ML070120268
| ML070120268 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 01/09/2007 |
| From: | Gerald Bichof Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 06-1083, EA-03-009 | |
| Download: ML070120268 (12) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY
- RICHMOND, VIRGINIA 2326 1 January 9, 2007 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Serial No.
06-1 083 NLOSIETS R2 Docket No.
50-339 License No.
NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
NORTH ANNA POWER STATION UNIT 2 REVISED ASME SECTION XI INSERVICE INSPECTION PROGRAM RELIEF REQUEST PARTIAL EXAMINATION OF REACTOR PRESSURE VESSEL HEAD-TO-FLANGE WELDS - CMP-020 R1 During the fall 2002 refueling outage, North Anna Power Station Unit 2 replaced the reactor pressure vessel head. The preservice examinations for the replacement head were conducted to the requirements of the 1995 Edition through the 1996 addendum of ASME Section XI. However, interferences due to lifting lugs and the weld configuration prohibited complete examination of the reactor pressure vessel (RPVH) head-to-flange weld.
Therefore, pursuant to 10 CFR 50.55a(g)(5)(iii), Dominion requested relief (CMP-020) from certain requirements of ASME Section XI Code associated with the examination of the reactor pressure vessel head-to-flange weld where only partial coverage was obtained. This relief was approved by the NRC staff in a November 13, 2003 letter (TAC MB7515).
North Anna Unit 2 is currently in the second period of the third lnservice Inspection Interval that started December 14, 2001 and is scheduled to end December 13, 201 0.
During the upcoming spring 2007 Unit 2 refueling outage (the last refueling outage of the second period of the third interval), the North Anna Unit 2 RPVH is scheduled for a bare metal visual examination of 100 percent of the RPV head surface (including 360" around each RPV head penetration nozzle) in accordance with the revised NRC order EA-003-009, dated February 20, 2004.
A volumetric examination of the RPVH penetrations is also scheduled to be performed from under the head.
Due to the amount of inspection activity scheduled for the head, Dominion is requesting a revision to the inspection frequency and coverage included in CMP-020 (one third of the weld in each period) to reduce the impact of the RPVH inspection effort on the outage schedule. The proposed frequency and coverage schedule is consistent with ASME Code Section IWB-2412(a) which allows one weld to be examined in any period during the interval. It is proposed that the inspection of the RPVH head-to-flange weld be completed in the third period of the third interval. The attached relief has been revised to include the modified inspection frequency and coverage.
Serial No. 06-1 083 Docket No. 50-339 Revised Partial Relief Request CMP-020R1 Page 2 of 3 This revised relief request has been approved by the Station Nuclear Safety and Operating Committees.
If you have any additional questions concerning this request, please contact Mr. Thomas Shaub at (804) 273-2763.
Very truly yours, Gerald T. Bischof Vice President - Nucl Attachment Commitments made in this letter: None
Serial No. 06-1083 Docket No. 50-339 Revised Partial Relief Request CMP-020R1 Page 3 of 3 cc:
U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth Street, SW Suite 23T85 Atlanta, Georgia 30303 Mr. J. E. Reasor, Jr.
Old Dominion Electric Cooperative lnnsbrook Corporate Center 4201 Dominion Blvd.
Suite 300 Glen Allen, Virginia 23060 Mr. J. T. Reece NRC Senior Resident lnspector North Anna Power Station Mr. S. P. Lingam NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 1 1555 Rockville Pike Mail Stop 8-HI 2 Rockville, Maryland 20852 Mr. R. E. Martin NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 1 1 555 Rockville Pike Mail Stop 8-HI 2 Rockville, Maryland 20852 Mr. M. M. Grace Authorized Nuclear Insurance lnspector North Anna Power Station
Serial No 06-1 083 Docket No. 50-339 REVISED ASME SECTION XI INSERVICE INSPECTION PROGRAM RELIEF REQUEST PARTIAL EXAMINATION OF REACTOR PRESSURE VESSEL HEAD-TO-FLANGE WELDS - CMP-020R1 NORTH ANNA POWER STATION UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
Virginia Electric & Power Company North Anna Power Station Unit 2 Third 10 Year Interval Request for Relief Number CMP-020R1 I. IDENTIFICATION OF COMPONENT Reactor pressure vessel head-to-flange weld (Weld 1, drawing 12050-WMKS-RC-R-1.2) for the replacement reactor vessel head.
II. CODE REQUIREMENTS North Anna Power Station is currently in the third interval and uses the 1995 Edition through 1996 Addenda of the ASME Code.
ASME Section XI - 1995 Edition through 1996 Addenda, IWB-2200 (c) and Table IWB-2500-1, examination category B-A, item number B1.40 requires volumetric and surface examinations, as defined by Figure IWB-2500-5, of essentially 100 percent of the weld length of the reactor pressure vessel closure head-to-flange weld. "Essentially 100 percent" as clarified by ASME Code Case N-460, Alternative Examination Coverage for Class 1 and Class 2 Welds, is greater than 90 percent coverage of the examination volume, or surface area, as applicable.
Ill. CODE REQUIREMENT FROM WHICH RELIEF IS REQUESTED In accordance with 1 OCFR50.55a(g)(5)(iii), relief is requested from the "essentially 100 percent" volumetric examination coverage requirement for the identified reactor pressure vessel head-to-flange weld. This requirement is considered impractical due to the configuration of the reactor pressure vessel head.
IV. BASIS FOR RELIEF The ultrasonic examination of the reactor pressure vessel head-to-flange weld is conducted in accordance with Section XI, Appendix I of the ASME Code, 1995 Edition through 1996 Addenda.Section XI, Appendix I states that the ultrasonic examination shall be conducted in accordance with Article 4 of Section V as supplemented by Table 1-2000-1 in the Appendix. Article 4,Section V requires the weld and the adjacent base metal be examined using nominal angles of 45 and 60 degrees (deviation is permitted if geometry limits the coverage, however, separation of angles must be 10 degrees) and a straight beam. Four basic scan directions are required for the angle beams; two perpendicular to the weld axis (axial scan) from opposite directions and two parallel to the weld axis (circumferential scan) from opposite directions. These requirements apply for each of the 45 and 60 degree angle beams used. Each of the 45 and 60 degree angle beams is required to pass through all of the weld volume in the four basic scan directions.
The cross-sectional geometry of the component at the reactor pressure vessel head-to-flange weld produces a high transitional angle between the flange and the domed
head.
Scanning from the flange side may not provide the necessary angular orientation to provide full examination coverage. Examination is limited to 0.5 inches from the weld toe due to the flange configuration. The reactor vessel closure head is a carbon steel vessel with stainless steel cladding on the inside surface. Due to this cladding, the ultrasonic beam cannot be "bounced" from the inside clad surface to increase the examination coverage. Therefore, a full-V examination from the flange side is not possible. Following operational service, radiographic examination of this weld will not be practical due to the projected high radiation levels at the inside surface of the head.
The reduction in preservice volumetric coverage is detailed in Table CMP-20R1-1.
Figures CMP-20R1-1 through CMP-20R1-5 are provided detailing the configuration limitations experienced. The preservice examination on the component listed above was completed to the extent practical as required by the Code.
Furthermore, three lifting lugs are located 120" apart.
Each lug obstructs the volumetric examination for approximately 8 inches, resulting in obstruction of 2 of the 45 feet of total weld length. This limits access to approximately 4 percent of the weld length. However, these lifting lugs result in only a 0.8 percent obstruction during the magnetic particle examination resulting in a 99.2 percent surface examination.
The limited volumetric examination and the surface examination should detect any general patterns of degradation that may occur in the areas covered, therefore providing reasonable assurance of the continued structural integrity of the subject weld.
V. ALTERNATE PROVISIONS The reactor pressure vessel head-to-flange weld will be examined in the third period to the extent permitted by the configuration of the reactor pressure vessel closure head as radiologically practical.
In addition, it is proposed that the pre-service examinations already completed at the reduced coverage be counted as meeting the Code requirements.
Table CMP-020R1-1 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40 Exam 45" Weld Metal I 60" Weld Metal I 45" Weld Metal 11 60" Weld Metal 11 0" Weld Metal Weld Metal = 11.3% of total exam volume (1 1.3% x 79.33%) = 9%
Base Metal = 88.7% of total exam volume (88.7% x 63.71 %) = 57%
Total Exam Coverage Achieved = 9% + 57% = 66%
45/60" Base Metal I 45" Base Metal 11 60" Base Metal 11 0" Base Metal Sketch CMP-20-1 CMP-20-2 CMP-20-3 CMP-20-3 CMP-20-3 Base Total CMP-20-4 CMP-20-5 CM P-20-5 CM P-20-5 Sketch Coverage 55%
52%
100%
100%
100%
88%
54%
54%
54%
Weighting Factor 2 sound beams19 2 sound beams19 2 sound beams19 2 sound beams19 1 sound beam19 Coverage 12.22%
1 1.56%
22.22%
22.22%
11.11%
Weld Total 2 sound beamsn 2 sound beamsn 2 sound beamsn 1 sound beam17 79.33%
25.14%
15.43%
15.43%
7.71 %
Sketch CMP-020R1-1 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40
Sketch PRT-020R1-2 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item 81.40
Sketch PRT-020R1-3 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40
North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item 81.40
Sketch PRT-020R1-5 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40