ML15218A137
| ML15218A137 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/30/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML15218A136 | List: |
| References | |
| NUDOCS 9506080555 | |
| Download: ML15218A137 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THE SECOND 10-YEAR INTERVAL INSPECTION INTERVAL REQUEST FOR RELIEF 94-05 FOR DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNIT 3 DOCKET NO. 50-287
1.0 INTRODUCTION
The Technical Specifications for Oconee Nuclear Station 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 and applicable addenda as required by Title 10 of the Code of Federal Regulations (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 second 10-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 12 months prior to the start of the 120-month inspection interval, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for the Oconee Nuclear Station, second 10-year inservice inspection (ISI) interval is the 1980 Edition through Winter 1980 Addenda. 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.
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-2 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.
By letter dated July 20, 1994, the licensee, Duke Power Company (DPC),
submitted Request for Relief No. 94-05, requesting deferral of the ASME Code requirements to perform ultrasonic examinations of 90% or more of the threads in the reactor vessel flange at Oconee Nuclear Station, Unit 3, during the second 10-year ISI interval.
With the examination technique used at the time of the testing, DPC was able to inspect only 78% of the threads. DPC subsequently determined that, by using an improved supplemental examination technique, it was practical to completely examine the threads. However, there were no remaining outages planned for the second ISI interval. DPC proposes to completely examine the threads during the next available Unit 3 outage in the first period of the third 10-year ISI interval.
The licensee requests that credit be given for these examinations for the third ISI interval as well as for the second interval.
The ISI schedule for this item will be shifted to the first period of subsequent 10-year ISI intervals.
2.0 EVALUATION The licensee has provided the following information in support of the subject relief requests:
Request for Relief No. 94-05:
The licensee requests relief from the Code required sequence of examination for the reactor vessel flange threads.
Code Requirement: ASME Section XI Paragraph IWB-2420(a) "The sequence of component examinations established during the first inspection interval shall be repeated during each successive inspection interval to the extent practical."
Basis for Requesting Relief:
Duke Power submitted request for relief serial number 92-12 to document welds examined ultrasonically with less than required examination coverage obtained. The threads in the reactor vessel flange was one of the items identified in this request for relief. As reported in the request for relief, Duke Power only examined 78% of the threads in the reactor vessel flange. After submittal of this request for relief, it was determined that Duke Power could in fact use supplemental techniques or scans to increase examination coverage on the threads in the reactor vessel flange and satisfy the coverage requirements of the code.
However, this determination was not made until after the last outage of
-3 the second ten year inservice inspection interval.
To take the unit off line and remove the reactor vessel head to examine the threads in the reactor vessel flange at this point, would create an extreme hardship on Duke Power.
The 78% examination coverage obtained did not identify any reportable indications. While not meeting code requirements, this examination does provide sufficient justification to allow examination to be delayed until the next refueling outage.
Licensee's Proposed Alternative Examination:
In lieu of performing the supplemental ultrasonic examination of the threads in the reactor vessel flange at this time, Duke Power will completely re-examine the threads in the reactor vessel flange during the next refueling outage. The next refueling outage is the first outage of the third inservice inspection interval.
Duke also proposes to allow this examination to satisfy the examination required in the third inservice inspection interval for unit 3. In order to maintain the examination frequency at approximately ten year intervals, this examination will be scheduled during the first inservice inspection period for all subsequent inservice inspection intervals.
Staff Evaluation:
The portion of Relief Request 92-12 pertaining to welds was granted by letter dated August 18, 1994. This evaluation is concerned with the the portion of Relief Request 92-12 related to the reactor flange threads and resubmitted as Relief Request 94-05. With the ultrasonic technique used in the second 10 year ISI interval, the inspection coverage was 78%, and no reportable indications were identified. After completing the inspection, the licensee determined that the Code-required coverage of 90% or better was achievable with the use of a supplemental examination technique. However, to meet the Code-required coverage in the second 10-year interval would result in a shutdown of Unit 3. Instead, the licensee has proposed to perform a complete examination of 90% or more of the threads during the next available refueling outage in the first period of the third 10-year ISI interval. This refueling outage is currently scheduled to begin in June, 1995, approximately 16 months after the end of the previous refueling outage during which 78% of the threads were examined. The staff finds this alternative acceptable because (1) the achieved inspection coverage during the second 10-year interval was only 12%
below the Code-required 90%, (2) no reportable indications were identified, and (3) the proposed complete examination of the threads during the first refueling outage of the third 10-year ISI interval will meet the coverage requirements of the Code, while only moderately exceeding the Code requirement for a 10-year interval between ISI examinations. Therefore, to require the shutdown of Unit 3 to permit the completion of the ultrasonic examination during the second 10-year ISI inspection interval would be a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
-4 The licensee also requests relief from the Code requirement that inservice inspections for this item be performed in the third period of future 10-year intervals, as was done in previous 10-year intervals. Because of the unusual circumstances described above, the complete examination of the reactor flange threads will be performed during the first period of the third 10-year ISI interval.
The licensee proposes to shift the ISI inspection schedule for this item to the first period of subsequent 10-year ISI intervals. This testing schedule is acceptable because the Code-specified 10-year interval between ISI tests would be maintained in future inservice inspections.
3.0 CONClUSION Paragraph 10 CFR 50.55a(g)(4) requires that components (including supports) that are classified as ASME Code Class 1, 2, and 3 meet the requirements, except design and access provisions and preservice requirements, set forth in applicable editions of ASME Section XI to the extent practical within limitations of design, geometry, and materials of construction of the components.
Pursuant to 10 CFR 50.55a(g)(5)(iii), the licensee concluded that conformance with certain Code requirements for ISI examinations would be impractical for its facility and proposed alternative examinations. The staff has reviewed the licensee's submittal and has concluded that the compliance with the Code would result in hardship or unusual difficulty without a compensating increase in quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii), relief may be granted as requested in Request for Relief No. 94-05 to perform the required ultrasonic examinations of the threads in the reactor vessel flange during the next available Unit 3 outage during the first period of the third 10-year ISI interval.
Future ISI testing of this item will be performed during the first period of subsequent 10-year ISI intervals.
Principal Contributor: S. Kirslis Date: May 30, 1995