ML18153A401
| ML18153A401 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 11/24/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18153A400 | List: |
| References | |
| NUDOCS 9712010232 | |
| Download: ML18153A401 (4) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR RELIEF NOS. SR-018 & SR-025 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION, UNIT 1 AND UNIT 2 DOCKET NOS. 50-280 AND 50-281
1.0 INTRODUCTION
The Technical Specifications for Surry Power Station. Units 1 and 2. state that the inservice inspection (ISI) 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). Section 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 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.
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 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 50.55a(b) to -
the extent practical within the limitations of design. geometry. and mat~rials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the initial 120-month inspection interval must comply with the requirements in the latest editio~ and addenda of the Code incorporated by reference in paragraph 10 CFR 50.55a(b) on the date 12 months prior to the date of issuance of the operating license subject to the limitations and modifications listed in paragraph 10 CFR 50.55a(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 50.55a(b) on the date 12 months prior to the date of start of the 120-month inspection interval.
subject to the limitations and modifications listed in paragraph 10 CFR 50.55a(b).
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2 The applicable code for Surry Power Station. Units 1 and 2. during the third 10-year ISI interval. is the 1989 Edition of the ASME Code Section XI.
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 Jicensee 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 June 2. 1997. Virginia Electric and Power Company, the licensee for Surry Power Station. Units 1 and 2. requested relief from the surface examination of reactor vessel closure head nuts by proposing an alternative VT-1 visual examination in Relief Request SR-18 (Unit 1) and SR-25 (Unit 2).
The NRC staff has reviewed and evaluated the licensee's request for relief and the supporting information. pursuant to the provisions of 10 CFR 50.55a(a)(3)(i).
- 2. 0 DISCUSSION Identification of Component:
Reactor vessel closure head nuts Unit Mark Component No.
Drawing Class No.
No.
1 N-01 through N-58 2
N-01 through N-58 1-RC-R-l 2-RC-R-l ASME Code Section XI Requirement:
No.
11448-WMKS-RC-R-l.4 11548-WMKS-RC-R-l.4 1
1 For Unit 1 and Unit 2. the 1989 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.
Licensee's Code Relief Request:
The licensee requests relief from performing the Code-required surface examination on the above identified reactor vessel closure head nuts.
Licensee's Basis for Requesting Relief:
(as stated)
"The 1989 Addenda of ASME Section XI Table IWB-2500-1. examination category B-G-1. item number 86.10 has changed the requirement from a surface examination to a visual (VT-1) examination.
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3 Extensive cleaning of these nuts is required for a surface examination to be performed. This extensive cleaning results in additional costs and the i nef f i ci ent use of available manpower resources.
Due to design factors. the stripping areas of the female threads in. a nut are approximately 1.3 times the areas of the *mating male threads (see ASME Bl.1.
Unified Inch Screw Threads). Accordingly. if a defect were to be developed during service. 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."
Licensee's Proposed Alternate Requirement:
(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) examination 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 one gallon per minute unidentified leakage. This value is calculated at least once per 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />s: and
- c.
The containment atmosphere particulate radioactivity is 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 over a 11 level of pl ant quality and safety will not be compromi sect."
- 3. 0 EVALUATION The licensee has proposed to perform a VT-1 visual examination of reactor vessel closure head nuts in lieu of the Code-required surface examination.
The staff reviewed the requirements of various editions of the 9pplicable ASME Code for the examination of nuts greater than 2" 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, pumps and valves. the examination method has always been a VT-1 visual examination.
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4 o
Subsequently, the 1989 Addenda to the ASME Code.Section XI. changed the examination method from surface examination to VT-1 visual examination for reactor vessel closure head nuts consistent with that of the other Class 1 components discussed above.
The Addenda to the Code also specified detailed acceptance standards qnd the required surface for the VT-1 visual examination.
Therefork. the staff has determined that a VT-1 visual examination combined with the stringent acceptance criteria will provide assurance of structural integrity and leak tightness: and thus. provide an acceptable.level of quality and safety.
- 4. 0 CONCLUSION The staff concludes that the licensee's proposed alternative. to perform a VT-1 visual examination for Item Number B6.10. 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)(i). the proposed alternative of the licensee's relief request Nos. SR-018 and SR-025 is authorized for Surry, Units 1 and 2. during the third 10-year interval.
Principal Contributor:
P. Patnaik Date: November 24, 1997