ML16141B205
| ML16141B205 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/29/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16141B206 | List: |
| References | |
| NUDOCS 9706020222 | |
| Download: ML16141B205 (5) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF NO. 96-02, REVISION 1 ON THE THIRD TEN-YEAR INSERVICE INSPECTION INTERVAL OCONEE NUCLEAR STATION, UNITS NO. 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, 50-287
1.0 INTRODUCTION
The Technical Specifications for Oconee Units 1, 2, and 3, state that the 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 (ASME Code) and applicable addenda as required by Title 10 of the Code of Federal Requlations (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).
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 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 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) on the date 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, for the current inservice inspection (ISI) interval is the 1989 Edition. 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 and modifications listed therein and subject to Commission approval.
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 9706020222 970529 PDR ADOCK 05000269
- PDR,
-2 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.
By letter dated July 24, 1996, and supplemented by letter dated April 1, 1997, Duke Power Company (licensee) requested relief from compliance with the applicable ASME Code,Section XI, by taking credit for limited volumetric examination in lieu of the Code-required volumetric examination of greater than 90 percent on steam generator primary side tubesheet-to-head welds, letdown heat exchanger primary side nozzle-to-vessel welds, and the steam generator shell circumferential weld.
The details of the welds'that are described in the licensee's submittals are based on Unit 2 data. However, for all welds listed, al1 configurations, including interferences, are the same for Units 1, 2, and 3. Therefore, the licensee is also seeking relief for the same welds on Units 1 and 3. In the submittal the licensee stated that if the actual examination coverage of the welds for Units 1 and 3 are less than that for Unit 2, additional requests for relief will be submitted on a case-by-case basis.
The staff has reviewed and evaluated the licensee's request and supporting information on the proposed alternative to the Code requirements for Oconee Units 1, 2 and 3, pursuant to the provisions of 10 CFR 50.55a(g)(6)(i).
2.0 DISCUSSION
Licensee's Request for Code Relief:
The licensee requests relief from the requirement of the ASME Code,Section XI, 1989 Edition, to examine 100 percent of weld volume of the Steam Generator Tubesheet-to-Head welds, the Letdown Cooler Heat Exchanger Nozzle to-Vessel welds, and the Steam Generator Circumferential Shell welds, due to interference and/or geometry.
Weld Identification:
- a. Steam Generator (Primary Side) Tubesheet-to-Head Welds:
2-SGA-WG58-1, Item Number B02.040.001 2-SGA-WG58-2, Item Number B02.040.002 1-SGA-WG58-1, Item Number B02.040.001 1-SGA-WG58-2, Item Number B02.040.002 3-SGA-WG58-1, Item Number B02.040.001 3-SGA-WG58-2, Item Number 802.040.002
- b. Heat Exchangers (Primary Side) Nozzle-to-Vessel Welds:
- 23.
2-LDCA-INLET-VI, Item Number B03.150.001 2-LDCA-OUTLET-V2, Item Number B03.150.002 1-LDCA-IN-V2, Item Number B03.150.001 3-LDCA-OUT-V6, Item Number B03.150.002 3-LDCA-IN-V, Item Number B03.150.001 3-LDCA-OUT-V5, Item Number B03.150.002
2-SGA-WG8-3, Item Number C01.010.002 1-SGA-WG8-3, Item Number C01.010.002 3-SGA-WG8-3, Item Number C01.010.003 Code Requirement:
The ASME Code,Section XI, 1989 Edition requires 100 percent volumetric examination of all welds identified in (a) and (b) and 100 percent volumetric examination of circumferential shell welds at gross structural discontinuities only, identified in (c) above.
When the entire examination volume cannot be examined due to interference or geometry, the Code Case N-460 allows credit for full volume coverage for any weld, if at least 90 percent of the volume is examined.
Licensee's Basis for Relief Request:
(As stated)
Steam Generator (Primary Side) Tubesheet-to-Head welds, 2-SGA-WG58-1 and 2-SGA-WG58-2 (Item Numbers B02.040.001 and B02.040.002 respectively) were examined to the maximum extent practical using ultrasonic techniques in accordance with the requirement of ASME Section V Code, Article 4, and ASME Section XI Code, Appendix I, 1989 Edition.
Reference Attachment A for drawing.
Weld 2-SGA-WG58-1 is limited to 72.5% coverage of the required ASME Section XI Code volume because of Upper Tube Sheet geometry, i.e, taper.
Weld 2-SGA-WG58-2 is limited to 71% coverage of the required ASME Section XI Code volume because of Lower Tube Sheet geometry, i.e, taper and support skirt interference.
Letdown Cooler Heat Exchangers (Primary Side) Nozzle-to-Vessel welds 2-LOCA-INLET-VI and 2-LDCA-OUTLET-V2 (Item Numbers B03.150.001 and B03.150.002 respectively) were examined to the maximum extent practical using ultrasonic techniques in accordance with the requirements of ASME Section V Code, Article 4, and ASME Section XI Code, Appendix I, 1989 Edition. Reference Attachment B for drawing.
Weld 2-LDCA-INLET-V1 is limited to 26.96% coverage of the required ASME Section XI Code volume because of branch connection interference.
-4 Weld 2-LDCA-OUTLET-V2 is limited to 26.96% coverage of the required ASME Section XI Code volume because of branch connection interference.
Pressure retaining welds in Pressure Vessels, Shell Circumferential weld 2-SGA-WG8-3 (Item Number C01.010.002) was examined to the maximum extent practical using ultrasonic techniques in accordance with the requirements of ASME Section V Code, Article 4, and ASME Section XI Code, Appendix I, 1989 Edition. Reference Attachment A for drawing.
This weld is limited to 64.5% coverage of the required ASME Section XI Code volume because of shell geometry, i.e, taper.
Licensee's Proposed Alternate Examination or Testing:
The licensee proposes to use the VT-2 visual examination, which is performed as part of system leakage test after each refueling outage, to complement the limited examination coverage of the welds in assessing their integrity.
3.0 EVALUATION The ASME Code,Section XI, 1989 Edition requires 100 percent volumetric examination of the above welds. The licensee performed a best-effort examination of the welds, but, due to weld geometry and/or interference, the required volumetric examination coverage could not be obtained. There is no other volumetric examination method which can be used successfully, as an alternative to ultrasonic examination, to examine the Code-required volume in the subject welds. If the Code requirements were imposed, the components would have to be redesigned and would have to be replaced, which places a severe burden on the licensee. The staff believes that the volumetric coverage that was obtained on each of the welds would have most likely detected any existing pattern of degradation, which would warrant further examination. Furthermore, the VT-2 visual examinations that are performed as part of system leakage test after each refueling outage and the 10-year hydrostatic test would confirm leak-tight integrity of the welds and hence, the operational readiness of the components.
4.0 CONCLUSION
The staff has reviewed the licensee's Request for Relief No. 96-02, Revision 1, which uses Oconee Nuclear Station Unit 2 as the basis and was extended by the licensee to include Units 1 and 3, and concludes that the limited volumetric examination described, complemented by the VT-2 visual examination of the subject welds, provides reasonable assurance of a leak tight pressure boundary and hence, an operational readiness for each of the components. Compliance with the Code requirements are impractical due to weld geometry and/or interference. If the Code requirements were imposed, the components have to be redesigned and installed, which would impose a significant burden on the licensee. Therefore, relief from the Code requirements is granted for Unit 2, pursuant to 10 CFR 50.55a(g)(6)(i). In addition, relief is also granted, pursuant to 10 CFR 50.55a(g)(6)(i) for the identical welds in Units 1 and 3, provided that the volumetric examination percentage of the identical welds in these units remain at least equal to or
-5 greater than the corresponding percentages described in this relief request.
In addition, the Code-required hydrostatic test will be performed at 1.25 times the system design pressure. The relief 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.
Principal Contributor:
Prakash Patnaik Date: May 29, 1997