CNL-25-054, – Response to Request for Additional Information, Set 3
| ML25087A216 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/28/2025 |
| From: | Hulvey K Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| EPID L-2024-SLE-0000, CNL-25-054 | |
| Download: ML25087A216 (1) | |
Text
10 CFR 54 1101 Market Street, Chattanooga, Tennessee 37402 CNL-25-054 March 28, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Units 1, 2, and 3 Renewed Facility Operating License Nos. DPR-33, DPR-52, and DPR-68 NRC Docket Nos. 50-259, 50-260, and 50-296
Subject:
Browns Ferry Nuclear Plant, Units 1, 2, and 3 - Response to Request for Additional Information, Set #3 (EPID: L-2024-SLE-0000)
Reference:
- 1. TVA letter to NRC, CNL-24-001, "Browns Ferry Nuclear Plant, Units 1, 2, and 3 - Application for Subsequent Renewed Operating Licenses," dated January 19, 2024 (ML24019A010) 2.
TVA letter to NRC, CNL-24-077, Browns Ferry Nuclear Plant, Units 1, 2, and 3 - Application for Subsequent Renewed Operating Licenses, Response to Request for Additional Information, Set #1 (EPID L-2024-SLE-0000), dated October 9, 2024 (ML24283A091) 3.
TVA letter to NRC, CNL-25-014, Browns Ferry Nuclear Plant, Units 1, 2, and 3 - Response to Request for Additional Information, Set #2 (EPID:L-2024-SLE-0000), dated January 8, 2025 (ML25008A150) 4.
NRC electronic mail to TVA, Browns Ferry SLRA - Request for Additional Information - Set #3, dated February 28, 2025 (ML25061A004)
By Reference 1, the Tennessee Valley Authority (TVA) submitted a subsequent license renewal application (SLRA) for the Browns Ferry Nuclear Plant (BFN), Units 1, 2, and 3, Renewed Facility Operating Licenses in accordance with Title 10 of the Code of Federal Regulations (10 CFR), Part 54, Requirements for Renewal of Operating Licenses for Nuclear Power Plants. By Reference 2, TVA provided the response to the first set of Nuclear Regulatory Commission (NRC) requests for additional information (RAIs) regarding the BFN SLRA. By Reference 3, TVA provided the response the NRCs second set of RAIs.
U.S. Nuclear Regulatory Commission CNL-25-054 Page 2 March 28, 2025 By Reference 4, TVA received a third set of NRC RAIs. The TVA RAI response is provided in the enclosure to this letter.
There are no new regulatory commitments in this letter. Should you have any questions regarding this submittal, please contact Peter J. Donahue, Director, Subsequent License Renewal, at pjdonahue@tva.gov.
I declare under penalty of perjury that the foregoing is true and correct. Executed on this 28th day of March 2025.
Respectfully, Kimberly D. Hulvey General Manager, Nuclear Regulatory Affairs and Emergency Preparedness
Enclosure:
Response to Request For Additional Information by the Office Nuclear Reactor Regulation, Set #3 cc:
NRC Regional Administrator - Region II NRC Branch Chief - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant NRC Project Manager, License Renewal Projects Branch (Safety)
State Health Officer, Alabama Department of Public Health (w/o Enclosure)
Digitally signed by Edmondson, Carla Date: 2025.03.28 14:43:56
-04'00'
Enclosure CNL-25-054 E-1 of 7 Response to Request For Additional Information by the Office of Nuclear Reactor Regulation, Set #3 The NRC Request for Additional Information (RAI) is provided in italicized font. The Tennessee Valley Authority (TVA) response is provided in unitalicized font.
Regulatory Basis 10 CFR 54.21(a)(3) requires an applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function(s) will be maintained consistent with the current licensing basis for the subsequent period of extended operation. One of the findings that the staff must make to issue a renewed license (10 CFR 54.29(a)) is that actions have been identified and have been or will be taken with respect to managing the effects of aging during the subsequent period of extended operation on the functionality of structures and components that have been identified to require review under 10 CFR 54.21, such that there is reasonable assurance that the activities authorized by the renewed license will continue to be conducted in accordance with the current licensing basis.
In order to complete its review and enable making a finding under 10 CFR 54.29(a), the staff requires additional information in regard to the matters described below.
NCSG RAI B.2.1.27-1a
Background:
In its response to RAI B.2.1.27-1 (ML24283A091), the applicant explained that non-electrically continuous fire protection piping could be negatively affected by stray current corrosion if a cathodic protection system was installed for in-scope buried steel piping. Based on subsequent discussions between the applicant and staff during the audit, the applicant provided birds-eye view maps (via letter dated February 12, 2025 (ML25043A035)) showing in-scope buried steel piping in relation to the non-electrically continuous fire protection piping. The purpose of providing these maps was to further support the applicants conclusion that cathodically protecting in-scope buried steel piping could have negative impacts (i.e., stray current corrosion) on nearby fire protection system piping.
Issue:
Based on its review of the birds-eye view maps, the staff noted that most of the in-scope buried steel piping is in the vicinity of the fire protection piping, such that cathodically protecting this in-scope buried steel piping could have negative impacts on nearby fire protection system piping. However, the staff noted that some of the in-scope buried steel piping was not in the vicinity of fire protection piping (i.e., the four parallel residual heat removal service water (RHRSW) lines at the bottom of SLRA Figure B.2.1.27-2). Based on these lines not being in the vicinity of fire protection piping, it is unclear to the staff why providing cathodic protection for these lines would be considered impractical.
Request:
Provide additional justification with respect to why providing cathodic protection for the four parallel RHRSW lines at the bottom of SLRA Figure B.2.1.27-2 would be considered
Enclosure CNL-25-054 E-2 of 7 impractical (e.g., a discussion of other metallic piping or structures in the vicinity of these lines that are not depicted in the birds-eye view maps).
TVA Response Cathodic protection (CP) is impractical due to the following:
The RHRSW piping was not designed with CP as a consideration and did not include design features typical of piping protected by CP (e.g., electrical continuity) as TVA design practices rely on coatings and material selection for corrosion protection.
The subject inline RHRSW piping is electrically discontinuous, see Figure 1.
The subject RHRSW piping is also electrically discontinuous between the parallel piping runs, see Figure 1.
Modifications to the RHRSW piping encased some sections in concrete, which makes providing CP difficult for this area, as does the proximity to high pressure fire protection (HPFP) piping on shore.
The subject piping has a significant portion underwater thus making installation of CP impractical (see SLRA Figure B.2.1.27-2).
This piping crosses beneath the protected area fence, runs adjacent to the channel diesel fire pump, and runs to the river. Metallic objects such as these which are not electrically bonded to the proposed CP system would potentially be subject to stray current corrosion.
Enclosure CNL-25-054 E-3 of 7 Figure 1 - Mechanical Isometric RHR Service Water
Enclosure CNL-25-054 E-4 of 7 NCSG RAI B.2.1.27-2
Background:
SLRA Tables 3.3.2-6, Raw Service Water System - Summary of Aging Management Evaluation, and 3.3.2-7, High Pressure Fire Protection (Diesel Driven Pump) System -
Summary of Aging Management Evaluation, state that loss of material due to general, pitting, crevice, and microbiologically-influenced corrosion for copper alloy piping and piping components exposed to soil will be managed by the Buried and Underground Piping and Tanks program.
GALL-SLR Report Table XI.M41-1, Preventive Actions for Buried and Underground Piping and Tanks, recommends that external coatings are provided for buried copper alloy piping. In addition, GALL-SLR AMP XI.M41 states for fire mains installed in accordance with NFPA 24, Standard for the Installation of Private Fire Service Mains and Their Appurtenances, preventive actions beyond those in NFPA 24 need not be provided if the system undergoes a periodic flow test in accordance with NFPA 25, Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. The staff notes that NFPA 24 provides provisions for external coatings in Section 10.8.3.5, Corrosion Resistance.
By letter dated February 12, 2025, the applicant revised SLRA Section B.2.1.27, Buried and Underground Piping and Tanks, to provide a basis for why external coatings for buried copper alloy piping are not necessary. The basis states the following (in part):
[t]he copper alloy piping associated with the High Pressure Fire Protection [HPFP]
System is not coated, but installed under NFPA 24 and will continue to be managed under NFPA 25 requirements.
[o]ngoing monitoring is conducted via periodic NFPA 25 flow tests. BFN [Browns Ferry Nuclear Plant] does not have any OE [operating experience] of degraded copper HPFP piping in the reviewed time period.
[t]he soil samples [referencing a 2023 soil sample report] ranged from a pH of 6.93 to 8.17 and are considered neutral to basic.
ASM Handbook, Volume 13C - Corrosion: Environments and Industries, notes that copper alloy performs well in buried applications when pH is neutral to alkaline and the concentration of aggressive ions is low. However, it also notes that external coatings are recommended where high chloride concentrations, high sulfate concentrations, and low pH values are present. In addition, Table 9-4, Soil Corrosivity Index from BPWORKS, of Electric Power Research Institute (EPRI) Report 3002005294, Soil Sampling and Testing Methods to Evaluate the Corrosivity of the Environment for Buried Piping and Tanks at Nuclear Power Plants, adds at least three soil corrosivity points once pH is less than 5.5 for copper alloys.
During its review of soil corrosivity data provided on SLRA pages B-127 and B-128, the staff noted pH values as low as 5.3 at BFN. In addition, based on its review of Enhancement No. 2 (as amended by letter February 12, 2025), the staff noted that no direct inspections (e.g.,
visual examinations from the external surface, ultrasonic examinations from the internal surface) of buried copper alloy piping will be performed prior or during the subsequent period of extended operation (SPEO).
Enclosure CNL-25-054 E-5 of 7 Issue:
It is unclear to the staff why external coatings for buried copper alloy piping are not necessary based on the following reasons:
The February 12, 2025, letter states that the environment is neutral to basic (i.e., pH of 6.93 to 8.17) and therefore not aggressive to buried copper alloys. However, it does not address the acidic conditions (i.e., pH of 5.3) in the initial SLRA submittal. Therefore, it is unclear to the staff if in-scope buried copper alloy piping is exposed to an aggressive environment.
The February 12, 2025, letter states that there is no OE related to degraded copper alloy piping. However, it is unclear to the staff if direct inspections of this piping have been performed. It is the staffs understanding that direct inspections of buried copper alloy piping have not been performed and will not be performed in the future.
Request:
Provide additional information to justify why external coatings are not necessary for in-scope buried copper alloy piping (e.g., results of any direct inspections that have been performed, commitments to perform direct inspections in the future, more specificity on the alloy type(s) involved and why they are suitable for this environment, more details on why the low pH values noted by the staff would not be representative of the environment to which in-scope buried copper alloy piping would be exposed to during the SPEO, etc.).
References:
ASM Handbook, Volume 13C - Corrosion: Environments and Industries. ASM International. 2006.
EPRI Report 3002005294, Soil Sampling and Testing Methods to Evaluate the Corrosivity of the Environment for Buried Piping and Tanks at Nuclear Power Plants.
Palo Alto, California: Electric Power Research Institute. November 6, 2015.
NFPA 24, Standard for the Installation of Private Fire Service Mains and Their Appurtenances. Quincy, Massachusetts: National Fire Protection Association. 2010.
NFPA 25, Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. Quincy, Massachusetts: National Fire Protection Association. 2011.
TVA Response The low pH reading of 5.3, shown below in Figure 2 is from a sample taken in 2009 at approximately 3 feet of depth and does not reflect the in-situ full soil characteristics at the pipe depth.
Enclosure CNL-25-054 E-6 of 7 Figure 2, BFN SLRA Appendix B, B-127 2009 Summary of Soil Sample Results Sample Location ID Resistivity (as received ohm-cm)
Native Potential
(-mV) pH CI (ppm)
Na (ppm)
Ca (ppm)
K (ppm)
SO4 (ppm)
Gravel Sand Silt Clay Water Corrosion Rate (mpy)
Corrosion Rate at Boundary Condition (mpy)
BROWNS FERRY 1 3,540 502 6.6 58 20 137 11 83 3
30 10 57 26.8 7.5 BROWNS FERRY 2 23,200 466 7.8 4
4 94 6
29 62 31 3
4 6.6 67.1 16.7 BROWNS FERRY 3 8,400 414 7.4 2
6 70 9
88 4
25 20 51 16.4 16.5 BROWNS FERRY 4 11,720 566 7.6 6
7 128 9
57 4
17 21 58 16.3 6.5 BROWNS FERRY 5 25,200 461 7.6 5
6 124 10 68 2
46 20 32 13.4 6.8 BROWNS FERRY 6 16,400 395 5.5 3
4 44 8
84 4
40 12 44 25.5 17.3 BROWNS FERRY 7 22,800 473 5.3 43 5
32 10 0
1 43 9
47 22.8 5.5 BROWNS FERRY 8 7,840 521 7.2 57 11 119 15 79 3
26 22 49 17.4 6.8 BROWNS FERRY 9 27,600 498 7.2 5
15 220 10 190 13 37 29 21 10.6 7.2 BROWNS FERRY 10 9,200 495 7.4 1
7 40 6
66 0
27 23 50 15.4 8.5 BROWNS FERRY 11 16,000 541 7.6 4
4 158 8
111 12 52 14 22 15.8 6.0 BROWNS FERRY 12 6,640 835 7.4 3
9 43 5
40 0
9 33 58 21.0 4.5 BROWNS FERRY 13 5,120 835 7.3 2
6 43 10 47 0
27 21 52 20.5 2.7 The American Society for Metals (ASM) Handbook, Volume 13C - Corrosion: Environments and Industries. ASM International, 2006, states (underlined for emphasis):
Copper is subject to changes in corrosion resistance with changes in temperature.
Electrolytic corrosion can occur on hot and cold water lines buried in a common trench.
To prevent corrosion, the two lines should be electrically isolated from each other.
Electrical isolation can be accomplished with the use of insulating-type couplings.
Copper or brass piping should not be used without a tape wrap coating and cathodic protection in environments where high chloride concentrations, high sulfate concentrations, and low pH values are present. Copper or brass should be electrically isolated from other structures if used in an aggressive environment. Connections of copper service lines to plastic mains should be accomplished using brass tapping saddles.
This recommendation for tape-wrap coating only applies the mitigating actions of tape wrap and cathodic protection when all three conditions are met, that is, high chloride concentrations, high sulfate concentrations, and low pH occur in a discreet sample. As shown in Figure 2, Sample Location ID, BROWNS FERRY 7, the in-situ soil has a pH of 5.3, a chlorine (Cl) concentration of 43 ppm, and a sulfate (SO4) concentration of 0 ppm. Thus, the soil does not meet all three characteristics as per the recommendation in the ASM Handbook referenced above.
The 2023 Summary of Soil Sample Results, shown in Figure 3 below, were taken at pipe depth.
The soil sample results demonstrate that the in-situ soil is indeed neutral to basic and therefore is not aggressive to copper alloys.
Enclosure CNL-25-054 E-7 of 7 Figure 3, BFN SLRA Appendix B, B-128 2023 Summary of Soil Sample Results Sample ID Resistivity (received ohm-cm)
Native Potential
(-mv) pH Cl (ppm)
NA (ppm)
Ca (ppm)
K (ppm)
Mg (ppm)
SO4 (ppm)
Gravel Sand Silt Clay Water LPR Corrosion Rate (mpy) 1-2 4700 327 8.17 2.74 3.01 87.7 46.4 2.47 22.1 34 42.7 6.39 16.9 17.6 15 1-3 4000 353 6.93 1.31 3.73 136 2.01 8.64 66.6 1.4 37.8 18.4 42.4 17.1 OVR*
1-4 2600 514 8.06 3.15 5.16 116 4.84 4
26.3 18.3 38.4 7.42 35.8 24.1 17.5 1-5 3700 625 7.19 2.46 5.16 113 5.53 10.6 18.2 2.8 33 10.7 53.5 26.1 13.1 1-6 6800 634 7.88 1.23 0.854 91.7 3.13 8.13 13.3 3.5 59.3 10.6 26.6 19.2 0.34 1-8 3800 245 7.86 2.25 13.3 98.8 2.19 4.19 38.5 2.9 48 18.2 30.9 15.1 OVR*
ALT 1 8300 367 7.01 1.12 2.2 40 12.1 2.33 72 0.2 46.9 17.6 35.3 14.8 25.5 ALT 4 4300 354 7.8 2.21 2.6 96.3 1.6 5.32 32.7 1.5 35.5 16.2 46.8 22.4 17.4
- Instrument not able to calculate Electric Power Research Institute (EPRI) report 300200529, Soil Sampling and Testing Methods to Evaluate the Corrosivity of the Environment for Buried Piping and Tanks at Nuclear Power Plants, provides a soil corrosivity index used to estimate corrosion rates. The EPRI Soil Index Criteria for "non-aggressive" soil has been met for the 2023 and 2009 soil samples for steel. The soil results have been compared to the EPRI Soil Index Criteria for copper alloys.
Even though EPRI does not list parameters for BFN copper piping, which is 99.99% copper (specifically ASTM B75 or B88), the results have been compared to the EPRI Soil Index Criteria for copper alloys and show the soils are non-aggressive.
Consistent with the guidance provided in the GALL, this piping is installed in accordance with NFPA 24 and is monitored in accordance with NFPA 25 (refer to SLRA B.2.1.16). According to NUREG-2191, Vol 2, Rev 1, Chapter XI-XI.M41 Mechanical,"...for fire mains installed in accordance with National Fire Protection Association (NFPA) 24, preventive actions beyond those in NFPA 24 need not be provided if (1) the system undergoes either a periodic flow test in accordance with NFPA 25... As described in SLRA B.2.1.27, TVA will monitor the high pressure fire protection system, and the raw service water copper piping fed from the high pressure fire protection system headers, by performing periodic flow tests in accordance with NFPA 25 to identify fire main leakage. Direct inspections are not deemed necessary as plant operating experience has shown an increase in leakage between flow tests would be self-revealing.