ML021900451
| ML021900451 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 07/02/2002 |
| From: | Grecheck E Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 01-490G, BL-01-001 | |
| Download: ML021900451 (6) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 July 2, 2002 U.S. Nuclear Regulatory Commission Serial No.
01-490G Attention: Document Control Desk NL&OS/ETS RO Washington, D.C. 20555 Docket Nos.
50-338/-339 License Nos.
NPF-4/-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNITS 1 AND 2 REQUEST FOR ADDITIONAL INFORMATION RESPONSE TO NRC BULLETIN 2001-01 RESULTS OF REACTOR VESSEL HEAD PENETRATION INSPECTIONS In a letter dated June 13, 2002 (Serial No. 01-490F), Virginia Electric and Power Company (Dominion) provided a revised evaluation of the remaining service life for those penetrations with flaws identified during the recent inspections performed on reactor vessel head penetration (RVHP) nozzles for North Anna Units 1 and 2.
The flaws in the affected penetrations were initially evaluated and reported using WCAP-14552 methodology, which included an assumed flaw aspect ratio of 6:1.
However, some of the flaws found at North Anna had aspect ratios larger than 6:1.
Subsequently, additional curves were prepared for flaw aspect ratios of 15:1, 20:1, 30:1, 65:1 and 100:1.
Using the appropriate bounding aspect ratio, the flaws were reanalyzed for North Anna Units 1 and 2. In a July 1, 2002 telephone conference call, the NRC staff requested additional information regarding the flaws on the affected penetrations. The additional information for the affected penetrations is presented in the attachment to this letter.
If you have any questions or require additional information, please contact us.
Very truly yours, Eugene S. Grecheck Vice President - Nuclear Support Services Attachment
cc:
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23 T85 Atlanta, Georgia 30303-8931 Mr. M. J. Morgan NRC Senior Resident Inspector North Anna Power Station Mr. J. E. Reasor, Jr.
Old Dominion Electric Cooperative Innsbrook Corporate Center, Suite 300 4201 Dominion Blvd.
Glen Allen, Virginia 23060 Mr. M. Grace Authorized Nuclear Inspector North Anna Power Station
SN: O1-490G Docket Nos.: 50-338/339
Subject:
RAI - NRC Bulletin 2001-01 COMMONWEALTH OF VIRGINIA
) )
COUNTY OF HENRICO
)
The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Eugene S. Grecheck, who is Vice President Nuclear Support Services, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this 2nd day of July, 2002.
My Commission Expires: March 31, 2004.
rNotary Public (SEAL)
Attachment NRC Bulletin 2001-01, Circumferential Cracking of Reactor Pressure Vessel Head (RVHP) Penetration Nozzles Request for Additional Information Remaining Service Life of Identified Flaws In Reactor Vessel Head Penetration Nozzles North Anna Units 1 and 2 Virginia Electric and Power Company (Dominion)
Request for Additional Information on the Remaining Lifetime of Identified Flaws In Reactor Vessel Head Penetration Nozzles NRC Question 1 For all flaws on the CRDM penetration tubes having revised service life below 4 years, please provide their flaw lengths, depths, locations (distances below or above the tip of the J-groove weld for both flaw ends). Confirm that the original version of the revised curves that were used in your evaluation is Figure 6-1a of WCAP-14552, Revision 2.
Response
Penetrations With Life Less Than Four Years (The most limiting flaw is listed for each penetration)
North Anna Unit 1 Fla FawLocation for Location for Penetration Length DepthStr lFaEnofFw (mm)
(mm) 31 44 3.27 102 mm Below Tip of Weld 58 mm Below Tip of Weld 33 63 2.23 32 mmn Below Tip of Weld 31l mm Above Tip of Weld 52 26 1.7 80 mm Below Tip of Weld 54 mm Below Tip of Weld 60 45
<1 113mm Below Tip of Weld, 68 mm Below Tip of Weld North Anna Unit 2 62 Cluster*
-<1 60 mm Below Tip of Weld 53 mm Above Tip of Weld
- Number of short axial flaws The revised curves represent the same information that is provided on Figure 6.1a in Revision 2 of WCAP-14552 for different aspect ratios. These curves were also created with a different size of initial flaw.
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NRC Question 2 Provide stress, stress intensity factor, and crack growth rate values at a/t = 0.1, 0.2, 0.4, 0.6, 0.75, and 0.95 for Penetration 31 which has a revised service life of 2.37 years. In addition, provide detailed information on your stress calculation, including justification for considering or not considering residual and thermal stresses in your stress calculation.
Response
North Anna Unit 1 Penetration 31 Actual Aspect Ratio 13.45:1 (15:1 aspect ratio used)
+/-
4 4
0.2 38.4 26.819 29.50 4.93 X 1U U 9.31 x 10-1 0.4 38.4 45.952 50.55 2.11 x 10 -lu 0.6 38.4 70.221 77.24 3.76 x 10 -'u 0.7 38.4 85.60 94.16 4.86 x 10 -1U 0.8 38.4 101.935 112.13 6.06 x 10 -1u 0.9 38.4 119.176 131.09 7.37 x 10 -'u
- 38.40 ksi is the yield stress of the material. The applied stress is close to 38.4 ksi.
Minor fluctuations in the stress were observed because of the modeling of elements.
The total stress is from residual stress and pressure stress. The steady state thermal stress is insignificantly small. Thermal transient stresses were insignificant because the quick fluctuations do not affect stress corrosion cracking.
These locations experience very small fatigue.
- Crack Growth Rate = (2.800 x 10-12) (K - 9)1-16 m/sec at 3300 C. A temperature correction factor of 0.526 is applied to correct the growth rate to 3160 C. Crack growth rates in the last column must be multiplied by 0.526. The growth rate used in the North Anna analysis is (1.473 x 10-12) (K - 9)1 6' m/sec.
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