ML12361A256

Request for Relief from the American Society of Mechanical Engineers (ASME) Code,Section XI, Reactor Vessel Head Flange Seal Leak Detection Piping - Relief Request No. 49

ML12361A256
Person / Time
Site:	Palo Verde
Issue date:	12/19/2012
From:	Mims D Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
102-06637-DCM/RKR/GAM
Download: ML12361A256 (7)

Text

10 CFR 50.55a iiAM A subsidiary of Pinnacle West Capital Corporation Dwight C. Mims Mail Station 7605 Palo Verde Nuclear Senior Vice President Tel. 623-393-5403 P. 0. Box 52034 Generating Station Nuclear Regulatory and Oversight Fax 623-393-6077 Phoenix, Arizona 85072-2034 102-06637-DCM/RKR/GAM December 19, 2012 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Palo Verde Nuclear Generating Station (PVNGS)Units 1, 2, and 3 Docket Nos. STN 50-528, 50-529, and 50-530 Request for Relief from the American Society of Mechanical Engineers (ASME) Code,Section XI, Reactor Vessel Head Flange Seal Leak Detection Piping -Relief Request No. 49 Pursuant to 10 CFR 50.55a(g)(5)(ii), Arizona Public Service Company (APS) is submitting a request for relief for the PVNGS Units 1, 2, and 3 third Inservice Inspection (ISI) interval.

Specifically, APS is requesting relief from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section Xl requirements regarding pressure testing the reactor vessel head flange seal leak detection piping. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.The Enclosure to this letter contains 10 CFR 50.55a Relief Request No. 49. APS requests approval of this relief request by March 30, 2013, to support the Unit 1 refueling outage.The need for this relief request was identified during an NRC ISI inspection of PVNGS Unit 2 during the fall refueling outage (2R1 7) in October 2012. The reactor vessel head flange seal leak detection piping was examined, using the proposed alternative method, during refueling outage 2R17 on October 20, 2012. PVNGS Unit 2 was in Mode 6, the reactor vessel head was removed, and the reactor cavity was filled. The associated ASME Code Class 2 piping system was subject to the static pressure head when the reactor cavity was filled. VT-2 examination of the accessible areas of the piping systems was performed and no evidence of leakage was identified.

The next Unit 2 refueling outage (2R18) during which the alternative examination method could be performed is scheduled to occur in Spring 2014, within the one-year extension of the current Unit 2 ISI inspection period (November 17, 2014). However, APS plans to credit A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway -Comanche Peak -Diablo Canyon -Palo Verde -San Onofre -South Texas -Wolf Creek ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Request for Relief from ASME Code,Section XI, Reactor Vessel Head Flange Leak Detection Piping -Relief Request No. 49 Page 2 the flange seal leak detection piping alternative examination performed in 2R17 for the current Unit 2 ISI period should it comply with the relief request as approved by the NRC.No commitments are being made to the NRC by this letter. Should you need further information regarding this submittal, please contact Robert K. Roehler, Acting Licensing Section Leader, at (623) 393-5241.Sincer

Enclosure:

10 CFR 50.55a Relief Request No. 49 DCM/RKR/GAM cc: E. E. Collins Jr. NRC Region IV Regional Administrator L. K. Gibson NRC NRR Project Manager for PVNGS M. A. Brown NRC Senior Resident Inspector for PVNGS ENCLOSURE 10 CFR 50.55a Relief Request No. 49 bI 10 CFR 50.55a Request Number 49 Proposed Alternative in Accordance with 10 CFR 50.55a(a)(3)(ii)

-- Hardship or Unusual Difficulty without Compensating Increase in Level of Quality and Safety --1. ASME Code Components Affected PVNGS Units: ASME Code Class:

References:

Examination Category: Item Number:

Description:

1, 2, and 3 Code Class 2 ASME Section XI, Table IWC-2500-1 and IWC-5222 C-H (All Pressure Retaining Components)

C7.10 Alternative Pressure Testing Requirements for the RPV Flange Leak-Off Piping NPS 1" RPV Flange Seal Leak-Off Piping Line Number RC-N-081 -CCBA-1" 01-P-RDF-0144, 02-P-RDF-0144, 03-P-RDF-0144 Component:

Plant Drawings: 2. Applicable Code Edition and Addenda The applicable ASME Boiler and Pressure Vessel Code (hereafter referred to as the "Code") edition and addenda is ASME Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2001 Edition through 2003 Addenda.3. Applicable Code Requirement IWC-2500, Table IWC-2500-1, Code Category C-H, Item Number C7.10 requires that all Class 2 pressure retaining components be subject to a system leakage test with a Visual, VT-2 examination each inspection period. The system leakage test is performed at the pressure obtained while the subject portion of the system is performing its normal operating function or during a comparable test.Per IWC-5222(a), the pressure retaining boundary includes the portion of the system required to operate or support the safety function up to and including the first normally closed valve.1 of 4 Relief Request No. 49 4. Reason for Request The ASME Code Section XI, 2001 Edition through 2003 Addenda requires that Class 2 pressure boundary piping shall be pressure tested once each inspection period. The reactor vessel head flange seal leak detection piping is separated from the reactor coolant pressure boundary by one passive metallic seal, which is the first of two O-rings. The pressure tap for the leak detection piping is located on the vessel flange mating surface. A second 0-ring is located on the outside of the pressure tap in the vessel flange. Failure of the inner O-ring is the only condition under which this line is pressurized.

Therefore, the line is not expected to be pressurized during the system pressure test following a refueling outage.The configuration of this piping precludes system pressure testing while the vessel head is removed because the pressure tap would have to be plugged. This would require a design modification to install mechanical threads into the pressure tap on the vessel flange. A threaded plug would need to be installed in the flange face to act as a pressure boundary for each test, then removed after the test. The installation of the modification and subsequent use would incur significant dose, which would be inconsistent with keeping dose as low as reasonably achievable (ALARA). This activity would also present a foreign material exclusion issue for the handling of a very small diameter plug that would be required to be installed to complete a leakage test at pressure.The configuration also precludes pressurizing the line externally with the head installed.

The closure head contains two concentric grooves that hold the inner and outer O-rings. The O-rings are held in place by a series of retainer clips that are housed in recessed cavities in the flange face. If a pressure test were to be performed with the head installed, the inner O-ring would be pressurized in a direction opposite to its design function.

This test pressure would result in a net inward force on the inner O-ring that would tend to push it into the recessed cavity that houses the retainer clips. The thin O-ring material could be damaged by the inward force.Purposely failing or not installing the inner O-ring in order to perform a pressure test would require a new O-ring set to be installed.

The time and radiation exposure associated with removing and reinstalling the closure head, replacing the outer 0-ring and re-cleaning of the vessel flange mating surface prior to head installation would be an undue hardship.

In addition, this special test would require a reactor coolant system heat-up / cooldown cycle. Therefore, compliance with the IWC-5222(b) system pressure test requirements results in an unnecessary hardship without a sufficient compensating increase in the level of quality and safety.5. Proposed Alternative and Basis for Use In lieu of the requirements of IWC-5222(b), a VT-2 visual examination of the accessible areas will be performed each inspection period on the piping subjected 2 of 4 I Relief Request No. 49 to the static pressure from the head of water when the reactor cavity is filled. This test will be part of the reactor coolant Class 2 leakage test. The test will be performed within the frequency specified by table IWC-2500-1 for a System Leakage Test (once each inspection period).If the inner O-ring should leak during the operating cycle it will be identified by an increase in pressure of the leak-off line above ambient pressure.

This leak detection piping has a pressure indicator in the Control Room. This high pressure would actuate an alarm in the Control Room, which would be closely monitored by procedurally controlled operator actions allowing identification of any further compensatory actions required.

This piping also acts as a leak-off line to collect leakage which would be routed to the Reactor Coolant Drain Tank.Additionally, the reactor vessel head flange seal leak detection piping would only function as a Class 2 pressure boundary if the inner O-ring fails, thereby pressurizing the line. If any significant leakage does occur in the leak detection piping during this time of pressurization, it would exhibit boric acid accumulation that would be discernible during the VT-2 visual examination to be performed as proposed in this request.6. Duration of Proposed Alternative This alternative is requested for the Third Inservice Inspection Interval for Palo Verde Nuclear Generating Station which began on the following dates: Unit 1-July 18, 2008; Unit 2 -March 18, 2007; and Unit 3 -January 11, 2008.7. Precedents (1) Comanche Peak Nuclear Power Plant, Second Inspection Interval Relief Request C-9. Alternative Pressure Testing Requirements for the RPV Flange Leak-Off Piping, as approved by the NRC in a letter dated December 19, 2011 (ADAMS Accession No. ML113110092)(2) LaSalle County Station Third Inspection Interval Relief Request 13R-08.Pressure Testing of the Reactor Vessel Head Flange Leak Detection System, as approved by the NRC in a letter dated January 30, 2008 (ADAMS Accession No. ML073610587)

(3) Susquehanna Steam Electric Station Third 10-Year Inservice Inspection (ISI)Interval Program Plan Request for Relief 3RR-07. Exemption for Pressure Testing Reactor Pressure Vessel Head Flange Seal Leak Detection System, approved by the NRC in a letter dated September 24, 2004 (ADAMS Accession No. ML042680078) 3 of 4 d Relief Request No. 49 The followinq precedents were for same lines that were designated Class 1: (4) Millstone Power Station Unit 3 Relief Request IR-3-1 1. Alternative Pressure Testing Requirements for the RPV Flange Leak-Off Piping, approved by the NRC Letter dated April 29, 2010 (ADAMS Accession No. ML101040042)

(5) North Anna Unit 1 Relief Request SPT-013. Examination Category B-P Pressure Retaining Components in the Reactor Coolant System, approved by NRC letter dated February 9, 2006 (ADAMS Accession No.ML060450517)

(6) Limerick Second Interval Relief Request RR-33. Pressure Testing of the Reactor Vessel Head Flange Leak Detection System (Unit 1 only), (ADAMS Accession No. ML090060218), as approved by the NRC in a letter dated January 27, 2009 8. References Code Case N-805, Alternative to Class1 Extended Boundary End of Interval or Class 2 System Leakage Testing of Reactor Vessel Head Flange O-ring Leak Detection System, was issued to the 2010 Edition of the ASME Section XI Code and is listed in Supplement 6 for Code Cases. However, Code Case N-805 has not been approved by the NRC and is not identified in Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section Xl, Division 1.4 of 4