ML17334A687

Forwards follow-up Info Re Final Results of Metallographic Exam Performed on Sample of SG Tubing Removed During 1997 SG Insp.Exam Conducted in Support of GL 95-05

ML17334A687
Person / Time
Site:	Cook
Issue date:	03/13/1998
From:	Fitzpatrick E INDIANA MICHIGAN POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
AEP:NRC:1166AN, GL-95-05, GL-95-5, NUDOCS 9803200076
Download: ML17334A687 (8)

Text

CATEGORY 1 REGULAY'MFORMATYOE DYSTRYBUTYOOSYSTEM (RYDS)

ACCESSION NBR:9803200076 DOC.DATE: 98/03/13 NOTARIZED: NO DOCKET FACIL-."50-315, Donald C.

Cook 'Nuclear Power Plant, Unit 1, Indiana M

05000315 50-316 Donald C.

Cook Nuclear Power Plant, Unit 2, Indiana M

05000316 AUTH.NAME AUTHOR AFFILIATION FITZPATRICK,E.

Indiana Michigan Power Co.

RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Forwards follow-up info re final results of metallographic exam performed on sample of SG tubing removed during 1997 SG insp.Exam conducted in support of GL-95-05.

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Indiana Michigan Power Company 500 Circle Drive Buchanan, Ml 491071395 INSIDE&f/l MICHIGAN POWER March 13, 1998 Docket No.: 50-315 AEP: NRC: 1166AN U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop 0-Pl-17 Washington, D.C. 20555-0001 Gentlemen:

Donald C.

Cook Nuclear Plant Unit 1 STEAM GENERATOR TUBE INSPECTION FOLLOW-UP TUBE SAMPLE REPORT This letter and its attachment provide follow-up information concerning the final results of the metallographic examination performed on a sample of steam generator (SG) tubing removed during our unit 1 1997 SG inspection.

This examination was conducted in support of generic letter 95-05.

Preliminary results were included in our unit 1 SG ninety day tube inspection report submitted in our letter AEP:NRC:1166AI, dated July 21, 1997.

Sincerely, E.

E. Fitzpatr ck Vice President

/vlb Attachments J.

A. Abramson A. B. Beach MDEQ -

DW & RPD

'NRC Resident Inspector J.

R.

Sampson I

P gc)'E 9803200076 9803i3 PDR ADQCK 050003i5 P

PDR IIIIIIIIilllllll!II!!Ii!!III'

ATTACHMENT TO AEP:NRC:1166AN STEAM GENERATOR TUBE INSPECTXON FOLLOW-UP TUBE SAMPLE REPORT

B Attachment to AEP:NRC:1166AN Page 1

INTRODUCTION During the Cook Nuclear Plant unit 1 1997 refueling outage, a steam generator (SG) tube sample was removed for the purpose of defect characterization and tube material data for compliance with generic letter 95-05, "Voltage Based Criteria for Westinghouse Steam Generator Tubes Affect'ed by Outside Diameter Stress Corrosion Cracking".

Preliminary results from the then in progress inspection were presented in our ninety day SG inspection

report, our letter AEP:NRC:1166AI, dated July 21, 1997.

The examination has since been completed and the final report was recently issued.

Tube R8/C19 was removed from SG-12 to below the fourth tube support plate (TSP).

Sections from the tube underwent a

series of laboratory examinations.

The primary area of interest for the examinations were the three TSP regions.

A summary of the report findings are presented below.

EXAMINATION

SUMMARY

Leak Testin Helium leak testing of the three tube sections containing TSP intersections was performed.

The inside diameter of the tubes was placed under a vacuum, while the outside diameter (OD) was placed under a helium blanket.

The tubes were held at test conditions for ten minutes with no leakage observed.

The leak detection limit was 1.6E-8 cc/sec.

Additionally, hydrostatic leak testing was performed on the two tube sections encompassing the first and second TSP regions.

Test pressures simulated normal operation and steam line break conditions'either tube segment exhibited throughwall leakage.

Burst Testin Burst testing of TSP and freespan regions indicated burst pressures in excess of 7,000 psi in all instances.

These results are well in excess of the minimum NRC structural requirements (3 delta P) contained in RG 1.121.

Table 1 summarizes the results for each location.

Note that the burst pressure for the first TSP region was confirmed to exceed 7,000 psi; however, operator error involving a mispositioned valve prevented a more accurate reading.

Table 1

Burst Test Data Location Burst Pressure (psi)

First TSP Freespan Second TSP 7,000

• 9, 980 9,326

• Ina vertent urst ue to operator error, 7,000 ps'epresents the minimum pressure certified by operator.

Attachment to AEP:NRC:1166AN Page 2

Edd Current Testin Laboratory eddy current testing was performed using the same probes and techniques utilized for the field examination.

Table 2 summarizes the results from the field and laboratory eddy current examinations, along with the results from the subsequent reviews of field data.

With the exception of the dents detected by the laboratory bobbin coil probe at 2H and 3H, which were not present in the field data, there were no significant differences between the field and laboratory eddy current signals.

Field eddy current data was re-reviewed, and the dent signals were confirmed to not have been present in the original data.

It was concluded that the dents were a result of tube sample removal operations.

Table 2

Field and Laboratory Eddy Current Testing Comparison Unit 1, SG-12, Tube R8/C19 Loc.

ECT - Field Results ECT - Field Comments ECT - Lab Results 1H 2H 3H BC:

DSI (1.16 volts)

RPC:

SAI (1.04 volts 111 phase angle)

BC:

DSI (0.87 volts)

RPC:

MAI (1.10 volts, 133 phase angle)

NDD OD 40%

TW by phase angle using 400/

100 kHz process channel; No dents; indication confirm-ed to be within TSP crevice OD 40%

TW by phase angle using 400/100 Khz process channel; No dents; Indication confirm-ed to be within TSP crevice No dents BC:

DSI (4 volts, shallow OD IGA)

RPC:

SAI (1. 11

volts, 115 phase angle)

BC:

Signal distorted by 16.69 volt dent RPC:

MAI (0.88 volt 134 phase angle)

BC:

DNT (11.22 volts)

Key:

BC DNT DSI MAI NDD OD RPC SAI TW Bobbin coil Dent Distorted signal at intersection Multiple axial indication No defect detected Outside diameter Rotating pancake coil Single axial indication Throughwall Metallo ra hical Examinations and Crack De th Measurements Metallographic examinations of the transverse sections from each of the three TSP regions indicated that

shallow, OD-initiated, intergranular attack (IGA),

and intergranular stress corrosion cracking (ZGSCC) were present, and that the cracking was axially

e Attachment to AEP:NRC:1166AN Page 3

aligned (no cellular IGA).

The predominant defect morphology was characterized as axial, OD-originated IGSCC.

Tube degradation was confined to the TSP regions.

Maximum crack depths observed during the metallographic examination

'of the three TSP regions were 41.6%,

36%,

and 23.6% throughwall, respectively.

Note that the later crack depth (23.6% at 3H) was observed after the tube had been swelled by approximately 10%

radial strain to facilitate visual inspections.

Therefore, it is not unexpected that this indication was not identified during the eddy current inspection as it was evidently at the lower threshold of eddy current detection based on the review of both the field and laboratory eddy current test results.

The maximum depths of the IGA/IGSCC on the burst rupture surfaces of the first and second TSPs was 50% and 40%, respectively.

The following table summarizes the crack depth results from both metallographical and scanning electron microscope analysis.

Table 3

Summary of Crack Depth Measurements (Inches, 0 Throughwall)

Location Metallography Typ 0 Max o Scan Elec. Micr.

Max+

First TSP Second TSP Third TSP 0.0046 9.2%

0. 010

'9.3%

0.002 3.7%'.

021 41.

6%'.018 36%

0.012 23.

6%'.012 24

~ 4 ~o 0.008 16'ot Measured

0. 025 50%

0. 020 40%'ot Measured Other Examinations Scanning electron microscope/electron dispersive spectroscopy and wavelength dispersive spectroscopy typically found

aluminum, silicon,

calcium, magnesium, manganese and iron oxides on the surface of the TSP regions, as well as the presence of low levels of lead and sulfur on the IGA/IGSCC and outer diameter surfaces of the tube.

These results were confirmed through Auger/x-ray photoelectron spectroscopy

analysis, which also indicated that nickel/chromium ratios were consistent with basically neutral pH conditions.

Tensile

testing, microhardness, bulk chemistry, Huey testing, deposit

analyses, and microstructural characterization did not indicate any abnormal conditions in the tube.

Conclusions The above inspection results confirm that the dominant degradation mechanism is axially orientated outside diameter stress corrosion cracking that is confined within the TSP regions.

No evidence of detectable crack-like circumferential indications were noted.

These findings remain consistent with previous tube pull results and eddy current testing.