CNS-14-125, Request for Relief Number 14-CN-002 Continued Use of High Density Polyethylene (Hdpe) Material in Nuclear Safety Related Piping Application
| ML14338A620 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 12/02/2014 |
| From: | Henderson K Duke Energy Carolinas, Duke Energy Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNS-14-125 | |
| Download: ML14338A620 (11) | |
Text
Kelvin Henderson Vice President ENERGY.
Catawba Nuclear Station Duke Energy CNO1VP 1 4800 Concord Road CNS-14-125 York, SC 29745 o: 803.701.4251 f: 803.701.3221 December 2, 2014 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. Letter from Duke Energy to NRC dated September 15, 2014
- 2. Electronic Mail from NRC to Duke Energy dated October 21, 2014 The Reference 1 letter transmitted 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 electronic mail provided an opportunity for Duke Energy to supplement the Reference 1 letter to facilitate the NRC acceptance review of the request for relief. Specifically, the Reference 2 electronic mail discussed the conduct of a periodic pressure test of the affected HDPE piping.
A telephone conference call was held between Duke Energy and the NRC on November 10, 2014 concerning the opportunity to supplement. During this conference call, Duke Energy indicated that the following information would be provided in response to the Reference 2 electronic mail:
- 1. Duke Energy would explain the challenges associated with the conduct of a periodic pressure test.
- 2. Duke Energy would modify the Reference 1 request for relief from a remainder of plant life duration to a 10-year fourth interval duration.
- 3. Duke Energy would provide a summary of relevant Catawba operating experience to further technically justify the use of HDPE material for the fourth 1 0-year interval.
www.duke-energy.comrn, (J
U.S. Nuclear Regulatory Commission Page 2 December 2, 2014 The attachment to this letter contains the requested information in the form of revised Request for Relief 14-CN-002. Revisions are indicated by change bars in the affected sections of the request. Duke Energy is requesting NRC review and approval of this request by June 30, 2015.
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.
Very truly yours, Kelvin Henderson Vice President, Catawba Nuclear Station LJR/s Attachment
U.S. Nuclear Regulatory Commission Page 3 December 2, 2014 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
Duke Energy Request for Relief Serial Number 14-CN-002 Page 1 of 8 Duke Energy Corporation (Duke Energy)
Catawba Nuclear Station, Units 1 and 2 Relief Request Serial Number 14-CN-002 Alternative to Section XI Requirements Under 10 CFR 50.55a(a)(3)(i) for Continued Service of Class 3 Buried Piping Replaced Pursuant to Relief Request 06-CN-003
Duke Energy Request for Relief Serial Number 14-CN-002 Page 2 of 8
- 1. ASME Code Component(s) Affected ASME Class 3 buried piping in the Catawba Nuclear Service Water System serving the diesel generator jacket water coolers.
2. Applicable Code Edition and Addenda
ASME Boiler and Pressure Vessel Code, Section Xl, 2007 Edition through 2008 Addenda.
3. 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. Reason for Request
The Construction Code of record for buried ASME Class 3 piping is the ASME Boiler and Pressure Vessel Code,Section III, Subsection ND, 1974 Edition including Summer 1974 Addendum. This Construction Code and later editions and addenda of this Construction Code do not provide rules for use of high density polyethylene (HDPE) material. ASME Code Case N-755 and Code Case N-755-1 were issued by the ASME Boiler and Pressure Vessel Code Committee for use of HDPE but have not been approved for use by NRC Regulatory Guide 1.84, "Design, Fabrication, and Materials Code Case Acceptability, ASME Section II1".
This relief request is being submitted for approval for continued use of HDPE material installed pursuant to Catawba Relief Request 06-CN-003. 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 ten-year ISI interval. This new relief request applies only to the HDPE material that was installed during the third ten-year ISI interval in accordance with Relief Request 06-CN-003. No additional use of HDPE material is being requested by this relief request.
5. Proposed Alternative and Basis for Use
Catawba proposes to continue use of the HDPE material installed in the Nuclear Service Water System during the fourth ten-year ISI interval. Pursuant to 10 CFR 50.55a(a)(3)(i), in lieu of the requirement of Section Xl IWA-4221(b)(1), this alternative to the
Duke Energy Request for Relief Serial Number 14-CN-002 Page 3 of 8 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 leaks in this piping from corrosion or degradation during this period.
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) ensures 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 since 1998 continues to demonstrate the acceptability of this material for this service.
The HDPE material installed in the non-safety related Low Pressure Service Water System (RL System) serves as a leading indicator of degradation or aging of HDPE material in service in the safety related Nuclear Service Water System (RN System) based on the following considerations:
- 1. The HDPE material used for the RL System is either the same HDPE material used for the RN System or is an HDPE material that is more susceptible to degradation. (Both bi-modal 4710 HDPE material and uni-modal 3408 HDPE material were used in the RL System. The uni-modal 3408 material has a lower resistance to slow crack growth than the bi-modal 4710 material used in the RN System.) HDPE materials used in both the RL System and the RN System were manufactured by the same resin manufacturer and the same pipe manufacturer. Pipe sizes for the RL System are as large as 32-inch Nominal Pipe Size (NPS). Pipe size and thickness for the RN System includes 12-inch NPS, Standard Dimensional Ratio (SDR) 11.
- 2. Installation practices were more rigorous for the RN System HDPE than the RL System HDPE. The RN System HDPE was installed in accordance with an approved bonding procedure by operators who were qualified to make bonded joints. In contrast, the RL System HDPE piping was installed by operators who had been trained, but there was not a procedure used for bonding. Also, the piping joints for the RL System did not use a data logger to record key joining process variables during the fusing process.
Duke Energy Request for Relief Serial Number 14-CN-002 Page 4 of 8
- 3. A 10% of nominal wall thickness gouge depth allowance was used for the RL System HDPE piping compared to a 3.5% of nominal wall thickness gouge depth allowance used for the RN System HDPE piping. RL System HDPE piping would be expected to exhibit degradation due to slow crack growth before the RN System HDPE piping. Using the installed RL System piping to identify degradation resulting from an installation practice is conservative for the RN System piping.
- 4. Both the RL System and the RN System use the same water source, Lake Wylie. The RL System HDPE piping has been installed for over fifteen years compared to RN System HDPE piping which has only been installed for about four years.
(Unit 2 HDPE for the RN System was put into service in October 2010 and Unit 1 HDPE for the RN System was put into service in June 2011.)
- 5. System design parameters (pressure and temperature) are similar for both the RL and the RN Systems. Using the RL System for monitoring HDPE for degradation effects due to temperature is conservative since the RN System HDPE is only subjected to temperatures above inlet header temperature during diesel generator operation. In contrast to the RN System HDPE, RL System HDPE is subjected to water temperatures above ambient lake temperature whenever the plant is operating, as many plant non-safety related heat exchangers and motor coolers reject heat loads to the RL System. Since installation of HDPE in the RN System, there have been about 300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> of operation for each discharge HDPE line with the diesel generator in operation.
- 6. HDPE has been used for RL System piping inside of the plant as well as for buried piping. The RL System piping installed inside of the plant is accessible for inspection and any leakage from this piping would be easily identified by plant personnel.
All of these factors combine to provide a high level of confidence that monitoring HDPE installed in the RL System is an effective way to assess aging or degradation of HDPE installed in the RN System.
The corrective action program will be used to address any failures in HDPE piping installed in the RL System in order to evaluate potential degradation of HDPE piping in the RN System.
Description of Proposed Alternative 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
Duke Energy Request for Relief Serial Number 14-CN-002 Page 5 of 8 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.
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.
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, 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 2634, "Standard Test Method for Laboratory testing of 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 2634 tensile impact test.
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.
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
Duke Energy Request for Relief Serial Number 14-CN-002 Page 6 of 8 or the scratches were removed by blending smoothly for cases where the remaining wall thickness exceeded the design wall thickness.
Examination VT-1 visual examination was required and performed for all fused joints. VT-2 examinations were performed during hydrostatic testing for all fused joints and external surfaces of the piping.
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. Also, the buried piping is not instrumented to measure change of flow at the ends. Neither the change in flow test [IWA-5244(b)(1)] nor the unimpaired flow test [IWA-5244(b)(2)] alone is sufficiently sensitive to detect small through-wall leakage in these buried components, due to relatively high system flow rates and the accuracy of flow measurement instrumentation. As such, there is no appreciable difference between the level of quality and safety achieved by performing either of these tests. Therefore, Duke Energy performs an unimpaired flow test [IWA-5244(b)(2)] in conjunction with 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. These visual examinations and unimpaired flow tests provide reasonable assurance of the structural and leak-tight integrity of the buried components. The unimpaired flow test with the visual examination is conducted each inspection period in accordance with ASME Section Xl, Table IWD-2500-1 for Class 3 pressure retaining components.
The unimpaired flow test is conducted in accordance with the Nuclear Service Water System flow balance for each train of the system. In accordance with Generic Letter (GL) 89-13, "Service Water System Problems Affecting Safety-Related Equipment", the flow balance is performed as part of Catawba's test program at the design basis flow rates to ensure that all components are not fouled or clogged and that
Duke Energy Request for Relief Serial Number 14-CN-002 Page 7 of 8 they will be able to receive their design basis flow rates simultaneously. Flow rates measured during flow balance testing are verified to meet flow acceptance criteria for each cooled component.
If the measured flow is less than the specified acceptance criteria, the Nuclear Service Water System train is declared inoperable and the appropriate Technical Specification Condition is entered. In addition, the condition is entered into the corrective action program for resolution.
In addition, conducting a pressure test that requires isolation of the affected HDPE piping would have significant impact on overall plant risk. In the system's current configuration, draining the system header, installing a blind flange, and refilling the supply piping to conduct the test will require longer than the 72-hour Technical Specification Completion Time for one train of the system.
Performing these pressure tests would put both units in a 72-hour Technical Specification Condition since only one train of the system would be operable. After 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, both units would have to be shut down in order to complete the pressure test. Conducting the test will also result in the inoperability of one diesel generator, thereby degrading emergency power supply reliability during the time it takes to complete the test.
Overpressure Protection The HDPE material has the same overpressure protection as the original carbon steel material.
Test Program for HDPE Material for Application in ASME Class 3 Piping The NRC Safety Evaluation for Relief Request 06-CN-003 requires 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 supports operation of the Catawba units for the remainder of plant life. In accordance with the NRC Safety Evaluation for Relief Request 06-CN-003, this research information will be submitted to the NRC for information only.
Conclusion The use of HDPE material in the diesel generator jacket water cooler application will continue to provide improved Nuclear Service Water System performance and will enhance system reliability. Based on the information provided in Relief Request 06-CN-003, the proposed alternative will continue to provide an acceptable level of quality and safety.
Duke Energy Request for Relief Serial Number 14-CN-002 Page 8 of 8
6. Duration of Proposed Alternative
The use of the proposed alternative is requested for the fourth ten-year ISI interval for Catawba Nuclear Station, Unit 1 and Unit 2. The Unit 1 and Unit 2 fourth ten-year ISI interval is currently scheduled to begin on August 19, 2015 and is currently tentatively scheduled to end on November 19, 2025.