ML15218A262
| ML15218A262 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/12/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML15218A261 | List: |
| References | |
| NUDOCS 9504170424 | |
| Download: ML15218A262 (4) | |
Text
.RREG UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF NO. 94-06 FOR DUKE POWER COMPANY OCONEE NUCLEAR STATION, UNIT 2 DOCKET NO. 50-270
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.
9504170424 950412 PDR ADOCK 05000270 PDR
-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.
In a letter dated July 18, 1994, the licensee, Duke Power Company, submitted Request for Relief No. 94-06, asking relief from the hydrostatic pressure testing requirements of the ASME Code for the second 10-year inservice inspection interval and for the testing of welds after replacement by welding of Main Steam System Valves 2MS-76 and 2MS-84, and Steam Drain System Valves 2SD-418, 2SD-419, 2SD-420 and 2SD-421. Relief is requested for the welds on the inlet (steam generator) side of these valves. In lieu of the Code required hydrostatic testing of these Class 2 items, the licensee proposed to perform the alternate examinations specified by ASME Section XI Code Cases N-416-1 and N-498.
In lieu of the hydrostatic test, Code Case N-416-1, "Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding, Class 1, 2 and 3," requires (a) NDE performed in accordance with the methods and acceptance criteria of the 1992 Edition of Section III, and (b) prior to or immediately upon return to service, a VT-2 visual examination performed in conjunction with a system leakage test at normal operating pressure and temperature. In lieu of the hydrostatic test, Code Case N-498, "Alternative Rules for:10-Year Hydrostatic Pressure Testing for Class 1 and 2 Systems," permits the use of a system leakage test at normal operating pressure and temperature, and a VT-2 visual examination of all components within the Class 2 boundary. Use of both Code cases was requested because the ASME Code requires hydrostatic testing for both the Oconee Unit 2 second 10-year ISI interval and following component replacement by welding. The licensee has performed the NDE of the replacement welds required by Code Case N-416-1 and the VT-2 visual examinations during system leakage tests required by both Code cases.
2.0 EVALUATION Request for Relief No. 94-06: The licensee requests relief from the Code required hydrostatic pressure testing for the second 10-year ISI interval for Oconee Unit 2 and for welds after replacement by welding of Main Steam System valves 2MS-76 and 2MS-84, and Steam Drain System valves 25D-418, 2SD-419, 25D-420 and 2SD-421. Relief is requested only for the welds on the inlet (steam generator) side of these Class 2 valves.
Code Requirement:
Paragraph IWA-4400(a) of Section XI of the ASME Code, 1980 Edition (with addenda through Winter 1980) states: "After repairs by welding on the pressure retaining boundary a system hydrostatic test shall be
-3 performed in accordance with IWA-5000." Hydrostatic testing in accordance with Table IWC-2500-1 is also required for the Oconee Unit 2 10-year ISI interval.
Licensee's Basis for requesting Relief:
Performing the hydrostatic test on 2MS-76 and 84 would require filling and pressurizing the secondary side of the 2A and 2B steam generators as well as several hundred feet of feedwater and main steam pipe associated with each steam generator. Well over 200 man-hours would be used just to prepare for and recover from the hydrostatic test. This time is needed for such items as:
- 1) installing additional supports for the main steam lines prior to the hydrostatic pressure test and restoration afterwards,
- 2) adjusting approximately 20 spring hangers for the main steam lines and restoration afterwards,
- 3) gagging 16 relief valves for the higher pressure and restoration afterwards,
- 4) repacking approximately 100 valves after the hydrostatic test (required due to both the higher hydrostatic test pressure and the use of water on valves designed for steam),
- 5) isolating over 30 instruments and restoring them afterwards, and
- 6) inspecting at least 10 other valves (relief valves and stop valves) after completion of the hydrostatic test.
This work would extend the outage at least 5 days and cost approximately 3 million dollars in lost revenues.
To perform the hydrostatic test on 2S0-418, 419, 420, and 421 would require system modification. The piping downstream of these valves is
[at] a lower design pressure. To perform the test from the downstream direction would over pressurize this piping. There is no connection on the upstream side of the valves to be able to pressurize these welds. A test connection would be required to be added to each line in order to establish a hydrostatic connection point, creating needless welds.
Licensee's Proposed Alternative Examination: The licensee proposed that the subject welds and their associated systems receive the alternative examinations specified in ASME Code Cases N-416-1 and N-498. In lieu of hydrostatic testing, Code Case N-498 requires a VT-2 visual examination of all Class I and Class 2 pressure retaining components within the system boundary, in conjunction with a system leakage test at nominal operating pressure. For Class 2 components replaced by welding, Code Case N-416-1 requires a nondestructive examination of the welds in addition to a VT-2 visual examination during a system leakage test at nominal operating pressure.
-4 The licensee has performed the alternative tests specified in Code Cases N-416-1 and N-498 when the welds for valves 2MS-76, 2MS-84, and 2SD-418 through 2SD-421 were made. These tests included the specified NDE and the system leakage test, with the associated VT-2 examination at nominal operating pressure.
Staff Evaluation: The system hydrostatic test required by the ASME Code for the 10-year ISI interval, and following weld repairs and component replacement by welding, is performed at a test pressure 1.25 times normal operating pressure. Because the subject welds cannot be isolated from the steam generators, hydrostatic testing would involve the significant practical difficulties associated with filling and pressurizing the steam generators, and disposing of the potentially contaminated test water. Also, the steam generators are limited by design as to the number of hydrostatic pressure tests (35) that are allowed in the plant's operating life span. Furthermore, industry experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures causing a preexisting flaw to propagate through-wall.
Leaks in most cases are being found at normal operating pressure. Hydrostatic testing subjects the system components to only a small increase in pressure over the design pressure and therefore does not present a significant challenge to pressure boundary integrity, since piping dead weight, thermal expansion, and seismic loads, which may present a far greater challenge to the structural integrity of a system than fluid pressure, are not part of the loading imposed during a hydrostatic test. Accordingly, hydrostatic pressure testing is primarily regarded as a means to enhance leakage detection during the examination of components under pressure, rather than as a measure to determine the structural integrity of the components.
Nondestructive examinations, such as by radiography, provide a more reliable indication of weld integrity. On the basis of this review, the staff has determined that the Code-required hydrostatic test would impose an undue hardship on the licensee without a compensating increase in quality and safety.
In lieu of the Code-required hydrostatic testing, the licensee has performed the alternative testing allowed by ASME Code Cases N-416-1 and N-498. These tests included NDE of the subject welds and a VT-2 visual examination during a system leakage test at normal operating pressure. The staff has determined that this alternative testing program meets the requirements of the Code Cases and provides reasonable assurance of continued structural reliability of the subject systems.
3.0 CONCLUSION
The staff has reviewed and evaluated the Ticensee's submittal, and it has concluded that compliance with the hydrostatic pressure testing requirements of the Code following repairs by welding on the subject steam generator valves would result in undue hardship without a compensating increase in quality and safety. The staff also finds that the licensee's proposed alternative testing program will provide reasonable assurance of the structural integrity of the pressure retaining boundary. Therefore, pursuant to 10 CFR 50.55a(a)(3)(ii),
the licensee's proposed alternative contained in Request for Relief No. 94-06, use of Code Cases N-416-1 and N-498, is authorized.
Principal Contributor: S. Kirslis Dated:
April 12, 1995