ML23241A843
| ML23241A843 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/29/2023 |
| From: | Constellation Energy Generation |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML23241A840 | List: |
| References | |
| EPID L-2023-LLR-0006 | |
| Download: ML23241A843 (1) | |
Text
ENCLOSURE 3 Response to Request for Additional Information - Non-Proprietary Version
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION REQUEST FOR ADDITIONAL INFORMATION PROPOSED ALTERNATIVE TO THE REQUIREMENTS FOR REPAIR/REPLACEMENT OF SALTWATER SYSTEM BURIED PIPING CONSTELLATION ENERGY GENERATION, LLC CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NUMBERS 50-317 AND 50-318 EPID: L-2023-LLR-0006 By letter dated February 24, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession ML21055A797), Constellation Energy Generation, LLC, (the licensee) submitted a proposed alternative, ISI-05-021, in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1). In ISI-05-021, the licensee proposed to repair the buried saltwater system piping using carbon fiber-reinforced polymer (CFRP) composite system in lieu of the repair/replacement in accordance with ASME Code,Section XI, IWA-4221(b) to meet the original Construction Code. The proposed alternative is for the Calvert Cliffs Nuclear Power Plant (CCNPP), Units 1 and 2 for the remainder of the fifth 10-year inservice inspection (ISI) interval which began on July 1, 2019, and is scheduled to end on June 30, 2029.
To complete its review, the U.S. Nuclear Regulatory Commission (NRC) staff requests the following additional information.
REGULATORY BASIS Pursuant to 10 CFR 50.55a(g)(4), components (including supports) that are classified as ASME Code Class 1, Class 2, and Class 3 must meet the requirements, except design and access provisions and preservice inspection (PSI) requirements, set forth in the ASME Code,Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plant Components.
Pursuant to 10 CFR 50.55a(z), alternatives to the requirements of paragraph (b) through (h) of Section 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The licensee must demonstrate that: (1) the proposed alternative would provide an acceptable level of quality and safety, or (2) compliance with the specified requirements of Section 50.55a would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
REQUEST FOR ADDITIONAL INFORMATION RAI-1 Enclosure 1, Sections 4(a)(i), Page 3 of 22, CCNP [Calvert Cliffs Nuclear Power Plant]
Unit 1, Salt Water (SW) System and (4)(a)(ii) CCNPP Unit 2, Salt Water (SW) System, state that the repair using CFRP composite is for the buried 30-inch and 36-inch diameter cement mortar lined bell and spigot ductile iron piping. Section 4(a)(v) states that the scope does not include pumps, valves, expansion joints, or threaded connections. Since the CFRP structural integrity is required to be maintained for the entire length of the repair, discuss whether the CFRP repair includes locations with bell and spigot joints and if any additional measures are needed for these locations.
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RESPONSE: ((
))
RAI-2-1 Enclosure 5, Attachment A, Section 5A.2.1, Page 9 of 36, states that the cement mortar lining may be removed from portions of the pipeline if deteriorated, or it may stay in place if in good condition. Enclosure 4, Attachment C, Table 1, Page 23 of 49, provides a minimum average requirement for shear bond strength between CFRP and cast iron of ((
)). Enclosure 5, Attachment A, Section 5A.3.1, Page 33 of 36, lists shear bond strength of CFRP on host pipe of (( )), which is also used in calculations. Since the terminal ends are critical for transfer of load from the rest of the CFRP repaired portion and the shear bond strength between the CFRP and host pipe at the terminal ends is the design parameter used for such load transfer, discuss the applicability of the shear bond strength values between CFRP and host ductile iron pipe at the terminal ends.
RESPONSE: ((
))
RAI 2-2 Enclosure 5, Attachment A, Section 5A.3.1, Page 33 of 36, states that the characteristic value of shear bond strength of CFRP on host pipe (( )) is based on previous tests of shear bond to steel substrate instead of more recent results of shear bond to ductile iron which showed greater bond strength. To assess the conservatism, discuss the magnitude or percentage increase in shear bond strength from the recent tests.
RESPONSE: ((
))
RAI 2-3 Enclosure 5, Attachment A, Section 5A.3.1, Page 32 of 36, lists the characteristic value of tensile strength for (( )) used in the design evaluations. CFRP repair consists of multiple layers and is exposed to the operating and accident temperatures.
Discuss whether this strength value is based on test results of a single layer of CFRP at room temperature.
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RESPONSE: ((
))
RAI-3-1 Enclosure 4, Attachment A, Page 6 of 49, states that when the system is placed in-service, the epoxy will continue to cure over time and increase the glass transition temperature (Tg_Field) even further during service. It is not clear to the NRC staff when the curing effect is complete. Discuss how long (days or months) the post curing effect continues, and at what point the cross linking of the polymer is complete for (( )).
RESPONSE: ((
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))
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RAI 3-2 Enclosure 4, Attachment C, Page 18 of 49 states that Tg_Ultimate for ((
)) is (( )). The epoxy was selected based on Tg of (( )). What is the corresponding glass transition temperature for curing temperature does (( ))?
RESPONSE: ((
))
RAI-3-3 The following cautionary note is provided in Section 401-VIII-4 CURE of ASME PCC 2018 standard.
Caution: Each polymer in the repair system can be cured to a range of glass transition temperatures. Repair systems will not achieve the ultimate glass transition temperature determined by the qualification testing specified in this Standard unless they experience the same temperature for the same period of time as the sample tested. Repairs designed for elevated temperature service will not meet the requirements of this Article unless they are subject to a post-cure (heating) cycle that matches the thermal history of the sample tested during qualification.
Discuss how the Calvert Cliffs CFRP piping repair installation will satisfy the requirements of cautionary note regarding glass transition temperature.
RESPONSE
401-VIII-4 states in its entirety:
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION CURE CAUTION: Each polymer in the repair system can be cured to a range of glass transition temperatures. Repair systems will not achieve the ultimate glass transition temperature determined by the qualification testing specified in this Standard unless they experience the same temperature for the same period of time as the sample tested. Repairs designed for elevated temperature service will not meet the requirements of this Article unless they are subject to a postcure (heating) cycle that matches the thermal history of the sample tested during qualification.
(a) Since the cure of a repair laminate is strongly influenced by temperature and the correct mixing of polymer constituents prior to lamination, the limits set by repair system supplier shall not be exceeded without approval from the repair system supplier.
(b) Where elevated temperatures are required for curing, the temperature shall be monitored throughout the curing process and adhere to repair system suppliers guidance.
(c) The time for full cure is dependent on the type of polymer used in the repair and ambient conditions. The extent of cure achieved during installation shall be the same as that assumed in the design.
(d) If the process system pressure has been reduced prior to repair, then the repaired component shall not be returned to its normal operating pressure until satisfactory cure has been achieved.
((
))
RAI-4-1 Piping systems are typically designed to include seismic loading. Enclosure 5, Attachment B, Table 2, Page 5 of 7, Maximum Loads from Non-Repair Side Applied at the Fixed Point of the Wall provides forces and moments applied at the fixed point of a wall from the non-repair side. The repair piping continues beyond the buried section across a wall to the above ground section of the piping. Is above ground piping at Calvert Cliffs and the connected buried ductile iron piping designed for seismic loading?
RESPONSE: ((
))
RAI 4-2 Enclosure 5, Attachment B, Table 2, Page 5 of 6 states that the buried piping is not subject to differential strains due to seismic events. Does this also apply to the connected above ground piping as well?
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RESPONSE: ((
))
RAI 4-3 Do the forces and moments in provided in Enclosure 5, Attachment B, Table 2, Page 5 of 6, from the non-repair side include seismic loading? In your response discuss the evaluation of the interface for additional loading due to CFRP from the CFRP repair side combined with the non-repair side and address whether the original buried ductile iron piping was designed to include seismic loading.
RESPONSE: ((
))
RAI-5-1 ((
)) Enclosure 1, Page 16 of 22, CFRP Composite System Installation Section describes the installation process. The last layer of the CFRP repair is exposed to water flow ((
)). Based on the layup used for the repair, the next layer is a ((
)). Discuss the effectiveness of ((
)) layer. Provide any test data from any previous testing.
RESPONSE: ((
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))
RAI 5-2 Enclosure 4, Attachment C, Page 27 of 49, alternative request states that the ((
)). Provide a discussion to justify the adequacy of CFRP repair to support the design basis loads.
RESPONSE: ((
))
RAI-6 Enclosure 4, Attachment C, Page 19 of 49, provides formulations for ((
)) for tensile strength and modulus that will be verified by post installation testing of samples which have been cured under similar conditions as the installed (( )) composite system. Since flexural strength is required for bending modes, confirm that these formulations also apply to flexural strength and modulus.
RESPONSE: ((
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))
RAI 7-1 Enclosure 4, Attachment C, Table 1, Page 22 of 49, provides minimum average requirements for mechanical properties of CFRP composite system ((
)). Enclosure 5, Attachment C, Section 5.6, CFRP System Properties, provides the ((
)) which is based on testing and used in the structural evaluations. However, the characteristic value of flexural strength was not provided. Provide the characteristic value for flexural strength.
RESPONSE: ((
))
RAI 7-2 Enclosure 5 Attachment C, Page 34 of 76, provides sample calculations for structural evaluation of the CFRP repair for ((
)) For example, ((
)) NRC staff concluded that this evaluation is based on tensile strain and tensile strength rather than strain based on flexural strength because the evaluation is for bending. Provide justification for the use of tensile strength rather than flexural strength noting that the flexural strength is significantly lower than tensile strength.
RESPONSE: ((
))
RAI 8-1 Partial lengths is used throughout the alternative request with no clear definition Provide a definition on partial length CFRP installation.
RESPONSE: ((
))
RAI 9-1 Since adequate curing is essential for structural integrity of the CFRP, discuss how the temperature during the post-installation cure will be recorded and obtained both axially and
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION radially; and between the CFRP terminal ends. In your response, provide the locations and distances between the temperature measuring devices such as thermocouples placed along the pipe length and through the thickness of the CFRP laminate to record the curing temperature both axially and radially. If the curing temperature will not be recorded both axially and radially, justify uniformity of the post-installation cure of the CFRP laminate to ensure adequate strength and modulus.
RESPONSE: ((
))
RAI-10-1 Describe the initial curing process during the installation of the CFRP repair system.
As part of the response discuss whether the temperature on the surface of each layer of composite including cure temperature and duration will be monitored. If temperature of each layer surface is not monitored during the initial curing, justify why that approach is sufficient to ensure adequate curing.
RESPONSE: ((
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION
))
RAI 11-1 The CFRP repair affects the host pipe inside diameter, flow pattern, and flow rate that are required to meet the plant design criteria. Enclosure 5, Attachment C, Section 5.6, CFRP System Properties, provides sample calculations using ((
)). What is the total thickness of the CFRP composite system including all structural and nonstructural layers after post-installation cure?
RESPONSE: ((
))
RAI 11-2 Does the thickness for the carbon and glass fiber fabrics provided in Enclosure 6 include the fully saturated (( )) condition?
RESPONSE: ((
))
RAI 11-3 Enclosure 6 describes installation of piping What is the thickness of ((
)) applied on the host pipe before installation of the (( )) and the thickness of
(( )) applied after installation of the (( ))?
RESPONSE: ((
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))
RAI 11-4 Provide evaluation that confirm the impact from turbulent flow on the CFRP caused by variation in pipe diameter with and without cement mortar is acceptable as described in.
RESPONSE: ((
))
RAI 11-5 Provide evaluation that confirm that the reduced pipe inside diameter has no effect on the flow rate and meets the design basis as discussed in Enclosure 9.
RESPONSE: ((
))
The original design of the Saltwater System included accommodating the discharge of two saltwater pumps on either of the underground headers. When the rules for separation of trains were developed this ability was removed from the system. During the Overhaul of the above ground piping, this change allowed the above ground piping to be reduced in size to 24 with no impact on design flows. A rule of thumb for sizing pipe is a typical velocity of 9 feet per second.
With only one saltwater pump aligned to each underground header the velocity is expected to be less than 5 feet per second. The reduction in inside diameter due to the new lining is considered negligible and no turbulent flow is expected.
RAI-12-1 The Enclosure 4, page 6 of 9, describes how ((
)). What is the normal operating temperature range and maximum faulted (accident) condition temperature for supply and return lines piping.
RESPONSE: As described in Enclosure 2 the scope of the relief request is the SW System supply line piping and CCW return line piping prior to the common return line piping. Below is the temperature information for the scope of the relief request:
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION Supply Lines (Only Use)
Supply Lines Also Used for Emergency Discharge CCW Return Line Prior to Common Return Line Normal Operating Temp.
Range 32°-90°F 32°-90°F
< 100°F Accident Operating Temp.
Range))
32°-90°F 121°F 120°F RAI-12-2 As discussed in Enclosure 4, what is the maximum ultimate heat sink water temperature during the faulted condition?
RESPONSE: 90°F is the maximum ultimate heat sink temperature during the faulted condition (refer to Enclosure 5, Attachment B, Table 1 (Page 2 of 7) for lines 36"-LC2-1001, 30"-LC2-1003, 30"-LC2-1005 for Unit 1 and 36"-LC2-2001, 30"-LC2-2003, 30"-LC2-2005 for Unit 2).
RAI-12-3 As discussed in Enclosure 4. what is the maximum water temperature at the outlet of the heat exchanger during the faulted condition?
RESPONSE: The piping at the outlet of the Service Water heat exchanger is not within the scope of this proposed alternative. The piping at the outlet of the Component Cooling heat exchanger has a maximum water temperature during the faulted condition of 120°F. The scope of the relief request ends at the point where the Component Cooling discharge piping ties into the common return line with Service Water system piping.
RAI-12-4 As discussed in Enclosure 4, what Is the maximum ultimate heat sink water temperature used as the maximum faulted temperature (Tmax)? Discuss the reasons for your answer.
RESPONSE: The maximum ultimate heat sink water temperature is used as the maximum faulted temperature for the three lines per unit identified in RAI-12-2. These are suction lines that only see Chesapeake Bay water temperatures. The Chesapeake Bay temperature varies seasonally but does not vary with plant conditions.
RAI-12-5 As discussed in Enclosure 4, describe how long it takes for the discharge line temperature to rise from the maximum normal operating temperature to the maximum achievable faulted accident condition temperature (( )). Provide a plot of temperature versus time after the accident.
RESPONSE: As discussed above, the discharge lines from the Service Water heat exchangers are not within the scope of this proposed alternative. For the discharge lines from the CCW heat exchanger, it is anticipated that ample mixing will occur such that the time to achieve the
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION maximum faulted accident temperature will not be instantaneous but will occur in a short period of time.
RAI-13-1 Enclosure 5, Section 5A.1.4, page 8 of 36, describes the design basis describes ((
)) is essential because ((
)). What is the operating experience related to external corrosion of the buried ductile cast iron host pipe at CCNPP and how potential corrosion will be mitigated to ensure structural integrity at the terminal ends?
Response: ((
))
RAI 13-2 Enclosure 5 Attachment B, Section 5B1.1 references cast iron. Since, grey cast iron is susceptible to selective leaching, how will the selective leaching of grey cast iron be managed?
RESPONSE: It is acknowledged that cast iron is susceptible to selective leaching. ((
))
RAI-14-1 Enclosure 5, section 5A.2.1 describes how ((
)). Enclosure 5, page 2 of 6, provides calculations using ((
)) and Enclosure 8, page 4 of 36 states that ((
)). For portions of the ductile iron pipe that has degraded completely away from the terminal end regions, discuss the structural integrity of the CFRP repair in local areas that may come in contact with soil and moisture.
RESPONSE: ((
))
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RAI 14-2 Based on the description in Enclosure 5. Page 32 of 36 NRC staff has concluded that the (( )) will not be applied as the first layer to the entire repaired pipe length, rather it will be applied only to the exposed metal substrate surface where the degraded cement mortar is removed. Enclosure 8, describes the (( )) and has two purposes, one is to act as a ((
)) and the second is to act as a ((
)) if the host metal substrate degrades during the life of the repair. Will the (( )) be applied as the first layer to the entire repaired pipe (i.e., over the intact cement mortar and the exposed metal surface where the degraded cement mortar is removed)? Discuss how it will be applied.
RESPONSE: ((
))
RAI 14-3 As discussed in Enclosure 8, if the (( )) will not be applied over the intact cement mortar, discuss the impact of potential water ingress of the ground water into the CFRP composite system when the host metal substrate degrades during the life of the repair.
RESPONSE: ((
))
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RAI 14-4 As discussed in Enclosure 5, is the CFRP layup sequence and number of layers the same for 30-inch diameter and 36-inch diameter piping? Explain why or why not.
RESPONSE: ((
))
RAI-15-1 Enclosure 4 discusses the flexural strength is required for bending modes. What is the flexural strength and modulus data of the CFRP laminate at approximate test temperatures of ((
)) cured at (( )) with cure duration consistent with the CFRP composite system at the plant. What are the final test conditions (e.g., cure duration, cure temperature and test temperature) and test data? Also provide the supporting test data for the ((
)) for flexural loading.
RESPONSE: ((
))
DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION DOCUMENT CONTAINS NON-PROPRIETARY INFORMATION RAI-16-1 Based on the information provided in Enclosure 4, the NRC staff has determined that the testing of (( )) is to ensure that the properties used in the design are validated. Will ((
)) be tested at the maximum achievable water temperature (( )) for flexural strength and modulus to ensure that the input for flexural properties (e.g., flexural design strain) used in the design analysis is adequate? If not, provide justification for why such tests are not necessary.
In addition, discuss the existing or previous laboratory or field test data for flexural loading that is relevant for the proposed alternative.
RESPONSE: ((
))
RAI-17-1 Enclosure 5 describes how ((
)).
(a) What is the double lap shear bond strength between the CFRP and host pipe at approximate test temperatures of (( )) cured at approximately (( )) with cure duration consistent with the CFRP composite system at the plant?
(b) What is the double lap shear bond strength between the CFRP and CFRP at approximate test temperatures of (( )) cured at approximately ((
)) with cure duration consistent with the CFRP composite system at the plant?
(c) What is the double lap shear bond strength between the GFRP and CFRP at approximate test temperatures of (( )) cured at approximately ((
)) with cure duration consistent with the CFRP composite system at the plant?
As part of your response, describe the final test conditions (e.g., cure duration, cure temperature and test temperature) and test data. Alternatively, provide test data supporting that the licensees design input for shear bond strength is adequate in comparison with the test data.
RESPONSE: ((
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))
RAI-18-1 Enclosure 5, Attachment C, contains broken symbols, formulas, and calculations that are not readable. Provide a copy that has the correct symbols and formulas.
RESPONSE: A new readable pdf copy is included as Enclosure 2.