ML14099A335
| ML14099A335 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 04/29/2014 |
| From: | Robert Carlson Plant Licensing Branch III |
| To: | Richard Anderson NextEra Energy Duane Arnold |
| Mahesh Chawla, NRR/DORL | |
| References | |
| TAC MF1481 | |
| Download: ML14099A335 (11) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. Richard L. Anderson Vice President Duane Arnold Energy Center 3277 DAEC Road Palo, lA 52324-9785 April 29, 2014
SUBJECT:
DUANE ARNOLD ENERGY CENTER-RELIEF FOR 2N° PERIOD LIMITED WELD EXAMINATIONS (TAG NO. MF1481)
Dear Mr. Anderson:
By letter dated April12, 2013 (Agencywide Document Access and Management System Accession No. ML13106A147), the licensee, NextEra Energy Duane Arnold, LLC, submitted Request for Relief (RR) NDE-R016 from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code {ASME Code),Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components, for the Duane Arnold Energy Center (DAEC) for several welds where the licensee was not able to achieve essentially 100 percent inspection coverage due to materials and geometric limitations.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) 50.55a(g){5)(iii),
the licensee requested relief and to use alternative requirements (if necessary), for in-service inspection (lSI) on the basis that the ASME Code requirements are impractical. The licensee requested relief from certain requirements of the ASME Code Sections IWB-2500 and IWC-2500 for essentially 100 percent inspection coverage for the welds identified in RR NDE-016 for DAEC.
The ASME Code of Record for the DAEC is the 2001 Edition, including the 2003 Addenda, of Section XI of the ASME Code. This request applies to the fourth 1 0-year interval for the lSI for DAEC. The NRC staff has completed its review of the relief request and concludes that due to the configuration issues at DAEC, the ASME Code requirements with respect to the subject welds are impractical.
The NRC staff has determined that the weld coverage achieved provides reasonable assurance of the structural integrity of the subject welds. Accordingly, the staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5),
and is in compliance with the requirements of 1 0 CFR 50.55a with the granting of these reliefs.
Therefore, the NRC staff grants relief for the subject examinations of the components contained in the RR NDE-R016 for the fourth lSI interval at DAEC, which ends on October 31, 2016. The licensee's requests for relief is granted pursuant to 10 CFR 50.55a(g){6)(i) for the DAEC fourth 1 0-year lSI interval. The staff has determined that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life, or property, or the common defense and security and is otherwise in the public interest giving due
consideration to the burden upon the licensee that could result if the requirements were imposed.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject request for relief remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.
If you have any questions, please contact the Project Manager, Mahesh Chawla at 301-415-8371 or via e-mail at Mahesh.Chawla@nrc.gov.
Docket No. 50-331
Enclosure:
Safety Evaluation cc w/encls: Distribution via ListServ Sincerely, Robert D. Carlson, Chief Plant Licensing Branch 111-1 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 DUANE ARNOLD ENERGY CENTER RELIEF REQUEST NO. NDE-R016 REGARDING SECOND PERIOD LIMITED WELD EXAMINATIONS DOCKET NUMBER: 50-331 (TAC NO. MF1481)
1.0 INTRODUCTION
By letter dated April 12, 2013 (Agencywide Document Access and Management System Accession No. ML13106A147), the licensee, NextEra Energy Duane Arnold, LLC, submitted Request for Relief (RR) NDE-R016 from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components, for the Duane Arnold Energy Center (DAEC) for several welds where the licensee was not able to achieve essentially 100 percent inspection coverage due to materials and geometric limitations.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) 50.55a(g)(5)(iii),
the licensee requested relief and to use alternative requirements (if necessary), for in-service inspection (lSI) on the basis that the ASME Code requirements are impractical. The licensee requested relief from certain requirements of the ASME Code Sections IWB-2500 and IWC-2500 for essentially 100 percent inspection coverage for the welds identified in RR NDE-016 for DAEC. This request applies to the fourth 1 0-year interval for the lSI for DAEC.
2.0 REGULATORY REQUIREMENTS Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 1 0-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code, which was incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The regulation in 10 CFR 50.55a(g)(5)(iii), states, in part, that licensees may determine that conformance with certain ASME Code requirements is impractical and that the licensee shall notify the Commission and submit information in support of the determination. Determinations Enclosure of impracticality in accordance with this section must be based on the demonstrated limitations experience when attempting to comply with the code requirements during the lSI interval for which the request is being submitted. Requests for relief made in accordance with this section must be submitted to the U.S. Nuclear Regulatory Commission (NRC) no later than 12 months after the expiration of the initial 120-month inspection interval or subsequent 120-month inspection interval for which relief is sought.
The regulation in 10 CFR 50.55a(g)(6)(i), states that the Commission will evaluate determinations under paragraph (g)(5) of this section that Code requirements are impractical.
The Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
The licensee has requested relief from ASME Code requirements pursuant to 10 CFR 50.55a(g)(5)(iii). The ASME Code of Record for the DAEC is the 2001 Edition, including the 2003 Addenda, of Section XI of the ASME Code.
3.0 TECHNICAL EVALUATION
3.1 Request for Relief NDE-R016, Examination Category 8-A, Item 81.40, Reactor Vessel Head to Flange Weld ASME Code Requirement ASME Code,Section XI, Item 81.40 requires essentially 100 percent volumetric and surface examination of the length of head-to-flange welds, as defined by ASME Code,Section XI, Figure IWB-2500-5. "Essentially 100 percent", as clarified by ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 Welds," is greater than 90 percent coverage of the examination volume, or surface area, as applicable. ASME Code Case N-460 has been approved for use by the NRC in Regulatory Guide 1.147, "lnservice Inspection Code Case Acceptability" (RG 1.147), Revision 16.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent volumetric examination of ASME Code, Class 1 RPV welds for the reactor vessel head to flange weld HCC-C001.
Licensee's Basis for Relief Request The volume of ASME Code-required coverage obtained for weld HCC-C001 is limited to approximately 76 percent due to the configuration of the weld, as shown in Figure 1 of to the submittal. The licensee states that there is "no feasible option in order to examine the remaining 24 percent of the weld."
Licensee's Proposed Alternative Examination The licensee did not propose alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical with no reportable indications.
Staff Evaluation The ASME Code requires essentially 100 percent volumetric examination of the accessible length of the subject RPV welds. However, complete examinations are restricted by the configuration of the head to flange weld. In order to increase the volumetric coverage on the subject welds, the RPV would require design modifications. Imposing this requirement would place a burden on the licensee therefore; the ASME Code-required 100 percent volumetric examinations are impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, ultrasonic {UT) examinations of the subject weld have been performed to the extent practical.
The licensee obtained volumetric coverage of approximately 76 percent. The staff notes that the nondestructive examination (NDE) procedure used for this exam incorporates the techniques qualified under Appendix VIII of the ASME Code,Section XI, by the Performance Demonstration Initiative. This alternative was approved under DAEC Relief Request NDE-R008. In addition, the licensee stated that "for the Class 1 examination Category B-P, a VT-2 examination is performed on the subject components of the Reactor Coolant Pressure Boundary during system pressure tests each refueling outage." No evidence of leakage has been identified through the visual examinations. Enclosure 2 of the submittal included a record of magnetic particle testing of the flange to head weld from stud hole 40 to 60 and 60 to 20, with no recorded indications. These exams provide additional assurance that the structural integrity of the subject component is maintained.
The licensee has shown that it is impractical to meet the ASME Code-required 100 percent volumetric examination coverage for the subject weld due to its design. Based on the volumetric and surface coverage obtained, it is reasonable to conclude that if significant service-induced degradation had occurred in the subject welds, evidence of it would have been detected by the examinations that were performed. Visual examinations and magnetic particle testing provide additional assurance. Therefore, the NRC staff concludes that the examinations performed provide reasonable assurance of structural integrity of the subject weld.
3.2 Request for Relief NDE-R016, Examination Category B-D. Item B3.90. Reactor Vessel Nozzles ASME Code Requirement ASME Code,Section XI, Examination Category B-D, Item B3.90 requires 100 percent volumetric examination, as defined by ASME Code,Section XI, Figures IWB-2500-7 (a) through (d), as applicable, of full penetration ASME Code, Class 1 RPV nozzle-to-vessel welds. ASME Code Case N-460, as an alternative approved for use by the NRC in RG 1.147, Revision 16, states that a reduction in examination coverage due to part geometry or interference for any Class 1 and 2 weld is acceptable provided that the reduction is less than 10 percent, i.e.,
greater than 90 percent examination coverage is obtained.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required volumetric examinations for the welds listed below in Table 3.2.1.
83.90 VIA-0001 Reactor Vessel Nozzle 80.2%
83.90 RCA-0001 Reactor Vessel Nozzle 78.3%
83.90 FWB-0001 Reactor Vessel Nozzle 80.2%
83.90 FWC-0001 Reactor Vessel Nozzle 80.2%
Licensee's Basis for Relief Request The nozzle-to-vessel welds listed in Table 3.2.1 above are accessible from the reactor vessel side, but the examination cannot be performed from the nozzle side because of the forging curvature.
Licensee's Proposed Alternative Examination The licensee did not propose alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical.
Staff Evaluation The ASME Code requires 100 percent volumetric examination of full penetration welded nozzle and inside radius sections in Class 1 vessels. Typical configurations of the subject nozzle-to-vessel welds are shown in Figure 2 to Enclosure 1 of the submittal, illustrating the forging curvature. The design configuration of the subject welds limits access for ultrasonic scanning.
In order to effectively increase the examination coverage, the nozzle-to-vessel welds would require design modifications. This would place a burden on the licensee; thus, 100 percent ASME Code-required volumetric examinations are considered impractical.
As shown on the sketches and technical descriptions included in the licensee's submittals, examinations of the subject RPV nozzle-to-vessel welds have been completed to the extent practical with volumetric coverage ranging from approximately 78.3 percent to 80.2 percent (see Table 3.2.1 above) of the ASME Code-required volumes. The RPV nozzle-to-vessel weld UT examinations were conducted with equipment, procedures and personnel in accordance with the applicable requirements of the ASME Code. Although UT scans were limited to the vessel side, studies have found that inspections conducted through carbon steel are equally effective whether the ultrasonic waves only have to propagate through the base metal, or have to also propagate through the carbon steel weldment. Therefore, it is expected that the UT techniques employed by the licensee would detect structurally significant flaws that might occur on either side of the subject welds due to the fine-grained carbon steel microstructures.
The licensee has shown that it is impractical to meet the ASME Code-required 100 percent volumetric examination coverage for the subject nozzle-to-vessel welds due to their design.
Based on the volumetric coverage obtained for the subject welds, and considering the licensee's performance of ultrasonic techniques employed to maximize this coverage, it is reasonable to conclude that if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that were performed. Therefore, the staff has determined based on above that the examinations performed provide reasonable assurance of structural integrity of the subject welds.
3.3 Request for Relief NDE-R016. Examination Category C-A. Item C1.20. Residual Heat Removal Heat Exchanger Head to Shell Weld ASME Code Requirement Examination Category C-A, Item C1.20, requires essentially 100 percent volumetric examination, as defined by Figure IWC-2500-1, of the length of Class 2 circumferential shell and head welds. "Essentially 100 percent", as clarified by ASME Code Case N-460, is greater than 90 percent coverage of the examination volume, or surface area, as applicable. ASME Code Case N-460 has been approved for use by the NRC in RG 1.147, Revision 16.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required volumetric examination of Class 2 circumferential shell and head welds shown in Table 3.3.1.
HEA-CA-5 Residual Heat Removal (RHR) Heat Exchanger A Head to Shell Weld Licensee's Basis for Relief Request 78%
Obtaining Code required coverage for Residual Heat Removal Heat Exchanger Head to Shell Weld HEA-CA-5 is impractical due to portions of the weld being obstructed by the heat exchanger tie-down brackets. This is illustrated in Figure 3 to Enclosure 1 of the submittal.
Licensee's Proposed Alternative Examination The licensee did not propose alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical.
Staff Evaluation Examination Category C-A, Item C1.20, requires essentially 100 percent volumetric examination, as defined by Figure IWC-2500-1, of the length of Class 2 circumferential shell and head welds. However, for the subject weld on the DAEC RHR heat exchanger, complete examinations are limited due to the design configuration. In order to achieve greater volumetric coverage, the RHR heat exchanger or adjacent components would have to be redesigned and modified. This would place a burden on the licensee, therefore the ASME Code examinations are considered impractical.
As shown on the sketches and technical descriptions included in Enclosure 2 of the licensee's submittal, examinations of the RHR Heat Exchanger Head to Shell Weld HEA-CA-5 have been performed to the extent practical, with the licensee obtaining approximately 78 percent of the required ASME Code examination volume. The examinations were limited due to the location of the heat exchanger tie-down brackets. The licensee examined the weld using 45-degree and 60-degree shear waves. No recordable flaw indications were observed. In addition, the licensee stated that "for the Class 2 examination Category C-H, a VT-2 examination is performed on the subject components of the RHR system during system pressure tests once per period." The exam was last performed in January 2011 and no evidence of leakage was identified for these components.
The licensee has shown that it is impractical to meet the ASME Code-required volumetric examination coverage for the subject weld due to the design geometry of the weld and proximity of heat exchanger tie-down brackets. Based on the volumetric coverage obtained, and the ultrasonic techniques employed, it is reasonable to conclude that, if significant service-induced degradation had occurred in the subject welds, evidence of it would have been detected by the examinations performed. Therefore, the NRC staff determined that the examinations performed provide reasonable assurance of structural integrity of the subject weld.
3.4 Request for Relief NDE-R016, Examination Category C-B. Item C2.21. Residual Heat Removal Heat Exchanger Nozzle Weld ASME Code Requirement Examination Category C-B, Item C2.21, requires 100 percent surface and volumetric examination, as defined by Figure IWC-2500-4(a) or (b), as applicable, of nozzle-to-shell (or head) welds in Class 2 vessels. ASME Code Case N-460, as an alternative approved for use by the NRC in RG 1.147, Revision 16, states that a reduction in examination coverage due to part geometry or interference for any Class 1 and 2 weld is acceptable provided that the reduction is less than 10 percent, i.e., greater than 90 percent examination coverage is obtained.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent volumetric and surface (for Weld 16-BFN-2111-1) examinations of the Class 2 nozzle-to-shell (or head) welds shown in Table 3.4.1.
Licensee's Basis for Relief Request The heat exchanger to nozzle weld can only be examined from the nozzle side because the nozzle and weld are perpendicular to the heat exchanger shell. To increase examination coverage, the existing configuration would require replacement with an altered configuration.
Licensee's Proposed Alternative Examination The licensee did not propose alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical.
Staff Evaluation The ASME Code requires 100 percent volumetric and surface examinations of Class 2 nozzle-to-shell (or head) welds. However, for the subject RHR heat exchanger nozzle weld, complete examinations are limited due to the component configuration. In order to achieve greater volumetric or surface coverage, as applicable, the component configuration would have to be redesigned and modified, which would place a burden on the licensee.
As shown on the sketches and technical descriptions included in Enclosure 2 of the licensee's submittal, examination of RHR heat exchanger nozzle weld HEA-CB-6 were performed to the extent practical, with the licensee obtaining 50 percent of the required examination volume. The examination was limited to a single side exam due to the component configuration as shown in Figure 4 of Enclosure 1 of the submittal.
Examinations of the RHR heat exchanger weld HEA-CB-6 were performed to the extent practical, with the licensee obtaining approximately 50 percent of the required examination coverage. The RHR heat exchanger weld examination was limited due to the configuration of the heat exchanger nozzle. Specifically, the nozzle weld is perpendicular to the heat exchanger shell.
The licensee has shown that it is impractical to meet the ASME Code-required 100 percent volumetric and surface examinations for the RHR exchanger nozzle weld HEA-CB-6 due to the nozzle's design and configuration. In addition, the licensee stated that "for the Class 2 examination Category C-H, a VT-2 examination is performed on the subject components of the RHR system during system pressure tests once per period." Therefore, based on the coverage obtained, it is reasonable to conclude that, if significant service-induced degradation had occurred, evidence of it would be have been detected by the examinations performed. The NRC staff concludes that the examinations performed provide reasonable assurance of structural integrity of the subject weld.
4.0 CONCLUSION
Due to the configuration issues at DAEC, the ASME Code requirements with respect to the subject welds are impractical. The NRC staff has determined that the weld coverage achieved provides reasonable assurance of the structural integrity of the subject welds. Accordingly, the staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(5), and is in compliance with the requirements of 10 CFR 50.55a with the granting of these reliefs. Therefore, the NRC staff grants relief for the subject examinations of the components contained in the Request for Relief NDE-R016 for the fourth lSI interval at DAEC. The licensee's requests for relief is granted pursuant to 10 CFR 50.55a(g)(6)(i) for the DAEC fourth 1 0-year lSI interval. The staff has determined that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life, or property, or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject request for relief remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.
Principal Contributor: C. Fairbanks
- via memo OFFICE NRR/LPL3-1/PM NRR/LPL3-1/LA NRR/EVIB/BC*
NRR/LPL3-1/BC NAME MChawla MHenderson SRosenburg RCarlson DATE 04/22/14 04/21/14 04/08/14 04/29/14