ULNRC-04776, C-3 Classified Inservice Inspection Results for Steam Generator Tube Inspections

C-3 Classified Inservice Inspection Results for Steam Generator Tube Inspections

ML023310230
Person / Time
Site:	Callaway
Issue date:	11/19/2002
From:	Witt W AmerenUE
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-04776
Download: ML023310230 (13)

Text

Union Electric PO Box 620 CallawayPlant Fulton, MO 65251 November 19, 2002 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 ULNRC-04776 Ladies and Gentlei wAmeren men:

UFE DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

FACILITY OPERATING LICENSE NPF-30 SPECIAL REPORT 2002-03 C-3 Classified Inservice Inspection Results for Steam Generator Tube Inspections The enclosed Special Report is submitted in accordance with Technical Specification 5.5.9, Table 5.5.9-2, which states:

"Results of steam generator tube inspections, which fall into Category C-3, shall be reported to the Commission within 30 days and prior to resumption of plant operation. This report shall provide a description of investigations conducted to determine cause of the tube degradation and corrective measures taken to prevent recurrence."

The required failure mechanism determination investigation and corrective measures taken to prevent recurrence have been completed and are detailed in the enclosed report.

Warren A. Witt Manager, Callaway Plant WAW/ewh 0, k Enclosure a subsidiaryof Ameren Corporation

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ULNRC-04776 November 19, 2002 Page 2 cc: U. S. Nuclear Regulatory Commission (Original and 1 copy)

Attn: Document Control Desk Mail Stop P 1-137 Washington, DC 20555-0001 Mr. Ellis W. Merschoff Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Jack N. Donohew (2 copies)

Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 7E1 Washington, DC 20555-2738 Manager, Electric Department Missouri Public Service Commission PO Box 360 Jefferson City, MO 65102

SPECIAL REPORT TO THE NRC STEAM GENERATOR A (EBB01A) CATEGORIZED AS C-3 CONDITION IN REFUEL 12 At 1110 on 11/05/02, AmerenUE Callaway Plant determined that steam generator A (EBB01) qualified as Category C-3 in accordance with the requirements of Technical Specification (T/S) 5.5.9, Table 5.5.9-2. At 1419 of that same day, the required ENS notification was made to the NRC Operations Center per 10CFR50.72(b)(2).

Additionally, T/S 5.5.9 refers to T/S 5.6.10 for further reporting requirements. T/S 5.6.10(c) states, "Results of steam generator tube inspections, which fall into Category C-3, shall be reported to the Commission within 30 days and prior to resumption of plant operations. This report shall provide a description of investigations conducted to determine cause of the tube degradation and corrective measures taken to prevent recurrence."

This report is intended to satisfy that requirement.

Callaway Steam Generator History The Westinghouse Model F steam generators installed at Callaway consist of approximately 78% low temperature mill annealed (LTMA) Alloy 600 tubing and 22%

(innermost 10 rows) Alloy 600 thermally treated (TT) tubing.

Callaway Plant first identified primary and secondary side Stress Corrosion Cracking (SCC) of the steam generator tubes in 1995 (Refuel 7). Since that outage, all four steam generators have been inspected each refueling, with the result that an increasing number of tubes have been repaired due to corrosion of the tubes at the hot leg top of tube sheet as shown in Figure 1 and Table 1. Sample RPC inspections are performed each outage at the support plates (dents), low row U-bends, and free span (dings) areas to provide early identification of any cracking that may occur in these locations. None has been identified to date.

The trend of top of tube sheet indications in all four steam generators is provided in Figure 1.

The extent of the tube degradation found during Refuel 12 was not unexpected. Past inspection results and tube degradation prediction models indicated that the degradation of the mill-annealed tubing would accelerate as the plant ages. This has generally been true of other plants with original Westinghouse steam generators fabricated with Alloy 600 MA tubing.

The tube degradation model for Callaway was updated prior to Refuel 12. Based on past experience, plant operating conditions, and experience at other plants, 123 tubes were predicted to be defective due to SCC (IDand OD) and IGA/SCC. The actual number identified was 113 in all four steam generators at the expansion transition or in the expanded portion of the tubing found using a Rotating Pancake Coil (RPC). Of the tubes with tubesheet defects, 84 were found in steam generator A as shown in Table 2 and Attachment 1. Since the number of defective tubes exceeded 1% of the inspected tubes for RPC inspection, the inspection results are classified as C-3.

Page I of 8

As Figure 1 demonstrates, Steam Generator A has consistently had more SCC indications than any other steam generator.

No service-induced degradation was identified in the 600TT tubing.

---.-- S/G A o B

- **-* S/G 20 50, 040 20 40___________, ___

10

• o IK"%,° 0

Jun-94 Oct-95 Mar-97 Mu,-98 Dec-99 Apr-01 Sep-02 Jan-04 DATE Figure 1 Top of Tubesheet Cracks Trending by Steam Generator Examination of Steam Generator A The original inspection scope for 'A' steam generator was as follows:

• 100% (5431 tubes) of the hot leg top-of-tubesheet with a +Point RPC probe

• 100% (5431 tubes) full-length of the tubes with a standard bobbin coil probe Upon completion of the original scope of inspection, a total of ninety-one (91) tubes (as identified in Attachment 1) required repair:

"* Three tubes as a result of anti-vibration bar (AVB) wear greater than 40%

through-wall

"* Four tubes due to small volumetric indications near support (or flow baffle) plates Page 2 of 8

• 84 tubes due to Stress-Corrosion Cracking (SCC) or Inter-Granular Attack (IGA) indications at the expansion transition region or in the expanded tube Seven of the 84 indications discovered in Steam Generator A were found in the region added to the inspection scope using the new H-Star requirements for the top of-tube sheet inspections.

Investigation for Cause of Degradation Stress-corrosion cracking (PWSCC/ODSCC) has been identified in the hot leg tube sheet expansion and transition regions in all Westinghouse-designed steam generators (operating at 607'F or above) fabricated with LTMA tubing which were not peened prior to the start of plant operations.

Callaway Plant has determined that, based on the definition of active damage mechanism provided in the EPRI PWR Steam Generator Examination Guidelines, hot leg expansion axial/circumferential PWSCC and hot leg top of tube sheet ODSCC/IGA are active damage mechanisms in Callaway's steam generators.

Stress Corrosion Cracking occurs in the high stress expansion transition located at or below the top of the tube sheet and can initiate from either the primary or secondary side, and occurs due to the combination of the following:

• high residual stresses in and slightly above the expansion transition,

• the concentration of bulk water impurities to aggressive levels in the residual crevice between tube and tubesheet at the TTS, and in occluded areas formed by sludge,

• the insulating effect of sludge at the "TSwhich can raise the tube OD metal temperature up to primary water temperature in some cases, and

• the presence of a thin cold worked layer on the tube OD from abrasive polishing, often with high residual stresses, which increases susceptibility to crack initiation.

All indications identified at the top of the tube sheet in Refuel 12 are small in size as shown in Figure 2 and 3. None exceeded the condition monitoring limits for the specific type of degradation identified. In-situ testing was performed on indications based on screening criteria developed in the Plant's Degradation Assessment. The screening criteria are specified based on the type of degradation that exists or could potentially exist in the steam generators. Five indications in Steam Generator A exceeded these screening criterion. All indications were tested to 3 times Normal Operating Primary to Secondary Pressure Differential (4350 psi). None of the indications exhibited any leakage at any target pressure up to 3 times normal operating differential pressure during the test sequence. A list of tubes tested in steam generator A and target pressures are attached. (Table 3)

There were no new forms of degradation found in steam generator A. All forms of degradation were anticipated and addressed in the Refuel 12 Degradation Assessment.

Page 3 of 8

110 100 M 80 0

S70 CL 60 - -

4)

E5

• 4O 30 20 Length of axial indication Figure 2 Refuel 12 Steam Generator Axial Indications 140 CO 120 a_

"2. 100 C

X x

a1 80 CU 260 E

""S 40 0 0 r1 111A ' BU PDA (percent degraded area)

Figure 3 Refuel 12 Steam Generator A Circumferential Indications Page 4 of 8

Table I Steam Generator A Indications and Tubes Repaired Since Refuel 7 Indication RF07 *RF08 RF09 **RF10 RFlI RF12 Axial ID 5 9 14 15 23 39 Circumferential ID 4 26 17 21 2 43 Axial OD 0 0 1 0 0 0 Axial unknown 1 3 0 0 0 0 Circumferential OD 2 1 0 3 1 0 Circumferential 0 6 0 0 0 0 unknown Volumetric Indications 0 5 0 3 0 4 Total tubes with TTS 11 47 32 41 26 84 indications Tubes plugged due to 0 0 0 0 0 3 AVB wear Tubes plugged due to 0 0 0 1 0 4 TSP wear Tubes plugged due to 0 0 0 0 0 0 loose parts Total tubes repaired 11 48 32 42 26 91

• 44 tubes were sleeved with Westinghouse Laser Welded Sleeves at the top of the tubesheet.

• • 31 tubes were sleeved with Framatome Electrosleeves at the top of the tubesheet.

Seven indications in RF12 are due to an expanded scope in the tubesheet based on the H-star criteria.

Refuel 7 - 1 tube has both axial PWSCC and circumferential ODSCC Refuel 12 - 2 tubes have both axial and circumferential PWSCC Table 2 Steam Generator A Tubes Plugged Inspection Period Steam Generator A Pre-service 8 Refuel 1 0 Spring '87 Refuel 2 3 Refuel 3 Refuel 4 6 Refuel 5 Refuel 6 19 Refuel 7 11 Refuel 8 4 Refuel 9 32 Refuel 10 11 Refuel 11 26 Refuel 12 91 TOTAL 211 Steam Generator A is 3.75% plugged Equivalent plugging due to sleeves is 3.79%

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90 80 70 M

" 60 C0.

0-0 10 Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04

,Outages Figure 4 Steam Generator A Cumulative TTS Degradation rn 45

--- Axial PWSCC 40= Circ PWSCC

-*Axial ODSCC J "CL35 ---- Circ ODSCC I--unknown circ /

30 -- *unknown axial 0

E 0._

25 r

20 15 10 0

Jun-94 Oct-95 Mar-97 Jul-98 Dec-99 Apr-01 Sep-02 Jan-04 outages Figure 5 Steam Generator A Cumulative TTS Degradation by Type Page 6 of 8

Table 3 Steam Generator A In-situ Pressure Testing Results Steam Generator A Tube/Defect/ Test Pressures Hold Time Leak Rate Average Pressurization Location (psi) (min) (gpm) Rate (psifsec)

Row Column 1550 2 0 15 23 97 2900 2 0 24 SCI @ TSH -8.4 3400 2 0 15 3900 2 0 14 4350 2 0 16 24 88 1550 2 0 15 SCI @ TSH -5.6 2900 2 0 29 3400 2 0 17 3900 2 0 14 4350 2 0 14 25 71 1550 2 0 12 MCI @ SBH-1.72 2900 2 0 14 3400 2 0 14 3900 2 0 17 4350 2 0 14 34 80 1550 2 0 8 SCI @ TSH -4.76 2900 2 0 15 3400 2 0 15 3900 2 0 11 4350 2 0 10 46 73 1550 2 0 14 SAI @ TSH +0.03 2900 2 0 17 3400 2 0 13 3900 2 0 15 4350 2 0 11 SAI - Single Axial Indication SCI - Single Circumferential Indication MCI - Multiple Circumferential Indication SBH - Bottom Hot Leg Sleeve TSH - Top of Tubesheet Hot Leg Actions to Prevent Recurrence All tubes with detected degradation at the top of the tubesheet were plugged in Steam Generator A. Additionally, all tubes with circumferential crack indications were stabilized and plugged. Callaway Plant anticipates similar degradation discovered in Refuel 12 at the end of Cycle 13. This is based on industry operating experience with Alloy 600 LTMA tubing and plant specific inspections results for the last 6 inspections. Callaway Plant will continue to perform a 100% top of tubesheet inspection with a RPC probe to the H-star distance during the next scheduled inspection. Callaway Plant anticipates replacing the existing steam generators in Refuel 14 with new Steam Generators utilizing Alloy 690 TT tubing. Industry experience has shown that this tubing is less susceptible to stress corrosion cracking.

Callaway Plant will continue to follow the requirements of NEI 97-06 and the referenced EPRI guidelines for future cycles of operation. These guidelines include maintaining primary and secondary water chemistry below recommended levels, primary to secondary leakage monitoring, inspection scope and frequency, pressure testing Page 7 of 8

degraded tubes, and performing integrity assessments to ensure tube structural and leakage integrity.

The Condition Monitoring and Preliminary Operational Assessment, performed in accordance with the EPRI Integrity Assessment Guidelines, during Refuel 12 addresses the as-found condition of the steam generator tubing and justifies operation for Cycle 13.

The assessment is based on degradation identified and conservative analysis to assure tube structural and leakage integrity for the entire cycle length.

Page 8 of 8

ATTACHMENT 1 - INDICATIONS IDENTIFIED IN STEAM GENERATOR A DURING REFUEL 12 ROW COL REPAIR REASON FOR IN-SERVICE REPAIR HOT LEG COLD LEG 1 34 PLUGGED PLUGGED MVI @ 01C -0.39 NO 11 68 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.12 NO 11 98 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.06 NO 12 64 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.23 NO 12 65 PLUGGED PLUGGED SAI @ TSH +0.1 NO 12 99 PLUGGED PLUGGED SVI @ TSH +0.07 NO 13 66 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.16 NO 13 75 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.16 NO 14 83 PLUGGED PLUGGED SAI @ TSH +0.08 NO 15 48 PLUGGED PLUGGED SVI @ 07H +0.26 NO 16 72 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.17 NO 17 43 PLUGGED PLUGGED SCI @ TSH -0.1 NO 17 51 PLUGGED PLUGGED SAI @ TSH +0.12 NO 17 101 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.06 NO 18 42 PLUGGED-STABILIZED PLUGGED MCI @ TSH -6.02 NO 18 44 PLUGGED-STABILIZED PLUGGED SCI @ TSH -0.96 NO 18 49 PLUGGED PLUGGED MAI @ TSH +0.01 NO 18 50 PLUGGED PLUGGED SAI @ TSH -0.01 NO 19 42 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.05 NO 19 68 PLUGGED-STABILIZED PLUGGED MCI @ TSH +0.24 NO 19 69 PLUGGED-STABILIZED PLUGGED SCI @ TSH -5.45 NO 20 39 PLUGGED PLUGGED SAI @ TSH -0.01 NO 20 50 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.11 NO 20 82 PLUGGED PLUGGED SAI @ TSH +0.08 NO 21 45 PLUGGED-STABILIZED PLUGGED SCI @ TSH -2.3 NO 21 59 PLUGGED PLUGGED SAI @ TSH +0.09 NO 21 64 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.06 NO 22 58 PLUGGED PLUGGED SAI @ TSH +0.05 NO 22 72 PLUGGED PLUGGED SAI @ TSH +0.07 NO 23 43 PLUGGED-STABILIZED PLUGGED SCI @ TSH -0.33 NO 23 78 PLUGGED-STABILIZED PLUGGED SCI @ TSH -7.88 NO 23 84 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.16 NO 23 97 PLUGGED-STABILIZED PLUGGED SCI @ TSH -8.4 NO 24 80 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.2 NO 24 88 PLUGGED-STABILIZED PLUGGED SCI @ TSH -5.6 NO 24 103 PLUGGED PLUGGED SAI @ TSH +0.1 NO 25 62 PLUGGED PLUGGED SAI @ TSH +0.06 NO 25 71 PLUGGED PLUGGED MCI @ SBH-1.72 NO*

25 88 PLUGGED PLUGGED SAI @ TSH +0.1 NO 25 91 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.00 NO 25 99 PLUGGED PLUGGED SAI @ TSH +0.00 NO 26 53 PLUGGED-STABILIZED PLUGGED SCI ( TSH -2.59 NO SAI @ TSH +0.06 NO 26 77 PLUGGED-STABILIZED PLUGGED MCI @ TSH +0.11 NO 26 109 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.07 NO 27 60 PLUGGED PLUGGED SAI @ TSH +0.05 NO 27 68 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.07 NO 27 83 PLUGGED-STABILIZED PLUGGED MCI @ TSH +0.05 NO Page 1 of 3

ATTACHMENT 1 - INDICATIONS IDENTIFIED IN STEAM GENERATOR A DURING REFUEL 12 ROW COL REPAIR REASON FOR IN-SERVICE REPAIR HOT LEG COLD LEG 27 100 PLUGGED-STABILIZED PLUGGED MCI @ TSH +0.14 NO 30 64 PLUGGED PLUGGED SAI @ TSH -0.03 NO 31 76 PLUGGED PLUGGED SAI @ TSH +0.08 NO 31 101 PLUGGED PLUGGED SAI @ TSH +0.13 NO 32 65 PLUGGED-STABILIZED PLUGGED SCI @ TSH -3.18 NO 32 82 PLUGGED PLUGGED SAI @ TSH +0.07 NO 33 74 PLUGGED PLUGGED SAI @ TSH +0.08 NO 33 108 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.08 NO 34 73 PLUGGED-STABILIZED PLUGGED SCI @ TSH -3.53 NO 34 80 PLUGGED-STABILIZED PLUGGED SCI @ TSH -4.76 NO 34 89 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.05 NO 34 98 PLUGGED PLUGGED SAI @ TSH +0.08 NO 37 83 PLUGGED PLUGGED SAI @ TSH +0.06 NO 38 88 PLUGGED PLUGGED SAI @ TSH +0.05 NO 39 37 PLUGGED PLUGGED 42% @ AV5 +0.15 NO 40% @ AV4 +0.00 NO 39 41 PLUGGED PLUGGED 42% @ AV4 -0.05 NO 39 61 PLUGGED PLUGGED SAI @ TSH +0.00 NO 39 83 PLUGGED PLUGGED SAI @ TSH +0.04 NO 39 88 PLUGGED-STABILIZED PLUGGED SCI @ TSH -1.98 NO 39 90 PLUGGED PLUGGED SAI @ TSH +0.02 NO 39 92 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.13 NO 41 54 PLUGGED PLUGGED SAI @ TSH +0.00 NO 41 82 PLUGGED PLUGGED SAI @ TSH +0.06 NO 41 95 PLUGGED PLUGGED MAI @ TSH +0.03 NO 42 62 PLUGGED-STABILIZED PLUGGED SCI @ TSH -0.62 NO 43 36 PLUGGED PLUGGED SVI @ TSH +0.03 NO 44 35 PLUGGED PLUGGED SVI @ TSH +0.09 NO 44 36 PLUGGED PLUGGED SVI @ TSH +0.13 NO 44 59 PLUGGED PLUGGED SAI @ TSH +0.05 NO 44 62 PLUGGED-STABILIZED PLUGGED SCI @ TSH -0.67 NO 44 75 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.09 NO 44 81 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.1 NO 46 48 PLUGGED PLUGGED 47% @ AV2 +0.00 NO 41% @ AV3 +0.00 NO 44% @ AV4 +0.00 NO 46 50 PLUGGED PLUGGED MAI @ TSH +0.00 NO 46 61 PLUGGED-STABILIZED PLUGGED MAI @ TSH -0.75 NO SCI @ TSH -0.74 NO 46 73 PLUGGED PLUGGED SAI @ TSH +0.03 NO 47 49 PLUGGED PLUGGED SAI @ TSH +0.00 NO 47 50 PLUGGED PLUGGED SAI @ TSH +0.01 NO 47 57 PLUGGED PLUGGED SVI @ FBH +0.07 NO 48 61 PLUGGED-STABILIZED PLUGGED SCI @ TSH -0.98 NO 48 70 PLUGGED-STABILIZED PLUGGED SCI @ TSH +0.06 NO Page 2 of 3

ATTACHMENT 1 - INDICATIONS IDENTIFIED IN STEAM GENERATOR A DURING REFUEL 12 ROW COL REPAIR REASON FOR IN-SERVICE REPAIR HOT LEG COLD LEG 49 48 PLUGGED PLUGGED SAI @ TSH +0.02 NO 59 62 PLUGGED PLUGGED SAI @ TSH +0.17 NO 59 167 PLUGGED PLUGGED SVI @ 02C +0. 13 NO

• Tube 25-71 does not require additional stabilization due to a 12.00" Westinghouse Laser Welded Sleeve installed at the Hot Leg Tube Sheet area.

SAI Single Axial Indication MAI Multiple Axial Indication SCI Single Circumferential Indication MCI Multiple Circumferential Indication SVI Single Volumetric Indication MVI Multiple Volumetric Indication TSH Tube Sheet Hot TSC Tube Sheet Cold AV# Anti-Vibration Bar (where # is the anti-vibration bar number)

O1H First Support Plate Hot TSH Top of Tubesheet Hot SBH Bottom of Sleeve Hot Page 3 of 3