ML20096B965

Forwards Response to NRC 951211 RAI Re GL 95-03, Circumferential Cracking of SG Tubes

ML20096B965
Person / Time
Site:	Callaway
Issue date:	01/12/1996
From:	Schnell D UNION ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-03, GL-95-3, TAC-M92228, ULNRC-3313, NUDOCS 9601170033
Download: ML20096B965 (10)

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. ,1901 Chouteau Avenue Post 0thce Box 149

. St louis. Missoud 63166 l 314 553 2650 l

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Union 1 ELECDUC NEl" *"*"'

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'@ January 12, 1996 l

U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station F1-137 Washington, D.C. 20555-0001 l l

Gentlemen: ULNRC-3313 TAC No. M92228 )

1 CALLAWAY PIANT DOCKET NUMBER 50-483 CIRCUMFERENTIAL CRACKING I OF STEAM GENERATOR TUBEE

References:

1) NRC Generic Letter 95-03, dated April 28, 1995

2) ULNRC-3226, dated June 27, 1995

3) K. M. Thomas ltr to D. F.

Schnell dated December 11, 1995 NRC Generic Letter 95-03 requested information concerning circumferential cracking of steam generator tubes. Our response was transmitted to NRC as Reference 2.

Attached please find additional information as requested by NRC in Reference 3. If you have any questions concerning this response, please contact us.

Very truly yours, Donald F. Schnell TWP/

Attachment

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1601c5 9601170033 960112" 6,

PDR ADOCK 05000483 P PDR

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-STATE OF MISSOURI )

) SS CITY OF ST. LOUIS )

-1 Donald F. Schnell, of lawful age, being first duly sworn upon oath says that he is Senior Vice President-Nuclear and i an officer of Union Electric Company; that he has read the  ;

foregoing document and knows the content thereof; that he has i executed the same for and on behalf of said company with full power and authority to do so; and that the facts therein stated are true and correct to the best of his knowledge, information and belief.

l By  ;/

l Donald P. Schnell i I

Senior Vice President  !

Nuclear SUBSCRIBED and sworn to before me this day  !

of Oa*tth , 1996. d' I F 9 0 $/LL/

r e eo BARBARA J. PFAFF, NOTARY PUBLIC-STATE OF MISSOURI MY COMMISSION EXPlRES APRIL 22,1997 ST.L0uts COUNTY

cc: T. A. Baxter, Esq.

Shaw, Pittman, Potts & Trowbridge 2300 N. Street, N.W.

Washington, D.C. 20037 M. H. Fletcher Professional Nuclear Consulting, Inc.

19041 Raines Drive Derwood, MD 20855-2432 ,

i L. Joe Callan ]

Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive Suite 400 Arlington, TX 76011-8064 Senior Resident Inspector callaway Resident Office U.S. Regulatory Commission RR#1 Steedman, MO 65077 i

Kristine M. Thomas (2) i Office of Nuclear Reactor Regulation l U.S. Nuclear Regulatory Commission-1 White Flint, North, Mail Stop 13E16 11555 Rockville Pike Rockville, MD 20852-2738 Manager, Electric Department Missouri Public Service Commission P.O. Box 360 Jeffersen City, MO 65102

Union Electric response to NRC Request for Additional Information Regarding Generic Letter 95-03 NRC Question 1 The following areas have been identified as being susceptible to circumferential cracking:

a. Expansion transition circumferential cracking

b. Small-radius U-bend circumferential cracking

c. Dented location (including dented TSP) circumferential cracking

d. Sleeve joint circumferential cracking Areas b, c, and d were not specifically addressed in your response, although you indicated that some tube support plate intersections were inspected. Please provide the requested information for these areas (and any other areas susceptible to circumferential cracking) per Generic Letter (GL) 95-03. The NRC staff realizes that some of these areas may not have been addressed because they may not be applicable to your plant; however, this should be clearly stated with the basis for the l' statement (e.g., "no sleeves are installed; therefore, the plant is not susceptible to sleeve joint circumferential cracking").

Your response indicated that some tube support plate intersections were inspected. Please clarify whether the j locations sampled were dented tube support plate intersections.

Describe the criteria for determining which locations were inspected. If a dent voltage threshold was (or will be) used for such a determination, the calibration procedure used (i.e.,

2.75 volts peak-to-peak on 4-20 percent through-wall ASME holes at 400/100 mix) should be provided. In addition, clarify the past inspection scope and your future inspection plans for dented locations.

Response to NRC Question 1 At Callaway Plant, the only crack indications found to date have been in the expansion transition region. All tubes affected have been removed from service.

Small Radius U-bend l

No indications of circumferential cracking have been found in j

the small radius U-bends. The first ten rows of tubes in Callaway's steam generators were thermally treated af ter l

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bending and prior to installation. Although the EPRI guidelines do not identify U-bend PWSCC as an expected damage mechanism for the Model F steam generator, we periodically inspect the short-radius U-bends with a rotating pancake coil (RPC) probe. The last such inspection was performed in Refuel 5 (3/20/92 to 5/17/92), at which time all row 1 and 2 U-bends i were inspected in Steam Generator C. One tube, C-R2C98 (Steam Generator C, Row 2, Column 98) was removed from service due to an undefined indication (UDI). This tube is further described in the response to Question 4. We plan to inspect the Row 1 U-bends in Steam Generator C during our next refueling outage, which is currently scheduled to begin in October 1996.

Dented Locations No service-induced denting has been identified in the Callaway steam generators. As stated in our response to Generic Letter 95-03, 100% bobbin coil inspection is performed in two steam  ;

generators during each outage. This ensures that all tube support plate intersections are examined every 3 years. To  ;

date, no damage mechanism has been identified in these areas.

This is expected since Callaway's steam generators have l stainless steel support plates with quatrafoil tube passages. I We will continue to monitor these areas for any indication of damage.

4 Sleeve joints No sleeves are installed in the Callaway steam generators.

Therefore, the plant is not susceptible to sleeve joint i circumferential cracking.

NRC Question 2 Clarify the extent (percentage of tubes sampled) of the rotating pancake coil (RPC) examinations performed in the thermally-treated alloy 600 tubes at the expansion transition location.

Response to NRC Question 2 Callaway has a total of 4856 (4 x 1214) thermally-treated tubes which comprise the first ten rows in each steam generator.

During Refuel 7 (3/25/95 to 5/11/95), 405 thermally-treated tubes were inspected with the RPC at the expansion transitions.

This represents an overall sample of about 8.3%. However, the examination concentrated on the sludge deposition zones of generators A and C where most of the crack indications were found in the mill-annealed tubing and where thermally-treated 2

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tubing would most likely be affected. No indications were ]

identified in thermally-treated tubing.  !

l NRC Question 3 j Provide the size of the indications detected at the expansion l transition region along with an assessment of their structural integrity. Discuss any other techniques used to assess their  ;

structural integrity (e.g., UT, in situ pressure tests, tube -

pulls).

Response to NRC Question 3 Table 1 lists all of the expansion transition indications found during Refuel 7. Westinghouse evaluated tube A-R18C54, which had the greatest mi::ed mode degradation. Their analysis

, determined that this tube satisfied Regulatory Guide 1.121 requirements and bounded the remaining degraded tubes. No other techniques were used to assess structural integrity.

NRC Question 4 Please clarify the following titles in Table 1 of your Generic Letter 95-03 response: " Undefined Defect Indication" and

" Unknown Axial Crack."

Response to NRC Question 4 In Table 1 of ULNRC-3226 (Reference 2), " Undefined Defect Indication" refers to an indication found in tube C-R2C98 during Refuel 5. This indication, not detected by bobbin coil, was found by RPC and was located just above the 7th cold leg support plate. As noted in our response to Question 1, all row 1 and 2 U-bends in generator C were inspected with RPC during Refuel 5 with no other indications detected. Since no degradation mechanism has been identified in this region, we considered this to be an anomalous indication. Our level III analyst judged this indication to be a distorted signal caused by its location in the U-bend transition. Nonetheless, we conservatively plugged the tube.

The term " Unknown Axial Crack" means we could not determine whether crack initiation was OD or ID.

NRC Question 5 During the Maine Yankee outage in July / August 1994, several weaknesses were identified in their eddy current program, as detailed in NRC Information Notice 94-88, " Inservice Inspection Deficiencies Result in Severely Degraded Steam Generator 3 )

4 Tubes." In Information Notice 94-88, the staff observed that several circumferential indications could be traced back to earlier inspections when the data was reanalyzed using terrain plots. These terrain plots had not been generated as part of the original field analysis for these tubes. For the rotating pancake coil (RPC) examinations performed at your plant at locations susceptible to circumferential cracking during the previous inspection (i.e., the previous inspection per your Generic Letter 95-03 response), discuss the extent terrain plots were used to analyze the eddy current data. If terrain plots were not routinely used at locations susceptible to circumferential cracking, state whether the RPC eddy current data has been reanalyzed using terrain mapping of the data. If terrain plots were not routinely used during the outage and your data has not been reanalyzed with terrain mapping of the data, discuss ycur basis for not reanalyzing your previous RPC data in light of the findings at Maine Yankee.

Response to NRC Question 5 Terrain plots are used at Callaway for every tube examined with the RPC probe. During future inspections, terrain plots will continue to be used for analyses of tube sections inspected with the RPC probe.

Union Electric reviewed pertinent historical data for tubes with expansion transition indications. This work was performed during Refuel 7 by a third party Level III analyst. The review included any available bobbin or RPC data for a particular tube. Eight possible precursor signals were identified. None of the precursor signals were significant enough to be considered a " missed" call. Table 2 (attached) provides this information.

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TABLE 1 TOP OF TUBESHEET INDICATIONS - REFUEL 7 (APRIL 1995)

S/G Row Col Indication Location Cire Extent Initiation Side Repair or Axial (ID, OD, or method l Length UN) (Plug or I l

i stake / plug)

( 1 A 21 47 SCI TSH -1.05 108 degrees ID Stake / plug A 11 50 SAI TSH - 0.16 0.30 inches UN Plug A 12 51 SAI TSH + 0.10 0.22 inches ID Plug A 18 54 SAI TSH - 0.05 0.32 inches ID See Below MCI TSH - 0.21 333 degrees OD Stake / plug l

A 13 55 SCI TSH - 0.18 0.17 inches OD Stake / plug l A 32 58 MAI TSH - 0.01 0.40 inches ID Plug A 12 61 MAI TSH - 0.08 0.24 inches ID Plug i A 12 69 SCI TSH - 0.13 136 degrees ID Stake / plug A 14 69 SCI TSH - 0.22 63 degrees ID Stake / plug A 19 80 SCI TSH - 2.62 116 degrees ID Stake / plug A 34 100 SAI TSH + 0.02 0.57 inches ID Plug C 14 41 MAI TSH - 0.04 0.40 inches OD Plug C 36 43 SAI TSH + 0.17 0.36 inches ID Plug C 12 55 MAI TLu + 0.42 0.64 inches OD Plug C 14 56 SV1 TSH + 0.01 0.54 inches OD Plug C 13 57 SVI TSil + 0.20 0.40 inches OD Plug C 14 57 SVI TSH - 0.08 0.39 inches OD Plug C 14 58 SVI TSH + 0.01 0.36 inches OD Plug C 15 58 SCI TSH - 0.09 139 degrees OD Stake / plug 5

1 TABLE 1 (cont.)

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S/G Row Col Indication Location Circ Extent Initiation Side Repair i or Axial (ID, OD, or method Length UN) (Plug or stake / plug)

C 13 59 SV1 TSH + 0.49 0.55 inches OD Plug C 15 60 SCI TSH - 0.26 83 degrees OD Stake / plug C 13 61 SAI TSH + 0.28 0.36 inches OD Plug C 14 61 SCI TSH - 0.08 190 degrees OD Stake / plug SAI TSH +0.05 0.39 inches UN See above C 43 80 MAI TSH - 0.19 0.35 inches ID Plug C 24 88 SAI TSH - 0.16 0.48 inches UN Plug i

C 14 100 SAI TSH - 0.01 0.26 inches OD Plug D 33 56 SAI TSH - 0.05 0.22 inches ID Plug D 16 61 SCI TSH - 0.06 142 degrees OD Stake / plug l

D 17 108 SVI TSH - 0.06 0.40 inches OD Plug SAI Single AxialIndication MAI Multiple AxialIndication SCI Single CircumferentialIndication MCI Multiple AxialIndication SVI Single Volumetric Indication 6

3 TABLE 2 HISTORICAL DATA REVIEW Steam Generator A Row Col 1995 MRPC 1993 Bobbin 1990 MRPC i

21 47 SCI No No data '

11 50 SAI No No data i

• 12 51 SAI Yes No l 18 54 SAI/ MCI No No 1

• 13 55 SCI No Possible SCI 32 58 MAI No No data 12 61 MAI No No I 12 69 SCI No No 14 69 SCI No No 19 80 SCI No No data

• 34 100 SAI Possible No data Steam Generator C l l

Row Col 1995 MRPC 1995 Bobbin 1992 Bobbin

• 14 41 MAI Yes Yes 36 43 SAI No Not reviewed 12 55 MAI No Not reviewed

• 14 56 SVI Yes Possible

• 13 57 SVI Yes Yes

• 14 57 SVI Yes Possible

• 14 58 SVI Yes Yes 15 58 SCI No Not reviewed 13 59 SVI Yes No 15 60 SCI No Not reviewed 13 61 SAI Yes No 14 61 SAI/ SCI No Not reviewed 43 80 MAI Yes No 24 88 SAI No Not reviewed 14 100 SAI No Not reviewed Steam Generator D Row Col 1995 MRPC 1993 Bobbin 33 56 SAI No 16 61 SCI No 17 108 -

SVI No

- Possible precursor signals l

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