ML20058N142
| 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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.WM 90-0139-O u,
Ue S. Nuclear Regulatory Comunission-
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- ATTN: Document Control. Desk f
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Docket No. 50-482: Response to Inspection Report 90-08~
Subject:
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! Gentlemen:
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' Attached,is.WolfCreek. Nuclear. Operating ^ Corporation's'/WCNOC))responseto
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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 of.the effectivenese of.the techniques utilized at Wolf. Creek -Generating.
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- Station; (WCGS) and concluded that the existing erosion-corrosion program is-
' effective in; identifying wall thinning due'to inside diameter pitting as
- well~as non-relevant volumetric anomalies..
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', (g LIfQyou: have 'any questions' concerning this matter,- please contact me or.
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Mr.:H.'K.:Chernoff of my staff.
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,Very truly yours,
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-Bart D. Withers a
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President and
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Chief Executive Officer.
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LD. V.': Pickett (NRC), w/a yg '
-M. E. Skow (NRC),- w/a Q[
J. S. Wiebe (NRC),.w/a g%
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An Equal opportursty Empteyer 84FACVET
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' Attachment to WM 90-0139'
'Page 1.of 3 J.
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y desponse to Inspection Report 90-08
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.G9AGM.GE I
.The results of the. examination for erosion / corrosion'of selected components.
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4 from the- -EssentialL Service Water System revealed isolated. areas that:
appeared to have pits'or material-anomalies.
Thickness measurements.tsken.
Lby the NRC inspectors were compared to'those taken by the licensee to verify b
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creas which may be below. minimum wall thic;:nes s.
LBecause of the' two 1
different instruments.used -in taking measutements'(NRC used a Nova-D100' 1-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.
~ ignificant. enough -to The indications identified did not Jappear to be s
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
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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 The,results of the_ review'are discussed:below.
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.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
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- pipe.
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-Attachment to WM 90-0139 is Page=2 of 3 p
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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
- thickne s s. violations with possible isolated pits a= follow-up examination is j
a-i performed using a -Krautkrame-Branson..USD-10.
This methodology is, 4
M consistent. with the vendor reconsnendations for: the DMX-1.
The vendor 1
[2 recommendations indicate.thatL during testing if ! the: instrument.(DMX-1)_
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
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'an ultrasonic flaw detection instrument or other suitable nondestructive.
a testing method to determine the cause:of-the suspicious reading.
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The USD is' a state-of-the-art,.
versatile flaw detection instrument utilized to evaluate =an: size small anomalies found during erosion-corrosion:
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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
This is based on an i
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= significant volumetric flaws -were identified.-.
H evaluation of the:USD-10 signal that displayed a'back wall l reflection =at the.
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nominal wall value (0.350').
The signal from.the anomaly was-the same-
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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'-
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t 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 are consistent with the NRC's with:the exception of location 13E.
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reading is surrounded by readings consistently at.350" or above indicating 4
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-an. isolated reading.
- As mentioned above,' an examination and_ evaluation.
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..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
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4 corrosion cracking (IGSCC) flaw detection.
Examinations ueing'the DMX-1 and j
the USD-10 are performed by Level II examiners.
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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3 NOVA D-100-
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'As tested Leondition '
Screen displaya 6 mha 1ransduoer e
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- ftrat* stgnal back i
displayed as wall -
thickness -
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Pack wall reflection.
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ror 0.356 -
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.350".
Back wall- @
inclusion indication noted. in noise level-j k
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