ML041260535

Steam Generator Tube Plugging Report

ML041260535
Person / Time
Site:	Millstone
Issue date:	05/03/2004
From:	Hartz L Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
04-266, FOIA/PA-2005-0210
Download: ML041260535 (6)

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Dominion Nuclear Connecticut, Inc.

M i I Ist one Power 5 tat ion

)Dominion k i p c Fcri y Rocid Wattrtord. C7 06385 May 3 , 2004 U.S. Nuclear Regulatory Commission Serial No.04-266 Attention: Document Control Desk MPS Lic/wdb RO Washington, DC 20555 Docket No. 50-423 License No. NPF-49 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3 STEAM GENERATOR TUBE PLUGGING REPORT This special report is being submitted pursuant to the requirements of Millstone Power Station Unit 3 (MPS3) Technical Specifications 4.4.5.5.a and 6.9.2. MPS3 Technical Specification 4.4.5.5.a requires that a special report be submitted to the U. S. Nuclear Regulatory Commission (NRC) within 15 days following completion of each inservice inspection of the steam generator tubes to document the number of tubes plugged.

The eddy current inspections conducted at the end of cycle 9 were completed on April 17, 2004. Attachment 1 of this letter contains tables summarizing the number of tubes examined and identifies tubes removed from service as a result of the examination.

The scheduled inspections were performed in MPS3 Steam Generators B and D. All operational tubes within these steam generators, a total of 11,180 (approximately 50 percent of the total population of tubes) were inspected with bobbin probes.

Additionally, an augmented sample (8,484 tube locations) was inspected utilizing rotating probes incorporating plus point coils. The plus point probe provides detection of both circumferential and axial cracks and has been qualified per the Pressurized Water Reactor Steam Generator Examination Guidelines, Appendix H, for the detection of cracking mechanisms. The rotating probe inspections were performed in areas of special interest including hot leg expansion transitions, low row u-bends, and dents as well as locations where the bobbin probe response was ambiguous. The 8,484-tube sample also included a scope expansion at top-of-tubesheet locations in the hot and cold legs triggered by loose part wear.

A total of ten tubes were plugged; all in D Steam Generator. Eddy current testing identified flaws greater than or equal to the plugging limit in three (3) tubes. The plugging limit is defined within Technical Specifications as an imperfection depth of 40 percent nominal tube wall thickness or greater. Additionally, tubes were removed from service on a discretionary basis. In total, the following tubes were plugged:

Required:

Two tubes were identified with loose part wear (single volumetric indications or SVls) greater than the plugging limit. The loose part (weld wire) was removed from the steam generator.

One tube was identified with an SVI exceeding the plugging limit. However, no potential loose part signal was present.

Serial No.04-266 Steam Generator Tube Plugging Page 2 of 3 Discretionary:

0 One tube was identified with anti-vibration bar (AVB) wear greater than 36 percent throughwall.

A cluster of five (5) tubes was identified with SVI signals. Three (3) of these tubes were identified with SVI signals of 16-26% throughwall. Additionally, three of the five were identified with a potential loose part signal present. Since the area is not accessible for visual inspection, all five tubes were removed from service.

0 One tube, row 1 column 1, was identified with an SVI in the tight u-bend region.

This indication (29%) appeared to be a manufacturing defect, similar to tubes plugged prior to startup. The indication was small and not detectable with the bobbin probe. This tube was removed from service on a discretionary basis.

All 10 tubes were removed from service by the installation of Framatome Alloy 690 Rolled Mechanical Tube Plugs on April 17, 2004.

The inspection results from Steam Generator B were classified as C1. The inspection results from Steam Generator D were classified as C2 due to loose part wear.

Consistent with NEI 97-06 Guidelines and the Millstone Steam Generator Program, a 20% expansion was performed at top-of-tubesheet locations split between the hot and cold legs of Steam Generator D to address the C2 classification due to loose part wear.

The majority of this expansion was in the cold leg with the remainder in the hot leg and exceeds the Technical Specification scope expansion requirements for a C2 result.

The complete results of the steam generator tube inspection will be submitted within twelve months in accordance with Technical Specification 4.4.5.5.b.

If you have any questions or require additional information, please contact Mr. David W.

Dodson at (860) 447-1791, extension 2346.

Very truly yours, Leslie N. Hartz Vice President - Nuclear Engineering

Serial No.04-266 Steam Generator Tube Plugging Page 3 of 3 Attachments: Steam Generator Tube Plugging 15 Day Report Commitments made in this letter: None.

cc: U.S. Nuclear Regulatory Commission Region I 475 Allendale Road King of Prussia, PA 19406-141 5 Mr. V. Nerses Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 8C2 Rockville, MD 20852-2738 Mr. S. M. Schneider NRC Senior Resident Inspector Millstone Power Station

ATTACHMENT 1 STEAM GENERATOR TUBE PLUGGING 15 DAY REPORT Millstone Power Station Unit 3 Dominion Nuclear Connecticut, Inc. (DNC)

Serial No.04-266 Docket No. 50-423 Steam Generator Tube Plugging Attachment 1 Page 1 of 2 TABLE 1 MILLSTONE 3 RF09 ECT

SUMMARY

IWlAL Number of Tubes (SG B and D only) 5626 5626 11252 Number of Tubes Inspected F/L w/Bobbin Probe 5256 51 96 10,452 Number of Tubes Inspected w/Bobbin Probe Hot Leg and 366 362 728 Cold Leg Candy Canes Previously Plugged Tubes 4 68 72 Number of Tube Inspections w/MRPC (Total) 3054 5430 8484

.Hot Lea Transitions - Oriainal ScoDe 281 3 281 3 5626

.Hot Leg Transitions - Scope Expansion 0 192 192

.Row 1 and 2 U-Bends - Original Scope 122 122 244

.Hot Leg Misc. Special Interest - Diagnostic Exams 93 185 278 and from Previous History (tubes)

C o l d Lea Transitions - Scope Expansion 0 2070 2070 G o l d Leg Misc. Special Interest - Diagnostic Exams and from Previous Historv (tubes) I l7 I l3 30 18 21 34 84 3

4 9

3 1

0 7

10 TABLE 2 - TUBES PLUGGED DURING RF09 (2 40%)

ROW COLUMN INDICATION ETSS 21 998.1 ETSS 96910.1 Comment 5 1 SVI 54 Yo 31 Yo Note 1 53 61 SVI 86 Yo 53 Yo Note 1 52 61 SVI 48 Yo 31 Yo Note 1 Note 1 : Small Volume Flaw evaluations are based on the size determined by ETSS 21998.1, which is known to become quite conservative as the flaw diameter increases. An example of this is that ETSS 21998.1 was utilized to estimate the depth of two flaws on a Millstone calibration standard (SN Z17513). The flaws were known to be 51 Yo and 31 %. The subject ETSS sized these flaws at 78% and 51 % respectively. The actual tube flaws, identified on Table 2, are more appropriately sized using ETSS 96910.1.

Serial No.04-266 Docket No. 50-423 Steam Generator Tube Plugging Attachment 1 Page 2 of 2 TABLE 3 DISCRETIONARY TUBES PLUGGED FOR AVB WEAR DURING RF09 D SIG ROW COLUMN Yo THROUGHWALL 43 58 37% -

ROW COLUMN  % THROUGHWALL ROW COLUMN Yo THROUGHWALL 1 1 29 Yo 51 32 PLP (Note 2) 50 33 26% 51 33 25%, PLP (Note 2) 50 34 PLP (Note 2) 51 34 16%

TABLE 5 -TOTAL TUBES PLUGGED TO DATE RF07- 0 51 51 RF08 8 3 11 RF09 0 10 10 TOTAL 34 4 11 78 127