ML20058N142

Responds to Insp Rept 50-482/90-08 Re Effectiveness of Techniques Used to Detect Erosion/Corrosion Degradation. Existing erosion-corrosion Program Effective in Identifying Wall as Nonrelevant Volumetric Anomalies

ML20058N142
Person / Time
Site:	Wolf Creek
Issue date:	08/09/1990
From:	Withers B WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
WM-90-0139, WM-90-139, NUDOCS 9008130259
Download: ML20058N142 (4)

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' W$LF CREEK - NUCLEAR OPERATING CORPORATION 1 '

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.WM 90-0139-

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pX Ue S. Nuclear Regulatory Comunission-

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ATTN: Document Control. Desk  ;

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Subject:

Docket No. 50-482: Response to Inspection Report 90-08~

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. -i N  ! Gentlemen: .i

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' Attached,is.WolfCreek. Nuclear. Operating ^ Corporation's'/WCNOC))responseto 1

, the'. request'.to. review and evaluate the effectiveness of the techniques;being" -

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, , Jused-to detect erosion / corrosion degradation'. WCNOC has conducted ~s' review

,n of.the effectivenese of.the techniques utilized at Wolf. Creek -Generating. U

- Station; (WCGS) and concluded that the existing erosion-corrosion program is-

, ' effective in; identifying wall thinning due'to inside diameter pitting as m

- well~as non-relevant volumetric anomalies..

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', (g LIfQyou: have 'any questions' concerning this matter,- please contact me or.

,e?' Mr.:H.'K.:Chernoff of my staff.

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,Very truly yours,

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-Bart D. Withers '

a w a/ President and

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Chief Executive Officer. ,

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-M. E. Skow (NRC),- w/a Q[g%

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J. S. Wiebe (NRC),.w/a

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T 4 P.O. Box 411/ Burtington, KS 66639 / Phone: (316) 364 8831 (

An Equal opportursty Empteyer 84FACVET

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' Attachment to WM 90-0139'

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desponse to Inspection Report 90-08

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,; .G9AGM.GE I 4 .The results of the. examination for erosion / corrosion'of selected components. [

from the- -EssentialL Service Water System revealed isolated . areas that: I appeared to have pits'or material-anomalies. Thickness measurements .tsken.

Lby the NRC inspectors were compared to'those taken by the licensee to verify

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b creas which may be below. minimum wall thic;:nes s . LBecause of the' two 1 1

different instruments .used -in taking measutements'(NRC used a Nova-D100' '

-digital gage the licensee 'used a - Krautkramer - USD-10 ~ ~ Ultrasonic . Flaw' I! Detector)- there were areas that required further investigation, this was~ j accomplished by having.the NRC-inspector.and~the licensse's : inspector 'take the two instruments;and compare the individual thickness. readings - .Usings  ;

the! digital thickness' gage =the indications were. easily found and duplicated, however, the Ultrasonic ~ Flaw detector could not find the same indications. <

The indications identified did not Jappear to be ~s ignificant. enough -to threaten thefintegrity of the components. However, the issue was identified .l to-licensee management so that they can review the' effectiveness of the i techniques being used in the erosion-corrosion program and take any-appropriate correct.ive actions. .;

J Resoonse: l Wolf Creek Nuclear. Operating Corporation (WCNOC)' conducted a' review '.of the' ,

examination techniques used in the erosion-corrosion program.; TheLreview  !

encompassed-a comparison of the operating characteristics of the examination [

instruments utilized = byf the NRC and WCNOC examiners. a review of records 'j associated with the components selected for. examination by the NRC, .and 'a i review of the qualifications of the examined and subsequent evaluations- . t i

The,results of the_ review'are discussed:below. q

.The examination instrument used by the NRC contractors was a Nova' D100 i digital gage. This instrument is typic.al of all~ digital read-out' thickness y

' instruments, . including those used at Wolf Creek Generating Station (WCGS). 1 Thez digital instruments produce a. sound wave that when reflected off a d

. volumetric anomaly-(such as a small inclusion) or the inside diameter (I.D.)

of the pipe, the' signal is measured and displayed as a digital read-out. ,

The read-out will be the distance to the anomaly or the back wall; of the 'I

, - pipe.

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, -Attachment to WM 90-0139 'l is '. Page=2 of 3 p i c 3

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.f , For the. erosion-corrosion program, WCNOC uses'a Krautkramer..BransonJ DMX-l'

• digital _ ' read-out - . thickness gage for . initial exantinations. If the' initial-3 ,

' examination identifies wall: thickness violations- and :near -minimum wall ,

a- - thickne s s . violations with possible isolated pits a= follow-up examination is j performed using a -Krautkrame- Branson..USD-10.

4 i This methodology is, M consistent. with the vendor reconsnendations for: the DMX-1. The vendor 1 recommendations indicate.thatL during testing if ! the: instrument .(DMX-1)_ .

[2 suddenly reads-a value which is.much thinner than the apparent thickness of the part,; it may be reading the-distance to a flaw rather than the~ distance _

@( l- to the back wall. If the condition occurs, the.part should be examined with [

% 'an ultrasonic flaw detection instrument or other suitable nondestructive. a

, testing method to determine the cause:of-the suspicious reading.

m, The USD is' a state-of-the-art,. versatile flaw detection instrument f' utilized to evaluate =an: size small anomalies found during erosion-corrosion: -

J' j and Inservice Inspection examinations. The signal from the I.D.. surface as tw "'

well'as volumetric' anomalies will be detected and displayed; on~ the screen-which allows - evaluation of the signal. Figure 1. illustrates the D100 ando j g, the USD-10 displays. .

/7 WCNOC performed an. examination of the isolated areas that appeared to havej l anomalies with the DMX-1 instrument and identified the same anomalies.as the ,

NRC :had-. identified. A follow-up : examination using the =USD-10. was j performed. The areas. were -examined and no relevant. I.D. flaws or l

7 = significant volumetric flaws -were identified.- . This is based on an i H evaluation of the:USD-10 signal that displayed a'back wall l reflection =at the.

((" nominal wall value (0.350'). The signal from .the anomaly was- the same-

[ amplitude 1 he that contained in the noise level of the scope indicating.that the signal recorded-by the Nova D100 was.the result.!of a small material'- y y

'g anomaly (such as an inclusion). ['

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A review of examination records of the areas-identified.in Attachment #3a of-M[' the NRC. inspection report identified that the readings- by WCNOC ' examiners --

jl1 are consistent with the NRC's with:the exception of location 13E. This J

( reading is surrounded by readings consistently at .350" or above indicating j

4 l' -an . isolated reading. ;As mentioned above,' an examination and_ evaluation.

..using the USD-10 confirmed that there were no relevant indications.

." The L WCNOC examiner performing' the examination and evaluation is certified by ,

N Electric Power Research Institute (EPRI)~ in :intergranular stress corrosion cracking (IGSCC) flaw detection. Examinations ueing'the DMX-1 and

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4 the USD-10 are performed by Level II examiners.

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f' Based upon the above information, WCNOC has concluded that the existing b erosion-corrosion ' program is effective in identifying wall thinning due to S I.D. pitting as well as non-relevant volumetric-anomalies, si m'[

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NOVA D-100-

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• ftrat* stgnal back displayed as wall -

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Inclusion p- -Sa@ n us d# ror 0.356 - --

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Back wall- @ .350" .

inclusion indication noted. in noise level- ->

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