ML16093A028
| ML16093A028 | |
| Person / Time | |
|---|---|
| Site: | Palisades, Indian Point, Grand Gulf, Pilgrim, Arkansas Nuclear, River Bend, Waterford, FitzPatrick  |
| Issue date: | 05/31/2016 |
| From: | Travis Tate Plant Licensing Branch 1 |
| To: | Mccann J Entergy Services |
| Guzman R, NRR/DORL/LPLI-1 | |
| References | |
| CAC MF6340, CAC MF6341, CAC MF6342, CAC MF6343, CAC MF6344, CAC MF6345, CAC MF6346, CAC MF6347, CAC MF6348, CAC MF6349 | |
| Download: ML16093A028 (18) | |
Text
Mr John F. Mccann UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 May 31, 2016 Vice President, Regulatory Assurance Entergy Services, Inc.
1340 Echelon Parkway Jackson, MS 39213
SUBJECT:
ARKANSAS NUCLEAR ONE, UNITS 1 AND 2; GRAND GULF NUCLEAR STATION, UNIT 1; JAMES A. FITZPATRICK NUCLEAR POWER PLANT; INDIAN POINT ENERGY CENTER, UNITS 2 AND 3; PALISADES NUCLEAR PLANT; PILGRIM NUCLEAR POWER STATION; RIVER BEND STATION, UNIT 1; AND WATERFORD 3 STEAM ELECTRIC STATION-RELIEF REQUEST RR-EN-15-1, PROPOSED ALTERNATIVE TO USE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE CASE N-789-1, "ALTERNATIVE REQUIREMENTS FOR PAD REINFORCEMENT OF CLASS 2 AND 3 MODERATE ENERGY CARBON STEEL PIPING FOR RAW WATER SERVICE, SECTION XI, DIVISION 1" (CAC NOS. MF6340, MF6341, MF6342, MF6343, MF6344, MF6345, MF6346, MF6347, MF6348, MF6349)
Dear Mr. Mccann:
By letter dated June 5, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML15159A200), as supplemented by letter dated January 29, 2016 (ADAMS Accession No. ML16029A341), and e-mail dated March 7, 2016 (ADAMS Accession No. ML16071A441 ), Entergy Operations, Inc. and Entergy Nuclear Operations, Inc. (Entergy or the licensee), requested relief from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWA-4000, for the repair of Class 2 and 3 moderate energy carbon steel raw water service system piping at the Entergy nuclear plants listed in relief request RR EN-15-1, Revision 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2),
the licensee proposed an alternative to use ASME Code Case N-789-1, "Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1," for the repair of the cooling water system piping on the basis that complying with the specified ASME Code requirement to repair the subject piping would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety.
The Nuclear Regulatory Commission (NRC) staff has reviewed the subject request and finds that complying with IWA-4000 of the ASME Code,Section XI, would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety. The staff finds that the licensee demonstrated that the proposed alternative in relief request RR EN-15-1, Revision 1, will provide reasonable assurance that the structural integrity and leakage integrity of the subject cooling water system piping will be maintained. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
The approval of the proposed alternative does not constitute, imply, or infer NRC approval of ASME Code Case N-789-1. All other requirements of the ASME Code,Section XI, for which relief has not been specifically requested and authorized by NRC staff remain applicable, including a third party review by the Authorized Nuclear In-service Inspector.
Specifically, the NRC staff authorizes the use of relief request RR EN-15-1, Revision 1, at the Arkansas Nuclear One, Unit 1, for the fourth and fifth 10-year inspection intervals; Arkansas Nuclear One, Unit 2, for the fourth 10-year inspection interval; Grand Gulf Nuclear Station, for the third and fourth 10-year inspection intervals; Indian Point Energy Center, Unit 2, for the fifth 10-year inspection interval; Indian Point Energy Center, Unit 3, for the fourth 10-year inspection interval; James A. Fitzpatrick Nuclear Power Plant, for the fourth 10-year inspection interval; Palisades Nuclear Plant, for the fifth 10-year inspection interval; Pilgrim Nuclear Power Station, for the fifth 10-year inspection interval; River Bend Station, for the third and fourth 10-year inspection intervals; and Waterford Steam Electric Station, Unit 3, for the third and fourth 10-year inspection intervals.
If you have any questions, please contact Richard V. Guzman, Senior Project Manager, at (301) 415-1030 or Richard.Guzman@nrc.gov.
Docket Nos. 50-313, 50-368, 50-255, 50-416, 50-293, 50-333, 50-458, 50-24 7' 50-286, 50-382
Enclosure:
Safety Evaluation cc w/enclosure: Distribution via Listserv Sincerely, o~c1Jild-Travis L. Tate, Chief Plant Licensing Branch 1-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE TO UTILIZE ASME CODE CASE N-789-1 RELIEF REQUEST RR EN-15-1, REVISION 1 ENTERGY OPERATIONS, INC ENTERGY NUCLEAR OPERATIONS, INC ARKANSAS NUCLEAR ONE, UNITS 1 AND 2; GRAND GULF NUCLEAR STATION, UNIT1; JAMES A. FITZPATRICK NUCLEAR POWER PLANT; INDIAN POINT ENERGY CENTER, UNITS 2 AND 3; PALISADES NUCLEAR PLANT; PILGRIM NUCLEAR POWER STATION; RIVER BEND STATION, UNIT 1; AND WATERFORD STEAM ELECTRIC STATION, UNIT 3 DOCKET NOS. 50-313, 50-368, 50-416, 50-333, 50-247, 50-286, 50-255, 50-293, 50-458, AND 50-382
1.0 INTRODUCTION
By letter dated June 5, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15159A200), as supplemented by letter dated January 29, 2016 (ADAMS Accession No. ML16029A341), and an e-mail dated March 7, 2016 (ADAMS No.
ML16071A441 ), Entergy Operations, Inc. and Entergy Nuclear Operations, Inc. (Entergy or the licensee), requested relief from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWA-4000, for the repair of Class 2 and 3 moderate energy carbon steel raw water service system piping at the Entergy nuclear plants listed in relief request RR EN-15-1, Revision 1.
Specifically, pursuant to Title 1 O of the Code of Federal Regulations (1 O CFR) 50.55a(z)(2),
the licensee proposed an alternative to use ASME Code Case N-789-1, "Alternative Requirements for Pad Reinforcement of Class 2 and 3 Moderate-Energy Carbon Steel Piping for Raw Water Service,Section XI, Division 1," for the repair of the cooling water system piping on the basis that complying with the specified ASME Code requirement would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety.
Enclosure
2.0 REGULATORY EVALUATION
Article IWA-4400 of the ASME Code,Section XI, requires that unacceptable flaws in ASME Code Class 2 and 3 components be corrected by repair or replacement activity or be accepted by supplemental examination and flaw evaluation.
Adherence to Section XI of the ASME Code is mandated by 1 O CFR 50.55a(g)(4), which states, in part, that ASME Code Class 1, 2, and 3 components (including supports) will meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI.
The regulation in 1 O CFR 50.55a(z) states, in part, that alternatives to the requirements of paragraph (g) of 10 CFR 50.55a may be used, when authorized by the Nuclear Regulatory Commission (NRC), if the licensee demonstrates that: (1) the proposed alternative provides an acceptable level of quality and safety; or (2) 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 the use of an alternative and the NRC to authorize the proposed alternative.
3.0 TECHNICAL EVALUATION
The affected components are ASME Code Class 2 and 3 moderate energy, carbon steel, raw water piping systems. Raw water is defined as water such as river, lake, well or brackish/salt water used in plant equipment, area coolers, and heat exchangers. Moderate energy is defined as less than or equal to 200°F (93°C) and less than or equal to 275 psig (1.9 MPa) maximum operating conditions.
3.2
Applicable Code Edition and Addenda
Table 1-Applicable Plants with Associated 10-Year Intervals and ASME Code Editions Plant
!.§!
ASME Section XI Edition/Addenda Interval Interval Interval Start End Arkansas Nuclear 4
2001 Edition/ 2003 Addenda 5/31/2008 5/30/2017 One 5
2007 Edition/ 2008 Addenda (Note 3l 5/31/2017 5/30/2027 Unit 1 (AN0-1) (Note 1l Arkansas Nuclear 4
2001 Edition/ 2003 Addenda 3/26/2010 3/25/2020 One Unit 2 (AN0-2)
Grand Gulf Nuclear 3
2001 Edition/ 2003 Addenda 5/31/2008 6/1/2017 Station (GGNS) (Note 1l 4
2007 Edition/ 2008 Addenda (Note 3l 6/2/2017 6/1/2027 Indian Point Energy 5
2007 Edition/ 2008 Addenda 6/1/2016 5/31/2026 Center Unit 2 (IPEC-
- 2) (Note 2)
Plant
!fil ASME Section XI Edition/Addenda Interval Interval Interval Start End Indian Point Energy 4
2001 Edition/ 2003 Addenda 7/21/2009 7/20/2019 Center Unit 3 (IPEC-
- 3)
James A Fitzpatrick 4
2001 Edition/ 2003 Addenda 3/1/2007 12/31/201 Nuclear Power Plant 6
(JAF)
Palisades Nuclear 5
2007 Edition/ 2008 Addenda 12/13/2015 12/12/202 Plant (PLP) (Note 2>
5 Pilgrim Nuclear Power 5
2007 Edition/ 2008 Addenda 7/1/2015 6/30/2025 Station (PNPS) (Note 2>
River Bend Station, 3
2001 Edition/ 2003 Addenda 5/31/2008 11/30/201 Unit 1 (RBS) (Note 1>
4 2007 Edition/ 2008 Addenda (Note 3>
12/1 /2017 7
11/30/202 7
Waterford Steam 3
2001 Edition/ 2003 Addenda 5/31/2008 6/30/2017 Electric Station, Unit 3 4
2007 Edition/ 2008 Addenda (Note 3>
7/1/2017 6/30/2027 (WF3) (Note 1)
Notes:
- 1)
The 3rd ISi [lnservice Inspection] intervals for GGNS, RBS, and WF3 and the 4th ISi interval for AN0-1 end within 1-1 /2 years of the requested relief request approval date. The licensee requested the approval this alternative for the 3rd and 4th GGNS, RBS, and WF3 intervals and the 4th and 5th AN0-1 intervals.
- 2)
The 4th ISi intervals for IPEC-2, PLP, and PNPS end prior to the requested relief request approval date. The licensee requested the approval of this alternative for the 5th IPEC-2, PLP, and PNPS ISi intervals.
- 3)
The licensee stated that AN0-1 GGNS, RBS, and WF3 will update to the 2007 Edition/2008 Addenda except as otherwise required by the NRC in 10 CFR 50.55a(g)(4)(ii).
The licensee stated that it performs repair/replacement activities in accordance with a fleet-wide, standardized Repair/Replacement Program based on the 2001 Edition/2003 Addenda of ASME Section XI. This Edition/Addenda of ASME Section XI will be used by all plants whenever the Code Case refers to IWA-4000 until the code bases of the Repair/Replacement Program is updated to the 2007 Edition/2008 Addenda as noted in Table 1 above.
3.3
Applicable Code Requirement
ASME Code,Section XI, IWA-4000 provides requirements for welding, brazing, metal removal, and installation of repair/replacement activities.
3.4
Reason for Request
As stated in its application, the licensee proposed alternatives to the requirement for replacement or internal weld repair of wall thinning conditions resulting from degradation in Class 2 and 3 moderate energy, carbon steel raw water piping systems in accordance with the ASME Code,Section XI, IWA-4000. The licensee stated that the repair replacement provisions of IWA-4000 cannot always be utilized when degradation or leakage is identified during plant operations. The licensee further stated that other approved alternative repair or evaluation methods are not always practical because of wall thinness and/or moisture issues.
The licensee stated that the proposed alternative will permit installation of a technically sound temporary repair to provide adequate time for evaluation, design, material procurement, planning, and scheduling of an appropriate permanent repair or replacement of the defective piping, considering the impact on system availability, maintenance rule applicability, and availability of replacement materials. The licensee contends that without its proposed alternative, compliance with the specified requirements of IWA-4000 would result in hardship and/or unusual difficulty, including higher risk associated with plant shut-downs and extended technical specifications actions, without a compensating increase in the level of quality and safety. Therefore, the licensee is proposing the alternative pursuant to 10 CFR 50.55a(z)(2) on the basis that compliance with the specified requirements would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety.
3.5
Licensee's Proposed Alternative and Basis for Use
Pursuant to 1 O CFR 50.55a(z)(2), the licensee proposes to implement the requirements of Code Case N-789-1, as an alternative to the requirements for IWA-4000, for the temporary repair of degradation in Class 2 and 3 moderate energy raw water piping systems resulting from mechanisms such as erosion, corrosion, cavitation, or pitting, but excluding conditions involving flow accelerated corrosion (FAC), corrosion assisted cracking, or any other form of cracking.
ASME Code Case N-789-1 provides provisions for the application of a metal reinforcing pad (pressure pad and structural pad) welded to the exterior of the piping system.
The license stated that sections 1, 3, 5, and 6 of the Code Case specify that materials, design, installation, and examination of reinforcement pads shall be performed in accordance with the Construction Code or ASME Section Ill. As allowed by IWA-4200 and IWA-4411, later Editions and Addenda of the Construction Code or ASME Section Ill may be used provided any required reconciliations are performed. The licensee clarified that it will only use Editions/Addenda of ASME Section Ill that have been approved by the NRC in 10 CFR 50.55a.
The licensee's January 29, 2016, letter included Revision 1 to RR EN-15-1 which supersedes its initial request, RR EN-15-1, Revision 0, dated June 5, 2015. The key requirements in Code Case N-789-1, including the licensee's clarifications and alternatives to the Code Case, are summarized below.
3.5.1 General Requirements Application of the reinforcing pad shall be performed in accordance with a Repair Replacement Plan satisfying the requirements of IWA-4150. The design, materials, and installation shall meet the requirements of the Construction Code and IWA-4000, except as stated in the Code Case.
If the minimum required thickness of reinforcing pad necessary to satisfy the requirements of Section 3 of the Code Case is greater than the nominal thickness for the size and schedule of the piping, this Code Case shall not be used. Additional reinforcement or repair is not permitted on top of an existing reinforcing pad. Reinforcing pads, including those installed during a refueling outage, shall not remain in service beyond the end of the next refueling outage. The Code Case may only be applied to piping not required to be ultrasonically examined for inservice inspection.
3.5.2 Initial Evaluation The material beneath the surface to which the reinforcing pad is to be applied and the adjacent area shall be ultrasonically measured to establish the existing wall thickness, including the extent and configuration of degradation to be corrected by the reinforcing pad.
The cause and rate of degradation shall be determined. If the cause is determined to be FAC, corrosion-assisted cracking, or any other form of cracking, this Code Case shall not apply. The extent and rate of degradation in the piping shall be evaluated to ensure that there are no other unacceptable locations within the surrounding area that could affect the integrity of the repaired piping. The dimensions of the surrounding area to be evaluated shall be determined by the licensee, considering the type of degradation present.
3.5.3 Design Type of Reinforcing Pads Reinforcing pads may be used for leak prevention only (i.e., pressure pad), or for leak prevention plus structural reinforcement of thinned areas including areas that do, or are expected to, penetrate the piping wall (i.e., structural pad).
Pressure pads are designed to retain pressure, and may be used only where the piping is predicted to retain full structural integrity until the next refueling outage assuming a corrosion rate of either two times the actual measured corrosion rate in that location, or four times the estimated maximum corrosion rate for the system.
The licensee provided clarification regarding it's corrosion rate determination for the pressure pads and stated that its designs of pressure pads will be based on a corrosion rate of two times the actual measured corrosion rate in that location. If a repair must be performed without sufficient time to determine the actual rate of corrosion at the repair location, then the pressure pad design will be based on a corrosion rate that is four times the estimated maximum (worst-case) corrosion rate for the same degradation mechanism in that system.
Structural pads are designed for pressure plus structural reinforcement and may be used where the piping is predicted not to retain full structural integrity until the next refueling outage.
General Design Requirements - Pressure and Structural Pads The design of reinforcing pads shall be in accordance with the applicable requirements of the Construction Code or the ASME Code, Section Ill (NC-3100, ND-3100 and NC-3600, ND-3600 including Appendix II).
The reinforcing pad shall be sized to encompass the unacceptable area with the attachment welds located on adjacent base material of sufficient thickness to accommodate the design stresses. The thickness of the reinforcing pad shall be sufficient to maintain required thickness until the next refueling outage. The tensile strengths of the plate and weld filler metal for the reinforcing pad shall be at least that specified for the base metal to which it is applied.
The predicted maximum degradation of the reinforced piping until the next refueling outage shall be included in the design. The predicted degradation of the piping shall be based on in-situ inspection of, and established data for, similar base metals in similar environments. If the reinforcing pad is predicted to become exposed to the raw water, the predicted degradation of the reinforcing pad shall be based upon established data for base metals or weld metals with similar chemical composition to that used for the reinforcing pad.
The following factors shall be included, as applicable, in the design and application of the pad:
(1)
Shrinkage effects, if any, on the piping; (2)
Stress concentrations caused by installation of the reinforcing pad or resulting from existing and predicted piping internal surface configuration; (3)
Effects of welding on any interior coating; and (4)
Added weight of the pad with respect to any design analyses that could be affected.
In its January 29, 2016, letter, the licensee stated that Paragraph 3.2(i) of Code Case N-789-1 includes an incorrect reference to NC-2650 for the flexibility analysis associated with Class 2 designs. The licensee stated that the correct reference should be NC-3650 and it will comply with NC-3650, as an alternative to the N-789-1 requirement to use NC-2650.
The licensee also stated that when gasket material is used in accordance with paragraph 3.2(1) of the Code Case (water-backed applications), it will also require removal of any residual moisture by heating prior to welding.
Specific Design Requirements - Pressure Pad Fillet-welded pressure pads shall be designed to withstand the membrane strain of the piping in accordance with the requirements of paragraph 3.2(a) of the Code Case such that the following criteria are satisfied:
(1)
The allowable membrane stress is not exceeded in the piping or the pad; and (2)
The strain in the pad does not result in fillet weld stresses exceeding allowable stresses for such welds.
Design as a reinforced opening in accordance with the Construction Code shall satisfy the aforementioned requirement. Pressure pads may be designed as structural pads in accordance with section 3.4 of the Code Case or as prequalified designs in accordance with Section 3.5 of the Code Case.
Specific Design Requirements - Structural Pad Structural pads shall meet the requirements of Section 3.2, Figure 1, of the Code Case and the following:
Unless otherwise established by analysis in accordance with the requirements of Section 3.2(a) of the Code Case, structural pads shall be attached by partial penetration attachment welds that extend for a distance of at least "s" in each direction beyond the area predicted, by the next refueling outage, to infringe upon the required thickness.
The thickness of the partial penetration attachment welds shall equal the thickness of the pad and the edges of the welds shall be tapered to the piping surface at a maximum angle of 45 degrees. Final configuration of the structural pad including attachment welds shall permit the examinations and evaluations required herein, including any required preservice or inservice examinations of encompassed or adjacent welds. Except for the tapered edges, the structural pad plate and attachment welds shall have a uniform thickness.
Prequalified Design Application of structural pads on straight pipe, standard elbows, and associated welds shall be exempt from the requirements of Section 3.2(a) of the Code Case, provided all of the following conditions are satisfied:
(a)
All other requirements of Sections 3.1, 3.2, and 3.4 of the Code Case are satisfied.
(b)
The axial length of structural pad plus width of partial penetration attachment welds shall not exceed the greater of 6 inches or the outside diameter of the piping.
(c)
The finished structural pad shall be circular, oval, or rectangular in shape.
(1) The maximum dimension compensated by a circular structural pad shall not exceed two-thirds of the nominal outside diameter of the piping.
(2) Rectangular structural pads shall be aligned parallel with or perpendicular to the axis of the piping.
(3) For oval structural pads, the end radii shall not be less than 0.75 vRtnom, and the axis of the structural pad shall be aligned parallel with or perpendicular to the axis of the piping.
3.5.4 Water-Back Applications Attachment welds on water-backed piping shall be applied using the shielded metal arc welding process with low-hydrogen electrodes. When welding a reinforcing pad to a leaking area, precautions shall be taken to prevent welding on wet surfaces, such as installation of a gasket or sealant beneath the pad. For piping materials other than P-No. 1, Group 1, the surface examination shall be performed no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of welding.
3.5.5 Installation The base material in the area to be welded shall be cleaned to bare metal. Weld metal shall be deposited using a groove-welding procedure qualified in accordance with the ASME Code,Section IX, and the Construction Code. Provisions for venting during the final closure weld, or for pressurizing for leak-testing, shall be included, if necessary.
3.5.6 Examination The completed attachment weld shall be examined using the liquid penetrant or magnetic particle method and shall satisfy the surface examination acceptance criteria for welds of the Construction Code or the ASME Code, Section Ill (NC-5300, ND-5300).
Except for the tapered edges, partial penetration attachment welds, including the piping base metal upon which they are applied, shall be ultrasonically measured to verify acceptable wall thickness. Partial penetration attachment welds shall be volumetrically examined when full penetration girth welds in the piping are required by the Construction Code to be volumetrically examined. Where configuration does not permit meaningful volumetric examination, the first layer, each 1/2 inch thickness of weld deposit, and the final surface shall be examined using liquid penetrant or magnetic particle in lieu of volumetric examination.
If volumetric examination is required, the full volume of the attachment weld, excluding the tapered edges, but including the volume of base metal required for the intended life of the reinforcing pad, shall be examined in accordance with the Construction Code or the ASME Code, Section 111, using either the ultrasonic or radiographic method, and shall, to the depth at the surface of the piping, satisfy the acceptance criteria for weldments of the Construction Code or the ASME Code, Section Ill (NC-5320, ND-5320 or NC-5330, ND-5330). Any volume of the piping beneath the reinforcing pad that is credited in the design shall satisfy the volumetric acceptance criteria of the ASME Code, Section Ill (NC-5320, ND-5320 or NC-5330, ND-5330),
as applicable.
3.5.7 Pressure Testing In lieu of the ASME Code,Section XI, IWA-4540, a system leakage test of the repair/replacement activity shall be performed in accordance with IWA-5000 prior to, or as part of, returning to service. Reinforcing pads attached to piping that has not been breached shall be equipped with pressure taps for performance of pressure testing.
3.5.8 lnservice Monitoring Upon completion of the repair, inspections shall be performed for structural pads, using ultrasonic or direct thickness measurement, to record the thickness of the plate, the thickness at the attachment welds, including the underlying base metal, and to the extent examinable in a 3-inch wide band, surrounding the repair, as a baseline for subsequent monitoring of the repair.
The licensee shall prepare a plan for additional thickness monitoring for structural pads using ultrasonic or direct thickness measurement to verify that minimum design thicknesses, as required by the Construction Code or the ASME Code, Section Ill, are maintained until the next refueling outage. The monitoring shall be monthly for the first quarter and the subsequent frequency shall be based on the results of the monitoring activities, but at least quarterly.
Provisions shall be made for access to structural pads on buried piping during operation to accomplish these examinations.
The licensee provided clarification regarding its implementation of Paragraph 8(b) [structural pads] of the Code Case. The licensee stated that it will perform monitoring [thickness measurement] on a monthly basis during the first quarter as required by Code Case N-789-1.
The licensee further stated that the subsequent monitoring frequency shall be based on corrosion rates calculated using reductions in thickness since the previous monitoring inspection, but at least quarterly.
Areas containing pressure pads shall be monitored monthly for evidence of leakage. If the areas containing pressure pads are not accessible for direct observation, monitoring shall be accomplished by observation of surrounding areas or ground surface areas above pressure pads on buried piping; or leakage collection systems, if available, shall be monitored.
If the results of the monitoring program identify leakage or indicate that the structural margins required by Section 3 of the Code Case will not be maintained until the next refueling outage, the pad will be removed and repair/replacement activities shall be performed prior to encroaching on the design limits. All reinforcing pads, regardless of when installed, shall be removed no later than the end of the next refueling outage.
3.5.9 Hardship Justification The licensee stated that the repair and replacement provisions of IWA-4000 cannot always be utilized when degradation or leakage is identified during plant operations. The licensee contends that its proposed alternative permits the installation of a technically sound temporary repair which permits time for evaluation, design, material procurement, planning, and scheduling of an appropriate permanent repair or replacement of defective piping, taking into consideration the impact on system availability, maintenance rule applicability, and the availability of materials.
The licensee stated that without the repair option described in its alternative, compliance with IWA-4000 would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety such as higher risk associated with plants shut-downs and extended technical specification actions.
The licensee noted that the ASME Board on Nuclear Codes and Standards approved Code Case N-789-1 on November 13, 2013. However, it has not been incorporated into NRC Regulatory Guide 1.147, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1," and thus is not available for application at nuclear power plants without specific NRC approval.
3.6 Duration of Proposed Alternative The licensee requested use of the proposed alternative for the duration of the ISi intervals identified above in Section 3.2, Table 1. For Grand Gulf Nuclear Station, Unit 1, River Bend Station, Unit 1 and Waterford Steam Electric Station, Unit 3, which end their current 3rd ISi interval within 1.5 years of the approval of this alternative, the licensee also includes the 4th ISi interval for these units. For Arkansas Nuclear One, Unit 1, which ends its current 4th ISi interval within 1.5 years of the approval of this alternative, the licensee also includes the 5th ISi interval for this unit.
The licensee stated that reinforcing pads installed before the end of the 10-year ISi interval will be removed during the next refueling outage after installation, even if that refueling outage occurs after the end of the 10-year ISi interval. In this case, absent detrimental defects or degradation, duration of the proposed alternative would be until the first refueling outage after the end date of the ISi interval for the applicable Entergy plant.
3.7 NRC Staff's Evaluation The NRC staff evaluated the adequacy of the proposed alternative in maintaining the structural integrity of the repaired subject piping. The staff focused on the following key elements of the proposed alternative, as previously discussed in Section 3.5, above: (1) general requirements; (2) initial evaluation; (3) design requirements; (4) water-back application; (5) installation; (6) examination; (7) pressure testing; (8) inservice monitoring; and (9) hardship justification.
The NRC staff notes that many requirements specified in Code Case N-789-1 are not discussed in this safety evaluation, but they should not be considered as less important. As part of the NRC-approved proposed alternative, all requirements in the Code Case must be followed. Any exceptions to the Code Case that are approved in this safety evaluation also need to be followed.
- 3. 7.1 General Requirements The NRC staff notes that the proposed alternative requires the reinforcing pad be applied in accordance with a Repair Replacement Plan satisfying the requirements of the ASME Code, IWA-4150. The design, materials, and installation requirements of the Construction Code and IWA-4000, except as stated in the Code Case, must be satisfied. Limitations in the proposed alternative general requirements ensure repairs permitted under the alternative are temporary and will be repaired during the next outage. Limitations in the proposed alternative also prevent multiple repairs in the same degradation location which would indicate that a licensee's initial assessment was not accurate. Based on the forgoing, the NRC staff finds that the proposed general requirements, including limitations, are appropriate and, therefore, acceptable.
3.7.2 Initial Evaluation The NRC staff finds that the proposed initial evaluation is acceptable because: (1) prior to installing the reinforcing pad, the proposed alternative requires that the base metal be ultrasonically examined to determine the cause and rate of degradation, which is necessary to determine if the degradation rate is such that a temporary repair is or is not appropriate and to determine if the degradation mechanism is not compatible with a temporary repair under the requirements of the alternative, such as FAC, corrosion-assisted cracking, or any other form of cracking; and (2) the proposed alternative requires that an initial inspection be performed to determine the extent of condition of the subject piping and to ensure structural integrity of the subject piping in the vicinity of the degraded area.
3.7.3 Design Requirements The licensee stated that Paragraph 3.2(i) of Code Case N-789-1 includes an incorrect reference to NC-2650 for the flexibility analysis associated with Class 2 designs. The correct reference should be NC-3650 and the licensee stated that it will comply with NC-3650. The NRC staff agrees that the reference to NC-2650 in Paragraph 3.2(i) of Code Case N-789-1 is incorrect and the correct reference is NC-3650 as stated by the licensee. Therefore, the staff finds the licensees use of NC-3650 in lieu of NC-2650 acceptable.
Paragraph 3.2(1) of code Case N-789-1 states that when permitted by the design, suitable gasket material may be applied inside the pad to prevent moisture during welding. The licensee stated that when applying Paragraph 3.2(1), it will remove any residual moisture by heating prior to welding. The staff finds this acceptable because removal of residual moisture by heating prior to welding aids in preventing welding defects caused by moisture in contact with the weld pool and decreases the possibility of delayed hydrogen cracking.
The NRC staff finds that the reinforcing pads will be designed in accordance with the applicable requirements of the Construction Code or the ASME Code, Section Ill (NC-3100, ND-3100, and NC-3600, ND-3600 including Appendix II).
The NRC staff notes that the proposed alternative clearly defined the pressure pads and structural pads such that each type of pad will be applied for specific pipe degradation and purpose.
The NRC staff notes that Code Case N-789-1, paragraph 3.1 (a)(1 ), specifies that a pressure pad is designed with a corrosion rate of either two times the actual measured corrosion rate in that location, or four times the estimated maximum corrosion rate for the system. In its January 29, 2016 letter, the licensee provided clarification regarding 3.1 (a)(1) and stated that in cases where the repair must be performed without sufficient time to determine the actual corrosion rate at the repair location, then the pressure pad design will be based on a corrosion rate that is_four times the estimated maximum (worst-case) corrosion rate for the same degradation mechanism in that system.
For the structural pad, the corrosion rate will be based on paragraph 3.2(f) in the Code Case, which requires that the predicted maximum degradation of the reinforced piping until the next refueling outage be included in the design. The predicted degradation of the piping will be based on in-situ inspection of, and established data for, similar base metals in similar environments. The proposed alternative requires that if the reinforcing pad is predicted to become exposed to the raw water, the predicted degradation of the reinforcing pad shall be based upon established data for base metals or weld metals with similar chemical composition to that used for the reinforcing pad.
The NRC staff notes that the Code Case does not provide specific corrosion rate determination for the structural pad. It is not clear to the staff that the corrosion rate used in the structural pad design would be bounding, other than the fact that the structural pad will be designed for the duration until the next refueling outage. As a compensatory measure, the proposed alternative requires inservice monitoring to ensure the structural integrity of the repaired pipe using a structural pad. In addition, the proposed repair is limited to a maximum duration of one operating cycle. The staff finds this relatively short duration of application limits the degradation.
Further, should the actual corrosion rate exceed the projected corrosion rate during the operating cycle and a leak develop at or around the installed pad, the proposed inservice monitoring will be able to detect such leakage and the operator will be able to take corrective action.
The NRC staff notes that the structural pad will be designed with partial penetration attachment welds that extend for a distance in each direction beyond the area predicted, by the next refueling outage, to infringe upon the required thickness. Final configuration of the structural pad including attachment welds will permit the examinations and evaluations required herein, including any required preservice or inservice examinations of encompassed or adjacent welds.
The proposed alternative requires that the thickness of the reinforcing pad will be sufficient to maintain required thickness until the next refueling outage.
Although concerns exist regarding the corrosion rate used in the structural pad design, the NRC staff finds that the proposed alternative will provide reasonable assurance of the structural integrity and leakage integrity of the repaired piping until the next refueling outage because:
(1) the structural pad will be designed to maintain required thickness until the next refueling outage; and (2) the proposed alternative requires periodic inservice monitoring as discussed further in this safety evaluation. Therefore, the NRC staff finds the aforementioned design requirements to be acceptable.
3.7.4 Water-Backed Applications The proposed alternative requires the use of the shielded metal arc welding process with low-hydrogen electrodes for the attachment welds on water-backed piping. The proposed alternative further requires precaution be taken when welding a reinforcing pad to a leaking area. For piping materials other than P-No. 1, Group 1, the licensee will perform the surface examination no sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after completion of welding. The NRC staff notes that waiting 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after welding ensures that if delayed hydrogen cracking were to occur, it would be detected during the surface examination. Therefore, the NRC staff finds the proposed requirements for water-backed application to be acceptable.
3.7.5 Installation The NRC staff finds that the proposed alternative requires the use a qualified welding procedure in accordance with the ASME Code,Section IX, and the Construction Code in addition to requirements specified in the Code Case. Therefore, the NRC staff finds the proposed installation requirements acceptable.
3.7.6 Examination The proposed alternative requires a surface examination (liquid penetrant or magnetic particle) and volumetric examination be performed of the pad, weld and base metal after the reinforcing pad is welded to the pipe in accordance with Section Ill of the ASME Code, or the Construction Code. The NRC staff finds the proposed acceptance examinations follows Section Ill of the ASME Code, and the Construction Code. Therefore, the staff finds the proposed acceptance examinations to be acceptable.
3.7.7 Pressure Testing The proposed alternative requires that a system leakage test will be performed in accordance with IWA-5000 prior to, or as part of, returning to the system to service. In addition, reinforcing pads attached to piping that have not been breached shall be equipped with pressure taps for performance of pressure testing. The NRC staff finds that the proposed pressure testing to be acceptable because it is consistent with IWA-5000 of the ASME Code,Section XI.
3.7.8 lnservice Monitoring For the structural pad, the proposed alternative requires that the pad be examined using ultrasonic or direct thickness measurement, to record the thickness of the plate, the thickness at the attachment welds, including the underlying base metal, and to the extent examinable in a 3-inch wide band, surrounding the repair, as a baseline for subsequent monitoring of the repair.
The licensee will monitor the structural pad monthly for the first quarter and the subsequent frequency will be based on the results of the monitoring activities, but at least quarterly.
For the pressure pad, the proposed alternative requires that the areas containing the pad be visually examined monthly for evidence of leakage. If the areas containing the pressure pad are not accessible for direct observation, the licensee will observe surrounding areas or ground surface areas above pressure pads on buried piping; or leakage collection systems, if available.
The licensee stated that if the results of the monitoring program identify leakage or indicate that the structural margins required by the Code Case will not be maintained until the next refueling outage, the pad will be removed and repair/replacement activities shall be performed prior to encroaching on the design limits.
The NRC staff finds that the proposed inservice monitoring requirements are acceptable because: (1) the frequency and the examination method are adequate to monitor the structural integrity of the pressure pad and structural pad; and (2) the acceptance criteria for the pressure pad and structural pad are clearly defined and adequate.
3.7.9 Hardship Justification The NRC staff finds that performing a plant shutdown to repair the subject piping would cycle the unit and increase the potential of an unnecessary transient, resulting in undue hardship.
Additionally, performing the ASME Code repair during normal operation would challenge the Technical Specification Completion Time and place the plant at higher safety risk than warranted. Therefore, the NRC staff determined that compliance with the specified ASME Code repair requirements would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety.
3.8 Summary The NRC staff finds that the proposed alternative will provide reasonable assurance of the structural integrity and leak tightness of the repaired cooling water system pipe because: (1) the scope of the application is clearly defined; (2) the pressure pad and structural pad will be designed in accordance with the Construction Code and ASME Code, Section Ill, and specific requirements as specified in Code Case N-789-1; (3) the degraded pipe will be examined and evaluated prior to the repair; (4) acceptance examinations will be performed to verify the condition of the repair; (5) the in-service monitoring will be performed to verify the pipe wall thickness and potential degradation; and (6) pressure testing will be performed in accordance with IWA-5000 of the ASME Code,Section XI.
4.0 CONCLUSION
As set forth above, the NRC staff finds that complying with IWA-4000 of the ASME Code,Section XI, would result in hardship and/or unusual difficulty without a compensating increase in the level of quality and safety. The staff finds that the licensee demonstrated that relief request RR EN-15-1, Revision 1, will provide reasonable assurance that the structural integrity and leakage integrity of the subject cooling water system piping will be maintained. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
The NRC staff notes that approval of this alternative does not imply or infer NRC approval of ASME Code Case N-789-1.
All other requirements of the ASME Code,Section XI, for which relief has not been specifically requested and authorized by NRC staff remain applicable, including a third party review by the Authorized Nuclear In-service Inspector.
The NRC staff authorizes the use of relief request RR EN-15-1, Revision 1, at the Arkansas Nuclear One, Unit 1, for the fourth and fifth 10-year inspection intervals, Arkansas Nuclear One, Unit 2, for the fourth 10-year inspection interval, Grand Gulf Nuclear Station, for the third and fourth 10-year inspection intervals, Indian Point Energy Center, Unit 2, for the fifth 10-year inspection interval, Indian Point Energy Center, Unit 3, for the fourth 10-year inspection interval, James A. Fitzpatrick Nuclear Power Plant, for the fourth 10-year inspection interval, Palisades Nuclear Plant, for the fifth 10-year inspection interval, Pilgrim Nuclear Power Station, for the fifth 10-year inspection interval, River Bend Station, for the third and fourth 10-year inspection intervals, and Waterford Steam Electric Station, Unit 3, for the third and fourth 10-year inspection intervals.
Principal Contributor: Robert Davis Date: May 31, 2016
- SE and concurrence sent via email OFFICE NRR/DORL/LPL 1-1/PM NRR/DORL/LPL 1-1/LA NRR/DE/EPNB/BC*
NAME RGuzman KGoldstein DAiiey DATE 5/19/16 4/5/16 3/24/16 OFFICE NRR/DORL/LPL 1-1/BC N RR/DORL/LPLl-1 /PM NAME TT ate RGuzman DATE 5/31/16 5/31/16