ML14307B109
| ML14307B109 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 11/01/2014 |
| From: | David Bice Entergy Nuclear Operations |
| To: | Andrea George Division of Operating Reactor Licensing |
| References | |
| Download: ML14307B109 (31) | |
Text
NRR-PMDAPEm Resource From: BICE, DAVID B (ANO) [DBICE@entergy.com]
Sent: Saturday, November 01, 2014 11:32 AM To: George, Andrea Cc: PYLE, STEPHENIE L
Subject:
ANO Relief Request Attachments: 2CAN111401.pdf Importance: High Attached is relief request. Thanks.
dave 1
Hearing Identifier: NRR_PMDA Email Number: 1676 Mail Envelope Properties (8FE62703F9AB724AA66CFA0770BCC84C49E6603E)
Subject:
ANO Relief Request Sent Date: 11/1/2014 11:32:25 AM Received Date: 11/1/2014 11:32:33 AM From: BICE, DAVID B (ANO)
Created By: DBICE@entergy.com Recipients:
"PYLE, STEPHENIE L" <SPYLE@entergy.com>
Tracking Status: None "George, Andrea" <Andrea.George@nrc.gov>
Tracking Status: None Post Office: JDCXMETSP002.etrsouth.corp.entergy.com Files Size Date & Time MESSAGE 51 11/1/2014 11:32:33 AM 2CAN111401.pdf 1301291 Options Priority: High Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
Recipients Received:
Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-4704 Stephenie L. Pyle Manager, Regulatory Assurance Arkansas Nuclear One 2CAN111401 November 1, 2014 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Supplement to Relief Request ANO2-ISI-017, Emergency Request Alternative to Utilize the Flaw Evaluation Methodology of ASME Code Case N-513-4, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1 Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6
Reference:
Entergy letter dated October 31, 2014, Emergency Request Alternative to Utilize ASME Code Case N-513-4, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1, Relief Request ANO2-ISI-017
Dear Sir or Madam:
By letter dated October 31, 2014, Entergy Operations, Inc. (Entergy) requested emergency NRC approval of a proposed alternative to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI for Arkansas Nuclear One, Unit 2 (ANO-2), in accordance with 10 CFR 50.55a(a)(3)(ii). The alternative is for the current fourth 10-year inservice inspection interval. This interval began on March 26, 2010.
As a result of a teleconference held between ANO and NRC staff at 1900 on October 31, 2014, the NRC determined changes to the Entergy request were required in order to fully meet NRC acceptance criteria. This letter therefore supersedes the reference letter and includes the additional information required.
Specifically, Entergy is requesting relief to apply the flaw evaluation methodology of N-513-4, to structurally evaluate Class 2 and 3 moderate energy piping including elbows, bent pipe, reducers, expanders, and branch tees. Although the flaw evaluation methodology of N-513-4 is requested, ANO-2 will continue to apply all other requirements contained within Code Case N-513-3, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1, as associated with the subject flaw.
2CAN111401 Page 2 of 3 This methodology is to be used to evaluate a through-wall flaw that was identified in a 6-inch branch connection from the Service Water (SW) supply header to the suction of the B Emergency Feedwater Pump. This line was determined to be inoperable and the unit entered a Technical Specification 72-hour allowable outage time (AOT) in accordance with Limited Condition of Operation (LCO) 3.7.3.1 on October 30, 2014, at 2118. Immediate repair or replacement of the pipe is not feasible during this LCO. Without approval of this relief, ANO-2 will be required to shutdown following expiration of the AOT and result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety.
It has been determined that the root cause of the flaw is microbiological induced corrosion (MIC). The majority of leaks in ANO-2 SW piping in the past have been MIC-induced. The associated piping system continues to be capable of performing its required safety function and is not susceptible to sudden or catastrophic failure.
The attached request maintains the quality and safety considerations of structures, systems, and components required for safe operation of ANO-2.
Entergy requests the use of the Code Case N-513-4 flaw evaluation methodology until a Section XI compliant repair / replacement can be completed prior to startup from the next refueling outage (fall of 2015) or exceeding the temporary acceptance criteria of Code Case N-513-3 and this relief request, whichever comes first. contains the request for alternative. The stress analysis is provided in with the NDE Data Sheet provided in Attachment 3.
Entergy requests approval of this relief prior to the expiration of the LCO AOT which will end at 2018 on November 2, 2014.
This letter contains new commitments included in Attachment 4.
Should you have any questions regarding this submittal, please contact me.
Sincerely, ORIGINAL SIGNED BY STEPHENIE L. PYLE SLP/rwc Attachments:
- 1. Relief Request ANO2-ISI-017
- 2. Structural Integrity Associates Calculation 1401289.301
- 3. UT Thickness Examination - Report 2-BOP-UT-14-040
- 4. List of Regulatory Commitments
2CAN111401 Page 3 of 3 cc: Mr. Marc L. Dapas Regional Administrator U. S. Nuclear Regulatory Commission, Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector Arkansas Nuclear One P. O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Ms. Andrea E. George MS O-8B1 One White Flint North 11555 Rockville Pike Rockville, MD 20852
ATTACHMENT 1 TO 2CAN111401 RELIEF REQUEST ANO2-ISI-017 to 2CAN111401 Page 1 of 5 RELIEF REQUEST ANO2-ISI-017 Component / Number: 2HCC-2003 (elbow) and 2HBC-33 (sweep-o-let)
Code Class: American Society of Mechanical Engineers (ASME Section III)
Class 3
References:
ASME Code,Section XI, 2001 Edition with the 2003 Addenda Code Case N-513-4
Description:
Service Water (SW) to 2P-7B, Emergency Feed Water (EFW)
Pump Suction Unit / Inspection Interval Arkansas Nuclear One, Unit 2 (ANO-2) / Fourth (4th) 10-year Applicability: interval, 2R24 Refueling Outage I. CODE REQUIREMENTS The applicable ASME Section XI Code Edition and Addenda for ANO-2 is the ASME Code,Section XI, 2001 Edition with the 2003 Addenda. Articles IWD-3120 and IWD-3130 require that flaws exceeding the defined acceptance criteria be corrected by repair / replacement activities or be evaluated and accepted by analytical evaluation.
ASME Code,Section XI, IWD-3120(b) requires that components exceeding the acceptance standards of IWD-3400 be subject to supplemental examination, or to a repair / replacement activity:
II. PROPOSED ALTERNATIVE
Background
On October 20, 2014, as documented in condition report CR-ANO-2-2014-02970, Operations personnel identified leakage in a dissimilar metal weld between an 18 std wall x 6 schedule 40 carbon steel sweepolet, and a 6 schedule 40 stainless steel 45° elbow on the SW piping to the suction of the B EFW pump. This leak is located in the Arkansas Nuclear One, Unit 2 (ANO-2) Auxiliary Building. The insulation around the subject line was wet; however, the leak rate at the time of discovery was 1 to 2 drops per hour. According to Operations, the current leak rate is 32 drops per hour. The piping in question forms a branch connection, via a sweepolet, with the main SW header.
NDE Report 2-BOP-UT-14-040 (Attachment 3) provides a detailed UT mapping of the area immediately around the leak. The UT data characterized the flaw at the leak location and verified that the flaw could be treated as a single flaw with respect to the proximity of other thinned regions. The UT report noted that the flaw could be characterized as a nonplanar flaw. The report states that the flaw is located in the toe of the weld on the sweepolet (carbon steel) side of the weld. The size of the pinhole is too small to measure (32 drops per hour). Based on the results of the report, the remaining to 2CAN111401 Page 2 of 5 piping beyond the flaw is sufficient to maintain a pressure-retaining boundary and postulated leakage does not exceed operability margins. The nonplanar indication is the result of microbiological induced corrosion (MIC). Such corrosion indications are historically limited to localized areas on ANO-2 SW piping and piping components and do not manifest in general thinning, cracking, or other prompt structural failure precursors. This isolated corrosion area can be reliably monitored to ensure flow and structural integrity are maintained.
The weld material is ER309/E309. ER309 yield strength is 57 ksi with an ultimate tensile strength of 86 ksi.
ASME Code Case N-513-3 is conditionally acceptable to the NRC (per Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, Revision 17). However, N-513-3 does not allow evaluation of flaws located away from attaching circumferential piping welds that are in elbows, bent pipe, reducers, expanders, and branch tees. ASME Code Case N-513-4 provides guidance for evaluation of flaws in these locations. This code case was recently endorsed by ASME on May 7, 2014. This code case has not been generically approved by the NRC.
SW System Description Briefly, the SW system for ANO-2 consists of two independent full capacity 100 percent redundant loops. Each SW loop is capable of supplying cooling water to the required components during normal and emergency conditions. This redundancy allows continued plant operation when a single component failure occurs. System crosstie valves provide additional redundancy by allowing one of the three SW pumps to be removed from service for maintenance. The remaining two pumps provide total system flow for both SW loops.
In the event of an emergency, the SW system can be the supply source for the EFW system (ANO-2 Technical Specification (TS) 3.7.1.3).
The design pressure for the ANO-2 SW system is 150 psig and the design temperature is 130 °F.
ANO-2 TS 3.7.3 requires that two SW loops shall be operable and powered from independent essential buses to provide redundant and independent flow paths in Modes 1, 2, 3, and 4. ANO-2 TS 3.7.4 requires the Emergency Cooling Pond (ECP) to be operable in Modes 1, 2, 3, and 4. Two EFW pumps and associated flow paths are to remain operable in Modes 1, 2, and 3 (ANO-2 TS 3.7.1.2).
On October 30, 2014, at 2118, Loop 1 of SW and EFW pump 2P-7B were declared inoperable and the appropriate TS actions entered. Immediate repair or replacement of the pipe is not feasible during this LCO. The inoperable loop is required to be restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the unit must be placed in Hot Shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Cold Shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> per ANO-2 TS 3.7.3. Based on the insignificance of the flaw, it appears inappropriate to challenge the operation of the plant.
to 2CAN111401 Page 3 of 5 Due to the fact that the original flaw is MIC-induced, and ANO-2 has extensive experience with similar flaws in this system and it is well understood by ANO-2 staff, consideration of flaw growth is not a significant concern. Therefore, it has been concluded that the overall condition and the continued operation of the associated SW loop until the next ANO-2 refueling outage is acceptable.
Proposed Alternative The NRC issued Generic Letter 90-05, Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping (Generic Letter 90-05), to address the acceptability of limited degradation in moderate energy piping. The generic letter defines conditions that would be acceptable to utilize temporary non-code repairs with NRC approval. The ASME recognized that relatively small flaws could remain in service without risk to the structural integrity of a piping system and developed Code Case N-513. NRC approval of Code Case N-513 versions in Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, allows acceptance of partial through-wall or through-wall leaks for an operating cycle provided all conditions of the Code Case and NRC conditions are met. The Code Case also requires the Owner to demonstrate system operability due to leakage and any implied /
potential spray.
ASME recognized that Code Case N-513-3 did not include flaw evaluation for piping components such as elbows, bent pipe, reducers, expanders, and branch tees. Code Case N-513-4 was recently approved by the ASME to expand the flaw evaluation methodology for use on these locations and to revise several other areas of the Code Case. It should be noted that Code Case N-513-4 is not listed in the latest revision of Regulatory Guide 1.147 (Revision 17, August 2014). Thus, there is no approved current methodology for ANO to evaluate the through-wall flaw.
ANO-2 will invoke all the requirements commensurate with Code Case N-513-3 associated with the identified condition, with the exception that ANO-2 will use the methodology from Code Case N-513-4 for flaw evaluations of piping components such as elbows, bent pipe, reducers, expanders, and branch tees.
III. BASIS FOR ALTERNATIVE Flaw Evaluation (N-513-4)
A structural evaluation using the methodology presented in Code Case N-513-4 was performed for the affected piping components. The evaluation used conservative allowable stress values based upon carbon steel materials with the highest moments applied. The basis for the evaluation includes Structural Integrity Associates (SIA) calculation number 1401289.301 (ANO calculation CALC-14-E-0200-01, Attachment 2).
The evaluation provides an allowable flaw size which assures a safety factor, compared to the critical crack size, in accordance with ASME Section XI, Appendix C.
to 2CAN111401 Page 4 of 5 Flooding / Spray Concerns (N-513-3)
The results of these evaluations are presented below.
Flooding / Spray Concerns The leakage at present is insignificant and does not present a flooding concern. No equipment susceptible to water damage is under or adjacent to the leakage site. The magnitude of the water loss can easily be accommodated by the room drainage system and does not pose a flooding concern. The leak is located in a well-lighted area (ANO-2 Auxiliary Building) that is frequented by Operations personnel on rounds. Thus if the leak rate experienced a rapid increase it would be quickly identified and addressed. A floor drain is located approximately 3 feet from the leak and is sized to remove normal leakage from this area of the plant. However, based on the structural assessment and engineering experience with respect to flaw growth, no significant leak rate increase is expected to occur.
Reduction in Flow to SW Supplied Components (N-513-3)
Due to the small leak magnitude there is no appreciable impact on flow to other components in the ANO-2 SW System. The flow margin above that required for the minimum margin component is bounded, assuming all leakage in this condition were taken from that component, per the latest SW flow test.
ECP Inventory Concerns (N-513-3)
The current leak is essentially imperceptible relative to ECP inventory and thus has no impact on ECP inventory.
Periodic Inspections (N-513-3)
Frequent periodic inspections of intervals of no more than 30 days. In addition, daily walkdowns shall be used to confirm analysis conditions remain valid.
Extent of Condition (N-513-3)
Augmented volumetric examinations will be performed at five of the most susceptible and accessible locations based upon similar geometry and similar material properties.
Additional inspections will be in accordance with the requirements of N-513-3.
to 2CAN111401 Page 5 of 5 IV. DURATION OF PROPOSED ALTERNATIVE The proposed alternative is for use of Code Case N-513-4 in the evaluation of the flaw identified in ANO-2 SW piping components. A Section XI compliant repair / replacement must be completed prior to startup from the next refueling outage (fall of 2015) or prior to exceeding the structural limits identified by the evaluation as approved by this relief request, or prior to a leak rate greater than 5 gpm, whichever comes first.
V. PRECEDENT By letter dated March 5, 2014 (ML14073A059), as supplemented by letter dated March 25, 2014 (ML14091A407), Entergy Nuclear Operations, requested authorization of a proposed alternative to certain requirements of the ASME Code,Section XI, Article IWD-3000 for the Pilgrim Station. Specifically, it was proposed to use alternate analytical evaluation criteria for acceptance of through-wall flaws. The alternate analytical evaluation criteria were based on the draft Code Case N-513-4. The NRC granted verbal authorization of the proposed alternative on March 26, 2014. The safety evaluation associated with the authorization was provided via letter dated September 30, 2014 (ML14240A603).
ATTACHMENT 2 TO 2CAN111401 STRUCTURAL INTEGRITY ASSOCIATES CALCULATION 1401289.301
File No.: 1401289.301 Project No.: 1401289 CALCULATION PACKAGE Quality Program: Nuclear Commercial PROJECT NAME:
ANO Leaking Flaw Evaluation CONTRACT NO.:
10423246, Change Request No. 00109841 CLIENT: PLANT:
Entergy Arkansas, Inc. Arkansas Nuclear One, Unit 2 CALCULATION TITLE:
Evaluation of a Through-Wall Leak in a Service Water Tee (Dwg 2HCC-2003-1)
Project Manager Preparer(s) &
Document Affected Revision Description Approval Checker(s)
Revision Pages Signature & Date Signatures & Date 0 1 - 12 Initial Issue Preparer:
Eric J. Houston Adam C. Roukema 10/31/2014 10/31/2014 Checker:
Brad P. Dawson 10/31/2014 Page 1 of 12 F0306-01R1
Table of Contents
1.0 INTRODUCTION
.........................................................................................................3 2.0 TECHNICAL APPROACH ..........................................................................................3 3.0 DESIGN INPUTS AND ASSUMPTIONS ...................................................................3 4.0 CALCULATIONS .........................................................................................................4 4.1 Minimum Required Wall Thickness ..................................................................5 4.2 Applied Loads ....................................................................................................5 4.2.1 Hoop Stress ........................................................................................................5 4.2.2 Axial Stresses .....................................................................................................5 4.3 Stress Intensity Factor Calculations...................................................................6 4.4 Critical Fracture Toughness Determination.......................................................7 5.0 RESULTS ......................................................................................................................8
6.0 CONCLUSION
S ...........................................................................................................8
7.0 REFERENCES
..............................................................................................................9 List of Tables Table 1: Applied Moment Loading for Bounding Moments ..................................................10 Table 2: JIC Values for A106 Gr. B Carbon Steel from NRCs Pipe Fracture Database [9] ..11 Table 3: Axial and Circumferential Structural Factors [2] .....................................................12 Table 4: Load Combinations for Circumferential Flaw Analyses ..........................................12 Table 5: Pressure Blowout Check...........................................................................................12 File No.: 1401289.301 Page 2 of 12 Revision: 0 F0306-01R1
1.0 INTRODUCTION
Arkansas Nuclear One has identified a pinhole leak in a 6-inch branch connection (Sweep-o-let) in the service water system. The system is safety related, and therefore requires an evaluation to demonstrate operability. The objective of this calculation is to determine the allowable through-wall flaw lengths in accordance with ASME Code Case N-513-4 [1].
2.0 TECHNICAL APPROACH The flaw evaluation herein is based on the criteria prescribed in ASME Code Case N-513-4, allowing for the temporary acceptance of through-wall flaws in moderate energy Class 2 or Class 3 piping. N-513-4 allows non-planar, through-wall flaws to be characterized and evaluated as planar (i.e., crack-like), through-wall flaws in the axial and circumferential directions.
In addition to straight pipe, N-513-4 evaluation criteria includes rules for the evaluation of piping components such as elbows, branch tees and reducers. Flaws in these components may be evaluated as if in straight pipe provided the stresses used in the evaluation are adjusted to account for geometric differences.
Details are provided in N-513-4 for determining these adjusted stresses. The leaking flaw is in the carbon steel sweep-o-let, near the dissimilar metal weld at the adjoining stainless steel elbow. Therefore, the evaluation approach for branch connections in N-513-4 is appropriate. Although the attached elbow material has significantly higher toughness than the carbon steel (which if used would result in a much larger allowable through-wall flaw) the influence of the higher toughness on the allowable through-wall flaw is ignored and the system is evaluated as only carbon steel.
N-513-4 has been approved and published by ASME. It is recognized in ASME committee that the technical approach is very conservative. Simple treatment of piping component flaw evaluation using hand calculations was an important objective in the development of the approach recognizing the trade-off being conservative results. N-513-4 allows for alternative methods to calculate the stresses used in the analysis to reduce conservatism. N-513-4 has not been generically reviewed by the NRC.
Code Case N-513-4 evaluation criteria rely on the methods given in ASME Section XI, Appendix C [2].
Linear Elastic Fracture Mechanics (LEFM) criteria are conservatively employed as described in Article C-7000. Equations for through-wall stress intensity factor parameters Fm, Fb and F are given in the Code Case, Appendix I. Allowable flaw lengths are determined through iteration comparing calculated stress intensity factors to a critical fracture toughness defined in C-7200 of Section XI, Appendix C.
3.0 DESIGN INPUTS AND ASSUMPTIONS The piping design Code of Construction is ASME Section III - 1971 with Addenda through Summer 1971
[3] except for the items listed below:
A) Use ASME Section III - 1971 Winter 1972 Addenda, NC-3611.1(b)(4)(c) and NC-3650 with Code Case 1606-1, for the following:
- a. Moments b. Design Loading Combinations File No.: 1401289.301 Page 3 of 12 Revision: 0 F0306-01R1
- c. Section Modulus d. Stress Limits B) Use ASME Section III - 1974 [4], NC-3673.2 for the following:
- a. Flexibility Factors b. Stress Intensification Factors The sweep-o-let material is ASME A105 Gr II carbon steel and the run piping is A106 Gr. B [5] carbon steel. For the analysis, A106 Gr. B carbon properties are conservatively used. In addition, the fracture toughness of the two materials are assumed to be comparable.
The following design inputs are used in this calculation:
- 1. Outside diameter = 6.625 inches [5, Line Item 14]
- 2. Nominal wall thickness = 0.280 inch (based on standard pipe size) [5, Line Item 14]
- 3. Design temperature = 130°F [6, Page 114]
- 4. Design pressure = 150 psig [6, Page 114]
- 5. Material stress allowable = 15 ksi [7, PDF Page 19]
- 6. Youngs modulus = 27,900 ksi [7, PDF Page 19]
- 7. NDE inspection results [8]
The moment loadings applied to the piping are obtained from the piping stress report [7] for the element located between nodes 25 and 225. The bounding moments are shown in Table 1.
Determination of the fracture toughness, JIC, used in the evaluation is based on Section XI, Appendix C, C-8320 [2], which specifies that reasonable lower bound fracture toughness data may be used to determine the allowable stress intensity factor, KIc. The NRCs Pipe Fracture Encyclopedia [9] contains numerous CVN test results for A106 Gr. B carbon steel at low temperature, which are reproduced in Table 2. The minimum reported value of 293 in-lb/in2 is used in the analysis.
The following assumptions are used in this calculation:
- 1. Poissons ratio is assumed to be 0.3.
- 2. The impact of weld residual stress on the structural stability of the observed flaw is assumed negligible. Weld residual stresses are secondary (i.e., self-limiting) and do not contribute significantly to gross structural failure in ductile materials in the presence of a through-wall flaw. In addition, the contribution, if any, to flaw growth due to secondary weld residual stresses is not required as the Code Case specifies a frequent re-inspection interval.
- 3. A corrosion allowance is not considered (the ongoing inspection requirements in Code Case N-513-4 address the possibility of flaw growth during the temporary acceptance period).
4.0 CALCULATIONS The applied stresses and resulting stress intensity factors are conservatively calculated using an evaluated wall thickness, teval, 0.175 inches.
File No.: 1401289.301 Page 4 of 12 Revision: 0 F0306-01R1
4.1 Minimum Required Wall Thickness An evaluation of ASME Section III, NC-3650 equations 3, 8, 9B, 9D, and 10 has been conducted using inputs discussed in Section 3.0. Based on these equations the minimum required wall thickness is 0.115 inch.
4.2 Applied Loads Axial and circumferential (i.e., hoop) stresses are calculated from the moment loads in Table 1 and the design pressure. The evaluated wall thickness, teval, is used to determine the section properties. The nominal wall thickness, tnom, is used to calculate the flexibility characteristic h in accordance with the guidance of N-513-4.
4.2.1 Hoop Stress For the allowable axial flaw length on a branch tee, the hoop streh, may be determined from Equation 13 of N-513-4:
= (1)
where:
p = internal design pressure, psig Do = outside diameter, in t = evaluated wall thickness = teval, in 4.2.2 Axial Stresses For the allowable circumferential flaw length, the axial stress due to pressure, deadweight and seismic
m, Equation 14 of N-513-4 is used.
Note that there is a typo in the published version of this equation; the correct form is:
= (2)
B1 is the primary stress index for pressure loading. As allowed by the Code Case, the primary stress indices B1 and B2 are taken from a more recent edition of the ASME Code [10, Table NB-3681(a)-1]. For branch connections, B1 is 0.5.
b, due to deadweight and seismic moments, Equation 15 of N-513-4 may be used:
= (3)
File No.: 1401289.301 Page 5 of 12 Revision: 0 F0306-01R1
where:
Mb = resultant primary bending moment, in-lbs.
I = moment of inertia based on evaluated wall thickness, in4 The coefficient B2 for branch connections is 0.5*C2 (but not < 1.0) and [10, NB-3683.8]:
/ /
= 1.5
(4)
where:
Rm = mean nominal radius of run pipe, in Tr = nominal wall thickness of run pipe, in rm = mean nominal radius of branch pipe, in Tb = nominal wall of branch pipe, in rp = outside nominal radius of branch pipe, in For e, due to thermal expansion, Equation 16 of N-513-4 may be used:
= (5)
where:
i = stress intensification factor Me = resultant thermal expansion moment, in-lbs.
The stress intensification factor is calculated based on a welding tee as [4, Figure NC-3673.2(b)-1]:
.! %.%&
= "/# and $= (6, 7)
where:
h = flexibility characteristic tn = nominal wall thickness of run piping, in r = mean radius of run piping, in 4.3 Stress Intensity Factor Calculations For LEFM analysis, the stress intensity factor, KI, for an axial flaw is taken from Article C-7000 [2] as prescribed by N-513-4 and is given below:
KI K Im K Ir where:
KIm = (SFmh 0.5 SFm = structural factor for membrane stress (see Table 3)
F = through-wall stress intensity factor parameter for an axial flaw under hoop stress (given in Appendix I of N-513-4)
File No.: 1401289.301 Page 6 of 12 Revision: 0 F0306-01R1
h = hoop stress, ksi a = flaw depth (taken as half flaw length for through-wall flaw per Appendix I of N-513-4), in Q = flaw shape parameter (unity per Appendix I of N-513-4)
KIr = KI from residual stresses at flaw location (assumed negligible)
Only the hoop stress influences the allowable axial flaw length, which is a function of pressure.
For LEFM analysis, the stress intensity factor, KI, for a circumferential flaw is taken from Article C-7000
[2] as prescribed by N-513-4 and is given below:
KI K Im K Ib K Ir where:
KIm = (SFm)Fmm0.5 Fm = through-wall stress intensity factor parameter for a circumferential flaw under membrane stress (given in Appendix I of N-513-4)
m = membrane stress, ksi KIb = [(SFbb e]Fb0.5 SFb = structural factor for bending stress (see Table 3)
b = bending stress, ksi
e = thermal stress, ksi Fb = through-wall stress intensity factor parameter for a circumferential flaw under bending stress (given in Appendix I of N-513-4)
KIr = KI from residual stresses at flaw location (assumed negligible)
Note that the through-wall flaw stress intensity factor parameters are a function of flaw length.
Table 4 shows the specific load combinations considered herein for the allowable circumferential flaw calculations.
4.4 Critical Fracture Toughness Determination For LEFM analysis, the static fracture toughness for crack initiation under plane strain conditions, KIc, is taken from Article C-7000 [2] as prescribed by N-513-4 and is given below:
J Ic E '
K Ic 1000 where:
JIc = material toughness, in-lb/in2 E' = E/(1- 2)
E = Youngs modulus, ksi
! "
File No.: 1401289.301 Page 7 of 12 Revision: 0 F0306-01R1
Based on the design input listed above, KIc = 94.7 ksi-in0.5. The allowable flaw lengths are determined iteratively by increasing flaw length until the stress intensity factor is equal to the static fracture toughness.
5.0 RESULTS Based on inputs in Section 3.0, moments in Table 1 and using equations from Section 4.0, the allowable through-wall flaw in the circumferential direction is 2.7 inches and the allowable through-wall flaw in the axial direction is 5.8 inches. The allowable through-wall flaw lengths are based on an evaluated wall thickness of 0.175 inch. Based on the inspection data given in Reference [8], the analyzed thickness and flaw lengths easily bound the observed thinning. Thus, the acceptance criteria of Code Case N-513-4 are met.
Code Case N-513-4, Paragraph 3.2(c) requires that the remaining ligament average thickness over the degraded area be sufficient to resist pressure blowout [1, Equation 8]. Table 5 shows the required average thickness, tc,avg, as a function of the equivalent diameter of the circular region, dadj, for which the wall thickness is less than tadj. Based on the inspection data given in Reference [8], the values in Table 5 easily bound the observed thinning. Thus, the Code Case requirement is met.
6.0 CONCLUSION
S Arkansas Nuclear One has identified a pinhole leak in a 6-inch branch connection (Sweep-o-let) in the service water system. Allowable through-wall flaw lengths have been calculated in accordance with ASME Code Case N-513-4. Because N-513-4 has not been generically reviewed by the NRC, justification for continued operation without repair or replacement until the next scheduled outage requires NRC review and approval.
The allowable through-wall flaw in the circumferential and axial directions is 2.7 inches and 5.8 inches, respectively. The allowable through-wall flaw lengths are based on an evaluated wall thickness of 0.175 inch. Table 5 shows the requirements to meet the Code Case pressure blowout limits.
The observed pinhole leak is easily bounded by the results of the analysis; thus, the acceptance criteria of Code Case N-513-4 are met. The system should be considered operable but degraded.
File No.: 1401289.301 Page 8 of 12 Revision: 0 F0306-01R1
7.0 REFERENCES
- 1. ASME Code Case N-513-4, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1, Cases of ASME Boiler and Pressure Vessel Code, May 7, 2014.
- 2. ASME Boiler and Pressure Vessel Code,Section XI, Appendix C, 2001 Edition with 2003 Addenda.
- 3. ASME Boiler and Pressure Vessel Code,Section III, 1971 Edition with Addenda through Summer 1971.
- 4. ASME Boiler and Pressure Vessel Code,Section III, 1974 Edition.
- 5. Entergy Drawing No. 2HBC-33-2, Sheet 1, Revision 16, Large Pipe Isometric Service Water Supply Header #1, SI File No. 1401289.201.
- 6. Entergy Calculation No. 88-E-0200-15, Revision 3, P-T Calculation for Unit 2 Service Water System, SI File No. 1401289.201.
- 7. Entergy Calculation No. 90-D-2003-08, Revision 3, Supply Piping Analysis for Piping in DCP 90-2003, SI File No 1401289.201.
- 9. Pipe Fracture Encyclopedia, US Nuclear Regulatory Commission, Volume 1, 1997.
- 10. ASME Boiler and Pressure Vessel Code,Section III, 2004 Edition.
File No.: 1401289.301 Page 9 of 12 Revision: 0 F0306-01R1
Table 1: Applied Moment Loading for Bounding Moments Deadweight OBE DBE Thermal (in-lbs) (in-lbs) (in-lbs) (in-lbs) 6902 21471 30657 5408 Notes:
- 1. Square Root Sum of the Squares (SRSS) is used to calculate moments from Reference [7].
- 2. Moments are from the bounding location, which is at node 225.
File No.: 1401289.301 Page 10 of 12 Revision: 0 F0306-01R1
Table 2: JIC Values for A106 Gr. B Carbon Steel from NRCs Pipe Fracture Database [9]
A106 Grade B Database Reference Temperature (°C) Temperature (°F) JIC (kJ/m2) 0.5 JIC (lbf-in/in2) KIC (ksi-in )
2 24 75 97 552 133 2 24 75 336 1919 249 16 25 77 81 464 122 16 25 77 418 2386 277 16 25 77 270 1542 223 16 25 77 193 1104 189 22 24 75 224 1278 203 22 20 68 112 641 144 22 20 68 117 668 147 22 23 73 214 1223 199 22 20 68 167 954 175 22 20 68 223 1271 202 22 20 68 108 617 141 23 52 126 116 663 146 23 23 73 103 590 138 23 23 73 105 600 139 23 23 73 93 528 131 24 23 73 76 431 118 24 23 73 82 469 123 24 57 135 51 293 97 25 23 73 77 439 119 25 23 73 70 400 114 25 57 135 62 356 107 90 20 68 235 1342 208 90 20 68 219 1251 201 90 20 68 255 1456 217 90 20 68 281 1605 228 90 20 68 281 1605 228 90 20 68 335 1913 248 90 20 68 421 2404 279 90 20 68 385 2198 266 90 20 68 175 999 180 90 20 68 172 982 178 90 20 68 178 1016 181 90 20 68 214 1222 199 90 20 68 275 1570 225 90 20 68 133 759 157 90 20 68 140 799 161 90 20 68 174 994 179 90 20 68 111 634 143 90 20 68 190 1085 187 90 20 68 71 405 114 90 20 68 110 628 142 90 20 68 104 594 138 90 20 68 104 594 138 90 20 68 97 554 134 90 20 68 89 508 128 90 20 68 88 502 127 90 20 68 267 1525 222 File No.: 1401289.301 Page 11 of 12 Revision: 0 F0306-01R1
Table 3: Axial and Circumferential Structural Factors [2]
Service Level Membrane Stress, SFm Bending Stress, SFb A 2.7 2.3 B 2.4 2.0 C 1.8 1.6 D 1.3 1.4 Table 4: Load Combinations for Circumferential Flaw Analyses Load Combination Service Level P+DW+TH A P+DW+TH+OBE B P+DW+TH+DBE D Table 5: Pressure Blowout Check dadj tc,avg 0.25 0.01 0.75 0.03 1.25 0.04 1.75 0.06 2.25 0.08 2.75 0.10 3.25 0.11 3.75 0.13 4.25 0.15 4.75 0.17 5.25 0.19 File No.: 1401289.301 Page 12 of 12 Revision: 0 F0306-01R1
ATTACHMENT 3 TO 2CAN101403 UT THICKNESS EXAMINATION REPORT 2-BOP-UT-14-040
Attachment 4 to 2CAN111401 List of Regulatory Commitments to 2CAN111401 Page 1 of 1 LIST OF REGULATORY COMMITMENTS The following table identifies those actions committed to by Entergy in this document. Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.
TYPE (Check one) SCHEDULED COMMITMENT COMPLETION ONE-TIME CONTINUING DATE ACTION COMPLIANCE Prior to startup from the next refueling outage (fall of 2015) or prior to exceeding the structural A Section XI compliant repair / replacement limits identified by 9
must be completed for the subject flaw. the evaluation as approved by this relief request, or prior to a leak rate greater than 5 gpm, whichever comes first.