L-08-339, Impractical American Society of Mechanical Engineers Code Section XI Weld Examination Requirements
| ML083390107 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 11/26/2008 |
| From: | Sena P FirstEnergy Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-08-339 | |
| Download: ML083390107 (8) | |
Text
FENOC Beaver Valley Power Station P.O. Box 4 FirstEnergy Nuclear Operating Company Shippingport, PA 15077 Peter P. Sena III 724-682-5234 Site Vice President Fax: 724-643-8069 November 26, 2008 10 CFR 50.55a L-08-339 ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
SUBJECT:
Beaver Valley Power Station, Unit No. 2 Docket No. 50-412, License No. NPF-73 Impractical American Society of Mechanical Engineers Code Section XI Weld Examination Requirements Pursuant to 10 CFR 50.55a(g)(5)(iii), FirstEnergy Nuclear Operating Company (FENOC) hereby provides the Nuclear Regulatory Commission (NRC) the basis for the determination that the inservice examination of the welds listed below, as specified by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section XI, or as specified by the NRC approved Risk-Informed Inservice Inspection Program, have been determined to be impractical. These determinations are based on experience obtained during the Beaver Valley Power Station, Unit No. 2 second ten-year inservice inspection interval. This interval ended August 28, 2008.
The affected welds are:
- 1. Reactor coolant system circumferential butt welds 2RCS-006-F-01 and 2RCS-006-F-02
- 2. Chemical and volume control system circumferential butt welds 2CHS-015-F-02, 2CHS-015-F-03, 2CHS-015-F-06, 2CHS-015-F-07, 2CHS-357-F-12-C, and 2CHS-357-F-13-C
- 3. Residual heat removal heat exchanger circumferential welds 2RHS-E21A-C-1 and 2RHS-E21A-C-2
- 4. Residual heat removal heat exchanger nozzle welds 2RHS-E21A-N-3 and 2RHS-E21A-N-4
- 5. Recirculation spray heat exchanger shell welds 2RSS-E21A-C-1 and 2RSS-E21A-C-1 1 U CLYR
Beaver Valley Power Station, Unit No. 2 L-08-339 Page 2
- 6. Reactor vessel circumferential weld 2RCS-REV21-C-4
- 7. Charging pump attachment weld 2CHS-P-21A-A-4 Information to support the basis for the impracticality determinations is provided in the Attachment to this letter.
There are no regulatory commitments contained in this letter. If there are any questions or if additional information is required, please contact Mr. Thomas A. Lentz, Manager -
Licensing, at 330-761-6071.
Sincerely, Peter P. Sena III
Attachment:
Impractical Inservice Inspection Determination for Various Beaver Valley Power Station, Unit No. 2 Welds cc:
NRC Region I Administrator NRC Senior Resident Inspector NRR Project Manager Director BRP/DEP Nuclear Safety Specialist (BRP/DEP)
Attachment L-08-339 Impractical Inservice Inspection Determination for Various Beaver Valley Power Station, Unit No. 2 Welds Page 1 of 6 1.0 Reactor Coolant System Circumferential Butt Welds The 100 percent examination volume requirement for reactor coolant system circumferential butt welds 2RCS-006-F-01 (F01) and 2RCS-006-F-02 (F02) has been determined to be impractical during the second ten-year inservice inspection interval. During this interval, examination requirements for Class 1 and 2 piping welds at Beaver Valley Power Station (BVPS) Unit No. 2 were governed by a Risk-Informed Inservice Inspection (RI-ISI) program authorized by the NRC in a letter and safety evaluation dated April 9, 2004 (Accession Number ML040780805).
The affected welds are located in piping segment RCS-01 1. This segment consists of the 27.5-inch inside diameter A351 Grade CF8A piping segment between the discharge of the 'B' reactor coolant pump and the cold leg loop isolation valve.
Only two circumferential welds (F01 and F02) exist in piping segment RCS-01 1.
During the second ten-year inservice inspection interval the RI-ISI program categorized piping segment RCS-01 1 as High Safety Significant and selected weld F01 for examination as a "l(b)" or sample selection. The postulated damage mechanism for segment RCS-01 1 was thermal fatigue. Therefore, the BVPS Unit No. 2 RI-ISI program requires 100 percent volumetric examination coverage on weld F01.
Due to examination limitations encountered with weld F01 during the second ten-year inservice inspection interval, weld F02 was added to the examination scope in accordance with the RI-ISI program and scheduled for examination. Limitations were also encountered on F02.
The following paragraphs describe examination coverage limitations encountered during the second ten-year inservice inspection interval for both welds.
Weld F01 is a circumferential butt weld joining the reactor coolant pump outlet to the 27.5-inch inside diameter SA351 Grade CF8A piping segment. A rigid restraint surrounding the reactor coolant pump outlet pipe restricts physical access for scanning in two (2) 16-inch circumferential areas at 90 degrees and 270 degrees (32 inches of circumference total). This physical access restriction precludes axial scanning from the upstream (pump) side of the weld for 32 inches. Additionally, both circumferential scan directions are restricted by the same restraint for approximately one half the required examination volume on the upstream side for 32 inches of circumference. Finally, the restraint also limits coverage of a small
Attachment L-08-339 Page 2 of 6 portion of the required volume on the upstream side of the weld for axial scans from the pipe side. Calculation of required volume coverage as a result of the limitations has determined that approximately 81 percent of the required examination volume for this weld has been obtained.
Weld F02 is a circumferential butt weld joining the 27.5-inch inside diameter A351 Grade CF8A piping segment to the 'B' cold leg loop-isolation valve. The tapered profile of the weld as well as the part geometry of the cast loop isolation valve both combine to prohibit any ultrasonic coverage from the downstream (valve) side of the weld. 100 percent coverage of the required examination volume was obtained from the upstream (pipe) side of the weld, and also in both circumferential scan directions. Simple averaging of the coverage attained results in a cumulative calculated coverage of 75 percent of the required examination volume.
As an alternative to examination of 100 percent of the volume of weld F01, the only remaining circumferential weld in the piping segment that was not otherwise required to be examined (F02) was added to the examination scope. Both welds were examined to the maximum extent practicable. In addition, these welds received VT-2 visual leakage examinations in accordance with Category B-P to provide assurance of continued reliability for the applicable piping segment.
2.0 Chemical and Volume Control System (CVCS) Circumferential Butt Welds The 100 percent examination volume requirement for chemical and volume control system circumferential butt welds 2CHS-01 5-F-02 (F02), 2CHS-01 5-F-03 (F03),
2CHS-015-F-06 (F06), 2CHS-015-F-07 (F07), 2CHS-357-F-1 2-C (F12-C), and 2CHS-357-F-1 3-C (F13-C) has been determined to be impractical during the second inservice inspection interval. During this interval, examination requirements for Class 1 and 2 piping welds at BVPS Unit No. 2 were governed by a RI-ISI program.
2.1 CVCS Welds in 8-Inch Lines The affected welds F02 and F07 are located within RI-ISI piping segments CHS-009 and CHS-008, respectively. These segments consist of 8-inch diameter, type 304 stainless steel piping between the charging pump suction isolation valves. Only two circumferential welds exist in each of these piping segments (F02 and F03 in segment CHS-009; F06 and F07 in segment CHS-008).
During the second ten-year inservice inspection interval the RI-ISI program categorized piping segments CHS-008 and CHS-009 as High Safety Significant based on consequence importance and selected welds F02 and F07 for examination as a "l (b)" or sample selection. The postulated damage mechanism for these segments was thermal fatigue. Therefore, the BVPS Unit No. 2 RI-ISI
Attachment L-08-339 Page 3 of 6 program requires 100 percent volumetric examination coverage on welds F02 and F07.
Due to examination limitations encountered with welds F02 and F07 during the second ten-year inservice inspection interval, welds F03 and F06 were added to the examination scope in accordance with the RI-ISI program and scheduled for examination. Limitations were also encountered on welds F03 and F:06.
The following paragraph describes examination coverage limitations encountered during the second ten-year inservice inspection interval for all four welds.
Examination coverage was limited from the upstream axial scan direction for welds F02 and F06 and from the downstream axial scan direction for welds F03 and F07.
Welds F02 and F03 are circumferential butt welds joining the ends of an 8-inch diameter section of piping to valves 2CHS-MOV8131A and 2CHS-MOV8131B.
Welds F06 and F07 are circumferential butt welds joining the ends of an 8-inch section of piping to valves 2CHS-MOV8130A and 2CHS-MOV8130B. The tapered profile of the welds as well as the physical configuration of the valves both combine to limit ultrasonic scan coverage from the valve side of the welds.
One hundred percent coverage of the required examination volume was obtained in both circumferential scan directions. Simple averaging of the coverage attained results in a cumulative calculated coverage of 80 percent of the required examination volume for each weld.
As an alternative to examination of 100 percent of the volume of weld F02 and F07, the only remaining circumferential welds in the associated piping segments that were not otherwise required to be examined (F03 and F06) were added to the examination scope. These four welds were examined to the maximum extent practicable. In addition, these welds received VT-2 examinations in accordance with Category C-H to provide assurance of continued reliability for the applicable piping segments.
2.2 CVCS Welds in 4-Inch Lines The affected welds F12-C and F13-C are located in piping segment CHS-018B.
This segment consists of 4-inch diameter, type 316 stainless steel piping between a charging pump discharge and a 4-inch to 3-inch reducer.
During the second ten-year inservice inspection interval the RI-ISI program categorized piping segment CHS-018B as High Safety Significant based on consequence importance. The RI-ISI program selected weld F12-C for examination as a "l (b)" or sample selection. The postulated damage mechanism for Segment CHS-018B was thermal fatigue. The BVPS Unit No. 2 RI-ISI program requires 100 percent volumetric examination coverage on weld F12-C.
Attachment L-08-339 Page 4 of 6 Due to examination limitations encountered with weld F12-C during the second ten-year inservice inspection interval, weld F13-C was added to the examination scope in accordance with the RI-ISI program and scheduled for examination.
Limitations were also encountered on weld F13-C.
The following paragraphs describe examination coverage limitations encountered during the second ten-year inservice inspection interval for both welds.
No coverage in the upstream axial scan direction was possible for weld F1 2-C due to the flange-to-reducer weld configuration. No coverage in the downstream axial scan direction was possible due to the pipe-to-flange weld configuration.
Weld F1 2-C is a circumferential butt weld joining a charging pump discharge spool piece downstream flange to a 4x3-inch reducer. Weld F13-C is a circumferential butt weld located on the charging pump discharge spool piece.
The tapered profile of the welds as well as the physical configuration of the flange weld both combine to prohibit any ultrasonic coverage from the flange side of the welds. One hundred percent coverage of the required examination volume was obtained in both circumferential scan directions for both welds. Simple averaging of the coverage attained results in a cumulative calculated coverage of 75 percent of the required examination volume for each weld.
As an alternative to examination of 100 percent of the volume of weld F12-C, weld F13-C was added to the examination scope. Both welds were examined to the maximum extent practicable. In addition, these welds received VT-2 examinations in accordance with Category C-H to provide assurance! of continued reliability for the applicable piping segment CHS-01 8B.
3.0 Residual Heat Removal Heat Exchanger Circumferential Welds The 100 percent examination volume requirement for residual heat removal system heat exchanger circumferential welds 2RHS-E21A-C-1 (C-1) (shell-to-flange) and 2RHS-E21A-C-2 (C-2) (shell-to-head) has been determined to be impractical during the second inservice inspection interval.
The required 100 percent examination volume was not achieved for the C-1 weld because physical limitations associated with the weld neck flange, which prohibits axial examination coverage from the flange side of the weld. Additionally, eight support gussets as well as the proximity of the inlet and outlet nozzles further limit physical access for scanning. Approximately 68 percent of the required examination volume was covered by the angle beam examination techniques performed in the second inservice inspection interval.
Attachment L-08-339 Page 5 of 6 The required 100 percent examination volume was not achieved for the C-2 weld due to physical limitations including horizontal welded supports, the proximity of the inlet and outlet nozzles, and the presence of a concrete support structure. Approximately 53 percent of the required examination volume was covered by the angle beam examination techniques performed in the second inservice inspection interval.
As an alternative to examination of 100 percent of the volume of welds C-1 and C-2, both welds were examined to the maximum extent practicable using a 45 degree axial angle supplemented with a 60 degree axial angle. In addition, these welds received VT-2 examinations in accordance with Category C-H to provide assurance of continued reliability of these welds.
4.0 Residual Heat Removal Heat Exchanger Nozzle Welds The 100 percent examination volume requirement for the residual heat removal heat exchanger nozzle welds 2RHS-E21A-N-3 (N-3) and 2RHS-E21A-N-4 (N-4) has been determined to be impractical during the second inservice inspection interval.
The volume examined was limited due to the physical configuration of the nozzle to vessel welds (which preclude scanning from both sides of the welds) and proximity of the adjacent channel head girth weld and horizontal support structures (which limit scan surface access). The 45 degree full-vee shear wave scan angle was supplemented by a 60 degree full-vee scan angle to extend the examination coverage to the maximum extent practical for these welds. Approximately 75 percent of the required volume of N-3 and N-4 was covered by examinations performed in the second ten-year inservice inspection interval.
As an alternative to examination of 100 percent of the volume of welds N-1 and N-2, both welds were examined to the maximum extent practicable using a 45 degree axial angle supplemented with a 60 degree axial angle, calibrated for full-vee examination range and manipulated and skewed where practicable to obtain the maximum coverage. In addition, these welds received VT-2 examinations in accordance with Category C-H to provide assurance of continued reliability of these welds.
5.0 Recirculation Spray Heat Exchanger Shell Welds The 100 percent examination volume requirement for the recirculating spray heat exchanger tube sheet to shell welds 2RSS-E21A-C-1 (C-1) and 2RSS-E21A-C-11 (C-11) has been determined to be impractical during the second inservice inspection interval.
The examination volume requirement has been determined to be impractical due to physical interference by heat exchanger seismic support lugs (two lugs near each weld) and nozzle reinforcing rings (reinforcing ring on one side of each weld). The
. I ;'
Attachment L-08-339 Page 6 of 6 ultrasonic (UT) examinations of these welds were limited to 87.7 percent of the required volume.
As an alternative to examination of 100 percent of the volume of welds C-1 and C-1 1, both welds were examined to the maximum extent practicable. The alternative examinations provide adequate assurance of the continued reliability of the welds.
6.0 Reactor Vessel Circumferential Weld The 100 percent examination volume requirement for the reactor vessel circumferential weld 2RCS-REV21-C-4 (C-4) has been determined to be impractical during the second inservice inspection interval.
The coverage limitation was due to the proximity of four core support lugs.
Scanning was conducted between and below the obstructing lugs with the scan boundaries maximized by visually assisted positioning of the exam head so that scan starts and stops were as close to the support lugs as tool configuration would allow. Additional scans were also performed with secondary exam sled rotations to maximize coverage from outboard facing transducers. The automated examination of the lower head to shell weld (C-4) was limited to 87.4 percent of the required volume.
As an alternative to examination of 100 percent of the volume of weld C-4, the weld was examined to the maximum extent practicable. This examination was supplemented by the visual examination performed on the interior of the vessel. The four support lugs were included in this examination. The alternative examinations provide adequate assurance of the continued reliability of the weld.
7.0 Charging Pump Attachment Weld The 100 percent examination volume requirement for the charging pump welded attachment 2CHS-P-21A-A-4 (A-4) has been determined to be impractical during the second inservice inspection interval. This is one of four welded attachments associated with the support structure of a charging pump. The required surface examination was limited because of the support leg, upon which the welded attachment rests, precludes access to the entire bottom weld of the attachment.
Approximately 76 percent of the required area was successfully examined.
As an alternative to examination of 100 percent of the surface of weld A-4, the welds for the remaining three welded attachments associated with the support structure of the charging pump that were not otherwise required to be examined were added to the examination scope. The four welds were examined to the maximum extent practicable because the same limitations existed for all four attachments. The alternative examinations provide adequate assurance of the continued reliability of the welds.