ML070820466
| ML070820466 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 03/23/2007 |
| From: | Gerald Bichof Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, NRC/NRR/ADRO |
| References | |
| 07-0202, EA-03-009, TAC MB7515 | |
| Download: ML070820466 (13) | |
Text
March 23, 2007 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Serial No.
07-0202 NLOSIETS RO Docket No.
50-339 License No.
NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
NORTH ANNA POWER STATION UNIT 2 ASME SECTION XI INSERVICE INSPECTION PROGRAM RELIEF REQUEST PARTIAL EXAMINATION OF REACTOR PRESSURE VESSEL HEAD-TO-FLANGE WELDS - PRT-001 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 (RPV) 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).
During the spring 2007 Unit 2 refueling outage (the last refueling outage of the second period), the North Anna Unit 2 RPV head 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 RPV head penetrations is also scheduled to be performed from under the head. Due to the amount of inspection activity scheduled for the head, the RPV head-to-flange weld will be completed in the third period of the third interval in accordance with the ASME Code requirements. The attached relief includes the modified inspection frequency and coverage.
In a January 28, 2003 letter (Serial No. 03-050A), Dominion provided typical RPV fabrication drawings to facilitate the NRC review of the relief request for the preservice examinations. Please use the drawings from the 03-050A letter to facilitate your review of this relief request.
Serial No. 07-0202 Docket No. 50-339 Relief Request PRT-001 Page 2 of 3 This relief request has been approved by the Station Nuclear Safety and Operating Committee.
If you have any additional questions concerning this request, please contact Mr. Thomas Shaub at (804) 273-2763.
Very truly yours, Gerald T. Bischof V
Vice President - Nuclear Engineering Attachment Commitments made in this letter: None 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 Inspector North Anna Power Station Mr. S. P Lingam 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
Serial No. 07-0202 Docket No. 50-339 Relief Request PRT-001 Page 3 of 3 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 Inspector North Anna Power Station
Serial No 07-0202 Docket No. 50-339 ASME SECTION XI INSERVICE INSPECTION PROGRAM RELIEF REQUEST PARTIAL EXAMINATION OF REACTOR PRESSURE VESSEL HEAD-TO-FLANGE WELDS - PRT-001 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 PRT-001
- 1. ASME Code Component Affected Reactor pressure vessel head-to-flange weld (Weld 1, drawing 12050-WMKS-RC-R-1.2), ASME Class 1.
2. Applicable Code Edition and Addenda
North Anna Power Station Unit 2 is currently in the second period of the third interval and uses the 1995 Edition through 1996 Addenda of the ASME Code. The third lnservice Inspection Interval started December 14, 2001 and is scheduled to end December 13,201 0.
3. Applicable Code Requirements
ASME Section XI - 1995 Edition through 1996 Addenda and Table IWB-2500-1, examination category B-A, item number 91.40 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.
In accordance with 10CFR50.55a(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. In addition, the examination of the reactor pressure vessel head to flange weld performed from the flange face is also not a practical examination to perform due to limitations to access to the flange face while on the head stand, radiation dose, and limited coverage issues due to configuration geometry.
4. Impracticality of Compliance
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, and 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.Section V, Article 4 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 at least 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 curved head.
Scanning from the flange side does 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. Therefore, a full-V examination is also not possible. Radiographic examination of this weld from the inside is not practical due to the anticipated dose associated with high radiation levels from the inside surface of the head. The reduced volumetric coverage is expected to be similar to the preservice examination which is detailed in Table PRT-001 -1.
Figures PRT-001-1 through PRT-001-5 are also provided detailing the configuration limitations experienced during the preservice examination.
Furthermore, the 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 which should result in a 99 percent surface exami nation.
Examination of the reactor pressure vessel head-to-flange weld performed from the flange face is also not a practical examination to perform due to radiation dose and limited coverage issues. Once the head is set on the head stand, access is limited due to the seal ring and the stand obstructing the required scan surface. To access the area under the head to perform scanning of the flange face would involve entering a high radiation area. In addition, the examination of the head-to-flange weld from a flange face is intended to interrogate the examination volume with the sound beam(s) oriented essentially perpendicular to the weld axis. As shown in Figure 2500-5 in the 1995 Edition11996 Addenda of the ASME Code, the curvature of the head and the location of the examination volume limit effective examination coverage when performing the examination from the flange face surface.
The inservice examination coverage on the head-to-flange will be completed to the extent practical as required by the Code, but coverage similar to the preservice is expected. Full Code required coverage is impractical for the head-to-flange weld without a design modification. 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.
5. Burden Caused by Compliance
Full Code required coverage is impractical for the head-to-flange weld due to the design of the head. It would be impractical to redesign the head.
Dose rates at the flange face of the reactor head are expected to be 500-600 mRem/hr. With an expected time for the inspection of six person-hours the dose for the job is estimated to be 3.0 - 3.6 person-rem. In addition, the curvature of the head and the location of the examination volume limit effective examination coverage when performing the examination from the flange face surface.
6. Proposed Alternative and Basis for Use
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 detailed in the enclosed figures and no examinations will be performed from the flange face.
7. Duration of Proposed Alternative
The use of this relief request is for the duration of the North Anna Unit 2 third lnservice Inspection Interval.
8. Precedents
In addition, preservice examinations have been previously approved by the NRC for North Anna Unit 2 on November 13,2003 (TAC MB7515), North Anna Unit 1 Docket Number 50-338, on May 27, 2004 (TAC MC1829), and Surry Power Station Unit 1, Docket Number 50-280, on May 28, 2004 (TAC MB1830). Similar requests have been approved to address head-to-flange coverage issues that are contained in this request. These include requests from Omaha Public Power District Fort Calhoun Station, Docket Number 50-285, approved May 20,2005 (TAC MC3220), Kewaunee Power Station, Docket Number 50-305, approved June 20,2006 (Accession Number ML061420171), and PPL Susquehanna Units 1 and 2, Docket Numbers 50-387 and 50-388, approved August 1,2006 (Accession Number ML061110407).
- 9. References ASME Code,Section XI, 1995 Edition, including Addenda through 1996.
Table PRT-001-1 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item 81.40 Exam Weld Metal = 1 1.3% 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%
Sketch Coverage Sketch 12.22%
1 1.56%
45" Weld Metal 11 60" Weld Metal 11 0" Weld Metal Weighting Factor 45" Weld Metal I 60" Weld Metal I Coverage 5 5 O/O 52%
CMP-20-1 CMP-20-2 22.22%
22.22%
11.11%
CMP-20-3 CMP-20-3 CM P-20-3 Weld Total 79.33%
2 sound beams19 2 sound beams19 100%
1 00%
1 00%
45/60" Base Metal 1 45" Base Metal I(
60" Base Metal 11 0" Base Metal 2 sound beams19 2 sound beams19 1 soundbead9 Base Total 63.71 O/o CMP-20-4 CMP-20-5 CMP-20-5 CMP-20-5 88%
54%
54%
54%
2 sound beams17 2 sound beams17 2 sound beamsff 1 sound bead7 25.14%
15.43%
15.43%
7.71 %
North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40
Figure PRT-001-2 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40 EXAM AREA
+
EFGH = 0 1166 X 6.6 - 5,716 in' DiRECTlON 1 Examrned EFGH = 1
Figure PRT-001-3 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40 Component: RPV closure Coverage Sketch No: 3 a3f 5 So&@: !BR/u Exem: Weld medal, 4 So 1 60° 11 and 0" EXAM AREA 0
FFGH = 0 8166 X 6.6 = 5 716 in'
Fiaure PRT-001-4 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40 Component: R W closure head io flange weld Covarago Sketch No: 4 d 5
&On&: 51;1%
Exam: Base metal. 45" / 60" -l NVO SOUND BEAMS
- AEHD + FJLCG
= (3 3 x 6 6 ) * (.5 x.7) * (28 x 5.4) = 40 4 8n"
- t40414488)=W%
Figure PRT-001-5 North Anna Unit 2 Pre-Service Examination Coverage Summary Reactor Pressure Vessel Closure Head to Flange Weld Category B-A, Item B1.40 Component: RPV closzdrs hesad to llan~%
weld Coverage Skatch No: 5 of 5 S c ~ t e : 50%
Exam: Bftse mate!, 45" 60' EXAMINED
. ~ ~ ~ 0 + F y f K G = j 3 3 x 6 6 ) + (
5xJ)=25281na a
(2521814488jr%%
- 56 % x i43' 145") = 54 %