ML18039A690
| ML18039A690 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/23/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18039A689 | List: |
| References | |
| NUDOCS 9903010200 | |
| Download: ML18039A690 (15) | |
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~P,8 RE0I UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, O.C. 2055&4001
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SAFETY EVALUATIONBY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE RELIEF FROM ASME BOILER AND PRESSURE VESSEL CODE SECTION XI RE UIREMENTS: RELIEF RE UEST NO. 2-ISI-6 FOR TENNESSEE VALLEYAUTHORITY BROWNS FERRY NUCLEAR PLANT UNIT2 DOCKET NUMBER: 50-260
1.0 INTRODUCTION
The Technical Specifications (TS) for the Browns Ferry Nuclear Plant (BFN), Unit 2, state that the inservice inspection 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 (88 PV) Code and applicable addenda as required by 10 CFR 50.55a(g}, except where specific written relief has been granted by the U.S. Nuclear Regulatory Commission (NRC or 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 difficultlywithout 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 pre-service 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 the first 10-year interval and subsequent intervals 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}
12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The applicable edition of Section XI of the ASME Code for the BFN Unit 2 second 10-year inservice inspection (ISI) interval is the 1986 Edition.
Pursuant to 10 CFR 50.55a(g)(5), ifthe 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, willnot 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 ifthe requirements were imposed.
ENCLOSURE 99030%0200 990223 PDR ADOCK 05000260 8
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4 2.0 EVALUATION H
By letter dated April 3, 1998, the licensee, Tennessee Valley Authority, submitted Request for Relief No. 2-ISI-6 for the Browns Ferry Nuclear Power Plant, Unit 2. The Idaho National Engineering and Environmental Laboratory, has evaluated the information provided by the licensee in support of 2-ISI-6.
Based on the results of the review, the staff adopts the contractor's conclusions and recommendations presented in the Technical Letter Report attached.
The basis for adopting the contractor's recommendations are summaiized below.
The ASME Code,Section XI, Examination Category B-D, Items B3.90 and B3.100 requires 100% volumetric examination of the reactor pressure vessel shell-to-vessel welds and IR
'ections, as defined by Figure IWB-2500-7.
In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the Code-required volumetric examination of shell-to-vessel welds listed in Table 2-ISI-6 of Attachment 2.
The licensee has performed the Code-required examinations to the extent practical and has maximized coverage by performing supplemental manual scans.
As a result, coverages of 52 to 77% have been achieved for the subject nozzle-to-vessel welds. Complete examination coverage is restricted by component configuration and adjacent physical obstructions.
To gain access for examination, design modifications would be required.
Imposition of this requirement would result in undue hardship on the licensee.
Further, the licensee has performed the Code-required examinations to the extent practical and has achieved coverages of 52 to 77% for the subject nozzle-to-vessel welds. Therefore, any existing patterns of degradation would have been detected by the examinations that were completed and thus a reasonable assurance of structural integrity has been provided.
The staff finds that the licensee's proposed. alternative provides reasonable assurance of structural integrity and safety for the subject welds. This conclusion is based on the fact that the subject welds have been examined to the extent practical and 52 to 77% of examination coverage of the welds was accomplished.
Therefore, a pattern of degradation, if present, would be detected.
- 3. CONCLUSION The staff concluded that the Code-required examinations are impractical to perform to the extent required by the Code.
Furthermore, the examinations performed by the licensee provide reasonable assurance of the continued inservice structural integrity of the subject components.
Therefore, Request for Relief No. 2-ISI-6 is granted pursuant to 10 CFR 50.55a(g)(6)(i). Granting the relief is authorized by law, will not endanger life, property, or the common defense and security, and is otherwise in the public interest, giving due consideration to the burden upon the licensee that could result ifthe requirements were imposed.
Principal Contributor: George Georgiev, NRR
Attachment:
Technical Letter Report Dated:
February 23, 1999
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s.o TECHNICAL LETTER REPORT ON SECOND 10-YEAR INTERVALINSERVICE INSPECTION REQUEST FOR RELIEF 2-Isl-6 REVISION 1 FOR TENNESSEE VALLEYAUTHORITY BROWNS FERRY NUCLEAR PLANT UNIT 2 DOCKET NUMBER: 50-260, 1.
INTRODUCTION By letter dated April 3, 1998, the licensee, Tennessee Valley Authority (TVA),
submitted Request for Relief 2-ISI-6, Revision 1, seeking relief from the requirements of the ASME Code,Section XI, for the Browns Ferry Nuclear Plant (BFN), Unit 2 second 10-year inservice inspection (ISI) interval. The Idaho National Engineering and Environmental Laboratory (INEEL) staff's evaluation of this request for relief is in the following section.
2.0 EVALUATION The information provided by Tennessee Valley Authority in support of Request for
'I Relief 2-ISI-6, Revision 1, from Code requirements has been evaluated and the basis for disposition is documented below.
The Code of record for the BFN, Unit 2 second 10-year ISI interval, which ends May of 2001, is the 1986 Edition of Section XI of the ASME Boiler and Pressure Vessel Code.
Re uest for Relief 2-ISI-6 Revision 1
Examination Cate or B-D Items B3.90 and B3.100 Reactor Pressure Vessel RPV Nozzle-to-Vessel Welds and Nozzle Inside Radiu IR Sections Code Re uirement:
Examination Category B-D, Items B3.90 and B3.100 require 100% volumetric examination of RPV nozzle-to-vessel welds and nozzle IR sections, as defined by Figure IWB-2500-7.
Licensee's Code Relief Re uest:
In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the Code coverage requirements for the RPV nozzle welds and nozzle IR section listed in'the table below.
Attachment
Weld ID Description Table 2-ISI-6, Revision I Coverage Limitation N1A 28" Recirc. Outlet 60%
Nozzle config., bioshield & thermo-couples N1B N2A N2B N2C N2G N2H N2J N3B 28" Recirc. Outlet 12" Recirc. Inlet 12" Recirc. Inlet 12" Recirc. Inlet 12" Recirc. Inlet
~12" Recirc. Inlet 12" Recirc. Inlet 12" Recirc. Inlet 26" Main Steam 55%
Nozzle config. & insulation support 77%
Nozzle config. & insulation support 77%
Nozzle config. & insulation support 55%
Nozzle config. & insulation support 75%
Nozzle config. & insulation support 72%
Nozzle config. & bioshield 77%
Nozzle config. & insulation support 52%
Nozzle config. & insulation support 77%
Nozzle config. &'insulation support N3D N4A 26" Main Steam 12" Feedwater 57%
59%
Nozzle configuration Nozzle config., adjacent nozzle &
insulation support ring N4B N4C 12" Feedwater 12" Feedwater 67%
Nozzle config. & insulation support 67%
Nozzle config. & insulation support N4F 12" Feedwater 54%
Nozzle config. & insulation support &.
adjacent insulation N5A N5B NBA N8A N9 10" Core Spray 10" Core Spray 4" Instrument Nozzle 4" Instrument Nozzle IR 4" CRD Return Line 53%
Nozzle config. & insulation support ring 75%
Nozzle config. & insulation support 65%
Nozzle config. & insulation support 68%
Nozzle configuration 73%
Nozzle configuration Licensee's Basis for Pro osed Alternative (as stated):
"The design configuration of the RPV nozzle-to-vessel welds precludes an ultrasonic examination of essentially 100 percent of the required volume.
The component design configuration limits ultrasonic examination coverage of the welds listed in Table 1 [paraphrased above].
"The design configuration of the small diameter (4-inch) instrumentation nozzle; the ASME Section XI, 1986 Edition, no addenda, requirement for the examination coverage to extend from the inside radius section along the nozzle bore axis to a distance equal to the vessel wall thickness; and the short weld blend radius on the vessel outside surface, preclude an ultrasonic examination of essentially 100 percent of the required volume.
The component design
configuration limits ultrasonic examination coverage of the inside corner region to the percentage listed in Table 1.
"Justification for Grantin of Relief:
"The design configuration of the subject nozzle-to-vessel welds precludes ultrasonic examination of essentially 100 percent of the required examination volume.
Access to the vessel-to-nozzle welds is by a series of doorways in the concrete biological shield wall. Insulation behind these doorways is designed for removal around the nozzle circumference.
In order to examine the welds in accordance with the Code requirement the RPV would require extensive design modifications.
The physical arrangement of the nozzle-to-vessel welds precludes ultrasonic examination from the nozzle side.
The limitations are inherent to the barrel-type nozzle-to-vessel weld design and is compounded by the close proximity of the biological shield wall.
"Scanning from the nozzle surface is ineffective due to the weld location and the asymmetrical inside surface where the nozzle and vessel converge.
Coverage was increased by scanning from the outside blend radius of the weld
'here practical.
Experience from the automated ultrasonic examination performed from the inside surface on BFN Unit 3, which is of similar design, has shown that the nozzle-to-vessel weld coverage will not be greatly improved even if performed from the inside surface utilizing the current state-of-the-art techniques.
"The configuration of the nozzle-to-vessel welds precludes ultrasonic examination from the nozzle side due to the weld location and the asymmetric inside surface where the nozzle and vessel converge.
The extent of examination coverage from the vessel side provides reasonable assurance that no flaws oriented parallel to the weld are present.
In addition, approximately 100 percent of the required ultrasonic-examination volume for flaws oriented transverse to the weld was performed from the vessel side.
"Design configuration of the small diameter (4-inch) instrumentation nozzle precludes ultrasonic examination of essentially 100 percent of the nozzle inside radius section due to the short weld blend radius on the vessel outside surface.
The examination volume successively examined included the most highly stressed area of the nozzle inside surface region.
The area that received no coverage was the required volume of the nozzle bore at the greatest radial distance from the vessel center-line where the stress concentrations are less than the stresses in the areas where examination coverage was obtained.
The examination coverage obtained provides reasonable assurance that no flaws are present.
"Radiographic examination as an alternate volumetric examination methods was determined to be impractical due to the radiological concerns.
Gaining access to the inside surface of the RPV to place radiographic film would require extensive personnel protection due to high radiation and contamination levels.
Also, due to the varying thickness at the outside blend radius of the weld several radiographs may be required of one area to obtain the required coverage
and/or film density.
The additional Code coverage gained by radiography is impractical when weighed against the radiological concerns.
"Therefore, TVA concludes that performing an ultrasonic volumetric examination of essentially 100 percent of the nozzle-to-vessel full penetration welds in the RPV would be impractical.
Further, it would also be impractical to perform other volumetric examinations (i.e. radiography) which may increase examination coverage.
A maximum extent ultrasonic examination of the subject areas provides an acceptable level of quality and safety.
TVA concludes that significant degradation, if present, would have been detected during an ultrasonic examination performed to the maximum extent practical of the subject welds and inside corner region.
As a result, reasonable assurance of operational readiness of the subject welds has been provided.
Therefore, pursuant to 10 CFR 50.55a(g)(5)(iii), TVA requests that relief be granted for the second inspection interval ~
Licensee's Pro osed Alternative as stated:
"None.
In lieu of the Code required essentially 100 percent volume ultrasonic examination, TVA proposes an ultrasonic examination of accessible areas to the extent practical given the component design configuration of the RPV nozzle-to-vessel welds and nozzle size."
Evaluation:
The Code requires 100% volumetric examination of the subject RPV nozzle-to-vessel welds and IR section.
However, complete examination of these areas is limited by component configuration (i.e., outside blend radius and set-in barrel design) and adjacent physical obstructions (i.e., biological shield wall, thermocouples, and insulation supports).
These restrictions limit access and make the Code coverage requirements impractical for the subject nozzle IR section and nozzle-to-vessel welds.
To meet the Code coverage requirements, design modifications would be necessary to provide access for examination.
Imposition of the Code requirements would result in an undue hardship on the licensee.
The licensee has performed the Code-required examinations to the extent practical and has maximized coverage by performing supplemental manual scans.
As a result, coverages of 52 to 77% have been achieved for the subject nozzle-to-vessel welds.
This level of coverage, in conjunction with the complete examination of the remaining RPV nozzle IR sections and nozzle-to-vessel welds, should have detected any existing patterns of degradation and provides reasonable assurance of the continued structural integrity for the RPV nozzles at BFN, Unit 2.
3.0 CONCLUSION
The INEEL staff evaluated the licensee's submittal and concludes that the subject nozzle-to-vessel welds cannot be examined to the extent required by the Code at BFN, Unit 2.
It is further concluded that reasonable assurance of the structural integrity has been provided by the examinations that were performed.
Therefore, it is recommended that relief be granted pursuant to 10 CFR 50.55a(g)(6)(i).
Mr. J. A. Scalice Tennessee Valley Authority BROWNS FERRY NUCLEAR PLANT CC:
Senior Vice President Nuclear Operations Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Jack A. Bailey, Vice President Engineering &Technical Services Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Karl W. Singer, Site Vice President Browns Ferry Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Decatur, AL 35609 General Counsel Tennessee Valley Authority ET 10H 400 West Summit Hill Drive Knoxville, TN 37902 Mr. Raul R. Baron, General Manager Nuclear Assurance Tennessee Valley Authority 5M Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Robert G. Jones, Plant Manager Browns Ferry Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Decatur, AL 35609 Mr. Mark J. Burzynski, Managar Nuclear Licensing Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801 Mr. Timothy E. Abney, Manager Licensing and Industry Affairs Browns Ferry Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Decatur, AL35609 Senior Resident Inspector U.S. Nuclear Regulatory Commission Browns Ferry Nuclear Plant I0833 Shaw Road Athens, AL35611 State Health Officer Alabama Dept. of Public Health 434 Monroe Street Montgomery, AL 36130-170I Chairman Limestone County Commission 310 West Washington Street Athens, AL 35611
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