ML20078S716
| ML20078S716 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/20/1994 |
| From: | Ohanlon J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 94-642, NUDOCS 9412290153 | |
| Download: ML20078S716 (4) | |
Text
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g VINGINIA ELECTHIC AND Powen COMPANY RICIIMOND,VildOINIA 202 01 December 20, 1994 U. S. Nuclear Regulatory Commission Serial No.94-642 Attention: Document Control Desk NAPS /MAE R5 Washington, D.C. 20555 Docket Nos.
50-338 l
50-339 License Nos. NPF-4 j
/
i Gentlemen:
l l
VIRGINIA ELECTRIC AND POWER COMPANY l
NORTH ANNA POWER STATION UNIT NOS. ~1 AND 2 l
ULTRASONIC TESTING CONCERNS i
INSPECTION REPORT NOS. 50-338/94-23 AND 50-339/94-23 NRC Inspection Report Nos. 50-338/94-23 and 50-339/94-23, dated October 26,1994, i
documented the results of a routine announced inspection conducted in the areas of Inservice examination of safety related welds, eddy current testing of steam generator tubing, and engineering plant modifications of high head safety injection flow i
instrumentation. This inspection was conducted on September 26 through 30,1994, j
for North Anna Power Station. The inspection identified unresolved item 338,339/94-23-01, " Credibility of Previous UT Examinations of S/G Upper-Head to Shell Welds l
Subject to Question." We have a comment on the concerns expressed by the inspector regarding the credibility of our weld examination process.
i j
lt was stated in the inspection report that the inspector observed calibration activities l
and the inprocess ultrasonic (UT) examinations on the upper head to shell circumferential seam of the Unit 1 "B' steam generator. The inspector expressed j
concern over the credibility of earlier examinations performed on this and
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corresponding welds in the other steam generators of Units 1 and 2. This was based l
on 1) the inservice inspection group was not aware of the actual weld size thickness j
and the thickness variation in the area of interest as evidenced by the fact that three j
different calibrations were required befc,re a credible examination could be performed, j
- 2) the baseline records for this weld showed no evidence to indicate that this variation 1
in material thickness was utilized for the sweep range calibration for the preservice l
examination of this weld, and 3) records reviewed of the corresponding weld in steam j
gen estor "C" showed no evidence to verify that as built weld size thickness was used for Eiibration purposes. Because of these concerns, the inspector stated that the cr.a.bility of examination of corresponding welds in steam generators on both units was in question and would have to be verified by examination on the next scheduled j
outage for each of the units.
i Virginia Electric and Power Company has reviewed completed examination reports for
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the upper head to shell circumferential seam welds and the main steam nozzle to head welds for steam generators which were required to be inspected during the first and second ten year interval for both units. Five sets of Unit 1 examination reports were identified which indicate that the ultrasonic test equipment was calibrated for a i
i 9412290153 941220 DR ADOCK 05000338 I} i PDR y,
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material thickness of 3.75 inches. Based on original fabrication information, the i
maximum material thickness in the required examination area may be less than 3.75 j
inches or as high as 4.00 inches.
At this time, we believe that the entire examination area was properly examined.
Therefore, this is not considered to be an operability problem. However, since the j
material thickness is not required to be recorded at the time of the examination, it cannot be verified that the material thicknesses identified in the five sets of test results -
l
' do not exceed 3.75 inches. It is estimated that in the worst case, assuming the i
material thickness was 4.00 inches, approximately 99% of the area would have been
. examined assuming no additional interferences. This area is shown on the attached sketch.
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The five sets of test results involve the Unit 1 upper head to shell circumferential seam i
welds on steam generators "A" and "C" and the Unit 1 main steam nozzle for steam generator "C." The material thickness of these areas will be determined during the next Unit 1 refueling outage, which is currently scheduled for March 2,1996. If it is determined that the material thicknesses are greater than 3.75 inches, these areas will j
be reexamined. All other Unit 1 test results showed that the ultrasonic test equipment i
had been calibrated for a material thickness of rapproximately 4.9 inches or greater.
i All of the Unit 2 examination reports had a calibration depth of at least 5.00 inches.
i Therefore, since the maximum material thickness in the examination area is 4.00 inches, it can be assured that the entire examination area'was examined, and no additional measurements are required for the Unit 2 steam generators.
i it was determined during the inspection that a note on drawings which are used to-
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perform this examination for both units was incorrect. The note stated that the material i
thickness in the area of examination is 3.62 inches. It has been determined that the i
note should have indicated that 3.62 inches was the minimum material thickness i
expected. A drawing change request has been submitted. The drawings will be j
revised prior to the next refueling outage, which is the Unit 2 outage currently j
scheduled for March 25,1995.
l If you have any questions, please contact us.
i Very truly yours, i
l t21hL4 l
James P. O'Hanlon j
Senior Vice President - Nuclear i
Attachment j
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i oc:
' O. S. Nuclear Regulatory Commission
', Region 11 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia 30323 Mr. R. D. McWhorter NRC Senior Resident inspector North Anna Power Station we+w ee i.--+,
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AREA POSSIBLY NOT EXAMINED (WORST CASE SCENARIO)
EXAM. VOLUME A-B-C-D=10.77 Sq. In.
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