ML20063G322
| ML20063G322 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 02/09/1994 |
| From: | Bowling M VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 94-013, 94-13, NUDOCS 9402160017 | |
| Download: ML20063G322 (7) | |
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VikOINIA ELucTurc ann Powna COMPANY NICIIMOND,VIHUINIA 232 61 February 9, 1994 U.S. Nuclear Regulatory Commission Serial No.94-013 Attention: Document Control Desk NA&F/JRH/jbl R1 Washington, D.C. 20555 Docket Nos.
50-338 50-339 License Nos. NPF-4 NPF-7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY HORTH ANNA POWER STATION UNITS 1 AND 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REACTOR VESSEL WELD UPPER SHELF ENERGY As requested during our teleconference with your staff on December 3,1993, the attached information provides additional data to support our estimates of the initial upper shelf energy for the North Anna Units.1 and 2 reactor vessel nozzle-to-intermediate shell welds (Welds Nos. 05A and 05B).
Based on our review of this information and information previously provided to the NRC in response to Generic Letter 92-01, Rev.1, we conclude that we have demonstrated current compliance with regulations governing reactor vessel integrity for North Anna Units 1 and 2. Further, we conclude that sufficient information has been provided to demonstrate compliance with applicable reactor vessel integrity regulations through the end-of-license, pending confirmation of actual fluences experienced by each unit's reactor vessel.
If you have any fudher questions, please contact us.
Very truly yours,
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M. L Bowling, Manager Nuclear Licensing & Programs i
Attachment
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U.S. Nuclear Regulatory Commission Region ll 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. R. D. McWhorter NRC Senior Resident inspector North Anna Power Station i
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F Attachment i
Response to NRC Request for Additional Information Reactor Vessel Weld Upper Shelf Energy.
North Anna Units 1 and 2 F
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Response to Request for Additional Information Generic Letter 92-01, Rev.1, Response for North Anna Units ! and 2 initial Upper Shelf Energy for Nozzio to Intermediato Shell Welds 05A and 058 i
Backnround In the Virginia Electric and Power Company response to Generic Letter 92-01, Rev.1, for North Anna Units 1 and 2 (BAW-2168, Rev.1, dated September 1992), the Unit 1 Nozzle to intermediate Shell Weld 05A was designated the limiting Unit 1 weld material in terms of the proximity of its irradiated upper shelf energy to the 50 ft-lb threshold at end-of-license. (See North Anna Unit 1, Table 2 of BAW-2168, Rev.1.) A footnote to this designation indicated that the initial upper shelf energy for this material was an estimated value. By letter dated July 29,1993, the NRC requested substantiation of the 90 ft-Ib estimate for the initial upper shelf energy of Weld 05A for both North Anna Units 1 and 2. The following response was provided:
The initial CvUSE value of 90 ft-Ib reported in the North Anna 1 and 2 Response to Generic Letter 92-01 (BAW-2168, Rev.1) is an estimate based on the lower bound of available data on similar materials (SMIT welds). As documented in BAW-1911, Rev.1 (" Reactor Pressure Vessel and Surveillance Program Materials Licensing information for North Anna Units 1 and 2," dated August,1986),
l measured CvUSE data is available for four SMIT welds: Unit 1 Weld WO4 (102 l
ft-Ib); Unit 1 Surveillance Weld Material WO4 (95 ft-lb); Unit 2 Weld WO4 (107 ft-lb); and Unit 2 Surveillance Weld Material WO4 (115 ft-lb). A conservative lower bound of these values is 90 ft-lb, The response to the NRC RAI also provided design basis end-of-license CvUSE calculations for the North Anna Units 1 and 2 05A welds. For Unit 1, the copper concentration and fluence suggested a decrease in upper shelf energy of 30%, resulting in an end-of-license CvUSE of 63 ft-lb. For Unit 2, the copper concentration and fluence suggested a decrease in upper shelf energy of 22%, resulting in an end-of-license CvUSE of 70.2 ft-Ib.
Similar calculations of irradiated CvUSE based on the 90 ft-Ib initial CvUSE estimate were provided for the North Anna Units 1 and 2 05B welds (Nozzle to intermediate Shell, 6% inside diameter). For both Units 1 and 2, the copper concentration and fluence values suggested decreases in upper shelf energy of 19%, resulting in end-of-license CvUSE values of 72.9 ft-lb. The Weld 05B calculations were based on inner surface fluences, since the 05B welds represent only the inner 6% of the nozzle to intermediate shell weld.
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NRC ' Comments l
in subsequent teleconferences with members of NRC staff, the Virginia Electric and Power Company method for determining the initial CvUSE values for the 05A and 058 welds was discussed. The NRC indicated that the weld wire heats for North Anna Unit 1 Weld 05A (25295), Unit 1 Weld 05B (4278), Unit 2 Weld 05A (4278), and Unit 2 Weld 05B (801) were not represented in the then-available initial upper shelf energy data for Rotterdam-fabricated welds. It was suggested by the NRC that Virginia Electric and Power Company attempt to find additional Rotterdam weld data to match the North Anna weld wire heats.
Additional Rotterdam Wold Data The following Rotterdam data have been located by both Virginia Electric and Power Company and the NRC:
Plant Wire Type Wire Heat CvUSE Catawba Ni Mo 895075 128 McGuire 2 Ni Mo 895075 132 North Anna 1 SMIT 40 25531 95 North Anna 2 S3 Mo 716126 115 1
Sequoyah 1 SMIT 40 25295 111 Sequoyah 2 S4 Mo 4278 105 Surry 2 S3 Mo 0227 91 Watts Bar 1 Ni Mo 899680 131 Watts Bar 2 S3 NiMo 895075 139 North Anna 1 SMIT 40 25531
- 102 North Anna 2 S3 Mo 716126**
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- During a teleconference, the NRC indicated that their materials database lists this weld wire heat as 25295. This CvuSE value is for North Anna Unit i Weld 04, weld wire heat 25531, as documented in BAW-1911, Rev.1, Table 2-3, and in our tetter dated December 11,1978 (" Pressure Vessel Fracture Toughness Properties, North Anna Units 1 and 2"). The North Anna Unit 1 surveillance weld is Weld 04.
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" During a teleconference, the NRC indicated that their materials database lists this weld wire heat as 4278 This CvUSE value is for North Anna Unit 2 Weld 04, weld wire heat 716126, as documented in BAW-1911, Rev.1, Table 2-10, and in our letter dated December 11,1978 (" Pressure Vessel Fracture Toughness Properties, North Anna Units 1 and 2"). The North Anna Unit 2 surveillance weld is Weld 04, j
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.This data increases our confidence in our 90 ft-lb lower bound initial CvUSE estimate for Rotterdam welds previously provided to the NRC.
1' Use of Sequoyah Units 1 and 2 Data for North Anna Units 1 and 2 05A Welds
-I and for the North Anna Unit 1 OSB Weld L
Measured data for the initial CvuSE of the North Anna Unit 1 Weld 05A wire heat (25295) is available from the Sequoyah Unit 1 surveillance program. On this basis the North Anna Unit 1 unirradiated CvUSE is estimated to be 111 ft-Ib, resulting in a calculated end-of-license CvUSE of:
111 * (1-0.30) = 77.7 ft-Ib.
Similarly, measured data for the initial CvUSE of the North Anna Unit 2 Weld 05A wire l-heat (4278) is available from the Sequoyah Unit 2 surveillance program. On this basis, L
the North Anna Unit 2 unirradiated CvUSE is estimated to be 105 ft-lb, resulting in a
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calculated end-of-license CvUSE of:
105 * (1-0.22) = 81.9 ft-Ib.
l The Sequoyah Unit 2 surveillance program CvUSE data is also applicable to North Anna l
Unit 2 Weld 05B (wire heat 4278). Based on an initial CvUSE of 105 ft-Ib, the North Anna Unit 2 Weld 05B is predicted to have an end-of-license CvUSE of:
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105 * (1-0.19) = 85.1 ft-lb.
As previously noted, the predicted 19% reduction in CvUSE for Weld 05B is based on l
an inner surface fluence, since weld 05B represents only the inner 6% of the nozzle to-intermediate shell weld.
No surveillance data is available for the Unit 2 058 weld (wire heat 801). However, because the 05B welds represent such a small fraction of the nozzle to intermediate shell weld (i.e., much less than the size of the design basis quarter-thickness flaw), the lack of initial CvUSE data for Unit 2 Weld 05B is inconsequential to calculations of margin to vessel fracture. In addition, the predicted percentage decrease in CvUSE for the 05B welds is bounded by that of the 05A welds. Therefore, further evaluation of Weld 05B is unnecessary.
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.o Conclusion l
Measured data for the initial CvUSE of the' North /.nna Unit 1 Weld 05A (wire heat 25295) is available from the Sequoyah Unit 1 surveillance program. Likewise, measured data for the initial CvUSE of the North Anna Unit 1 Weld 05B.and Unit 2 Weld 05A (wire i
heat 4278) is available from the Sequoyah Unit 2 surveillance program. Based on this -
data, end-of-license CvUSE values in excess of 50 ft-lb have been calculated for the North Anna Unit 1 and 2 05A welds and Unit 105B weld.
Because the North Anna Units 1 and 2 05B welds represent such a small fraction of the nozzle to intermediate shell weld (i.e., much less than the size of the design basis quarter-thickness flaw), the lack of initial CvUSE data for Unit 2 Weld 05B is
' inconsequential to calculations of margin to vessel fracture. Therefore, Virginia Electric and Power Company concludes that further evaluation of Weld 05B is unnecessary.
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