ML20199E497

Safety Evaluation Authorizing Proposed Alternative of Licensee Relief Requests NDE-35 & NDE-37,for Plant,Units 1 & 2 During Second 10 Yr Interval

ML20199E497
Person / Time
Site:	North Anna
Issue date:	11/14/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20199E495	List: ML20199E491 ML20199E497
References
NUDOCS 9711210226
Download: ML20199E497 (4)

Text

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• 4009 p- \ UNITED STATES

• g NUCLEAR REGULATORY COMMISSION R WASHINGTON, D.C. 30646 4001 k*****/

SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF NOS. NDE-35 & NDE-37 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STtTION. UNIT 1 AND UNIT 2 DOCKET NOS. 50-338 AND 50-339

1. 1HIBQDUCT103 The Technical Specifications for North Anna Power Station. Units 1 and 2, state that the inservice inspectior and testing of the American Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 components shall be performed in accordan;e with Section XI of the ASME Boiler and P. essure 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)(1). 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 (1) 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.

Fursuant 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 Section XI of editions of the ASME Boiler and Pressure Vessel Code and Addenda that become effective subsequent to editions specified in paragraphs (g)(2) and (g)(3) and that are incorporated by reference in paragraph 10 CFR 50.55(a)(b) to the extent practical within the limitations of design geometry, and materials of construction of the componants. The regulations require that inservice examination of components and system pressure tests conducted during the initial 120 month inspection interval mest comply with the requirements in the latest edition and addenda of the Code incoraorated by reference in paragraph 10 CFR 50.55(a)(b) on the date 12 montas prior to the date of issuance of the operating license subject to the limitations and modifications listed in paragraph 10 CFR 50.55(a)(b). Inservice examination of components and system pressure tests conducted during the successive 120-month inspection interval must comply with the requirements of the latest edition and addenda of the Code incorporated by reference in paragraph 10 CFR 50.55(a)(b) on the date 12 months prior to tM date of start of the 120-month irspection interval, subject to the limitations and modifications listed in paragraph 10 CFR 50.55(a)(b).

ENCLOSURE W"idn G

?dsaste PDR

The applicable ASME Code.Section XI. for North Anna Power Station. Units 1 and 2. during the second 10-year inservice inspection (ISI) interval, are the 1983 Edition. Summer 1983 Addenda and the 1985 Edition, respectively. 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 Lcility. 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 00.55a(g)(6)(1), the Commission may grant relief and may impose

- alternative requirements that are determined to be authorized by law. will not

• endanger 11fe, 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 June 2,1997. Virginia Electric and Power Company, the licensee for North Anna Power Station. Units 1 and 2. requested relief from the surface examination of reactor vessel closure head nuts by aroposing an alternative VT-1 visual examination in Relief Requests NDE-35 (Jnit 1) and NDE-37 (Unit 2).

The Civil Engineering and Geosciences Branch Division of Engineering, has reviewed and evaluated the licensee's request for relief and the supportire information, pursuant to the provisions of 10 CFR 50.55a(a)(3)(1).

2.0 DISCUSSION

Identification of Comoonent: Reactor vessel closure head nuts Maji Mark Comoonent Drawina Class L ttL. No. &

1 N-01 through N-58 1-RC-R-1 11715-WMKS-RC-R-1.4 1 2 N-01 through N-58 2-RC-R-1 12050 WMKS-RC-R-1.4 1 i

ASME Code Section XI Reouirement:

Unit 1: The 1983 Edition. Summer 1983 Addenda of ASME Section XI Table IWB-2500-1 examination category B-G-1 item number B6.10 requires a surface examin tion of the reactor vessel closure head nuts.

Unit 2: .The 1986 Edition of ASME Section XI Table IWB-2500-1 examination category B-G-1, item number B6.10 requires a surface examination of the reactor vessel closure head nuts.

2

R Licensee's Code Relief Reouest:

The 11censee requests relief from performing the Code-required surface namination on the above identified reactor vessel closure head nuts, licensee's Basis for Reauestino Relief: (as stated)

"The 1989 Addenda of ASME Section XI Table IWB-2500-1. examination category B G-1, item number BC.10 has changed the requirement from a surface examination to a visual (VT-1) examination.

Extensive cleaning of these nuts is required for a surface examination to be performed. This extensive cleaning results in additional costs and the inefficient use of available manpower resources.

Due to design factors, the stripping areas of the female threads in a nut are approximaialy 1.3 times the areat of the mating male threads (see ASME Bl.1.

Unified Inch Screw Threads). Accordingly, if a defect were to be developed during ser/ ice. they would occur in the threads of the bolt or stud before developing in the nut's threads because of higher stresses in the male threads. When reactor vessel head fasteners are tightened for closure or loosened for opening, the studs are tensioned and the nuts are run on the threads with no load as the load is taken by the stud or bolt through the tensioning device."

Literjee' ProDosed Alternate Reauiremtat: (as stated)

"It is proposed that the requirements of the 1989 Addenda of ASME Section XI Table IWB-2500-1. Examination Category B-G-1. Item Number B6.10 (visual. VT-1) be substituted for the Code surface examination. In addition:

a. A visual (VT-2) exami,1ation will be performed during the normally scheduled system leakage test each refueling outage;

b. Technical Specifications require that the reactor coolant system leak rate be limited to ene gallon per minute unidentified leakage. This value is calculated at least once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />; and

c. The containment atmosphere particulate radioactivity 1s checked every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

The proposed alternative examinations stated above will ensure that the overall level of plant quality and safety will not be compromised."

3.0 EVALUAT10t{;

The licensee has proposed to perform a VT-1 visual examination of reactor vessel closure head nuts in lit.u of the Code-required surface examination.

The staff reviewed the requirements of various edition of the applicable ASME 3

.. n Code on the examination of nuts greater than 2 inch in diameter in Examination Category B-G 1, and noted the following:

o for the reactor vessel closure head nuts under the applicable criteria, a -

surface examination is specified as the examination method in Table IWB-2500-1: however, there is neither any acceptance standard nor the specification of required surface that needs examination. These items were under preparation by ASME and, therefore, were subject to owner's evaluation with no guidance from the Code. For the nuts used in other Class 1 components, such as steam generators, pressurizer, heat exchangers, piping, pimps and valves, the examination method has always been a VT-1 visual examination, o Subsequently, the 1989 Addenda to the ASME Code,Section XI, changed the examination method from surface examination to VT-1 visual exan,ination for reactor vessel closura head nuts consistent with that of the other Class 1 components discussed above. The Addenda to the Code also specified detailed acceptance standard and the required surface for the VT-1 visual examination.

Therefore, the staff has determined that a VT-1 visual examination combined with the stringent acceptance criteria should provide an acceptable level of quality and safety by ensuring adequate structural integrity and leak tightness of the nuts.

4.0 CONCLUSION

The staff concludes that the licensee's aroposed altemative, to perform a VT-1 visual exhmination for Item Number 36.10. Examination Category B G-1 in Table IWB-2500-1 for reactor vessel closure head nuts in conjunction with the applicable acceptance criteria, provides an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(1). the p,'oposed citernative of the licensee's relief request Nos. NDE-35 and NDE-37 is authorized for North Anna Units 1 and 2 during the second 10-year interval.

Accordingly, relief is authorized pursuant to 10 CFR 50.55a(a)(3)(i).

Principal Contributor: P. Patnaik Date: November 14, 1997 4

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