ML14079A477

Request for Alternate ISPT-02 Regarding System Leakage Test of Reactor Pressure Vessel Head Flange Seal Leak-Off Piping

ML14079A477
Person / Time
Site:	Watts Bar
Issue date:	03/27/2014
From:	Jessie Quichocho Plant Licensing Branch II
To:	Church C Tennessee Valley Authority
Hon A, NRR/DORL/LPLII-2, 415-8480
References
TAC MF3354
Download: ML14079A477 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 27, 2014 Christopher Church, Vice President Tennessee Valley Authority Watts Bar Nuclear Plant P.O. Box 2000 Spring City, TN 37381

SUBJECT:

WATTS BAR NUCLEAR PLANT, UNIT NO. 1 *REQUEST FOR ALTERNATIVE ISPT*02 REGARDING SYSTEM LEAKAGE TEST OF REACTOR PRESSURE VESSEL HEAD FLANGE SEAL LEAK*OFF PIPING (TAC NO. MF3354)

Dear Mr. Church:

By letter dated January 10, 2014, as supplemented by letters dated February 21, 2014 and March 13, 2014, Tennessee Valley Authority (TVA, the licensee) submitted to the Nuclear Regulatory Commission (NRC) a request for alternatives (RFA) ISPT[Inspection System Pressure Testing]*02 to certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV Code),Section XI [or ASME Code for Operation and Maintenance of Nuclear Power Plants {OM Code)] requirements at Watts Bar Nuclear Plant, Unit No.1.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) Section 50.55a(a)(3)(ii), the licensee proposed an alternative system leakage test of the reactor pressure vessel head flange seal leak*off piping on the basis that complying with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that TVA has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a{a)(3)(ii). Therefore, the NRC staff authorizes the use of RFA ISPT*02 at Watts Bar, Unit 1, for the remainder of the second 10-year lnservice Inspection interval that commenced on May 27, 2007, and will end on May 26, 2016.

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

C. Church If you have any questions, please contact the Project Manager, Andrew Hen at 301-415-8480 or via e-mail at Andrew.Hon@nrc.gov.

• Sincerely,

. ~ckk s1e . Q ichocho, Chief lant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390

Enclosure:

Safety Evaluation cc w/encl: Distribution via ListServ

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR ALTERNATIVE ISPT-02 REGARDING SYSTEM LEAKAGE TEST OF REACTOR PRESSURE VESSEL HEAD FLANGE SEAL LEAK-OFF PIPING TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 1 DOCKET NUMBER 50-390

1.0 INTRODUCTION

By letter dated January 10, 2014 (Agencywide Documents Access and Management System Accession No. ML14013A302), as supplemented by letters dated February 21, 2014 (Accession No. ML14055A271 ), and March 13, 2014 (Accession No. ML14073A600), Tennessee Valley Authority (the licensee) submitted for the U.S. Nuclear Regulatory Commission (NRC) approval request for alternative (RFA) ISPT[Inspection System Pressure Testing]-02. The licensee proposed an alternative to a certain requirement of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI. The request relates to the inservice inspection (lSI) requirement of Sub-Article IWC-5221 when the licensee performs a system leakage test of the reactor pressure vessel (RPV) head flange seal leak-off piping.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) Section 50.55a(a)(3)(ii), the licensee proposed an alternative system leakage test of the RPV head flange seal leak-off piping, given the basis that complying with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

2.0 REGULATORY EVALUATION

Pursuant to 10 CFR 50.55a(g)(4), the ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for lnservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals must 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),

12 months prior to the start of the 120-month interval, subject to the conditions listed therein.

Enclosure

Pursuant to 10 CFR 50.55a(a)(3), alternatives to the requirements of paragraph (g) of 10 CFR 50.55a may be used, when authorized by the NRC, if the licensee demonstrates (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.

Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the NRC to authorize the alternative requested by the licensee.

3.0 TECHNICAL EVALUATION

3.1 The Licensee's Request for Alternative The component affected by this request is the RPV head flange seal leak-off detection piping (1-PIPE-68-B) and (1-47W813-1) extending from the two RPV taps and terminating at the inline isolation valve 1-FCV-68-22 of the common header to the reactor coolant drain tank. The subject piping is classified as a pressure retaining component under ASME Code Class 2, IWC-2500, Table IWC-2500-1, Examination Category C-H, Item Number C7.1 0. The RPV head flange seal leak detection line consists of 21 feet of 3/4 inch and 3/8 inch piping, and less than 12 inches of 1 inch piping. The design conditions for the pipe are 2500 pound per square inch absolute at 650 degrees Fahrenheit (°F). In a letter dated February 21, 2014, the licensee stated that the piping was manufactured from stainless steel SA376, TP304 material, and is Schedule 160.

The ASME Code of Record for the second 10-year lSI interval at Watts Bar Unit 1, is the 2001 Edition through 2003 Addenda of the ASME Code.

The ASME Code,Section XI, IWC-2500, Table IWC-2500-1, Examination Category C-H, establishes requirements to conduct the system leakage testing according to IWC-5220 and the VT-2 visual examination according to IWA-5240 during each inspection period. As required by IWC-5221, the system leakage test shall be conducted at the system pressure obtained while the system, or portion of the system, is in service performing its normal operating function or at the system pressure developed during a test conducted to verify system operability.

The licensee proposed an alternative to IWC-5221. In lieu of normal operating pressure, the licensee proposed to use the static pressure head of 11 pounds per square inch gauge (psig),

developed at the taps from the elevation of 25.5 feet of water above the reactor vessel closure flange when the cavity is flooded, to perform the system leakage testing of the leak-off piping.

The licensee stated that the VT -2 visual examination of the accessible portions (from the biological shield wall to 1-FCV-68-22) of the leak-off piping will be performed at ambient conditions when the RPV head is off and the reactor cavity is flooded above the RPV flange for a minimum of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. The VT -2 visual examination of the inaccessible portions (from the biological shield wall to the RPV flange taps) of the leak-off piping will be performed by observing the area near the leak-off line for evidence of leakage in conjunction with the visual inspection of the RPV hot leg nozzle safe end welds. The licensee in a letter dated March 13, 2014, stated that in order to reduce the dose associated with the hot leg inspection and the

VT -2 visual examination of the leak-off pipe, the same personnel will be utilized to perform both examinations simultaneously while making a single entry inside the biological shield wall. Both the hot leg inspection and the VT -2 visual examination of the inaccessible area of the leak-off pipe are scheduled during the core off-load period with the reactor cavity flooded to the normal refueling level that provided the same static pressure head. The licensee stated that the VT -2 visual examination of the inaccessible portion of the RPV flange leak-off line will be able to detect evidence of boric acid residue, staining, or any other indications of past leakage.

The licensee stated that the RPV head flange leak detection line is separated from the reactor pressure boundary by one 0-ring (inner 0-ring) located on the RPV flange. A second 0-ring (outer 0-ring) is located on the opposite side of the tap in the RPV flange. The line that connects to the inner 0-ring is required during plant operation to detect leakage from and failure of the inner flange seal 0-ring. The licensee continually monitors for leakage past the RPV head flange seal leak detection line 0-rings using the plant instrumentation (temperatures in excess of 140 oF).

The licensee stated that the configuration of the RPV head flange leak detection lines precludes manual system leakage testing while the RPV head is removed. The configuration of the RPV flange taps combined with the small size of the taps and the high test pressure requirement prevents the taps from being temporarily plugged. Plugging or installing a pressure connection would require machining threads in each flange opening with attendant concern over chips from machining that may become a foreign material threat for the fuel integrity or the lines.

Additionally, machining would require extensive time, and the radiation level at the RPV flange is estimated at 20 to 40 milliroentgen equivalent man per minute (mrem/min). After machining the threads, installation and removal of the plugs and pressure connections would require additional time for personnel to be at the radiation area with estimated dose rate of 20 to 40 mrem/min.

The licensee stated that while the RPV head is installed, an adequate pressure test cannot be performed because the inner 0-ring is designed to withstand pressure in one direction only.

Pressurization in the opposite direction to perform the required leak test would likely damage the inner 0-ring. Purposely failing the inner 0-ring to perform the ASME Code leakage test would require additional time to de-tension the RPV head, install the new 0-rings, and reset and re-tension the RPV head. The licensee stated in a letter dated February 21, 2014, that the radiation dose for these activities is estimated to be 1 to 1.5 roentgen equivalent man per hour.

In addition, attempt to pressure test the lines in the beginning of a refueling outage when the RPV head is on would most likely result in failure of the 0-ring, which would prevent achieving the required test pressure.

The licensee submitted RFA ISPT-02 for the remaining of the second 10-year lSI interval that commenced on May 27, 2007, and will end on May 26, 2016. The licensee stated that the second 10-year lSI interval was shortened to 9 years due to the first 10-year lSI interval being extended by 1 year to 11 years. The NRC staff notes that the reduction or extension of lSI interval within one calendar year is permitted under the ASME Code,Section XI, IWA-2430.

3.2 NRC Staff Evaluation The NRC staff has evaluated RFA ISPT-02 pursuant to 10 CFR 50.55a(a)(3)(ii). The NRC staff focuse its review on whether compliance with the specified requirements of 10 CFR 50.55a(g),

or portions thereof, would result in hardship or unusual difficulty, without a compensating increase in the level of quality and safety.

The NRC staff determined that compliance with the ASME Code,Section XI, IWC-5221, pressure requirement to perform system leakage testing of the RPV head flange seal leak-off piping would result in hardship. The basis for the hardship is as follows. The licensee would have to modify the existing flange taps during the refueling outage when the reactor head is removed. The modification of flange tap involves machining threads to install a plug or pressure connections. These activities could introduce foreign materials into the reactor pool as well as the lines. The time spent for modifications, preparing and pressurizing the lines to perform the ASME Code system leakage test, and removal of plugs or connections after completion of the test would expose personnel to additional radiation dose. Pressurizing the leak-off lines while the RPV head is installed would not be possible due to design and configuration of the RPV head flange taps, and the inner 0-ring. The inner 0-ring is designed to withstand pressure in one direction only. Therefore, the NRC staff determines that unnecessarily challenging the Foreign Material Exclusion program and the 'as low as is reasonably achievable' exposure goal constitute a hardship.

The NRC staff finds that the licensee's proposed system leakage test will subject the RPV flange seal leak-off piping to the highest pressure that is obtainable without major design modifications to existing configurations of both the vessel flange face and the leak-off piping.

Specifically, the static pressure head of 11 psig developed from the elevation of water above the vessel flange during the cavity flood-up will be used to pressurize the leak-off line piping to perform system leakage test. By performing the VT -2 visual examination (according to IWA-5240) of the accessible area of the leak-off lines, the licensee will be able to detect any leakage if it originated from an existing flaw in the leak-off piping and its welded connections after maintaining the static test pressure. For the inaccessible area of the leak-off lines, the licensee will use the VT-2 visual examination (according to IWA-5240) to detect evidence of any leakage such as boric acid residue and staining by observing the surrounding area of the leak-off piping. The VT -2 visual examination of the inaccessible area of the leak-off lines will be performed concurrently with the RPV hot leg nozzle safe end weld inspections because single entry inside the biological shield wall to perform both examinations will significantly reduce the accrual of radiation dose by the involved personnel. The NRC staff determined that any evidence of leakage, if it originated from an existing flaw in the leak-off piping and its welded connections will be identified by the VT-2 visual examination.

The licensee stated that there has not been any documented history of degradation of the RPV flange leak-off piping within its fleet and the industry. The NRC staff review of operating experience, including Watts Bar Unit 1, did not identify any documented known degradation mechanism such as stress corrosion cracking and fatigue in the vessel flange leak-off piping and its welded connections.

Furthermore, the NRC staff determined that the existing reactor coolant leakage detection systems are sufficient to provide warning to the control room operator in an unlikely event of a

through-wall leak in the RPV leak-off piping. The NRC staff finds that if the subject piping developed a through-wall flaw, the reactor coolant leakage detection systems will be able to identify the leakage during normal operation, and the licensee will take appropriate corrective actions in accordance with the plant technical specifications.

Therefore, the NRC staff finds that the proposed system leakage testing using proposed test pressure is adequate to provide a reasonable assurance of structural integrity and leak tightness of the RPV flange seal leak-off piping.

4.0 CONCLUSION

As set forth above, the NRC staff determines that the proposed alternative provides reasonable assurance of structural integrity and leak tightness of the RPV head flange seal leak-off piping.

The NRC staff finds that complying with the specified ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(a)(3)(ii). Therefore, the NRC staff authorizes the use of RFA ISPT-02 at Watts Bar, Unit 1, for the remainder of the second 10-year lSI interval that commenced on May 27, 2007, and will end on May 26,2016.

All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the staff remain applicable, including the third party review by the Nuclear In-service Inspector Principal Contributor: A. Rezai

C. Church If you have any questions, please contact the Project Manager, Andrew Hon at 301-415-8480 or via e-mail at Andrew.Hon@nrc.gov.

Sincerely, IRA!

Jessie F. Quichocho, Chief Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390

Enclosure:

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• NRR/DORL/LPL2-2/BC NAME AHon BCiayton GKulesa JQuichocho DATE 3/21/14 3/21/14 03/19/2014 3/27/14 OFFICIAL RECORD COPY