ML11291A059

End-of-Cycle 20 Steam Generator Tube Inspection Report

ML11291A059
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Site:	Millstone
Issue date:	10/07/2011
From:	Jordan A Dominion, Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
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ML11291A059	List: ML11291A059
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11-533
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Text

Dominion Nuclear Connecticut, Inc.

Millstone Power Station Dominion Rope Ferry Road Waterford, CT 06385 OCT 07 2011 U.S. Nuclear Regulatory Commission Serial No.11-533 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 20 STEAM GENERATOR TUBE INSPECTION REPORT In accordance with the Millstone Power Station Unit 2 (MPS2) Technical Specification (TS), Section 6.9.1.9, Dominion Nuclear Connecticut, Inc., hereby submits, the End of Cycle 20 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. Active 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 active degradation mechanism,

f. Total number and percentage of tubes plugged; to date, and

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. William D.

Bartron at (860) 444-4301.

Sincerely, Site Millstone

,4DOI

Serial No.11-533 Docket No. 50-336 Page 2 of 2 Enclosujres: (1)

Commitments made in this letter: None.

cc: U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406-1415 C. J. Sanders NRC Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08-B3 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station

Serial No.11-533 Docket No. 50-336 ENCLOSURE Millstone Power Station Unit 2 End of Cycle 20 Steam Generator Tube Inspection Report MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC. (DNC)

Serial No.11-533 Docket No. 50-336 Enclosure, Page 1 of 11 End of Cycle 20 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. (DNC) is submitting this 180-day report which describes the results of the MPS2 End of Cycle (EOC) 20 steam generator (SG) examinations. Based upon the subsequent entry into Mode 4 on April 30, 2011, this report is required to be submitted by October 27, 2011.

Background:

MPS2 is a two loop Combustion Engineering pressurized water reactor with Babcock and Wilcox replacement SGs. Each SG is designed to contain 8523 U-bend thermally treated Inconel 690 tubes. The tubing is nominally 0.750 inch outside diameter with a 0.0445 inch nominal wall thickness. The nominal hot leg temperature is 601°F.

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

The following are the key design parameters of the MPS2 SGs.

Tubing Material Inconel 690 thermally treated with post bend stress relief of U-bends Row 1-8.

Number of tubes 8523 Tube Size 0.750" OD, 0.0445" wall Tube Pitch/Layout 1.00"/triangular pitch Shortest Tube Radius Row 3, 3.905" radius, Rows 1-3 are staggered.

Outer Row Tube Radius 72.5" Tubesheet Thickness 21.75" Support Plates Seven lattice grid support structures. Largest axial dimension is 3.15."

Anti-Vibration Bars Twelve fan bars support all tube rows. Rows 1-5 contact F01 and F12 only. Higher rows have progressively more fan bar support structures.

Largest fan bar width is 3.15."

Tubesheet Joint Full hydraulic expansion MPS2 SGs were replaced in 1992 during Refueling Outage 11. As of EOC20 (April 2011),

the SGs have accrued approximately 12.4 Effective Full Power Years (EFPYs) of operation.

In accordance with EPRI PWR SG Examination Guidelines, the first sequential period

Serial No.11-533 Docket No. 50-336 Enclosure, Page 2 of 11 begins after the first inservice inspection. Hence, programmatically, the MPS2 SGs have accrued 11.1 EFPYs.

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 the 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 end of Cycle 20 was completed on April 16, 2011. The examinations, personnel, and equipment conformed to the requirements of NEI 97-06, Rev. 2, Steam Generator Program Guidelines; EPRI Pressurized Water Reactor Steam Generator Examination Guidelines, Rev. 7; and Millstone Unit 2 Technical Specifications. One hundred percent of the operational tubes in SG 1 and SG 2 (a total of 17,035 tubes), were inspected full length from the tube end of the hot leg (TEH) to the tube end of the cold leg (TEC). The majority of the tubing length was examined with bobbin probes. An augmented sample of 5,109 tube locations was inspected with array coil probes and 853 tube locations were inspected with diagnostic rotating coils.

For both SG 1 and SG 2, the array coil probe examination 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 to the first support. The primary purpose of this examination was the detection of foreign objects or foreign object wear in the most probable and most susceptible regions of the SGs.

The rotating coil examinations of both SGs included both a pre-planned scope and a 2R20 special interest (SI) emergent scope. The pre-planned scope included 2R18 historical locations, reported dents or dings (DNT or DNG), overexpansions or bulges (OXP or BLG), percent through-wall indications (%TW), a sample of non-quantifiable historical indications (NQH), and wear indications (WAR). The emergent scope included 2R20 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 eddy current examinations described above, primary-side visual examinations were performed in both channel heads of each SG. These visual examinations (as-found / as-left) included the divider plate / tubesheet interface and previously installed tube plugs.

Secondary-side visual examinations included:

Serial No.11-533 Docket No. 50-336 Enclosure, Page 3 of 11

• 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 (SG 1 only).

See Attachment 1, "Acronyms," for explanation of acronyms. See Attachment 2, "Millstone Power Station Unit 2 Steam Generator Arrangement," for illustration of SG component locations.

The inspection summary is documented in Table 1.

b. Active degradation mechanisms found The existing degradation mechanisms found during 2R20 included fan bar wear and volumetric degradation from foreign object wear.

c. Nondestructive examination techniques utilized for each degradation mechanism, Table 2 identifies the examination techniques utilized for each identified degradation mechanism.

d. Location, orientation (if linear), and measured sizes (if applicable) of service induced indications, Four fan bar wear indications were detected and sized during 2R20. The maximum depth of these indications was 15% TW and all four indications had been reported during the previous examination.

SG Row Column Structure  % TW 1 40 155 FB 6 11 1 140 93 FB 8 12 2 37 120 FB 7 9 2 99 80 FB 6 15 The following discussion provides a summary of foreign objects and 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 array probe, a 100% bobbin coil

Serial No.11-533 Docket No. 50-336 Enclosure, Page 4 of 11 examination, bounding examinations with +PointTM, secondary side inspection (SSI) of the top of tubesheet annulus and bundle periphery, and foreign object search and retrieval (FOSAR), as required.

There were no historical foreign object wear locations in SG 1. Three new adjacent tube wear locations in SG 1 (tubes R119 C66, R120 C67, and R121 C66) were detected with a maximum wear depth of 22% TW in tube R120 C67. Visual examination of this area detected a piece of weld slag. Attempts to remove the weld slag were unsuccessful.

Since the part could not be removed, these tubes were stabilized on the cold leg with tubesheet stabilizers and then plugged.

SG 2 had 10 previously reported foreign object wear locations with no significant change in depth size from 2R18. There were two new wear locations in R44 C5 (10% TW) and in R128 C107 (28% TW). Neither location had an eddy current signal indicating that a foreign object was present and no part was found by visual examination. Therefore, the tubes were left in-service.

There were three other locations where foreign objects were found, but no wear was detected:

• SG 1 had a screw found by SSI in the cold leg periphery at R121 C126 and R120 C127. The screw extended into the tube bundle contacting several tubes. The screw was tightly lodged between the tubes and could not be removed so the seven bounding tubes were stabilized and plugged. The seven tubes that were stabilized and plugged are R121 C126, R120 C127, R119 C126, R118 C127, R117 C126, R116 C127, and R115 C126.

" SG 2 had a machine curl at R31 C4, R32 C5, and R33 C4 on the hot leg side that could not be removed. These tubes were stabilized in the hot leg with tubesheet stabilizers and then plugged.

• SG 2 also had a piece of flexitallic gasket trapped between two lines of tubes near the cold leg periphery. The tubes bounding the flexitallic were R93 C144, R94 C143, R95 C142, R95 C144, R96 C141, R96 C143, R97 C142, and R98 C141.

Since the flex material could not be removed, the affected tubes were stabilized on the cold leg with tubesheet stabilizers and then plugged.

Table 3 provides information on the indications reported during 2R20.

e. Number of tubes plugged during the inspection outage for each active degradation mechanism, Twenty-one (21) tubes were removed from service during 2R20. All of the tubes were removed from service discretionarily due to foreign objects that could not be removed from the SGs. All affected tubes were stabilized on the affected leg and then plugged.

The total number of tubes plugged during 2R20 is provided below.

Serial No.11-533 Docket No. 50-336 Enclosure, Page 5 of 11 Tubes Plugged During 2R20 SG 1 SG 2 Reason for Plugging Plugged Plugged Unretrieved Foreign Object With or 10 11 Without Wear <40% (discretionary)

f. Total number and percentage of tubes plugged to date, The total number of tubes plugged and the percentages are shown below.

Tube Pluqqing Percentages Number Plugged SG 1 Plugged SG 2 Plugged Prior to 2R20 8* 2 During 2R20 10 11 Total After 2R20 19 13 Percentage 0.22 0.15 Overall Percentage 0.19

• 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. Since this location was never tubed, it is not counted as a plugged tube, however, it is counted for tube plugging percentage.

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 2R20.

Serial No.11-533 Docket No. 50-336 Enclosure, Page 6 of 11 Table I - Millstone 2R20 ECT Summary SG 1 SG 2 Total Number of Inservice Tubes 8,514" 8,521 17,035 Number of Tubes Inspected F/L w/Bobbin Probe 8,514 8,521 17,035 Previously Plugged Tubes 8* 2 10 Number of Tubes Incomplete w/Bobbin Probe due to 0 0 0 Obstruction Number of Tubes Inspected with Array Probe

• Hot Leg Transitions - Original Scope (tubes) 1250 1250 2500

• Cold Leg Transitions - Original Scope (tubes) 1250 1250 2500

• Hot Leg Transitions - Previous History (locations) 14 36 50 eCold Leg Transitions - Previous History (locations) 24 21 45

• Hot Leg Added Inspections - (locations) 0 0 0

• Cold Leg Added Inspections - (locations) 14 0 14 Number of Inspections w/MRPC (Total) 374 479 853 oHot Leg Previous History (locations) 32 60 92

@Hot Leg Special Interest (locations) 34 21 55

• Hot Leg Newly Reported DNT/DNG >=2V (locations) 3 5 8

• Cold Leg Previous History (locations) 25 32 57 oCold Leg Special Interest (locations) 29 15 44

• Cold Leg Newly Reported DNT/DNG >=2V (locations) 7 4 11

• U-Bend Previous History (locations) 17 17 34

• U-Bend Special Interest (locations) 2 1 3

• U-Bend Newly Reported DNT/DNG >=2V (locations) 4 2 6 9PLP / SVI Bounding Special Interest (locations) 221 322 543 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 10 11 Tubes with Max SVI / VOL / WAR<20% 2 2 4 Tubes Plugged as a result of SVI / VOL / WAR> 40 % 0 0 0 Tubes Plugged as a result of no qualified sizing 0 0 0 Tubes Plugged as a result of FB Wear > 37 % 0 0 0 Tubes Plugged as a result of an Obstruction 0 0 0 Tubes Plugged on a discretionary basis (loose part wear 7 11 18 potential - no wear detected - part not removed)

Tubes Plugged on a discretionary basis (loose part wear with 3 0 3 part not removed)

Total Tubes Plugged as a Result of this Inspection 10 11 21

• 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. Since this location was never tubed, it is not counted as a plugged tube.

Instead, the number of tubes in SG 1 reflects one less than in SG 2.

Serial No.11-533 Docket No. 50-336 EOC20 SG Tube Inspection Report Enclosure, Page 7 of 11 Table 2 - Degradation Mechanisms and Inspection Techniques Depth Sizing Parameters Degradation Probe EPRI Demonstrated Detection Sizing Axtual %TW vs. Technique Analyst Total Total Mechanism(s) ETSS /Extended Applicability NDE %TW Uncertainty Uncertainty Uncertainty Uncertainty Applicability (Sy.x) %TW %TW @ 95/50

%TW %TW Fan bar wear and Bobbin 96004.3 Structures / All CMOA y = 0.97x + 2.5 3.1 11.6 5.1 12.4 lattice support wear (Rev. 13) None Fan bar wear, +PointTM 96910.1 All Structures All CM @ y= 1.01x + 4.30 6.68 3.34 7.48 12.3 lattice support wear (Rev. 10 and PLP Wear Structures and and PLP wear (part (Part present) CM @ PLP present)

Foreign object wear Bobbin 27091.2 PLP Wear/ All Information y = 0.79x + 12.85 13.49 6.75 15.08 24.81 (Rev. 0) None Only X-Probe 24998.1 Pitting / All N/A N/A N/A N/A N/A N/A (Rev. 0) PLP Wear

+PointTM 27901 .1 Circ groove/ All CMOA y= 1.05x - 1.97 2.3 1.15 3.78 4.27 (Rev. 0) None Freespan (part not present)

+PointTM 27902.1 Axial groove/ All CMOA y= 0.98x + 1.89 2.32 1.16 3.82 4.25 (Rev. 0) None Freespan (part not present)

+PointTM 27903.1 Tapered All CMOA y= 0.97x + 2.80 2.11 1.06 3.47 3.86 (Rev. 0) football / None Freespan (part not present)

+Point TM 27904.1 Tapered round All CMOA y= 1.00x + 0.48 1.99 1.00 3.27 3.66 (Rev. 0) hole / None Freespan (part not present)

+PointTM 27905.1 Flat wear All CMOA y= 1.09x - 4.31 2.05 1.03 3.37 3.84 (Rev. 0) None Freespan (part not present)

+PointTM 27906.1 Tapered wear All CMOA y= 0.96x + 1.67 1.43 .72 2.35 2.61 (Rev. 0) None Freespan (part not present)

+PointTM 27907.1 450 tapered All CMOA y= 1.05x - 2.10 2.59 1.3 4.26 4.81 (Rev. 0) wear / None Freespan (part not present)

Serial No.11-533 Docket No. 50-336 Enclosure, Page 8 of 11 Table 3 - Service Induced Indications Rw Axial Circ. Depth Signal Present Foreign SG 1

R 40 Col 155 Location F06-1.85" ETSS 96004.3 Length (in) 3.15" 4 Length (in) na Maximum Depth 2R20 11 %TW J Reported Prior Outage 12%TW/

Initially Reported 2R14 Prior to Current Outage?

Yes Cause Fan Object Remaining?

na In-Situ Tested?

No Plugged &

Stabilized?

No (2R18) Bar Wear 1 119 66 TSC+0.19" 96910.1 0.36 0.34 13 %TW na 2R20 No Foreign Yes No Yes Object Wear 1 120 67 TSC+0.38" 96910.1 0.33 0.37 22 %TW na 2R20 No Foreign Yes No Yes Object Wear 1 121 66 TSC+0.11" 96910.1 0.33 0.37 10 %TW na 2R20 No Foreign Yes No Yes Object Wear 12%TW Fan 1 140 93 FOS-0.51" 96004.3 3.15" Y na 12 %T-w 2R14 Yes na No No (2R18) Bar Wear 2 28 5 01C-2.46" 27901.1 0.27 0.42 27 %TW 29 rW 2R15 Yes Foreign No No No (2R18) Object Wear 2 29 4 01C-1.88" 27901.1 0.27 0.40 25 %TW 25 %TW 2R18 Yes Foreign No No No (2R18) Object Wear 9 %TW Fan 2 37 120 F07-0.76" 96004.3 3.15"! na 9 %'1NW 2R15 Yes na No No (2R18) Bar Wear 2 44 S 01C-6.12" 27902.1 0.46 0.34 10 %TW na 2R20 No Foreign No No No Object Wear 2 59 10 01C-6.84" 27901.1 0.35 0.42 24 %TW 23 %TW 2R15 Yes Foreign No No No (2R18) Object Wear 2 98 143 TSH+8.60" 27903.1 0.35 0.37 25 %W 26 %TW 2R18 Yes Foreign No No No (2R18) Object Wear 11 %TW Fan 2 99 80 F06+1.27" 96004.3 3.15" Y na 15 %TW 2R15 Yes na No No (2R18) Bar Wear 2 118 41 01H-11.71" 27902.1 0.46 0.32 10 %TW 11 % 2R18 Yes Foreign No No No (2R18) Object Wear 2 119 42 01H-11.30" 27903.1 0.41 0.40 28 %TW 29 %TW 2R18 Yes Foreign No No No (2R18) Object Wear 2 123 46 01H-6.46" 27903.1 0.32 0.34 26 %TVV 27 %TW 2R15 Yes Foreign No No No (2R18) Object Wear 2 124 45 01H-4.94" 27903.1 0.41 0.37 31 %TW 31 %TW 2R18 Yes Foreign No No No (2R18) Object Wear 2 125 48 01H-4.78" 27903.1 0.38 0.40 36 %TW 37 %TW 2R15 Yes Foreign No No No (2R18) Object Wear 2 126 49 01H-4.31" 27903.1 0.38 0.40 38 %TW 39 %TW 2R15 Yes Foreign No No No (2R18) Object Wear 2 128 107 TSH+0.02" 27901.1 0.27 0.34 28 %TW na 2R20 No Foreign No No No Object Wear

ý4Conservative assumption

Serial No.11-533 Docket No. 50-336 EOC20 SG Tube Inspection Report Enclosure, Page 9 of 11 Attachments Attachment Title 1 Acronyms 2 Millstone Power Station Unit 2 Steam Generator Arrangement

Serial No.11-533 Docket No. 50-336 EOC20 SG Tube Inspection Report Enclosure, Page 10 of 11 Attachment I 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 Intergranular Attack LPI Loose Part Indication MBM Manufacturing Burnish Mark MP 2 Millstone Unit 2 NDE Non-Destructive Examination NQH Non-Quantifiable Historical Indication NQI Non-Quantifiable Indication OXP Over Expansion PCT Percent Through-Wall PLP Possible Loose Part POD Probability of Detection PTE Partial Tubesheet Expansion

%TW Percent Through-Wall R Row RPC Rotating Pancake Coil SCC Stress Corrosion Cracking SG 1 Steam Generator Number 1 SG 2 Steam Generator Number 2 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.16-127 Request for Withholding Proprietary Information Enclosure 9 Page2of2 Serial No. 11 ~533 .

Docket No. 50-336 EOC20*SG Tube lnspectlon Report Enclosure, Page 11 of 11 Attachment 2 Millstone Power Station Unit 2 Steam Generator Arrangement

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