CNS-15-046, Request for Relief Number 14-CN-002 Continued Use of High Density Polyethylene (Hdpe) Material in Nuclear Safety Related Piping Application
| ML15142A412 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 05/18/2015 |
| From: | Henderson K Duke Energy Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNS-15-046, TAC MF4864, TAC MF4865 | |
| Download: ML15142A412 (11) | |
Text
Kelvin Henderson DUKE Vice President ENERGY.
Catawba Nuclear Station Duke Energy CNO1VP I 4800 Concord Road York, SC 29745 CNS-15-046 o: 803.701.4251 f: 803.701.3221 May 18, 2015 10 CFR 50.55a U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555
Subject:
Duke Energy Carolinas, LLC (Duke Energy)
Catawba Nuclear Station, Units 1 and 2 Docket Numbers 50-413 and 50-414 Request for Relief Number 14-CN-002 Continued Use of High Density Polyethylene (HDPE) Material in Nuclear Safety Related Piping Application
References:
- 1. Letters from Duke Energy to NRC dated September 15, 2014 (ADAMS Accession Number ML14265A043) and December 2, 2014 (ADAMS Accession Number ML14338A620)
- 2. Letter from NRC to Duke Energy dated April 22, 2015 (ADAMS Accession Number ML15110A089)
The Reference 1 letters transmitted and supplemented Request for Relief 14-CN-002. This request for relief is to support the continued use of a proposed 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 Reference 2 letter transmitted Requests for Additional Information (RAls) associated with this request for relief.
The purpose of this letter is to respond to the Reference 2 RAIs. The attachment to this letter provides the RAI responses. The format of the attachment is to restate each RAI, followed by its associated response.
There are no regulatory commitments contained in this letter or its attachment.
If you have any questions concerning this material, please call L.J. Rudy at (803) 701-3084.
(Lit www.duke-energy.com
U.S. Nuclear Regulatory Commission Page 2 May 18, 2015 Very truly yours, Kelvin Henderson Vice President, Catawba Nuclear Station LJR/s Attachment
U.S. Nuclear Regulatory Commission Page 3 May 18, 2015 xc (with attachment):
V.M. McCree Regional Administrator U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257 G.A. Hutto Ill, Senior Resident Inspector U.S. Nuclear Regulatory Commission Catawba Nuclear Station G.E. Miller, Project Manager (addressee only)
U.S. Nuclear Regulatory Commission Mail Stop 8 G9A Washington, D.C. 20555
ATTACHMENT RESPONSE TO NRC REQUESTS FOR ADDITIONAL INFORMATION (RAIs) 1
REQUEST FOR ADDITIONAL INFORMATION RELIEF REQUEST 14-CN-002 USE OF HOPE IN CLASS 3 SERVICE WATER PIPING DUKE ENERGY CAROLINAS, LLC CATAWBA NUCLEAR STATION, UNITS 1 AND 2 DOCKET NOS. 50-413 AND 50-414 TAC NOS. MF4864 AND MF4865 By letter dated September 15, 2014, Duke Energy Carolinas, LLC, submitted a relief request for the Catawba Nuclear Station, Units 1 and 2 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML14265A043). The proposed relief would authorize continued use of High Density Polyethylene in Class 3 Service Water Piping for the fourth 10-year ISI Interval at Catawba Nuclear Station, Units 1 and 2. In order for the NRC staff to complete its review of the relief request, the following additional information is requested.
- 1. Please eenfirm9 your ConStruction Code Of reeerd fOr burfied ASMVE Class 3 piping tis-ASIVE BeileF and rressure Vessel Codc, Sectoen I!", Subscctwcn ND, 107-4 Editicn through Summe.r 174 Addend."1 Duke Energy Response:
No response is required.
- 2.
In the submittal you state that approximately 20,000 linear feet of HDPE material in non-safety related Low Pressure Service Water System (RL system) has been in service since 1998 and that the continued operability of this system provides evidence of long-term reliability of HDPE material. Have there been any indications of leaking or flaws in the RL buried piping? If so, what was the method of repair for this piping?
Duke Energy Response:
Leaks in the HDPE RL system piping that have occurred are tabulated below in Table 1.
1 In a teleconference on April 13, 2015, Duke identified that the Construction Code of record was specified in Section 2 of the relief request. No further information is needed with regard to this question.
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Table 1 Summary of HDPE Leaks, Failures, and Flaws Date Problem Description Method of Repair Disposition for Inspection of RN System Piping 10-28-2004 Electro-fusion coupling leak in RL system.
Coupling replaced and fused.
No inspection is required for this problem for RN (Coupling had not been fused.)
system. Electro-fusion couplings were not used for RN system piping. Controlled procedures were used for RN system installation to assure proper fusing of joints.
2-24-2006 Butt fusion failure in RL system during Failed joint cut out and replaced.
No inspection is required for this problem for RN construction hydro test. Failure was caused by a Failure analysis performed by Sterling system.
faulty heating element in the heater plate used to Refrigeration Corporation for Duke Controlled procedures that required data logger and fuse the piping.
Energy. Summary of report dated QC inspection during fusing would have identified April 15, 2006 follows this table.
failed element. Forty-three percent of the fused joints were cut out and impact tensile tested. This high rate of testing would have identified any equipment problems during installation of RN system piping. All RN system piping was hydro tested with no failures.
Part of joint was partially fused when one of the resistance elements in the heater plate failed.
1-19-2007 Crack in saddle branch fitting in RL system.
Larger branch fittings are now used to No inspection is required for this problem for RN Crack resulted from weight of vent valve support external weights. Summary system.
supported by the branch connection.
of Duke Energy Laboratory Report Branch fittings were not used for RN system piping.
- 3748 follows this table.
2-21-2007 Assessment of RL system project was Repairs for failures listed by this No inspection is required for this problem for RN performed. Leaks, failures, and material assessment are addressed in the first system.
deficiencies were summarized. The leaks and two items above.
Items described in the assessment were utilized to failures described in this summary are listed as develop or enhance procedures for material handling, the first two items above.
material procurement, and material receiving for RN system piping.
8-21-2010 Flange joint leak in RL system occurred during Bolting for flange joint was re-torqued Inspection of RN system HDPE flanges for leakage construction hydro test.
to stop leakage.
shall be performed. (Refer to RAI question 4 response for additional details.)
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Table 1 Summary of HDPE Leaks, Failures, and Flaws Date Problem Description Method of Repair Disposition for Inspection of RN System Piping 6-30-2014 Flange joint leak in RL system was caused by Bolting for flange joint was re-torqued Inspection of RN system HDPE flanges for leakage gasket unloading resulting from seasonal to stop leakage.
shall be performed. (Refer to RAI question 4 expansion and contraction of piping.
response for additional details.)
1-22-2015 Electro-fusion coupling leak in RL system piping Pipe coupling and pipe were replaced.
No inspection is required for this problem for RN was caused by improper installation.
Summary of Duke Energy Laboratory system.
Report #5377 follows this table.
Electro-fusion couplings were not used for RN system piping. Controlled procedures were used for RN system installation to assure proper fusing of joints.
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April 15, 2006 Laboratory Report prepared by Sterling Refrigeration Corporation for Duke Energy On March 2, 2006, a fused joint in RL system pipe segment CE-62086 failed. The pipe segment was constructed using 20" (DR 11) High Density Polyethylene Pipe (HDPE). The subject pipe segment was installed during the period of August 4-16, 2004. The failed joint was produced using a Christie Fusion Machine. The subject joint was exposed to several 10 psi pressure tests and one 65 psi hydrostatic test, after which the line sat idle for 18 months. In 2006, line segment CE-62049 was attached to CE-62086 and tested. During the hydrostatic test (65 psi target test pressure), the subject joint started leaking and completely failed at 38 psi.
The failed joint was removed from the system and transported to the Duke Energy Materials Laboratory. Duke Energy personnel and a team from the Electric Power Research Institute (EPRI) performed an ultrasonic examination (UT) of the failed joint. The specimen was then packaged and shipped to the McElroy Manufacturing Company for high-speed tensile testing. After this testing was complete, the pieces were returned to the Duke Energy Materials Laboratory.
Sterling Refrigeration Corporation was tasked to support an evaluation for the determination of the cause of failure.
After a review of the evidence, the cause of the joint failure was the improper application of heat while making the joint. While the heater plate that had been used in the fusion process to make the subject joint was not available for examination, evidence points to a heater plate malfunction.
The heater is constructed using two thin flat metal plates with a core of electric heating elements. The heating elements are designed/programmed to raise the temperature of the flat metal plates to 450-4750F. The fusion process requires the ends of the pipes to be brought in contact with the heater via axial compressive loads on the pipe.
The heater should heat the ends of the pipe to a temperature in excess of 450°F.
The pipes are held in contact for a temperature-soaking period. This allows more HDPE material to increase in temperature. If the mating ends do not reach the critical fusion temperature, a homogenous fusion will not occur.
Evaluation of the failed joint found an "Arc of Fusion" where full or partial fusion occurred between the two pipe surfaces. The length of the arc was about 17 inches (or 27% of the total pipe circumference of 63 inches). At the center of the arc, about 6 inches was fully fused and was confirmed by the tensile tests. The remaining arc joint surfaces were held together by a "sticky" bond. This failed joint condition was created by the malfunctioning heater plate.
Without being able to examine the actual heater plate used to make subject joint, the only assumption that can be made is that some heater elements failed. In the area of the heater plate adjacent to the "Arc of Fusion", the heater apparently worked correctly.
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This conclusion was confirmed by discussion with Duke Energy staff that had interviewed the construction crew. They found that the crew felt the Christie Fusion Machine was not performing correctly and took the machine out of service. The heater plate was found to be faulty and was replaced during the time frame that the failed joint was made.
Duke Energy Laboratory Report #3748 An RL flow element was found to be leaking water where the 1" branch connection attached to the 8" HDPE run pipe. The connection supports two small valves, metal piping, and instrumentation without additional support. The small piping also extends into a climbing path used to access the underside of the condenser, so it was suspected that the pipe could have been bumped or stepped on at some point. The connection was a vendor-made socket fusion joint which had been in service for several years.
Cracking in the 1" branch pipe was stress related. The stresses appeared to be bending stresses related to the weight of the cantilevered load (valves and piping) being supported by the 1" pipe. The cracking was analogous to a fatigue-type mechanism:
Occurred at a restrain point Occurred on the top side of the pipe, the site of maximum bending stress Crack direction was OD to ID with multiple initiation sites Cracks followed circumferential machining marks, which acted as slight stress risers Crack planes were flat and normal to the pipe axis The socket-type fusion joint attaching the 1" branch connection to the 8" pipe was intact and was not involved in the leak.
There was no indication of tearing or plastic deformation along the OD surface of the 1'" pipe, so it did not appear that the cracking was due to the pipe having been stepped upon or otherwise subjected to a single overstress event.
Duke Energy Laboratory Report #5377 In January 2015, during an RL pump swap, a leak occurred at an 8" HDPE pipe coupling. The leak decreased significantly after the usual two-pump alignment was restored. The coupling was left in place until the Unit 2 End of Cycle 20 Refueling Outage, during which it was cut out and sent to the Metallurgy Laboratory for evaluation.
The pipe on one end of the coupling had not been fully inserted prior to fusing; however, a good bond was present on this pipe on all eight planes examined.
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The leak occurred where material had extruded out beyond the end of the other pipe. This feature is a fairly reliable indicator of misalignment of the pipe within the coupling. The thicker walled pipe was cut square and was fully inserted, but it was apparently slightly cocked. This condition allowed molten material to flow out beyond the end face of the pipe on one side only, as was observed here. The arc of extruded material covered approximately 180 degrees. The failure to fully insert the pipe on the other end may have contributed to this misalignment, if the smaller pipe was not providing the expected amount of support to the coupling.
- 3. You state that portions of the RL piping are inside the plant and, as such, are accessible for inspection. Provide the inspection history for this piping, including type of inspection, frequency of inspection, and repair history. What is the future inspection plan/procedure for this piping?
Duke Energy Response:
As the RL system is a non-safety related system, proceduralized and documented inspections of RL system piping are not conducted. However, operator rounds, system engineer walkdowns, and system maintenance activities provide frequent inspections that have identified leakage and system material degradation.
Operator rounds performed each shift account for the most frequent inspection of RL system piping. Any leakage from RL piping is identified and documented in either the Corrective Action Program or the Fluid Leak Management (FLM) program.
The RL system engineer is required to perform a system walkdown annually. Any system leakage or piping degradation found during this inspection would be evaluated using the Corrective Action Program.
Plant maintenance activities also provide inspections. Leakage or degradation of piping found during maintenance of equipment such as valves, pumps, or heat exchangers are identified and evaluated using the Corrective Action Program.
Laboratory analyses are routinely performed for any piping failures. Laboratory results are used to determine failure cause, to plan additional inspections if required, and to prevent failure recurrence.
Using RL system HDPE piping as a leading indicator for identifying degradation of RN system piping and for determining inspections indicates that periodic inspections are required for the HDPE flanged joints installed in the RN system.
RL system experience to date does not indicate the need for other inspections of RN system HDPE.
Refer to Table I above for the repair history of this piping.
- 4. If the RL piping starts to show degradation, what enhanced monitoring of the RN piping would be put into place?
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Duke Energy Response:
The degradation mechanism characterized in the RL system will serve as a leading indicator in order to evaluate any potential relevant conditions within the RN system HDPE. Through the site Corrective Action Process, enhanced monitoring and/or inspections for the RN system piping will be performed as appropriate following identification and evaluation of RL system deficiencies or degradation mechanisms. The enhanced monitoring and/or inspection techniques selected will be commensurate with the RL system HDPE degradation mechanism identified and documented within the Corrective Action Process.
In addition, as a result of recent operating experience with HDPE flange joint leakage within the RL system, Catawba will perform visual VT-2 inspections of accessible RN system HDPE flanges. These inspections will encompass eleven underground vaults containing a total of sixteen 12-inch NPS HDPE flanged joints.
These inspections will require removal of the vault covers for access in order to perform the visual VT-2 inspections. These inspections will occur during the fourth ISI interval. Any relevant conditions found during the inspections of the HDPE RN system flanges will be evaluated through the Corrective Action Process.
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