ML20138G193
| ML20138G193 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/16/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20138G183 | List: |
| References | |
| NUDOCS 9610180279 | |
| Download: ML20138G193 (4) | |
Text
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UNITED STATES
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,j NUCLEAR REGULATORY COMMISSION
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION THE SECOND 10-YEAR INTERVAL INSERVICE INSPECTION PLAN RE0 VEST FOR RELIEF NO. SPT-14. REVISION 1 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION. UNIT 2 DOCKET NUMBER:
50-339 1.
INTRODUCTI0t{
The Technical Specifications for North Anna Power Station, Unit 2, 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 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).
The 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 preposed 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 the ASME Code,Section XI, for North Anna Power Station, Unit 2, during the second 10-year inservice inspection (ISI) interval, is tia 1986 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.
1 Enclosure l
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PDR ADOCK 05000339 P
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Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examinati0n 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 impmed.
By letter dated June 24, 1996, Virginia Electric ad Power Company, the licensee for North Anna Power Station, Unit 2, requested a revision to the relief previously granted to the licensee on August 8, 1995, from the requirements of the 1986 edition of the ASME Boiler and Pressun Vessel Code,Section XI, in regard to corrective measures for system pressure tests, as stated in Subsection IWA-5250 (a)(2).
The NRC staff has reviewed and evaluated the licensee's request and ti.e supporting information on the proposed revision to relief request SPT-1* for North Anna, Unit 2, pursuant to the provisions of 10 CFR 50.55a(a)(3)(i).
2.0 EVALVATION
REVISION TO RELyrF RE0 VEST N0 SPT-14:
The licensee was granted a relief from the requirement of 1986 ASME Code,Section XI, Subsection IWA-5250 (a)(2), which allowed the licensee to remove and VT-3 visually examine one bolt closest to the source of leakage as part of evaluation instead of removal of bolting at a bolted connection during a system pressure test.
1986 ASME Code Section XI Reauirement:
Subsection IWA-5250 (a)(2) states that the source (s) of leakage detected during the conduct of a system pressure test shall be located and evaluated by the Owner for corrective action.
For leakage occurring at a bolted connection, the bolting shall be removed, VT-3 visually examined for corrosion, and evaluated in accordance with IWA-3100.
Licensee's Revised Code Relief Reauest: The licensee requests to revise its approved Code relief to require removal of the closest bolt to the leakage for VT-3 visual examination during a system pressure test only if a systematic evaluation concludes that a bolt removal is warranted.
Licensee's Basis for Reouestina Relief:
" Leaking conditions at a bolted connection may be an important variable in the degradation of fasteners. However, leakage is not the only variable, and some cases may not be the degradation mechanism. Other variables to be 2
i considered are: bolting materials, leaking medium, duration of the leak, and orientation of the leak (not all bolts may be wetted). These variables are important to consider before disassembling a bolted connection for a visual VT-3 examination.
Removal of bolting at a mechanical connection may not be the most prudent decision and may cause undue hardship without a compensating increase in the level of quality or safety.
Virginia Power proposes an alternative to the requirements of IWA-5250 (a)(2) that will provide an equivalent level of quality and safety at Class 1, 2, and 3 bolted j
connections."
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Licensee's Proposed Alternative Examination:
" Leakage discovered at a bolted connection by visual VT-2 examination during a system pressure test will be evaluated to determine the susceptibility of the bolting to corrosion and potential failure.
This evaluation will consider l
the following variables:
1.
Location of leakage; 2.
History of leakage; 3.
Fastener materials; l
4.
Evidence of corrosion with the connection assembled; 5.
Corrosiveness of the process fluid; 6.
History and studies of similar fastener material in a similar environment; and 7.
Other components in the vicinity that may be degraded due to the leakage.
When evaluation of the above variables is concluded and the evaluation determines that the leaking condition has not degraded the fasteners, then no further action is necessary.
If evaluation of the variables above indicates the need for further evaluation, or no evaluation is performed, then the bolt closest to the source of leakage will be removed. The bolt will receive a visual VT-3 examination, and be evaluated in accordance with IWA-3100(a).
This visual VT-3 examinaticn may be deferred to the next outage of sufficient duration if the evaluation supports continued service. When the removed bolting shows evidence of rejectable degradation, all remaining bolts shall be removed and receive a visual VT-3 examination and evaluation in accordance with IWA-3100(a)."
Evaluation /
Conclusions:
In accordance with the 1986 edition of the ASME Code,Section XI, when leakage occurs at bolted connections, all bolting is required to be removed for VT-3 visual examination.
In lieu of the Code-required removal of bolting to perform a VT-3 visual examination, the licensee has proposed to perform an evaluation of the bolted connection to determine the susceptibility of the bolting to corrosion and the potential for failure.
If the initial evaluation indicates the need for a more in-depth evaluation, t
the bolt' closest to the source of leakage will be removed, VT-3 examined, and evaluated in accordance with IWA-3100(a).
This alternative allows the licensee to utilize a systematic approach and sound engineering judgment, provided that as a minimum, all of the seven evaluation factors listed in the licensee's proposed alternative are considered. As a result, the licensee's 4
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alternative to the Code-required removal of bolting at a joint when leakage occurs will provide an acceptable level of quality and safety, as the integrity of the joint will be maintained. Therefore, the staff concludes that the licensee's proposed alternative be authorized pursuant to 10 CFR 50.55a(a)(3)(1).
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