NL-11-2556, HNP-ISI-RR-12, Version 1, Analytical Evaluation of Residual Heat Removal Service Water Piping
| ML113570234 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 12/22/2011 |
| From: | Ajluni M Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-11-2556 | |
| Download: ML113570234 (12) | |
Text
Southern Nuclear Operating Company, Inc.
40 Inverness Center Parkwa,/
Post Office Box 1295 Birmingham. Alabama 35201-1295 Tel 205.992 SOOO SOUTHERN A December 22, 2011 COMPANY Docket Nos.: 50-366 NL-11-2556 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Edwin I. Hatch Nuclear Plant - Unit 2 HNP-ISI-RR-12, Version 1, Analytical Evaluation of Residual Heat Removal Service Water Piping Ladies and Gentlemen:
Pursuant to 10 CFR 50.55a(g)(5)(iii), Southern Nuclear Operating Company (SNC) hereby requests Nuclear Regulatory Commission (NRC) approval of the enclosed analytical evaluation of wall thinning in Residual Heat Removal Service Water (RHRSW) piping, relief request HNP-ISI-RR-12, Version 1, using the technical guidance of Code Case N-597 -2. Neither ASME Section XI Code requirements nor an NRC approved Code Case are available to address this issue. The details of the analytical evaluation of RHRSW piping are contained in relief request HNP-ISI-RR-12, Version 1, provided in Enclosure 1 to this letter.
The wall thinning was discovered while performing UT examinations on the Unit 2 Division I RHRSW supply to the Reactor Building. Additional details of the UT thickness measurements are provided in Enclosure 2.
SNC requests approval of HNP-ISI-RR-12, Version 1 by January 31,2012.
This letter contains no NRC commitments. If you have any questions, please contact B. D. McKinney at (205) 992-5982.
Respectfully submitted, M. J. Ajluni Nuclear Licensing Director MJA/JLS/lac
U. S. Nuclear Regulatory Commission NL-11-2556 Page 2
Enclosures:
- 1. Relief Request HNP-ISI-RR-12, Version 1.0, Analytical Evaluation of RHR Service Water Piping
- 2. Ultrasonic Thickness Data Sheets for 2E11-18-6BC-A cc: Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Chief Nuclear Officer Mr. B. L. Ivey, Vice President-Regulatory Affairs Mr. D. R. Madison, Vice President - Hatch Ms. P. M. Marino, Vice President - Engineering Mr. B. J. Adams, Vice President - Fleet Operations RTYPE: CHA02.004 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. P. G. Boyle, NRR Senior Project Manager - Hatch Mr. E. D. Morris, Senior Resident Inspector - Hatch
Edwin I. Hatch Nuclear Plant - Unit 2 HNP-ISI-RR-12, Version 1, Analytical Evaluation of Residual Heat Removal Service Water Piping Relief Request HNP-ISI-RR-12, Version 1.0 Analytical Evaluation of RHR Service Water Piping to NL-11-2556 Relief Request HNP-ISI-RR-12, Version 1.0 Analytical Evaluation of RHR Service Water Piping COMPONENT:
ASME CODE:
CODE REQUIREMENT:
IMPRACTICALITY OF COMPLIANCE:
ASME Code Class 3 18-inch Nominal Pipe Size (NPS) carbon steel piping with a nominal wall thickness of 0.500-inch in the Residual Heat Removal Service Water (RHRSW) system. This 18-inch diameter piping is the normal supply header for the Unit-2, Division 1, Reactor Building load listed below:
- RHR Heat Exchanger 2E11 B001 B The ASME Code of Record is the 2001 Edition of ASME Section XI with Addenda through 2003. Hatch is in the fourth lSI interval which ends on December 31, 2015.
There are no Section XI lSI requirements for the subject piping except for periodic pressure testing and visual examination of component supports and welded attachments. Ultrasonic (UT) thickness measurements were performed on selected RHRSW piping during buried piping inspections.
The LIT thickness measurements on one location resulted in a below minimum-wall thickness measurement. These results were documented in Hatch Condition Report # 379325, issued on December 1, 2011. The Southern Nuclear Operating Company (SNC) Corporate Stress Group was asked to evaluate this location to determine its acceptability. Neither ASIV1E Section XI Code requirements nor an NRC-approved Code Case are available to address this issue. The SNC Corporate Stress Group determined that ASME Code Case N-597-2, "Requirements for Analytical Evaluation of Pipe Wall Thinning", was an appropriate Code Case to perform this evaluation. Code Case N-597-2 is referenced in Revision 16 of NRC Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, dated October 2010; however, the NRC has listed five additional conditions. The actions taken by SNC to address these five conditions are shown in the Proposed Alternative and Basis for Use section of this relief request.
Neither ASME Section XI Code-required provisions nor an NRC-approved Code Case are available at this time. Another means by which to evaluate pipe wall thinning was considered; specifically Code Case N 480. However, this Code Case has been annulled and was superseded by Code Case N-597. Therefore, this relief request to use N-597-2 is the only viable option for continued service without a temporary non-Code repair. SNC will describe the analytical evaluation in the Proposed Alternative and Basis for Use section of this relief request.
E1-1 to NL-11-2556 Relief Request HNP-ISI-RR-12, Version 1.0 Analytical Evaluation of RHR Service Water Piping BURDEN CAUSED BY COMPLIANCE: The Hatch Unit 2 Required Action Statement (RAS) for one subsystem of the RHRSW system in-operability is limited to only seven days. Per the Unit 2 Bases for Technical Specification (TS) B 3.7.1, the RHRSW System consists of two independent and redundant subsystems. Each subsystem is made up of a header, two 4000 gpm pumps, a suction source, valves, piping, heat exchanger, and associated instrumentation.
Either of the two subsystems is capable of providing the required cooling capacity with two pumps operating to maintain safe shutdown conditions.
The time needed to effect a repair of the affected piping in accordance with the ASME Code would exceed the time allowed in the TS RAS, which would then require shutdown of the reactor.
TS Bases paragraph B 3.7.1 states the following: "The safety analyses for long term cooling were performed for various combinations of RHR System failures. The worst case single failure that would affect the performance of the RHRSW System is any failure that would disable one subsystem of the RHRSW System. As discussed in the FSAR, Paragraph 6.2.1.4.3 (Ref. 4) for these analyses, manual initiation of the OPERABLE RHRSW subsystem and the associated RHR System is assumed to occur 10 minutes after a DBA. The RHRSW flow required to support the assumed heat removal rate is 3540 gpm per pump with two pumps operating in one loop with up to 8% tubes plugged in the RHR heat exchanger (Note that the RHRSW flow of 3540 gpm is greater than the flow necessary for Unit 2 but is used here to be consistent with Unit 1). In this case, the maximum suppression chamber water temperature and pressure are approximately 210°F and 27 psig, respectively, well below the design temperature of 340°F and maximum allowable pressure of 62 psig."
The piping class governing the construction and operation of the affected pipe is ASME Section III Class 3. It also is governed by the repair/replacement requirements specified in ASME Section XI Class 3.
This piping therefore falls within the scope of Technical Reference Manual T 3.4.2, Structural Integrity.
PROPOSED AL TERNATIVE AND BASIS FOR USE:
The use of the technical guidance of ASME Code Case N-597-2 requires that Hatch Unit 2 address the following NRC conditions:
NRC Condition 1 "Code Case must be supplemented by the provisions of EPRI Nuclear Safety Analysis Center Report 202L-R2, 'Recommendations for an Effective Flow Accelerated Corrosion Program' (Ref. 6), April 1999, for developing the inspection requirements, the method of predicting the rate of wall thickness loss, and the value of the predicted remaining wall E1-2 to NL-11-2556 Relief Request HNP-ISI-RR-12, Version 1.0 Analytical Evaluation of RHR Service Water Piping thickness. As used in NSAC-202L-R2, the term 'should' is to be applied as 'shall' (Le., a requirement)."
SNC Response to Condition 1 The EPRI Report 202L-R2 is not applicable in this case because RHRSW has oxygen content significantly higher than FAC components. Similar to the FAC program at the SNC plants, SNC has implemented a Fleet Service Water Program which includes the development of inspection requirements, determining the rate of wall thickness loss plus the calculation of values for the predicted remaining life. The affected piping is already included in the Fleet Service Water Program.
NRC Condition 2 "Components affected by flow-accelerated corrosion to which this Code Case are applied must be repaired or replaced in accordance with the construction code of record and Owner's requirements or a later NRC approved edition of Section III, "Rules for Construction of Nuclear Power Plant Components," of the ASME Code (Ref. 7) prior to the value of tp reaching the allowable minimum wall thickness, tmin, as specified in 3622.1 (a)(1) of this Code Case. Alternatively, use of the Code Case is subject to NRC review and approval per 10 CFR 50.55a(a)(3)."
SNC Response to Condition 2 As noted in the SI\\JC response to Condition 1, this relief request does not apply to FAC-susceptible piping; however, the issue of repair/replacement still exists. The Fleet Service Water Piping Program requires that an evaluation be performed to determine when thinned material requires corrective action under a repair/replacement activity.
Results of the on-going UT thickness measurements of the affected piping will be compared to the tmin value, as discussed in the SNC response to Condition 5, to determine when a repair/replacement activity would be performed.
NRC Condition 3 "For Class 1 piping not meeting the criteria of -3221, the use of evaluation methods and criteria is subject to NRC review and approval per 10 CFR 50.55a(a)(3)."
SNC Response to Condition 3 The affected RHRSW piping is Class 3 and therefore, this note does not apply.
NRC Condition 4 "For those components that do not require immediate repair or replacement, the rate of wall thickness loss is to be used to determine a suitable inspection frequency so that repair or replacement occurs prior to reaching allowable minimum wall thickness, tmin."
E1-3 to NL-11-2556 Relief Request HNP-ISI-RR-12, Version 1.0 Analytical Evaluation of RHR Service Water Piping SNC Response to Condition 4 Hatch proposes to perform UT thickness measurements as described in the On-going Action Plan as provided below.
NRC Condition 5 "For corrosion phenomenon other than flow accelerated corrosion, use of the Code Case is subject to NRC review and approval. Inspection plans and wall thinning rates may be difficult to justify for certain degradation mechanisms such as MIC and pitting."
SNC Response to Condition 5 The submittal of this relief request addresses the issues noted in this condition: A copy of the initial UT data sheets are provided as Enclosure
- 2.
Hatch CR 379325 was written on December 1,2011 and documents the following ultrasonic thickness measurements - a thinned area was measured as 0.273 inches on the 18-inch diameter RHRSW system normal supply header for Unit-2, Division 1. According to Bechtel Calculation 0020 (VOL 999, Bin 999) for RET 03-052, the generic calculated acceptable minimum wall thickness for this piping is 0.311 inches. The adjacent piping was ultrasonically scanned and was found to have acceptable wall thickness.
The SNC Corporate Stress Group was requested to perform the analytical evaluation and Code Case N-597-2 was used to determine the Code-required minimum pipe wall. The evaluation notes that this piping supports Unit 2, Division 1, and is along a straight segment on the RHRSW system shown on Hatch-2lsometric S-23570 to be ASME,Section III, Class 3. The design pressure is 525 psi and the pipe specification designator is 2E11-GBC, which has a nominal diameter of 18-inches and a nominal wall thickness of 0.5-inch. The pipe is made of seamless ASTM A-106, Grade B carbon steel material. This material has a normal stress allowable of 15,000 psi.
The detailed evaluation per ASME Code Case N-597-2 resulted in a calculated minimum wall of 0.183 inches. This allowable local thickness is thinner than the lowest UT reading of 0.273 inches and therefore, the criteria of Code Case N-597-2 is met and the pipe continues to comply with the ASME Code requirements.
Because of the absence of ASME Section XI Code requirements and the annulment of ASME Code Case N-480, SNC proposes that the technical guidance of Code Case N-597-2 be used for evaluating pipe wall thinning in the RHRSW system. The use of that technical guidance provides reasonable assurance of structural integrity and SNC requests that relief be authorized per 10 CFR 50.55a(g)(6)(i).
E1-4 to NL-11-2556 Relief Request HNP-ISI-RR-12, Version 1.0 Analytical Evaluation of RHR Service Water Piping ON-GOING ACTION PLAN:
STATUS:
AL TERNATIVE DURATION:
As a result, the immediate performance of either a temporary, non-Code repair or a permanent Code repair is not warranted at this time. A permanent Code-compliant repair will be performed during the next refueling outage currently scheduled to begin in February 2013 or during a system outage of sufficient length to effect repairs.
The degradation mechanism that has caused the wall thinning is indeterminate at this time since it is internal to the pipe. However, based on the ultrasonically-observed pattern of the Haw, the cause is expected to be localized corrosion. Additional areas of this piping were examined ultrasonically and no locations found below minimum wall. This data provides assurance as to a lack of potential additional broadness issues. provides additional details of the UT thickness measurements.
On-going UT thickness measurements and analytical evaluations will be performed as described below:
- The affected area will be ultrasonically examined on a 3~-day frequency until SI\\JC establishes a wear rate. This will assure that unexpected degradation is not occurring and that the structural integrity of the piping is being maintained.
- Analytical evaluation will be performed based on each set of UT thickness measurements using ASME Code Case N-597-2 as discussed in this relief request.
- The examination and evaluation results will be documented in the Corrective Action Program.
This alternative is awaiting NRC approval.
This relief request will remain in effect until an ASME Section XI Code repair/replacement is performed prior to reaching the allowable minimum wall thickness based on the ongoing ultrasonic thickness measurements.
E1-5
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