ML20134K003

Forwards Figure That Goes W/Previous E-mail & More Recent Table of Preliminary Results of Tube Insps

ML20134K003
Person / Time
Site:	Prairie Island
Issue date:	02/03/1997
From:	Leveille J NORTHERN STATES POWER CO.
To:	Wetzel B NRC (Affiliation Not Assigned)
References
TAC-M96654, TAC-M96655, NUDOCS 9702130066
Download: ML20134K003 (8)

Text

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TAC NOS. M96654/96655

. Docket Nos. 50-282/30-306 Facsimile Cover Sheet Northern States Power Company Prairie Island Nuclear Generating Plant 4

To: Beth Wetzel From: Jack Leveille Company: NRR Address: 1717 Wakonade Drive East l

Welch, Minnesota 55089 Phone: 301-415-1355 Phone: 612-388-1121,X4662 2

Fax: 40iHHHke999-Fax: 612-330-5743

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Date: Feb.3,1997 l

Number of pages including this cover sheet:

3 i

Comments:

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i Here is the Figure that goes with the previous E-mail and a more recent table of the j

preliminary results of tube inspections.

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' F E-3-97 MON 11:29 FAX NO, 6123305743 P.01 9

Prairie Island Unit 2 9701 S/G Inspection Results Category C 3 inspection Results Preliminary Report to NRC - February 3,1997 Preliminary Summary of Tubing inspection Results 1 tube with a reroll has 2 drop / min leakage (21 SG R18C44) 9 tubes with rerolls have minor seepage 1 tube has an axial indication at the reroll upper transition zone About 240 RTZ PWSCC are predicted as candidates for Reroll and F* criteria About 24 tubesheet indications are predicted to be plugged About 0? indications are candidates for the pending EF* criteria About 20 other indications are predicted to be plugged (mostly CLTSP Thinning)

No circumferential indications have been found No possible tube support plate ligament indications have been found in Situ Pressure Testing Equipment is on site - candidates will be selected from the leaking rerolled tube, the seeping rerolled tubes, new RTZ indications and other tubesheet crevice Indications, and free span indications greater than 0.3 inch long.

Schedule Inspection:

Started on January 30,1997 Repair:

Scheduled to start on February 8,1997

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In situ pressure testing to be done at beginning of repair phase

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post.it-brand tax transmittat memo 75717a' F"

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h Pt 2am nP NRC297A. DOC c.sesaw

FEB.- 3-97 MON 11:29 FAX NO. 6123305743 P.02 ET Examination and Primary Side Visual inspection Plan Status /No of Tubes Examination Description 21 SG 22 SG Hot Leg Tubesheet: 100% MRPC with + Point TEH to TSH + 4 inches 56 %

3256 86 %

3216

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Cold Leg Tubesheet: 20% MRPC with + Point IEC to TSC + 4 inches (1st time for + Point in CL Tbsht)

Done 652 Done 644 MRPG with + Point of all existing rerolls 56 %

288 56 %

113 Bobbin - 100% Full Length 33 %

3256 45%

3216 UBend MRPG with + Point

- all Rows 1 and 2 183 185 Supplemental RPG with + Point from Bobbin Results

+ Point rotating coil of HL B&W plugs (1st time for

+ Point in B&W plugs) 19 13 Post Installation Examination of all new Rerolls with i

+ Point and Bobbin coils Visual Examination of All Plugs Done 132 172

_ Visual Examination of Tubesheet under Secondary

• "8 Hydro pressure of 700 to 800 psig.

Done This is the second use of the + Point coilin the Unit 2 steam generators, except where noted above Supplemental Rotating Coil Examinations are done on the following bobbin calls:

.Any ADR, DRI, DSI, DTI, PLP, UDI, PSI

• All Dents > 5.0 volts

. Selected bobbin calls > 40%

The qualified sizing techniques being used are 1) wear at anti-vibration bars or loose i

parts and 2) wastage at outer peripheral lower cold leg tube support plates.

There are no sleeves in Unit 2 Visual Inspections for Leakage under Secondary Side Pressure Tests were schedule due to a constant 2 to 4 GPD leak during the previous cycle.

1 2am RPP NRC297A. DOC 2

FEB 3-97 MON 14:33 FAX N0. 6123305743 P.02 1

i Preliminary Results of Tubing inspections l

j Results - Feb 2,97 i

Location / Degradation Mechanism 2180 22 SG VisualInspection of Plugs No Problems Planned i

-Visual Inspection for Leakage with 700 to 800 pslo 10 tubes' in Pro 0ress

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HL Tube End Axlat indications /PWSCC7 10 23 HL Roll Transition Zone AxialIndications/PWSCC 117 88 i

_HL Tubesheet Crevice Region Sec. Side IGA / SCC 2

1 HL Top of Tubesheet/ IGA / SCC 2

8 HL Additional Aerolls (installed in 9505)/PWSCC 1'

i Free Span / Unknown i

Top of Tubesheet CL/ Unknown 2

1 i

Peripheral Lower Cold Leg Tube Support i

Plates /Wastace 3

Hot Leg Tube Support Plates /Some type of IGA?

3 Cold Lea Tube Support Plates /Not Wastage l

_ Anti-vibration B_ar Locations, Wear l

Rows 1 and 2 U Bends, PWSCC Loose Parts / Wear 4

__O_ ther Tube Support Plate Li0 ament Possible Indications I

'One tube,21 SG R18C44, with a reroll has a substantial RTZ axial indication and is i

the primary source of the operationalleakage. Nine tubes with rerolls and RTZ l

Indications have signs of moisture.

'One reroll has developed a singe axialindication at the upper roll transition.

i Repair Criteria:

i 240 % TWO (2 50% Old AVB locations) for EPRI Appendix H qualified sizing j

techniques (cold leg tube support plate thinning and wear)

Any Axlal, Circumferential, Volumetric or Mixed Mode RPC indication j

F-Star Criteria for Lower Region of Tubesheet e

EF-Star Criteria for Upper Region of Tubesheet (pending NRC approval) j e

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Plug Removal i

Steam Generator Cold Leg 21 40 22 105 l

Total 145 i

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2/347 Rif NRC297A DOC 1291 PM 3

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i FEB.- 3-97 MON 11:30 FAX N0, 6123305743 P.04 ei I

REROLL LEAKAGE PERFORMANCE j

Reseons for Leakage - R18C44 i

Hydraulic expansion process can open the roll transition zone crack or other cracks j

present in the hydraulle expansion zone. Examination of the g505 post reroll RPC shows si;nificant change in the Indication. It is postulated that the indication became through wali during the hydraulic expansion (was not leaking during hydro prior to

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rerolling). Primary to recondary side leakage did appear during startup in July 1995 i

and stayed fairly constant the entire cycle. This indicates the reroll was not leak tight.

No other indications are present in the tubesheet region in this tube.

The operational experience over the last cycle indicates that the reroll process is still a viable repair tool. The leakage through the one large leak was constant throughout the 570 day cycle. Seepage of moisture within the other 9 tubes occurred after 2 days at about 740 psig secondary side pressure. This is a very conservative pressure test due to the reverse pressure conditions and the time pressure was maintained j

compared to normal ASME Code requirements for hydrostatic pressure tests.

After reviewing the NRC Safety Evaluation Report, the Prairie Island Technical l

Specification 4.12 and its basis, and NSP's responses to additional questions for the l

F* License Amendment Request, it is our position that the F' criteria is a leak limiting criteria and that leakage from reroll joints is acceptable within the requirements of the i

SER and the Technical Specification. We expected the hard roll joints to be leak tight if no hard scale was present, but it appears conditions in the tubesheet crevice region will not always provide leak tight reroll joints and will not always provide a distinguishing torque trace. We are investigating possible causes for the leakage i

through the hard roll and it will be a couple of days before we complete this i

irvostigation.

Preliminary Action Plan for Evaluating Rerolls with Leakage Evaluate previous torque traces, calibration records, etc.

j Conduct profilometry of selected rerolls.

Determine leak rate at MSLB conditions with in situ pressure tests of selected i

rerolled tubes Evaluate process parameters against qualification report j

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Confirm changes in RTZ ET Indications after hydraulic expansion 3

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2m7 m hRCN7A. DOC 4

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FEB-3-97 MON 11:31 FAX N0. 6123305743 P.05 1

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Additional Roll Expansion Process - ABBCE l

1.

Eddy Current examination using Rotating Pancake Coil (RPC) technology (or equivalent) of the tubesheet region to determine that there is sound tubing (i.e. No j

detectable degradation by RPC) in the region of the additional roll expansion.

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Brushing of the inside diameter to clean the tube in the region of the re-roll.

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Hydraulic expansion over a 5 inch length starting at j

1.5 inches from the tube end.

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Hard roll expansion of 1.25 inches of tubing centered

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at 4.5 inches from the tube end. (leaves about 1 inch between the original hard roll and the new hard roll) d 5.

Eddy current examination using a bobbin probe and i

a rotating pancake coil to look for cracks in the new hard roll and hydraulic expanded region.

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Reexamination of the F* tube F* region for the next i

two refueling outages.

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i 2cE RPP NRC297ADOC j

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FEB6 3-97 fiON 14:33 FAX NO, 6123305743 P.03 l UFDATED P.!, OPNS PRAlalE ISLAND NUCLEAR GENERATING PLANT NORTHERN STATES POWER COMPANY MADIATION PROTECTION PROCEDURES

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EXPANSION OF STEAM GENERATOR REV: 1

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F* AND ADDITIONAL ROLL D27'23

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FIGURE 1 - F STAR AND ADDITIONAL ROLL EXPANSION (F*/ REROLL) hh h

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o 0 ETA!L 1 DETAIL 2 DETAIL 3 ORIGINAL HYDRAULIC REPAIR HYDRAULIC &

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EXPANSION & REROLL REPA!R REROLL I.,anms l

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,=co. msuas yp 4 F-STAR AND ADDITIONAL ROLL EXPANSION (F / REROLL) j.g,pg erka l ac, 2 j

leCRTHERN STATES POWC4 CobpAM E*.c PRAIRIE ISLAND NUCLEAR GEN. PLANT l

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, [ FEb '3-97110N 11:32 FAX NO. 6123305743 P.07 Secondary Side Inspection Plan Visual Inspections for internals Integrity (one steam generator)

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inspection for indication of wrapper drop in both steam generators via the

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handholes. There has previously been no noticeable drop.

Visualinspection of anti-rotation device

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Possible visual inspection of wedge block region at top tube support plate, if accessible via a swirl vane (will not expend a lot of effort)

Visual inspection of the wrapper support plate blocks and windows in one steam

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generator Visual inspection for gross wastage of flow holes in top support plate at outer

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periphery Standard Inspections in one steam generator each outage a

1 Visualinspection of feed ring holes and plugs j

2 MT inspection of Inner radius of feedwater nozzle elbow i

3 Visual inspection of inner radius of upper shell transition weld 4

Visualinspection of feedwater ring hangers 5

Welch Allyn inspection of u-bend region of tubes through a swirl vane 6

Visual inspection for cleanliness of drain pots from Chevron separators 7

UT inspection for wall thinning of feedwater ring tee has been done previously (was satisfactory) 1 Analysis of ET data for support plate damage per guidelines below 1

Use Computerized Data Screening to look at all tubes for significant ligament cracks 2

Examine all possible support plate ligament indications from the bobbin results with RPC.

2/J47 RPP NRC297A. DOC y