically the MPS2 SGs have accrued 16.5 EFPYs.

See Attachment 2 of this enclosure, "Millstone Power Station Unit 2 Steam Generator Arrangement," for an illustration of SG component locations.

Report:

TS 6.9.1.9 reporting requirements (in bold text) are provided below, followed by DNC's response:

A report shall be submitted within 180 days after initial entry into MODE 4 following completion of an inspection performed in accordance with TS 6.26, Steam Generator (SG) Program. The report shall include:

a. The scope of inspections performed on each SG, The MPS2 SG eddy current testing (ECT), conducted at the EOC 24 was completed on April 21, 2017. The examinations, personnel, and equipment conformed to the requirements of NEI 97-06, Rev. 3, Steam Generator Program Guidelines; Electric Power Research Institute Pressurized Water Reactor Steam Generator Examination Guidelines, Rev. 7; and MPS2 TSs.

Serial No.17-353 Docket No. 50-336 Enclosure, Page 2 of 8 The EOC 24 ECT inspection is summarized in Table 1. All of the operational tubes in both SGs (a total of 17,014 tubes), were inspected full length with bobbin probes. An augmented sample of 5,325 tube locations was inspected with rotating probe coils (RPCs).

The RPC examination in each SG included a 50% sample of the outer six rows of the hot and cold leg periphery and open tube lane at the top of tubesheet. The primary purpose of this examination was the detection of foreign objects or foreign object wear in the most susceptible regions of the SG. In addition, the RPC examinations included both a pre-planned scope, and 2R24 special interest (SI) emergent scope. The pre-planned scope included historical locations of interest, dents or dings (ONT or ONG),

overexpansions or bulges (OXP or BLG), percent through-wall indications (% TW), and a sample of non-quantifiable historical indications (NQH). The emergent scope included 2R24 bobbin coil SI locations such as non-quantifiable indications (NQI), possible loose parts (PLP), and various hot leg and cold leg PLP bounding locations.

In addition to the ECT examinations, primary-side visual examinations were performed in both channel heads of each SG. These visual examinations (as-found/as-left), revealed no degradation of the divider plates, divider plate retaining bars/welds, primary closure rings/welds, or cladding. Visual examinations performed on all previously installed plugs identified no indications of plug degradation, leakage, or misplacement.

Secondary-side visual examinations were performed in both SGs. These examinations included:

  • Post-sludge lancing visual examination of the top-of-tubesheet annulus and no-tube lane to assess as-left material condition and cleanliness, and to identify and remove any retrievable foreign objects.
  • Visual investigation of accessible locations having eddy current indications potentially related to foreign objects, and removal of retrievable foreign objects.
  • Steam drum visual inspections to evaluate the material condition and cleanliness of .

key components such as moisture separators, drain systems, and interior surfaces.

The results of all secondary-side visual examinations performed were satisfactory, with no degradation detected.

b. Degradation mechanisms found, Fan bar wear and volumetric wear from foreign objects were the only degradation mechanisms found during the EOC 24 tube examinations. A listing of the flaws detected is provided in Table 3.

Serial No.17-353 Docket No. 50-336 Enclosure, Page 3 of 8 Fan Bar Wear A total of four fan bar wear indications in four tubes were reported during the EOC 24 examinations (two indications in each SG). These four indications had been reported during previous examinations.

Secondary Side Foreign Object Wear A comprehensive program was developed for detection of foreign objects and foreign object wear. This program consisted of planned examinations for known locations, a 50% examination of the outer six rows with the +Point' probe, a 100% bobbin coil examination, bounding examinations with +Point', secondary side inspection (SSI) of the top of tubesheet annulus and bundle periphery, and foreign object search and retrieval (FOSAR), as required. A total of 16 foreign object wear indications were identified.

Per Table 3, SG 1 (or SG 25) had one tube wear location that was newly detected with a wear depth of 23% in tube R92 C143, located approximately 11" above the hot leg tubesheet. A review of previous bobbin data indicates that this wear has been present in this tube since 1997; however, this was the first time that a +Point probe had been used at this location.

Also per Table 3, SG 2 (or SG 26) had 12 previously reported foreign object wear locations with no significant change in depth size from 2R22. SG 2 also reported three new wear locations in R122 C123 (34% TW), in R124 C123 (36% TW) and in R125 C122 (23% TW). None of these locations had an indication of a foreign object and FOSAR found no part at any of these locations.

With no significant change in the historical foreign object wear locations and no parts identified at the new foreign object wear locations, these tubes do not represent a threat to tube integrity over the next three cycles. The combination of the 100% bobbin coil examination of the full tube bundle, the +Point' examination of the outer six rows of the periphery and open tube lane, and the SSI examination of the tubesheet annulus and periphery, there is reasonable assurance that there are no currently existing parts within the tube bundle high flow region that could threaten tube integrity over the next three cycles.

c. Nondestructive examination techniques utilized for each degradation mechanism, Table 2 identifies the examination techniques used for each detected degradation mechanism.
d. Location, orientation (if linear), and measured sizes (if applicable) of service induced indications, A listing of the tube degradation identified during 2R24 is provided in Table 3.

Serial No.17-353 Docket No. 50-336 Enclosure, Page 4 of 8

e. Number of tubes plugged during the inspection outage for each degradation mechanism, No SG tubes were removed from service during 2R24.
f. The number and* percentage of tubes plugged to date, and the effective plugging percentage in each steam generator, Table 4 provides the total number of tubes plugged and the percentages.
g. The results of condition monitoring, including the results of tube pulls and in-situ testing.

No tubes were pulled and no in-situ pressure tests were performed. The condition monitoring assessment concluded that the structural integrity, operational leakage, and*

accident-induced leakage performance criteria were not exceeded during the operating interval preceding 2R24.

Serial No.17-353 Docket No. 50-336 Enclosure, Page 5 of 8 Table 1: Millstone End of Cycle 24 ECT Summary SGl SG2 Total Number of Installed Tubes 8523* 8523 17046 Number of Tubes In Service Prior to 2R24 8504 8510 17014 Number of Tubes Inspected F/L w/Bobbin Probe** 8504 8510 17014 Previously Plugged Tubes 19* 13 32 Number of Tubes Incomplete w/Bobbin Probe due to Obstruction 0 0 0 Number of Exams with +Point' (Total) 2623 2702 5325

  • Hot Leg Tubesheet TSH +3/-3 Periphery 1256 1269 2525
  • Hot Leg Tubesheet PTE 1 0 1
  • Hot Leg Tubesheet OlHTSH 3 7 10
  • Hot Leg Tubesheet PLP Bounding 18 49 67
  • Cold Leg Tubesheet TSC +3/-3 Periphery 1245 1253 2498
  • Cold Leg Tubesheet OlCTSC 0 4 4
  • Cold Leg Tubesheet TSC + 10/-3 11 0 11
  • Cold Leg Tubesheet PLP Bounding 22 30 52
  • Hot Leg Special Interest 34 39 73
  • U-Bend Special Interest 7 5 12
  • Cold Leg Special Interest 6 11 17
  • Hot Leg Additional RPC 20 22 42
  • Cold Leg Additional RPC 0 13 13 Tubes with Max FB Wear~ 40 % 0 0 0 Tubes with Max FB Wear ~20% but <40% 0 0 0 Tubes with Max FB Wear <20% 2 2 4 Tubes with Max SVI /VOL/ WAR> 40 % 0 0 0 Tubes with Max SVI /VOL/ WAR~20% but <40% 1 13 14 Tubes with Max SVI /VOL/ WAR<20% 0 2 2 Total Tubes Plugged as a Result of this Inspection 0 0 0
  • One tubesheet location in SG 1 (R57 C156) was not drilled in the cold leg tubesheet. The hot leg hole for this tube was plugged with a welded plug. Although this location was never tubed, it is included in the counts of installed tubes and plugged tubes.
    • A number of tubes were examined in hot leg I cold leg segments to achieve full length coverage.

Serial No.17-353 Docket No. 50-336 Enclosure, Page 6 of 8 Table 2: Detection and Sizing of Fan Bar and Loose Parts Induced Tube Wear Degradation Classification Location Probe Type Mech an ism Existing w ear Anti-Vibration Bars Detection and Sizing - Bobbin Tube We ar (Foreign Detection - Bobbin, +Point' Existing Freespan and TTS Objects) Sizing - +Point'

Serial No.17-353 Docket No. 50-336 Enclosure, Page 7 of 8 Table 3: Location, Orientation (If Linear), and Measured Sizes (If Applicable) of Service Induced Indications Depth Axial Circ Maximum Reported Signal Present Foreign Length Length Depth Prior Initially Prior to Current Object In-Situ Plugged &

SG Row Col Location ETSS (in) (in) 2R24 Outage Reported Outage? Cause Remaining? Tested? Stabilized?

12%TW Fan Bar 25 40 155 F06-1.76" 96041.3 3.15* N/A 13%TW 2R14 Yes N/A No No 2R23 Wear 14%TW Fan Bar 25 140 93 F08- 0.66" 96041.3 3.15* N/A 19%TW 2R14 Yes N/A No No 2R23 Wear NOD Foreign 25 92 143 TSH+10.91" 27901.1 0.24 0.37 23%TW 2R24 Yes No No No 2R23 Object Wear 27%TW Foreign 26 28 5 TSC+21.65" 27901.1 0.28 0.43 25%TW 2R15 Yes No No No 2R22 Object Wear 25%TW Foreign 26 29 4 TSC+22.2" 27901.1 0.27 0.43 26%TW 2R18 Yes No No No 2R22 Object Wear 8%TW Fan Bar 26 37 120 F07-0.83" 96041.3 3.15* N/A 12%TW 2R15 Yes N/A No No 2R22 Wear 11%TW Foreign 26 44 5 TSC+17.91" 27902.1 0.43 0.38 10%TW 2R20 Yes No No No 2R22 Object Wear 24%TW Foreign 26 59 10 TSC+17.33" 27901.1 0.38 0.43 23%TW 2R15 Yes No No No 2R22 Object Wear 20%TW Foreign 26 98 143 TSH + 8.76" 27901.1 0.33 0.37 20%TW 2R18 Yes No No No 2R22 Object Wear 15%TW Fan Bar 26 99 80 F06+1.28" 96041.3 3.15* N/A 13%TW 2R15 Yes N/A No No 2R22 Wear 12%TW Foreign 26 118 41 TSH +12.81" 27902.1 0.48 0.37 12%TW 2R18 Yes No No No 2R22 Object Wear 24%TW Foreign 26 119 42 TSH +12.97" 27903.1 0.38 0.43 29%TW 2R18 Yes No No No 2R22 Object Wear NOD Foreign 26 122 123 TSH + 2.53" 27901.1 0.33 0.54 34%TW 2R24 No No No No 2R22 Object Wear 22%TW Foreign 26 123 46 TSH +18.15" 27903.1 0.23 0.37 25%TW 2R15 Yes No No No 2R22 Object Wear 26%TW Foreign 26 124 45 TSH +19.27" 27903.1 0.38 0.32 31%TW 2Rl8 Yes No No No 2R22 Object Wear NOD Foreign 26 124 123 TSH + 1.77" 27901.1 0.38 0.43 36%TW 2R24 No No No No 2R22 Object Wear 32%TW Foreign 26 125 48 TSH +19.53" 27903.1 0.33 0.43 36%TW 2R15 Yes No No No 2R22 Object Wear NOD Foreign 26 125 122 TSH +1.36" 27902.1 0.53 0.37 23%TW 2R24 No No No No 2R22 Object Wear 34%TW Foreign 26 126 49 TSH +19.97" 27903.1 0.49 0.48 39%TW 2R15 Yes No No No 2R22 Object Wear 29%TW Foreign 26 128 107 TSH +0.06" 27901.1 0.28 0.37 26%TW 2R20 Yes No No No 2R22 Object Wear i1 *~()_f1Se':".<J!i\le<J~Sl,lf!1~_c;l_l~n~h ... ',

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Serial No.17-353 Docket No. 50-336 Enclosure, Page 8 of 8 Table 4: Current Tube Plugging Status SG 1 SG 2 Tubes Plugged Prior to 2R24 19 13 Tubes Plugged During 2R24 0 0 Total Plugged Following 2R24 19 13 Percentage Plugged 0.22 0.15 Overall Percentage Plugged 0.19 Since no sleeving has been performed in the MPS2 SGs; the effective plugging percentage is the same as the actual plugging percentage.

Serial No.17-353 Docket No. 50-336 Enclosure, Attachment 1, Page 1 of 1 Attachment 1 Acronyms B&W Babcock & Wilcox BLG Bulge CHN Channel c Column CM Condition Monitoring CMOA Condition Monitoring and Operational Assessment COL Column DEG Degrees DEP Deposit DNG Ding DNT Dent ECT Eddy Current Testing EFPY Effective Full Power Years ELEV Elevation EPRI Electric Power Research Institute ETSS Examination Technique Specification Sheet FB Fan Bar F/L Full Length FOSAR Foreign Object Search and Retrieval IGA lntergranular Attack LPI Loose Part Indication MBM Manufacturing Burnish Mark MPS2 Millstone Power Station Unit 2 NDD No Degradation Detected NDE Non-Destructive Examination NQH Non-Quantifiable Historical Indication NQI Non-Quantifiable Indication ODSCC Outer Diameter Stress Corrosion Cracking OXP Over Expansion PLP Possible Loose Part POD Probability of Detection PTE Partial Tubesheet Expansion PWSCC Primary Water Stress Corrosion Cracking

%TW Percent Through-Wall R Row RPC Rotating Probe Coil sec Stress Corrosion Cracking SG 1 Steam Generator Number 1 SG 2 Steam Generator Number 2 SI Special Interest SLG Sludge SSI Secondary Side Inspection SVI Single Volumetric Indication TEC Tube End Cold-leg TEH Tube End Hot-leg TSC Top of Tube Sheet Cold-leg TSH Top of Tube Sheet Hot-leg VOL Volumetric Indication WAR Wear Indication

Serial No.17-353 Docket No. 50-336 Enclosure, Attachment 2, Page 1 of 1 Attachment 2 Millstone Power Station Unit 2 Steam Generator Arrangement 01C::

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