ML15113A712
| ML15113A712 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 07/01/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML15113A711 | List: |
| References | |
| NUDOCS 9907070104 | |
| Download: ML15113A712 (7) | |
Text
FRE~ut UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF NO. 98-03 FROM ASME CODE SECTION XI REQUIREMENT DUKE ENERGY CORPORATION OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
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 (B&PV) Code and applicable addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(6)(g)(i). Section 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 difficulty 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 pre-service examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components,'Wto 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 Oconee Nuclear Station, Units 1, 2, and 3, Third 10-Year Interval Inservice Inspection (ISI) is the 1989 Edition.
2.0 EVALUATION By letter dated September 16, 1998, Duke Energy Corporation (licensee), submitted its Third 10-Year Interval ISI Program Plan Request for Relief (RR) No. 98-03 for Oconee Nuclear Station, Units 1, 2, and 3. The Idaho National Engineering and Environmental Laboratory (INEEL), has evaluated the information provided by the licensee in support of its third 10-Year 9907070104 990701 Enclosure PDR ADOCK 05000269 P
-2 Interval 151 Program RR No. 98-03 for Oconee Nuclear Station, Units 1, 2, and 3. Based on the results of this review, the staff adopts the contractor's conclusions presented in the technical letter report attached.
The information provided by the licensee in support of the requests for relief from the Code requirements has been evaluated and the basis for disposition is documented below.
RR No. 98-03: ASME Code,Section XI, Examination Category B-D, Items B3.1 10 and B3.120 require 100 percent volumetric examination of all pressurizer nozzle-to-vessel welds and inside radius (IR) sections as defined by Figure IWB-2500-7(a) each inspection interval.
Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from examining three pressurizer sensing nozzle-to-vessel welds for each Oconee unit and their associated IR sections.
The staff reviewed the information and figures provided by the licensee that describe the limitations associated with examination of the subject welds and IR sections. The staff determined that the Code examination requirements are impractical for these components. To obtain complete volumetric coverage, design modifications would be required, causing a significant burden on the licensee. However, the staff recommends that the licensee pursue the use of computer modeling to achieve greater coverage, as proposed by the licensee.
The licensee proposed to perform the volumetric examinations to the extent practical. For the Unit 2 pressurizer sensing nozzle-to-vessel welds, approximately 29 percent of the required volume of each nozzle was examined. For the associated IR sections, approximately 66 percent of the required volume of each nozzle was examined. In addition to the limited volumetric examination, the licensee proposes to use a system leakage test (VT-2 visual examination), performed after each refueling outage, to complement the volumetric examination.
The examinations performed in Unit 2 and the examinations to be performed in Units 1 and 3 will detect significant degradation, if present, and provide reasonable assurance of structural integrity of the subject components. The relief is authorized by law and will not endanger life or property or the common defense and security and is, therefore, in the public interest giving due consideration to the burden upon the licensee that would result if the requirements were imposed on the facility. Therefore, relief is granted pursuant to 10 CFR 50.55a(g)(6)(i).
3.0 CONCLUSION
The staff concludes that the subject Code inservice examinations are impractical to perform to the extent required by the Code. If the Code requirements were imposed it would be a burden on the licensee, because in order for the licensee to meet the Code requirements the subject components would have to be redesigned. In addition, the examinations performed in Unit 2 and the examinations to be performed in Units 1 and 3 will detect existing significant degradation, if present, and provide reasonable assurance of structural integrity of the subject components. Therefore, relief is granted pursuant to 10CFR50.55a(g)(6)(i). The relief is authorized by law and will not endanger life or property or the common defense and security and
-3 is, therefore, in the public interest giving due consideration to the burden upon the licensee that would result if the requirements were imposed on the facility. If actual examination coverages for Units 1 and 3 are not essentially the same or greater than achieved on Unit 2, specific relief requests will be necessary.
Attachment:
Technical Letter Report Principal Contributor: Thomas McLellan Date:
July 1, 1999
TECHNICAL LETTER REPORT ON THIRD 10-YEAR INTERVAL INSERVICE INSPECTION REQUEST FOR RELIEF 98-03 FOR DUKE ENERGY CORPORATION OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 DOCKET NUMBERS: 50-269, 50-270, AND 50-287
- 1.
INTRODUCTION By letter dated September 16, 1998, Duke Energy Corporation (the licensee), submitted Request for Relief No. 98-03 seeking relief from the requirements of the American Society Mechanical Engineer (ASME) Code,Section XI, for the Oconee Nuclear Station, Units 1, 2, and 3, third 10-year inservice inspection (ISI) interval. The Idaho National Engineering and Environmental Laboratory (INEEL) staff's evaluation of the subject request for relief is in the following section.
- 2.
EVALUATION The information provided by Duke Energy Corporation in support of the request for relief from Code requirements has been evaluated and the basis for disposition is documented below. The Code of record for the Oconee Nuclear Station, Units 1, 2, and 3, third 10-year ISI interval, which is scheduled to end in July, September, and December, 2004, respectively, is the 1989 Edition of Section XI of the ASME Boiler and Pressure Vessel Code.
Request for Relief No. 98-03, Examination Category B-D, Items B3.1 10 and B3.120, Pressurizer Nozzle-to-Vessel Welds and Inside Radius Sections Code Requirement: Examination Category B-D, Items B3.1 10 and B3.120 require 100 percent volumetric examination of all pressurizer nozzle-to-vessel welds and inside radius sections as defined by Figure IWB-2500-7(a) each inspection interval.
Licensee's Code Relief Request: In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from examining three pressurizer sensing nozzle-to-vessel welds for each Oconee Unit, and their associated inside radius sections, to the extent required by the Code. The item numbers, which are the same for each of the three Oconee Units, are:
Nozzle-to-Shell Welds Nozzle Inside Radius B03.110.006 B03.120.006 B03.110.007 B03.120.007 B03.110.008 B03.120.008 Attachment
-2 Licensee's Basis for Requesting Relief (as stated):
'While the examinations have been completed only for Unit 2 at this time, relief is also being sought for Units 1 and 3 for the same welds. If, for some reason, the actual examination coverages of the welds referenced in this Request for Relief for Units 1 and 3 are less than those listed for Unit 2 in Section IV of this request, additional Requests for Relief will be submitted on a case by case basis."
"Pressurizer Sensing Nozzle-to-Vessel Welds 2-PZR-WP26-4, 2-PZR-WP26-5 and 2-PZR-WP26-6 (Item Numbers B03.110.006, B03.110.007 and B03.110.008) were examined to the maximum extent practical using ultrasonic techniques in accordance with the requirements of ASME Section V, Article 4, and ASME Section XI, Appendix 1, 1989 Edition.
"These welds are limited to 28.8 percent coverage of the required volume because of the nozzle configuration. In order to achieve more coverage, the nozzles would have to be re-designed to allow scanning from both sides of the weld.
"Pressurizer Sensing Nozzle-to-Vessel Inside Radius Sections 2-PZR-WP26-4, 2-PZR-WP26-5 and 2-PZR-WP26-6 (Item Numbers B03.120.006, B03.120.007 and B03.120.008) were examined to the maximum extent practical using ultrasonic techniques in accordance with the requirements of ASME Section V, Article 4, and ASME Section XI, Appendix 1, 1989 Edition.
"These welds are limited to 65.8 percent coverage of the required volume because of the nozzle configuration. Duke Energy is investigating the use of computer modeling to determine the feasibility of achieving greater coverage."
"The Code requires 100 percent volumetric examination of all Pressurizer Nozzle to-Vessel Welds [and Inside Radius Sections]. However, the taper on the nozzle side of the weld restricts scanning and prevents complete volumetric coverage of Pressurizer Sensing Nozzle-to-Vessel Welds 2-PZR-WP26-4, 2-PZR-WP26-5 and 2-PZR-WP26-6. Therefore, the 100 percent volumetric examination is impractical for these nozzle-to-vessel welds [and inside radius sections]. To meet Code examination requirements, modifications to the nozzles would be necessary to allow scanning from both sides of the weld. Modification to this portion of the reactor coolant system would create a considerable burden on Duke Energy.
"Duke Energy obtained 28.8 percent coverage of the Pressurizer Sensing Nozzle to-Vessel Inside Radius Sections 2-PZR-WP26-4, 2-PZR-WP26-5 and 2-PZR WP26-6 [65.8 percent coverage on the associated inside radius sections]. It is recognized that this represents a small part of the required Code examination volume. However, in conjunction with the Code required VT-2 visual examination after each refueling outage and the 10-year hydrostatic test; Duke Energy believes this provides reasonable assurance of the continued structural integrity of the subject nozzle-to-vessel welds.
-3 "Pursuant to 10 CFR 50.55a(g)(6)(i), granting this relief for the Pressurizer Sensing Nozzle-to-Vessel Welds [and Inside Radius Sections] will provide reasonable assurance of weld/component integrity,...'is authorized by law and will not endanger life or 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, if the requirements were imposed on the facility."'
Licensee's Proposed Alternative Examination (as stated):
"The use of radiography as an alternative volumetric examination of the Pressurizer Sensing Nozzle-to-Vessel Welds [and Inside Radius Sections] referenced in this request is not a viable option. Restrictions to performing radiography are primarily due to inability to access the inside of the Pressurizer to place film or to position a radiographic source.
"Duke Energy proposes to use the pressure test and VT-2 visual examination to compliment the limited examination coverage. The Code requires (reference Table IWB-2500-1, Item Number B15.20) that a system leakage test be performed after each refueling outage. Additionally a system hydrostatic test (reference Table IWB-2500-1, Item Number B15.21) is required once during each 10-year inspection interval. These tests require a VT-2 visual examination for evidence of leakage.
This testing will provide adequate assurance of pressure boundary integrity.
"In addition to the above Code required examinations (volumetric and pressure test), there are other activities which provide a high level of confidence that, in the unlikely case that leakage did occur through these welds, it would be detected and isolated. Specifically, leakage from these welds would be detected by monitoring of the Reactor Coolant System (RCS), which is performed once each shift under procedure PT/1,2,3/A/0600/1 0, 'RCS Leakage'. This RCS leakage monitoring is a requirement of Technical Specification 3.1.6, 'Leakage'. Leakage is also evaluated in accordance with this technical specification. The leakage could be detected through several methods. One method is the RCS mass balance calculation.
Another method is by use of the Reactor Building air particulate monitor. This monitor is sensitive to low leak rates; the iodine monitor, gaseous monitor and area monitor are capable of detecting any fission products in the coolant and will make these monitors sensitive to coolant leakage. In addition to the radiation monitors, leakage is also monitored by a level indicator in the Reactor Building normal sump.
Another check would be a loss of level in the Letdown Storage Tank.
"Duke Energy has examined the welds referenced in this request to the maximum extent possible utilizing the latest in examination techniques and equipment. Duke Energy will continue to perform ultrasonic examination of all welds identified in Section I of this request (for all units) to the maximum extent practical, within the limits of original design and construction, in accordance with the requirements of ASME Section V, Article 4, and ASME Section XI, Appendix 1, 1989 Edition, and Code Case N-460. This will provide reasonable assurance of weld/component
-4 integrity. Thus, an acceptable level of quality and safety will have been achieved, and public health and safety will not be endangered by allowing relief from the aforementioned Code requirements."
Evaluation: The Code requires 100 percent volumetric examination of the pressurizer nozzle-to-vessel welds and inside radius (IR) sections each inspection interval. The INEEL staff reviewed the information and figures provided by the licensee that describe the limitations associated with examination of the subject welds and IR sections.
Because of the surface geometry, the Code examination requirements are impractical for these components. To obtain complete volumetric coverage, design modifications would be required, causing a significant burden on the licensee.
The licensee proposed to perform the volumetric examinations to the extent practical.
For the Unit 2 pressurizer sensing nozzle-to-vessel welds, approximately 29 percent of the required volume of each nozzle was examined. For the associated inside radius sections, approximately 66 percent of the required volume of each nozzle was examined.
In addition to the limited volumetric examination, the licensee proposes to use a system leakage test (VT-2 visual examination), performed after each refueling outage, to complement the volumetric examination. The examinations performed in Unit 2, and the examinations to be performed in Units 1 and 3, should detect existing areas of degradation, if present, and provide reasonable assurance of structural integrity.
- 3.
CONCLUSION The INEEL staff evaluated the licensee's submittal and concluded that the subject inservice examinations cannot be performed to the extent required by the Code at the Oconee Nuclear Station, Units 1, 2, and 3. Based on the impracticality of performing the volumetric examinations required by the Code, the burden on the licensee if the Code requirements were imposed, and the examinations that can and will be performed, it is recommended that relief be granted pursuant to 10 CFR 50.55a(g)(6)(i). If actual examination coverages for Units 1 and 3 are less than those obtained for Unit 2, additional requests for relief will be necessary.