ML20035H531
| ML20035H531 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 04/29/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20035H529 | List: |
| References | |
| NUDOCS 9305050203 | |
| Download: ML20035H531 (9) | |
Text
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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,g WASHINGTON, D. C. 20555
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ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF FIRST TEN-YEAR INSERVICE INSPECTION INTERVAL RE0 VESTS FOR REllEF TENNESSEE VALLEY AUTHORITY SE0VOYAH NUCLEAR PLANT. UNIT 2 If0CKET NUMBER 50-328
1.0 INTRODUCTION
Technical Specifications 4.0.5 for Sequoyah Nuclear Plant (SQN), Unit 2, states that inservice inspection and testing of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable Addenda as required by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i),
10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components.
The regulations require that inservice examination of components and system pressure tests conducted during each ten-year interval comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) on the date twelve months prior to the start of the 120-month inspection interval, subject to the limitations and modifications listed therein.
The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations a d modifications listed therein.
Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
9305050203 930429 PDR ADDCK 05000329 p
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, By letter dated June 15, 1992, the Tennessee Valley, Authority (licensee) submitted to the NRC the First Ten-Year Interval Inservice Inspection (ISI)
Program Plan, and Revisions 17 and 16 for SQN Units 1 and 2 respectively, included in the licensee's submittal were associated requests for relief from the ASME Code Section XI requirements that the licensee determined to be impractical to perform during the First Ten-Year ISI interval for Units 1 and 2.
The staff has reviewed and evaluated the requests for relief and supporting information for Unit 2.
The licensee provided additional information regarding Unit 2 Request for Relief No. 151-15 by a telephone conference on January 14, 1993.
Our evaluation and conclusions are discussed in the following sections.
The latest revisions to the First Ten-Year Interval ISI Program Plans for Units 1 and 2 will be evaluated separately.
The requests for relief for Unit I were evaluated previously.
2.0 EVALUATION Unit 2 - RR 151-15 Volumetric Examinations of Full Penetration Welds of Nozzles in Vessels, and Volumetric and Surface Examinations of Pressure Retainino Dissimilar Metal Welds Code Recuirement:
Section XI, Table IWB-2500-1, Examination Category B-D
" Penetration Welds of Nozzles in Vessels - in:pection Plan B", items B3.90 and B3.100 requires 100 percent volumetric examinations of Reactor Vessel Nozzle-to-Vessel Welds and Nozzle-Inside-Radius Section as defined by figure IWB-2500-7.
Table IWB-2500-1, Examination Category B-D, Footnote 3 (1st Inspection Interval) - At least 25 percent but not more then 50 percent (credited) of the nozzles shall be examined by the end of the 1st inspection period and remainder by the end of inspection interval.
Table IWB-2500-1, Examination Category B-D, Footnote 4 (Successive Inspection Intervals 2nd, 3rd, and 4th) - At least 25 percent but not more than 50 percent (credited) of the nozzles shall be examined by the end of the 1st inspection period and the remainder by the end of the 3rd inspection period of each inspection interval.
Table IWB-2500-1, Examination Category B-D, Footnote 5 (Deferral of Inspection to End of Interval) - If examinations are conducted from the inside the component and the nozzle weld is examined by straight beam ultrasonic method from the nozzle bore the remaining examinations required to be conducted from the shell inside diameter may be performed at or near the end of each inspection interval.
Section XI, Table IWB-2500-1, Examination Category B-F " Pressure Retaining Dissimilar Metal Welds", item B5.10 requires a 100 percent volumetric and surface examination of Class 1 pressure retaining welds in piping as defined by Figure IWB-2500-8.
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I Table IWB-2500-1, Examination Category B-F, footnote 2 - For the reactor vessel nozzle safe-ends, the examinations may be performed coincident with the vessel nozzle examinations required by Examination Category B-D.
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Licensee's Code Reauest: The licensee requests authorization to use an alternative examination schedule instead of performing the Code required volumetric examinations on the Reactor Vessel Nozzle-to-Vessel Welds, Nozzle-Inside-Radius Section, and Nozzle-to-Safe End Dissimilar Metal Welds as required in Section XI, Table IWB-2500-1.
t Licensee's Basis for Reauestina Alternative Examination:
The licensee stated that SQN is a four-loop pressurized water reactor with four inlet and four i
outlet RV nozzles.
The RV nozzle-to-vessel welds and inside radius sections i
are ultrasonically examined from the RV inside diameter using automated inspection devices. With the RV core barrel in place, the outlet nozzles are accessible for examination from the nozzle bore only.
The inlet nozzles are inaccessible for examination until the core barrel is removed.
Unit 2 is in the second period of the first Ten-Year Inservice Inspection Interval. During the first period, the accessible volume of the nozzle-to-vessel welds (100 percent of the weld volume was accessible) and inside radius sections (50 percent of the weld volume was accessible) on SQN's four outlet nozzles were ultrasonically examined from the nozzle bore.
The remaining examinations of the inside radius sections for the four outlet nozzles are to be completed during the third period, thus satisfying the requirements of Table IWB-2500-1, Examination B-D, item Nos. B3.90 and 83.100, footnotes 3, 4, and 5.
In addition, to the RV nozzles examinations, the RV nozzle-to-safe end welds are ultrasonically examined using an automated inspection device when the nozzle is examined from the bore. During the first period, the nozzle-to-safe end welds on four outlet nozzles were ultrasonically examined from the inside diameter and surface examined from the outside diameter.
The nozzle-to-safe end welds on the four inlet nozzles will be similarly-examined during the i
third inspection period.
This will satisfy the requirements of Table IWB-2500-1, Examination Category B-F, Item No. B5.10, Footnote 2.
The ASME Code provides for the continuation of the first and third period examinations during the second, third, and fourth inspection intervals thus, establishing a ten-year examination frequency. TVA proposes to alter the inspection schedule by performing an additional examination of the RV nozzle-to-vessel welds and inside radius sections for SQN's four outlet nozzles during the third inspection period of the first interval.
Performance of these additional examinations will thereby establish a new Ten-Year examination schedule for the second, third, and fourth inservice inspection interval s.
The ten-year examination frequency required by the Code would continue to be maintained. Additional benefits include:
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One-time installation and removal of the automated inspection o
device from RV flange rather than twice during an inspection interval.
' Performance of additional RV outlet nozzle examinations during the
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o-first inspection interval.
An overall reduction in personnel radiation exposure, thus o
supporting ALARA.
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o A reduction in the number of times automated devices and associated materials and equipment must be decontaminated.
i A cost saving to TVA of 1.8 million dollars over the 40 year _ life o
of the plant, j
i In consideratton of the licensee's performance of additional i
o examinations during the first interval and the radiation exposure.
required to perform inspections under the current Section XI l
examination schedule the licensee concludes that compliance with i
the specific requirements would result in an unnecessary hardship without a componsating increase in the level of quality and safety.
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q Licensee's Procosed Alternative Examination:
The licensee proposes that SQN's i
four RV outlet nozzles will be ultrasonically examined twice during the first' inspection interval.
The second examination would occur during the third period.
This includes examination of the outlet nozzle-to-vessel welds by.the straight beam ultrasonic method from the nozzle bore and examination of the outlet nozzle inner radius sections. These examinations will be in. addition to the examinations required to be conducted on the outlet nozzle-to-vessel i
welds and inner radius section from the RV shell ins.ide diameter during the third inspection period.
SON's four RV outlet nozzle-to-safe end welds will also be examined twice during the first inspection-interval (third period). The examination will include an automated ultrasonic examination from the~ inside diameter and a surface examination from the outside diameter.
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During the second, third, and fourth inspection intervals, all RV nozzle-to-vessel welds and inside radius sections and RV nozzle-to-safe end welds will be examined during the third inspection period.
4 Staff Evaluation:
Paragraph IWB-2420(a), " Successive Inspections," states that the sequence of component examination established in-the first inspection interval shall be repeated during successive inspection intervals, to the extent practical. The intent of the Code is that examinations or portions of examinations of the RPV welds should be performed at intervals not to exceed 10 years. Deferring the subject examinations until the third period of the i
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second interval is acceptable for SQN, Unit 2 because the licensee will reexamine the subject welds during the last period of the first inspection interval; therefore, 10 years will not have lapsed between examinations. The eicensee's proposed alternative to examine the RPV nozzle-to-vessel welds and inside radii in the last inspection period of the Second Ten-Year Interval will provide an acceptable level of quality and safety, and reasonable assurance that the structural integrity of the plant's systems, components, I
and supports will be maintained. Accordingly, the licensee's alternative is i
authorized for use pursuant to 10 CFR 50.55a(a)(3)(i).
Unit 2 - RR-ISI-16 Volumetric Examination of Circumferential Shell Welds for Residual Heat Removal Heat Exchancer j
Code Reauirement:
Table IWC-2500-1, Examination Category C-A, Item No. C1.10 j
requires 100 percent volumetric examinations of circumferential shell welds, i
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l Licensee's Code Reauest:
The licensee requests relief from performing 100 percent volumetric examinations of circumferential shell welds for Unit 2 i
Residual Heat Exchangers (two per unit).
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Licensee's Basis for Reouestino Relief:
The licensee stated that each heat exchanger consists of an inlet-outlet head chamber with one inlet and one outlet nozzle and two integrally attached support brackets and a circumferential vessel shell-to-flange weld.
The design configuration of the nozzles and support brackets restricts examination of the vessel-to-flange weld.
The vessel shell weld is 133 inches in length.
The weld examinations are distributed in three segments.
Segment RHRW-16-A-1 (37 inches) was l
ultrasonically examined in the first inspection period and the licensee achieved approximately 81 percent examination coverage.
Segment RHRW-16-A-2 (38 inches) was examined in the second period and the licensee achieved approximately 64 percent examination volume coverage.
Segment RHRW-16-A-3 (38-
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inches) is scheduled for examination for the third period and the licensee estimated that 82 percent examination volume of the weld could be performed.
The licensee concluded that based on the examination performed and an estimation of the remaining third period examination, approximately 75 percent examination volume coverage of the RHR heat exchanger circumferential weid will be achieved.
Licensee's Prooosed Alternative Examination:
The licensee prcposed in addition to the visual examination performed during system leakage and hydrostatic pressure tests, it will perform a best-effort ultrasonic examination on one vessel-to-flange weld on one heat exchanger to achieve as much Code coverage as possible and achieve meaningful results.
l Staff Evaluation:
The staff determined that it would be impractical for the licensee to perform the Code required volumetric examinations on the RHR Heat Exchangers circumferential shell welds RHR-16-A-1,
-2, and -3, because the e
design of the nozzles and support brackets render the surfaces inaccessible for the examination.
The heat exchangers would have to be redesigned by modifying the nozzles and brackets in order to perform the Code required examinations.
The licensee-determined that, based on the examinations performed during the First and Second Periods of the First Ten-Year ISI e
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- I Interval and the Third Period examinations estimated coverage of 82 percent of weld RHRW-16-A-3, a total of 78 percent of the RHR heat exchanger circumferential weld will be examined for the First Ten-Year ISI Interval.
i Because it is impractical to volumetrically inspect 100 percent of the RHR heat E XChanger circumferential weld, the licensee has proposed as an alternative to perform a best-effort ultrasonic examination that would total approximately 78 percent of the weld, and perform visual examinations during system leakage and hydrostatic pressure tests.
The staff has determined that the licensee's proposed alternative examination i
would provide an acceptable level of quality and safety, and reasorable assurance that the structural integrity of the plant's systems, components, j
and supports will be maintained. Therefore, pursuit to 10 CFR 50.55a(g)(6)(i), the staff has determined that the Code requirements are impractical to performed on the RHR circumferential vessel shell-to-flange l
weld and that relief may be granted, and the licensee's alternative i
examination is acceptable.
i Unit 2 - RR-ISI-17 Surface Examinations of Intearally Welded Support Attachments Code Recuirement:
Table IWC-2500-1, Examination Category C-C, Item No. C3.40, requires surface examinations of piping integrity welded supports attachments.
Licensee's Basis for Recuestina Relief: The licensee stated that due to the design vintage of Sequoyah Nuclear Plant it would be impractical to inspect all of the integrally welded attachments of certain component supports. The integrally welded support attachments may have access limitations as well as non-removable hanger (pipe clamp) interference.
For example, access is limited to examine component FDR-245-IA of the feedwater System because of a penetration in the valve room wall, and is inaccessible due to a non-removable pipe clamp and restraint.
Licensee's proposed Alternative Examination:
The licensee proposes to perform surface and visual examinations of the component supports as practical.
Components for which relief is requested are:
System Component ID Code Coveraqg
(% Surface Examination)
Limitations Feedwater 2-FDH-245-IA 54%
Access limited due to feedwater piping penetration in valve room.
Limitation on integrally welded lugs due to nonremovable pipe clamp and restraint and pipe penetration.
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, Feedwater 2-FDH-284-IA 71%
Access limited due to feedwater piping-l penetrations in
'j containment.
t Limitations on integrally welded attachment due to permanent support attachment at the piping
'i penetration.
Safety 2-SIH-10-IA 0%
Totally inaccessible.
Injection Integral attachment installed in-a wall in -
fan room.
Process pipe i
goes through AC duct
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which is 4 to 5 inches i
from wall making
.I integral attachment inaccessible for surface examinations.
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Staff Evaluation: The staff determined that the Code requirements are impractical for the licensee to perform on these integrally welded support attachments, because the attachments have access limitations and non-removable hanger (pipe clamp) interference, which would have to be redesigned. This i
modification would result in an unusual difficulty without a compensating increase in the level of quality and safety.
In the Case of Safety Injection Component 2-SIH-10-IA, the component is totally inaccessible because the integral attachment is installed in a wall where process pipe goes through AC duct that is 4 to 5 inches from the wall.
Thus the integral attachment is inaccessible for surface examination.
For this component, the licensee has proposed to perform an visual examination, which will ensure'that the structural integrity will be maintained and provide an acceptable level of quality and safety for Component 2-SIH-10-1A.
For feed. vater Components 2-FDH-245-IA and 2-FDH-284-IA, access is limited due to nonremovable pipe clamp and restraint and pipe penetration, and permanent-I support attachment at'the piping penetration, respectively. However, the licensee can perform a surface examination on 54 percent of Component 2-FDH-245-IA and a surface examination on 71 percent on Component 2-FDH-284-IA. The staff has concluded that, with the combination of the percentage of surface examinations that can be performed and visual examinations performed, the l
proposed alternative examinations will maintain the structural integrity of Feedwater Components 2-FDH-245-IA and 2-FDH-284-IA and provide an acceptable level of quality and safety.
j Therefore, pursuit to 10 CFR 50.55a(g)(6)(1) the staff has determined that the Code requirements are impractical to performed on Safety Injection Component 2-SIH-10-IA and feedwater Components 2-FDR-245-IA and 2-FDH-284-IA, and that relief may be granted and that the licensee's alternative examination is acceptable.
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Unit 2 - RR 151-18 Volumetric Examination on Reactor Pressure Vessel Closure l
Head-to-Flance Weld Code Reouirement:
Table IWB-2500-1, Examination Category B-A, Item No. Bl.40, l
Volumetric Examination of Reactor Pressure Vessel Closure Head-to-Flange Weld.
Licensee's Code Reouest:
The licensee requests relief from performing a 100 percent volumetric examination on the Reactor Pressure Vessel Closure Head-to-Flange Weld.
licensee's Basis for Reouestina Relief: The licensee stated the Reactor Vessel (RPV) closure head-to-flange weld, WO8-09, is 45 feet in 1.ength.
The weld examinations are distributed in three segments of 15 feet lengths each inspection period.
The weld segments are identified as: WO8-09A(0" - 180"),
WO8-09B(180" - 360"), and WO8-09C(360" - 540").
Due to the design I
configuration of the closure head, no examinations may be performed from the flange side.
Limited examinations from the ring side are due to the head lifting lugs located at 0 degrees, 120 degrees, and 240 degrees. WO8-09A was examined by ultrasonics (UT) in the first inspection period and the licensee achieved approximately 40 percent examination volume coverage. WO8-098 was UT examined in the second inspection period and achieved 40 percent examination i
volume coverage.
WO8-09C is scheduled for examination during the third period with a estimated volume coverage of 40 percent.
It should be noted that i
approximately 100 percent of the weld volume was examined from the OD surface from the closure head ring side.
However, the required 1/2T base metal area was not completely examined on the flange side, because of the configuration l
of the reactor closure head.
Due to the extreme limited scanning area the licensee will only be able to achieve approximately 40 percent examination coverage of the RPV closure head-to-flange weld.
I Licensee's Prooosed Alternative Examination:
The licensee proposed as an alternative examination that, in addition to the visual examination performed during system leakage and hydrostatic pressure tests, performance of a best-effort ultrasonic examination to achieve as much Code coverage as possible and i
achieve meaningful results.
In addition, the licensee will perform a 100 percent surface examination (Magnetic Particle) of the closure head-to-flange weld flex area, of all accessible areas, in the third inspection period.
Staff Evaluation:
The staff determined from data provided by the licensee that the Code required volumetric examination of the head-to-flange weld is impractical to perform because the weld is obstructed by lifting lugs and the tapered portion of the flange.
In order to examine the welds in accordance with the requirement, the reactor vessel would require extensive design modifications.
Imposition of this requirement on the licensee would result in a hardship without a compensating increase in the level of safety or quality.
The licensee indicated that it could examine 40 percent or 72 inches of weld WO8-09C (this weld segment is 180 inches long) during the Third Period of the First Ten-Year ISI Interval. The total weld inspected out of the 540-inch weld length of the head-to-flange weld for the First Ten-Year ISI Interval will be 216 inches or 40 percent of the weld.
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. The licensee has proposed as alternative examinations, performance of an ultrasonic examination to the maximum extent practical.
This would be 40 percent volume of weld WO8-09C, 100 percent surface examination, and visual examinations during system leakage and hydrostatic pressure tests. Thus, the limited Section XI volumetric examination of 40 percent of weld WO8-09C, along with the surface examination and visual examination, will provide an acceptable level of quality and safety, and adequate assurance that inservice flaws have not developed in the subject reactor vessel welds, or that they will be detected and removed or repaired prior to the return of the RPV to service.
Therefore, pursuant to 10 CFR 50.55a(g)(6)(i) the staff has determined that the Code requirements are impractical to perform on the head-to-flange weld, that relief may be granted as requested, and that the licensee's proposed alternative examinations are acceptable
3.0 CONCLUSION
Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee determined that conformance with certain Code requirements are impractical at Sequoyah Unit 2 and submitted supporting information. The staff has reviewed the licensee's submittal and concluded that there are cases where relief can be granted as requested and alternative examinations may be authorized.
Pursuant to 10 CFR 50.55a(g)(6)(i) the staff concluded that the requirements are impractical for requests for Relief Nos. 151-16, 151-17, and 151-18 and that relief may be granted as requested.
The granting of these reliefs is authorized by law and will not endanger life, property, or the common defense and security, and is otherwise in the public interest.
Relief has been granted giving due consideration do to the burden upon the licensee that could result if the requirements were imposed on the facility.
The staff also concluded that the alternative examination for Request No. 151-15 may be authorized and that the proposed alternative would provide an acceptable level of quality and safety, and reasonable assurance that the structural integrity of the plant's systems, components, and supports will be maintained.
Principal Contributor:
T. McLellan Dated:
April 29, 1993