RA-23-0310, Proposed Alternative for Continued Service of High-Density Polyethylene (Hdpe) Material in Class 3 Buried Piping
| ML25150A316 | |
| Person / Time | |
|---|---|
| Site: | Catawba  (NPF-035, NPF-052) |
| Issue date: | 05/29/2025 |
| From: | Ellis K Duke Energy Carolinas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-23-0310 | |
| Download: ML25150A316 (1) | |
Text
Kevin M. Ellis General Manager Nuclear Regulatory Affairs, Policy &
Emergency Preparedness Duke Energy 13225 Hagers Ferry Rd., MG011E Huntersville, NC 28078 843-951-1329 Kevin.Ellis@duke-energy.com Serial: RA-23-0310 10 CFR 50.55a May 29, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Catawba Nuclear Station, Unit Nos. 1 and 2 Renewed Facility Operating License Nos. NPF-35 and NPF-52 Docket Nos. 50-413 and 50-414
SUBJECT:
Proposed Alternative for Continued Service of High-Density Polyethylene (HDPE) Material in Class 3 Buried Piping
REFERENCES:
- 1. NRC letter, Catawba Nuclear Station, Units 1 and 2, Relief 06-CN-003 for use of Polyethylene Material in Buried Service Water Piping (TAC Nos. MF0234 and MF0235),
dated May 27, 2009 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML091240156)
- 2. NRC letter, Catawba Nuclear Station Units 1 and 2: Proposed Relief Request 14-CN-002, Alternative to American Society of Mechanical Engineers (ASME)Section XI Requirements for Class 3 Buried Piping (TAC Nos. MF4864 and MF4865), dated June 19, 2015 (ADAMS Accession No. ML15161A376)
Ladies and Gentlemen:
Pursuant to 10 CFR 50.55a(z)(1), Duke Energy Carolinas, LLC (Duke Energy) is proposing an In-service Inspection (ISI) alternative for the Catawba Nuclear Station (CNS), Unit Nos. 1 and 2.
Specifically, this request is for the continued use of an alternative of HDPE material in lieu of steel material in Nuclear Service Water System piping associated with the emergency diesel generator jacket water coolers. The use of HDPE was previously approved for CNS in the Third and Fourth ISI intervals via the Reference 1 and 2 safety evaluations, respectively. This request is for the Fifth ISI interval and through the remainder of the current renewed operating licenses for each unit.
The proposed alternative is described in Enclosure 1.
Duke Energy requests approval of this proposed alternative prior to the end of the Fourth ISI interval, scheduled to end on June 28, 2026. If you have additional questions, please contact Ryan Treadway, Director - Nuclear Fleet Licensing, at 980-373-5873.
U.S. Nuclear Regulatory Commission RA-23-0310 Page 2 Sincerely, Kevin M. Ellis General Manager Nuclear Regulatory Affairs, Policy & Emergency Preparedness
Enclosures:
- 1. Proposed Alternative for Continued Service of High-Density Polyethylene (HDPE)
Material in Class 3 Buried Piping cc:
USNRC Region II Regional Administrator USNRC Senior Resident Inspector for CNS USNRC NRR Project Manager for CNS
RA-23-0310 Proposed Alternative for Continued Service of High-Density Polyethylene (HDPE)
Material in Class 3 Buried Piping 8 Pages Follow
RA-23-0310 Page 1 of 8 1.0 ASME CODE COMPONENT(S) AFFECTED:
ASME Class 3 buried piping in the Catawba Nuclear Station (CNS), Units 1 and 2 Nuclear Service Water System (RN System) serving the diesel generator jacket water coolers.
Four (4) 12-inch emergency diesel jacket water supply lines (1A, 1B, 2A, 2B) and four (4) 12-inch emergency diesel jacket water return lines (1A, 1B, 2A, 2B) 2.0 APPLICABLE CODE EDITION AND ADDENDA:
The applicable ASME Section XI code of record for the Fifth ISI interval at CNS Units 1 and 2 was determined in accordance with the requirement of 10 CFR 50.55a(g)(4)(ii),
which states, in part, that successive 120-month inspection intervals must comply with the requirements of the latest edition and addenda of the Code incorporated by reference in paragraph (a) of this section 18 months before the start of the 120-month inspection interval. The Fifth ISI Interval for CNS Units 1 and 2 is scheduled to start on March 29, 2026. Therefore, the Fifth ISI Interval code of record for CNS Units 1 and 2 in accordance with the requirements of the latest edition and addenda of the Code incorporated by reference in 10 CFR 50.55a (Reference 8.1) on September 29, 2024 is the ASME Section XI, 2019 Edition (Reference 8.2).
3.0 APPLICABLE CODE REQUIREMENT:
IWA-4221(b) requires that "An item to be used for repair/replacement activities shall meet the Construction Code specified in accordance with (1), (2), or (3) below" and IWA-4221(b)(1) requires that "When replacing an existing item, the new item shall meet the Construction Code to which the original item was constructed."
4.0 REASON FOR REQUEST:
The Construction Code of record for buried ASME Class 3 piping is the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPV),
Section III, Subsection ND, 1974 Edition including Summer 1974 Addendum. This Construction Code and later editions and addenda of this Construction Code (at the time of installation of the subject ASME Class 3 buried piping), did not provide rules for use of high density polyethylene (HDPE) material and ASME Code Case N-755 and Code Case N-755-1 were issued by the ASME BPV Committee for use of HDPE but were not approved for use by Nuclear Regulatory Commission (NRC) Regulatory Guide 1.84, "Design, Fabrication, and Materials Code Case Acceptability, ASME Section III."
This relief request is being submitted for approval for continued use of HDPE material installed pursuant to Catawba Relief Requests 06-CN-003 (Precedent 7.1) and 14-CN-002 (Precedent 7.2). Catawba Relief Request 06-CN-003 provided conditions under which polyethylene material may be used for ASME Section III, Division 1, Class 3, buried piping systems. Relief Request 06-CN-003 was originally submitted by Duke Energy on October 26, 2006, supplemented in response to NRC Requests for Additional Information (RAIs), and approved by the NRC on May 27, 2009. The NRC Safety Evaluation for Relief Request 06-CN-003 only approved the use of HDPE material for the Third ISI Interval. Relief Request 14-CN-002 was originally submitted by Duke Energy on September 15, 2014, supplemented by a revision to the relief request and in
RA-23-0310 Page 2 of 8 response to NRC RAIs, and approved by the NRC on June 19, 2015. The NRC Safety Evaluation for Relief Request 14-CN-002 only approved the use of HDPE material for the Fourth ISI Interval. This new relief request applies only to the HDPE material that was installed during the Third ISI Interval in accordance with Relief Request 06-CN-003.
No additional installation of HDPE material in Class 3 applications is being requested by this relief request.
5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:
Catawba proposes to continue use of the HDPE material installed in the Nuclear Service Water System for the remainder of the current renewed operating licenses. Pursuant to 10 CFR 50.55a(z)(1), in lieu of the requirement of ASME Section XI IWA-4221(b)(1), this alternative to the original Construction Code provides an acceptable level of quality and safety for repair/replacement activities for ASME Class 3 buried piping. HDPE material installed pursuant to Relief Request 06-CN-003 has been in service since 2010 for Unit 2 and since 2011 for Unit 1. There have been no known leaks in this piping from corrosion or degradation during this period.
5.1 Basis for Use of Proposed Alternative The primary advantage in using HDPE material versus carbon steel pipe material is its resistance to fouling, corrosion, and microbiologically induced corrosion (MIC). The resistance of HDPE material to corrosion and fouling (i.e., tubercle formation and MIC) improves long term reliability from a structural integrity and flow standpoint.
More than 20,000 linear feet of HDPE material in service in the Catawba non-safety related Low Pressure Service Water System (RL System) since 1998 continues to demonstrate the acceptability of this material for this service. Catawba monitors the non-ASME Class 3 HDPE piping installed in the RL System as a means of validating integrity of the buried ASME Class 3 HDPE piping. RL HDPE accessible system piping is observed during Operator rounds. Any leakage found during either activity would be evaluated using the Corrective Action Program. These factors combine to provide a high level of confidence that monitoring HDPE installed in the RL System is a leading indicator for potential aging or degradation of HDPE installed in the RN System.
The following information supports the acceptability of HDPE use at CNS for the remainder of current renewed operating licenses A.
Materials Based on Catawba experience, HDPE material does not experience fouling or corrosion and is not susceptible to galvanic attack, since polyethylene is an electrical insulating material. By comparison, installed carbon steel metallic service water piping at Catawba has experienced severe fouling and significant internal and external corrosion.
Polyethylene is also not susceptible to localized degradation from microbiological attack, which has occurred frequently with some corrosion resistant steel alloys.
The specific HDPE material (PE-4710) used at CNS was tested prior to installation and resulted in a Pennsylvania Edge Notch Test (PENT) value of greater than 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> without failure. This test result shows CNSs HDPE material has adequate slow crack growth (SCG) resistance, providing reasonable assurance of long-term structural
RA-23-0310 Page 3 of 8 integrity of CNSs HDPE piping. The backfill material for the buried HDPE is an inert structural fill material that will not react with the outer diameter of the piping. This eliminates the concern of an exterior degradation mechanism from the external environment, which precludes generation of flaws that would serve as a crack initiation site.
B.
Design The same design criteria are used for HDPE material and the original carbon steel material. Both polyethylene and the original carbon steel materials are qualified for identical loading conditions (e.g., pressure, temperature, seismic).
The ASME Boiler and Pressure Vessel Code,Section XI, 1998 Edition with 1999 and 2000 Addenda was used for repair/replacement activities for installation of the HDPE material that was installed pursuant to Relief Request 06-CN-003 (Precedent 7.1).
C.
Fabrication and Installation Catawba fusing procedures are based on fusing process variables from PPI TR-33/2006, "Generic Butt Fusion Joining Procedure for Field Joining of Polyethylene Pipe".
Catawba verified PPI TR-33 pressure and temperature procedure parameters by tensile impact testing coupons using 12-inch NPS, standard dimension ratio (SDR) 11 fused joints made at all of the procedure limiting values.
During installation of the HDPE material, Catawba conducted in-process tensile impact testing of fused joints in accordance with ASTM F2634, "Standard Test Method for Laboratory Testing of Polyethylene (PE) Butt Fusion Joints using Tensile-Impact Method". Relief Request 06-CN-003 required tensile impact testing of a minimum of 10%
of field joints for each production shift and also tensile impact testing of a minimum of one-random joint for each four work shift periods. In actuality, 43% of the field joints were tensile impact tested during installation, exceeding the 10% minimum requirement by a large margin. 14% of the joints were randomly chosen for tensile impact testing. All joints tested passed the ASTM F2634 tensile impact test and provided high level of confidence in installed fused joints.
Extensive in-process tensile impact testing during HDPE material installation, use of qualified fusing procedures, fusing operator training, data logger recording of fusing parameters, engineering review of data logger results, hydrostatic testing of completed joints, camera inspection inside of completed joints, and quality assurance inspection of joints during and after fusing provide a very high level of confidence in the integrity of the piping joints.
D.
Flaw Depth Allowance A maximum scratch depth allowance of 0.041 inches was used for installation of HDPE material pursuant to Relief Request 06-CN-003. This corresponds to a scratch depth allowance of 3.5% of the pipe wall thickness. Pipe with unacceptable scratches was either cut out or the scratches were removed by blending smoothly for cases where the remaining wall thickness exceeded the design wall thickness.
RA-23-0310 Page 4 of 8 E.
Examination VT-1 visual examination was required and performed for all fused joints for acceptability both on the inside and outside diameter. VT-2 examinations were performed during hydrostatic testing for all fused joints and external surfaces of the piping.
F.
Testing All HDPE material and fused joints were hydrostatically pressure tested at 1.5 times the design pressure plus 10 psig after the installation of the piping.
The buried piping segments of the Class 3 Nuclear Service Water System at Catawba Units 1 and 2 are bounded by butterfly valves that are not designed or expected to provide an adequate leak-tight boundary that is necessary for an accurate pressure decay test. To perform an accurate rate of pressure loss test, extensive maintenance or system modifications would be required.
Pursuant to RAI No. 4 for Relief Request 14-CN-002 (Reference 8.3), as a result of documented operating experience with the HDPE flange joint leakage in the RL System, Catawba has performed VT-2 visual examinations of accessible RN System HDPE flanges during the Fourth ISI Interval. These inspections encompass eleven underground vaults containing sixteen HDPE flanged joints. Four examinations completed to date were performed with satisfactory results and the remaining 12 examinations are planned to be completed no later than the end of the Fourth ISI Interval scheduled to end on June 28, 2026 for CNS Units 1 and 2. The Fourth ISI Interval end date was extended as permitted by IWA-2430(c)(1), while the start of Fifth ISI Interval was pulled forward to align Catawba Units 1 and 2 with other Duke Energy nuclear sites to the 2019 Edition of ASME Section XI Code. In no case during this overlap period of intervals will any one exam be credited for both intervals.
Pursuant to Relief Request 14-CN-002, Duke Energy also performs an IWA-5244(b)(2) unimpaired flow test in conjunction with IWA-5244(b)(1) visual examinations of the ground surface areas. For each segment of buried pipe, periodic flow testing is performed in accordance with the flow balance test procedure for each train. These surveillance procedures require flow to be measured, recorded, and compared to established acceptance criteria to provide assurance that flow is not impaired during operation. In addition to the unimpaired flow test, Duke Energy performs a visual examination of the ground surface areas above components buried to detect evidence of through-wall leakage in buried components. All Fourth ISI Interval periodic unimpaired flow tests and ground surface visual examinations have been completed and were satisfactory with no relevant conditions.
The ground surface visual examinations in conjunction with unimpaired flow tests provide reasonable assurance of the structural and leak-tight integrity of the buried components. The unimpaired flow test with visual examination of ground surfaces are conducted each inspection period in accordance with ASME Section XI, Table IWD-2500-1, IWD-5220 (Reference 8.2) for Class 3 pressure retaining components. In addition, Catawba will continue to perform supplemental VT-2 visual examinations of accessible RN System HDPE flanges (eleven underground vaults containing sixteen HDPE flanged joints) each inspection interval for the remaining life of plant. This is the
RA-23-0310 Page 5 of 8 same additional examination requirement as previously approved in the Fourth ISI Interval Relief Request 14-CN-002 (Precedent 7.2 and Reference 8.3).
G.
Overpressure Protection The HDPE material has the same overpressure protection as the original carbon steel material.
H.
Ongoing Testing and Research for HDPE Material for Application in ASME Class 3 Piping The NRC Safety Evaluation for Relief Request 06-CN-003 required that Catawba submit information obtained from the ongoing testing and research prior to submitting the Catawba Unit 1 and Unit 2 Fourth Ten-Year ISI Interval Plan. Research and testing performed by EPRI for HDPE material to date provides evidence that the continued use of HDPE will provide an acceptable level of quality and safety for the remainder of plant life. In accordance with the NRC Safety Evaluation for Relief Request 06-CN-003, this research information was submitted to the NRC for information only (Reference 8.4).
I.
RL System HDPE Operating Experience As the RL system is a non-safety related system, proceduralized and documented inspections of RL system piping are not conducted. However, operator rounds and system maintenance activities provide frequent inspections that have identified leakage and system material degradation. As documented in RAI responses in Reference 8.3, the RL system HDPE piping serves as a leading indicator for identifying potential degradation of RN system piping. A summary of HDPE leaks, failures, and flaws was provided in Table 1 of RAI #2 from Reference 8.3. In addition to the previous operating experience, two new RL branch connection leaks were identified during operator rounds as described in the Table below. Each leak was entered into the sites Corrective Action Program and resolved through a complete replacement of the affected HDPE piping.
The leaking PE-3408 material associated with flow elements 0RLFE7430 and 0RLFE7460 was replaced with PE-4710 which is considered a chemical upgrade and stronger than the previous material. Only PE-4710 HDPE material and no branch fittings were installed in RN system applications per Relief Request 06-CN-003.
RA-23-0310 Page 6 of 8 Table 1 - Summary of RL HDPE Leak, Failures, and Flaws Date Problem Description Method of Repair Disposition for Inspection of RN System Piping 04/01/2024 During operator rounds, a leak was discovered at the fused branch connection joint for 0RLFE7430 (A KR HX (Heat Exchanger) RL Flow). The leak was initially quantified at approximately 11 DPM (drops per minute).
The highest leak rate was quantified at 6323 DPM.
The PE-3408 piping and fittings to the 1A KR (Recirculated Cooling Water System) Coolers were removed and replaced in the same configuration with PE-4710 material. All fused joints were fabricated and tested at the vendor facility and installation in the field was flanged to the existing cooler.
No inspection is required for this problem for RN System. Branch fittings were not used for RN system piping nor was PE-3408 material.
6/25/2024 During operator rounds, a leak was discovered at the fused branch connection joint for 0RLFE7460 (D KR HX RL Flow) is leaking at various rates when observed at various times. The highest leak rate was quantified at 72 DPM.
The PE-3408 piping and fittings to the 1D KR Coolers were removed and replaced in the same configuration with PE-4710 material. All fused joints were fabricated and tested at the vendor facility and installation in the field was flanged to the existing cooler.
No inspection is required for this problem for RN System. Branch fittings were not used for RN system piping nor was PE-3408 material.
J.
Conclusion The use of HDPE material in the diesel generator jacket water cooler application will continue to provide improved RN System performance and will enhance system reliability. There has been no indication of RN joint issues, and the piping system is operating satisfactorily during plant operation. Based on the information provided in Relief Requests 06-CN-003, 14-CN-002, and the above, the proposed alternative will continue to provide an acceptable level of quality and safety.
RA-23-0310 Page 7 of 8 6.0 DURATION OF PROPOSED ALTERNATIVE:
The use of the proposed alternative is requested for the Fifth ISI Interval at Catawba Nuclear Station, Unit 1 and Unit 2, and throughout the remainder of the current renewed operating licenses for each unit as follows:
Docket Number License Expires CNS Unit 1 05000413 12/05/2043 CNS Unit 2 05000414 12/05/2043
7.0 PRECEDENTS
Precedent 7.1 was the original NRC Safety Evaluation that approved the technical basis and conditions under which HDPE material may be used for ASME Section III, Division 1, Class 3, buried systems and was applicable only for the Third ISI Interval. Precedent 7.2 was the NRC Safety Evaluation which approved continued use of HDPE material at CNS for the Fourth ISI Interval. Precedents 7.3 through 7.5 provided similar relief of buried HDPE material in Class 3 applications for the remaining operational life of Callaway and Hatch Nuclear Plants, including through plant life extension.
7.1 NRC letter from M. Wong, USNRC, to J.R. Morris, Catawba Nuclear Station, Catawba Nuclear Station, Units 1 and 2, Relief 06-CN-003 for use of Polyethylene Material in Buried Service Water Piping (TAC Nos. MF0234 and MF0235), May 27, 2009 (ML091240156).
7.2 NRC letter from R.J. Pascarelli, USNRC, to K. Henderson, Catawba Nuclear Station, Catawba Nuclear Station Units 1 and 2: Proposed Relief Request 14-CN-002, Alternative to American Society of Mechanical Engineers (ASME)
Section XI Requirements for Class 3 Buried Piping (TAC Nos. MF4864 and MF4865), June 19, 2015 (ML15161A376).
7.3 NRC letter from R.J. Pascarelli, USNRC, to F. Diya, Ameren Missouri, Callaway Plant, Unit 1 - Request for Relief Related to the Inservice Inspection Program for Class 3 Buried High-Density Polyethylene Piping (EPID L-2018-LLR-0039),
November 26, 2018 (ML18313A069).
7.4 NRC letter from M.T. Markley, USNRC, to F. Diya, Union Electric Company, Callaway Plant, Unit 1 - Request for Relief I4R-01, Alternative to ASME Code Inservice Inspection Requirements for Class 3 Buried Piping (TAC No. MF4271),
May 12, 2015 (ML15064A125).
7.5 NRC letter from M.T. Markley, USNRC, to C.R. Pierce, Southern Nuclear Operating Company, Inc, Edwin I. Hatch Nuclear Plant, Unit 2, Alternative HNP-ISI-ALT-HDPE-01 for use of High Density Polyethylene in Plant Service Water Piping (TAC No. MF6712), December 21, 2015 (ML15337A414).
RA-23-0310 Page 8 of 8
8.0 REFERENCES
8.1 Federal Register (Vol. 87, No. 207, October 27, 2022) - American Society of Mechanical Engineers 2019-2020 Code Editions.
8.2 American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section XI, 2019 Edition.
8.3 Duke Energy Letter from K. Henderson to USNRC, Request for Relief Number 14-CN-002 Continued Use of High Density Polyethylene (HDPE) Material in Nuclear Safety Related Piping Application, dated May 18, 2015 (ADAMS Accession No. ML15142A412).
8.4 Duke Energy Letter from K. Henderson to USNRC, Transmittal of Industry High Density Polyethylene (HDPE) Test Results to NRC, dated December 8, 2014 (ADAMS Accession No. ML14345B039).