ML102780086

Issuance of Relief Request RR-89-68 Regarding Use of American Society of Mechanical Engineering Code Case N-722-1

ML102780086
Person / Time
Site:	Millstone
Issue date:	10/27/2010
From:	Chernoff H Plant Licensing Branch 1
To:	Heacock D Dominion Nuclear Connecticut
Sandeers, Carleen, NRR/DORL, 415-1603
References
TAC ME2309, FOIA/PA-2011-0115
Download: ML102780086 (7)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 27, 2010 Mr. David A. Heacock President and Chief Nuclear Officer Dominion Nuclear Connecticut, Inc.

Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711 SUB~IECT: MILLSTONE POWER STATION, UNIT NO.2-ISSUANCE OF RELIEF REQUEST RR-89-68 REGARDING USE OF AMERICAN SOCIETY OF MECHANICAL ENGINEERING CODE CASE N-722-1 (TAC NO. ME2309)

Dear Mr. Heacock:

By letter dated October 1, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML092740662), Dominion Nuclear Connecticut, Inc. (DNC or the licensee), submitted relief request RR-89-68 requesting to use the alternative requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)

Case N-722-1 when implementing Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(g)(6)(ii)(E) for Millstone Power Station, Unit NO.2 (MPS2). The proposed alternative would eliminate the need for the visual examinations of a series of welds in the reactor pressure vessel (RPV) flange seal leak-off line at MPS2, for the third 10-year inservice inspection (lSI) interval.

The Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the proposed use of ASME Code Case N-722-1 for welds in the RPV flange seal leak-off line at MPS2 provides an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC authorizes the use of RR-89-68 for the third 1O-year interval at MPS2. The third 10-year lSI concluded on March 31,2010.

All other ASME Code,Section XI, requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the authorized Nuclear Inservice Inspector.

D. Heacock -2 If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.

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f IC 4arold K. Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336

Enclosure:

As stated cc wI encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION THIRD 10-YEAR INSERVICE INSPECTION INTERVAL RELIEF REQUEST RR-89-68 MILLSTONE POWER STATION, UNIT NO.2 DOMINION NUCLEAR CONNECTICUT, INC.

DOCKET NUMBER 50-336

1.0 INTRODUCTION

By letter dated, October 1, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML092740662), Dominion Nuclear Connecticut, Inc. (DNC or the licensee), submitted relief request RR-89-68 requesting to use the alternative requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)

Case N-722-1 when implementing Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a(g)(6)(ii)(E) for Millstone Power Station, Unit NO.2 (MPS2). The proposed alternative would eliminate the need for the visual examinations of a series of welds in the reactor pressure vessel (RPV) flange seal leak-off line at MPS2, for the third 10-year in-service inspection (lSI) interval.

2.0 REGULATORY EVALUATION

The lSI of the ASME Code Class 1, 2, and 3 components is performed in accordance with Section XI of the ASME Code and applicable addenda as required by 10 CFR 50.55a(g), except where specific relief has been granted by the U.S. Nuclear Regulatory Commission (NRC) pursuant to 10 CFR 50.55a(g)(6)(i). 10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if the licensee demonstrates that: (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 pre service 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 1O-year interval and subsequent intervals comply with the requirements in the latest edition Enclosure

-2 and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The ASME Code of Record for the MPS2 third 1O-year lSI interval is the 1989 Edition with no Addenda.

10 CFR 50.55a(g)(6)(ii) states that the Commission may require the licensee to follow an augmented lSI program for systems and components for which the Commission deems that added assurance of structural reliability is necessary. 10 CFR 50.55a(g)(6)(ii)(E) requires augmented lSI of reactor vessel bottom-mounted instrumentation penetration nozzles of pressurized-water reactors in accordance with ASME Code Case N-722, subject to the conditions specified in paragraphs (2) through (4) of 10 CFR 50.55a(g)(6)(ii)(E).

DNC requests relief from certain requirements of 10 CFR 50.55a(g)(6)(ii)(E) for the third 10-year lSI interval at MPS2 under 10 CFR 50.55a(a)(3).

3.0 TECHNICAL EVALUATION

3.1 Affected Systems and Components The items for which relief is requested are three Alloy 600/82/182 welds classified as ASME Code Class 1, B15.100 instrument connections in the RPV flange seal leak-off line monitoring tube. These welds are incased within the RPV flange. The RPV flange seal leak-off line is a combination of a %" SB-166 Alloy 600 tube and a %" SB-167 Alloy 600 pipe. The three connections are a partial penetration weld on the flange inside surface, a butt weld joining the tube-to-pipe sections, and a socket weld joining the pipe to a stainless steel elbow at the end of the pipe section.

3.2 Proposed Alternative DNC proposes to use ASME Code-approved Code Case N-722-1 in lieu of Code Case N-722 for the requirements associated with the Class 1 welds made of Alloy 600/82/182 materials in the RPV flange seal leak-off line at MPS2.

3.3 Licensee's Basis for Request The RPV flange seal leak-off line is used to support the identification of inner O-ring seal leakage. This system is essentially a drain system. During normal operation, this leak-off line does not experience flow and is not pressurized. Therefore, these welds would not normally be exposed to an environment that could cause primary water stress-corrosion cracking (PWSCC);

the identification of which is the primary focus of ASME Code Case N-722. Therefore, it is reasonable that the RPV flange seal leak-off line does not belong in the same scope of piping and components that are included in ASME Code Case N-722.

In accordance with 10 CFR 50.55a(g)(6)(ii)(E), MPS2 must follow ASME Code Case N-722 for the Alloy 600/82/182 ASME Code Class 1 B15.100 instrument connection in the RPV flange seal leak-off line. Code Case N-722 requires the welds in the RPV seal flange leak-off line be visually inspected once per 10-year interval. The welds in this system are not accessible for direct bare metal visual inspection. Instead, DNC proposes to use ASME Code Case N-722-1.

ASME Code Case N-722-1 is a revision to ASME Code Case N-722 that was approved for use

-3 by the ASME Code on January 26,2009. ASME Code Case N-722-1 does not require visual examinations of the welds in the RPV flange seal leak-off line. This proposed alternative has an acceptable level of quality and safety because the welds in the RPV flange seal leak-off line are not normally subject to continuous contact with reactor coolant during normal operation, and are not subject to PWSCC concerns. Therefore, this proposed alternative provides an acceptable level of quality and safety equal to what can be gained by performing examinations of these welds to the current Code Case N-722 requirements.

3.4 NRC Staff's Evaluation The NRC staff's review of this request was based on 10 CFR 50.55a(a)(3)(i) which states that:

The proposed alternatives would provide an acceptable level of quality and safety On September 10, 2008, the Commission added new requirements in paragraph 50.55a(g)(6)(ii)(E) that pertain to reactor coolant pressure boundary visual inspections. In accordance with 50.55a(g)(6)(ii)(E), the visual inspection requirements for Item Number B15.100, Reactor Vessel Instrument Connections, must be performed once per interval.

The intention of ASME Code Case N-722 was to provide a bare metal visual inspection frequency for Alloy 600/82/182 components in U.S. pressurized-water reactors, with the exception of the upper head penetration nozzles, as these inspections are addressed in another ASME Code Case (Code Case N-729-1). The basis for the inspection is to identify PWSCC. In order for PWSCC to initiate in a component, it requires a susceptible material, a tensile driving stress and a suitable environment. Alloy 600/82/182 material in contact with primary coolant provides a suitable environment for PWSCC. Although the weld material is considered susceptible and a tensile driving stress could exist, without a suitable environment the NRC staff considers PWSCC unlikely. The generic scope of terminology used in ASME Code Case N-722, "instrument connections" to the RPV that use Alloy 600/82/182 materials, has included the instrument connection welds of the RPV flange seal leak-off line which are not normally exposed to primary coolant and therefore are not normally susceptible to PWSCC. Therefore, the NRC staff finds that the RPV flange seal leak-off line instrument connections at MPS2 do not need to be a part of this additional augmented inspection requirement.

ASME-approved Code Case N-722-1 does not require visual examination of the RPV flange seal leak-off line. Code Case N-722-1 is currently under rule making, but is not currently approved for use by the NRC staff. However, based on the information provided above, the NRC staff finds that the licensee's proposed alternative to use the inspection requirements of ASME Code Case N-722-1 in lieu of N-722 for the RPV flange seal leak-off line when implementing the requirements of 10 CFR 50.55a(g)(6)(ii)(E) provides an acceptable level of quality and safety. Therefore, the NRC staff finds sufficient basis to authorize relief under 10 CFR 50.55a(a)(3)(i).

4.0 CONCLUSION

Based on the discussions above, the NRC staff concludes that the use of Code Case N-722-1 for the RPV flange seal leak-off line welds meets the intention of 50.55a(g)(6)(ii)(E). The NRC staff also concludes, based on the above discussion, that RR 89-68 provides an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff

-4 authorizes the use of relief request RR 89-68 for the third 10-year lSI interval at MPS2. The third 10-year lSI concluded on March 31, 2010.

All other ASME Code,Section XI, requirements for which relief has not been specifically requested and approved remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.

Principal Contributor: J. Collins Date: October 27,2010

D. Heacock -2 If you have any questions, please contact the Project Manager, Carleen Sanders, at 301-415-1603.

Sincerely,

/raJ Harold K. Chernoff, Chief Plant Licensing Branch 1-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336

Enclosure:

As stated cc wi end: Distribution via Listserv Distribution:

PUBLIC Branch Reading RidsAcrsAcnw_MailCTR Resource RidsNrrDorlLpl1-2 Resource RidsNrrDciCpnb Resource RidsNrrLAABaxter Resource RidsNrrMillstone Resource RidsOgcMailCenter RidsRgn1 MailCenter Resource RidsSecyMailCenter Resource SWilliams, EDO R-1 JCollins, NRR ADAMS Accession N0.: ML102780086 *Bsy Memo Dated OFFICE LPL 1-2/PM LPL 1-2/LA DCI/CPNB LPL 1-2/BC NAME CSanders ABaxter TLupold* HChernoff (w/comment)

DATE 10/18/10 10/18/10 09/02/2010 10/27/10 10/27/10 OFFICAL RECORD COpy