ML23095A059
| ML23095A059 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/22/2023 |
| From: | Pearman P Tennessee Valley Authority |
| To: | Janjic V Office of Nuclear Reactor Regulation, State of TN, Dept of Environment & Conservation |
| References | |
| TN002645 | |
| Download: ML23095A059 (1) | |
Text
l TENNESSEE VALLEY AUTHORITY 1101 Market Street, BR 2C, Chattanooga, Tennessee 37402 Sent Via Electronic Transmittal March 22, 2023 Mr. Vojin Janjic (Water.Permits@tn.gov)
Division of Water Resources Tennessee Department of Environment and Conservation (TDEC)
William R. Snodgrass Tennessee Tower 312 Rosa L. Parks Avenue, 11th Floor Nashville, Tennessee 37243
Dear Mr. Janjic:
TENNESSEE VALLEY AUTHORITY (TVA)- SEQUOYAH NUCLEAR PLANT (SQN)-
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES) PERMIT NO.
TN0026450- REQUEST FOR PERMIT MODIFICATION In order to comply with the Clean Water Act §316(b) requirements and permit temperature monitoring requirements, TVA is requesting permit modifications as explained below. Enclosed is a Deltares study report and an updated NPDES application that reflects the changes for the proposed outfall. This includes:
- 1. Updated Site Map
- 2. Updated Flow Schematic
- 3. New NPDES Form 2E Also enclosed is a Station 14 relocation study that assessed the placement of Station 14 and recommends relocation of the station.
Proposed Outfall 119 - Fish Return Line Discharge On January 27, 2021, TVA updated TDEC regarding the chosen method of compliance with impingement mortality standards of the existing facility §316(b) cooling water intake rule. In order to comply with the standards, TVA plans to replace the existing water screens with modified traveling screens and construct an approximately 1,750-foot-long fish return line to convey fish backwashed from the modified travelling intake screens to a location downstream of the intake.
TVA collaborated with Deltares, a consultant for applied research in the field of water, to model the fish return in various river flow scenarios to help determine if the existing upstream location was viable to comply with the rule. After modelling four locations, the consultant found that two of the locations upstream of the intake channel were expected to result in re-impingement rates of 25%-75% if the returned fish remained lethargic. No significant re-impingement of lethargic fish is expected when fish are returned downstream of the intake at locations three and four.
Mr. Vojin Janjic:
Page2 March 22, 2023 TVA chose location three, directly downstream of the SQN intake as the terminus for the fish return line. As this is a new location for the discharge of backwash water from the traveling water screens, TVA is requesting a permit modification to add this location as a new outfall (Outfall 119) to the existing permit.
The existing water screens discharge both fish and debris from the intake to the Tennessee River via Outfall 116. This line will remain and discharge only debris backwash once the construction of the fish return line is completed and the traveling water screens replaced. TVA requests that no reporting requirements are implemented, mimicking the current requirements for Outfall 116 and 117. On Form 2E, TVA requests a waiver for the effluent characteristics due to the nature of the proposed discharge.
Relocation of Temperature Monitoring Station 14 As part of the thermal compliance requirements for Outfall 101, SQN has three water temperature monitoring stations that measure water temperature at multiple depths at a 15-minute interval. Before 2006, the ambient water temperature station was Station 13, located at the intake skimmer wall. Data analysis of river temperatures demonstrated that Station 13 was not truly representative of the ambient river conditions when the flow is low, so TVA added Station 14, located approximately 7 miles upstream of the plant, as the new upstream temperature monitoring station.
Since Station 14 was installed, TVA has determined that the location has caused safety issues.
In order to be kept outside of the navigation channel, the station is close to the shoreline which limits pathways for boats to avoid collision with the station when traveling at high speeds.
However, it has been hit numerous times by boats, most recently in January 2023, which caused damage to the anchoring system and the box containing instrumentation, though no instrumentation inside the box was damaged. The Coast Guard has recently informed TVA that this station is "too close to the buoy line" (i.e. the navigation channel boundary) and must be moved.
In addition to the safety issues, TVA postulates the station's location in close proximity to the shore also causes temperature issues. The rapid heating and cooling of the nearby land mass causes its temperature readings to be influenced in a measurable way. Changes to the land temperature during summer heat events, strong thunderstorms (which induce mixing), and strong cold fronts that come through the region all alter the land temperature more quickly than the water temperature influencing the temperature readings at the station. Station 14 has significant stratification during summer heat that is easily mixed away by heavy wind or rain events in summer thunderstorms. These rapid temperature changes increase the Delta-T between its location and the plant effluent, causing excessive cooling tower use in the spring and fall to mitigate conditions created by weather and not the plant. If Station 14 was located farther away from the shore, these weather events would not impact its temperature measurements.
Mr. Vojin Janjic Page 3 March 22, 2023 Starting in 2019, TVA conducted a study to assess the placement of Station 14 and evaluate two alternative sites that could be more representative of the river conditions. Test Site 1 is located at Tennessee River Mile (TRM) 488. 7 (approximately five miles upstream of the diffusers) and Test Site 2 is located at TRM 487.9 (approximately four miles upstream of the diffusers). Analysis of the data, along with the water temperature data from Watts Bar Dam, 45.4 miles upstream of SQN, demonstrated that in the fall after a strong cold front, water temperatures at Station 14 become cooler than the release temperatures from Watts Bar Dam.
This is atypical because water temperatures typically increase as the river flows south. This reinforces the theory that the temperature station is too close to shore and easily influenced by brief weather events. This phenomenon did not occur at test site 1, the site farthest from the shoreline. It occurred at a lesser degree at Test Site 2, which is closer to the shoreline than Test Site 1.
Given the data collected over a wide range of flows and months, TVA is proposing to relocate Station 14 to the Test Site 1, approximately five miles from the plant's diffusers and requests that the permit is modified to reflect the proposed location. This location would collect water temperature data that is more stable and representative of the water flowing in the river, rather than water influenced by localized phenomena. It will also provide ample space for boats to navigate around the monitoring station making it less of a hazard to boat traffic and satisfy the Coast Guard's concern of the close proximity to the navigation channel boundary.
TV A appreciates your consideration of the requested changes. If you have questions or need additional information, please contact Callan Pierson by e-mail at cpierson@tva.gov.
Sincerely, Paul Pearman Senior Manager Water Permits, Compliance, and Monitoring Enclosures cc:
Ms. Jennifer Innes (Jennifer.lnnes@tn.gov)
Ms. Sarah Terpstra (Sarah.Terpstra@tn.gov)
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
EPA Identification Number TN5640020504 NPDES Permit Number TN0026450 Facility Name Sequoyah Nuclear Plant (SQN)
Form Approved 03/05/19 0MB No. 2040-0004 FORM 2E NPDES
&EPA U.S. Environmental Protection Agency Application for NPDES Permit to Discharge Wastewater MANUFACTURING, COMMERCIAL, MINING, AND SILVICULTURAL FACILITIES WHICH DISCHARGE ONLY NONPROCESS WASTEWATER SECTION 1. OUTFALL LOCATION (40 CFR 122.21(h)(1))
1.1 Provide information on each of the facilit 's outfalls in the table below.
C Outfall Receiving Water Name Latitude Longitude
.2 Number
'1ii u
35° 13 1
44" as*
os' oi'
.9 119 Tennessee River N
w
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I I
0 I
0 I
SECTION 2. DISCHARGE DATE (40 CFR 122.211(h)(2))
a, 2.1 Are you a new or existing discharger? (Check only one response.)
a, j j 0
New discharger D
Existing discharger -+ SKIP to Section 3.
~
0 2------------------------------------------i 0
Specify your anticipated discharge date: 0310112024 SECTION 3. WASTE TYPES (40 CFR 122.21 (h)(3))
3.1 3.2 3.3 What types of wastes are currently being discharged if you are an existing discharger or will be discharged if you are a new discharger? (Check all that apply.)
D Sanitary wastes Restaurant or cafeteria waste D
Non-contact cooling water Does the facility use cooling water additives?
0 Yes 0
Other nonprocess wastewater (describe/explain directly below)
Backwash water from the intake water screens D
No -+ SKIP to Section 4.
List the coolin water additives used and describe their com sition.
Cooling Water Additives list The facility uses cooling water additives which are not Composition of Additives tt available to ou 4.1 Have you completed monitoring for all parameters in the table below at each of your outfalls and attached the results to this application package?
D Yes 0
No; a waiver has been requested from my NPDES permitting authority attach waiver re uest and additional information -+ SKIP to Section 5.
4.2 Provide data as re uested in the table below.1 See instructions for s ecifics.
Number of Maximum Daily Parameter orPollutant Analy&e1 Dhscharge (if actual data s
units reported}
Mass Cone.
Biochemical oxygen demand (BODs)
Total suspended solids (TSS)
Oil and grease Ammonia (as N)
Discharge flow pH (report as range)
Temperature (winter)
Temperature (summer)
Average Daily Discharge s
- units Mass Cone.
Source (use codes per instructions) 1 Sampling shall be conducted according to sufficiently sensitive test procedures (i.e., methods) approved under 40 CFR 136 for the analysis of pollutants or pollutant parameters or required under 40 CFR chapter I, subchapter Nor 0. See instructions and 40 CFR 122.21(e)(3).
EPA Form 3510-2E (revised 3-19)
Page 1
EPA Identification Number NPDES Perm~ Number Facility Name Form Approved 03/05/19 TN5640020504 TN0026450 Sequoyah Nuclear Plant (SQN) 0MB No. 2040-0004 4.3 Is fecal coliform believed present, or is sanitary waste discharged (or will it be discharged)?
Yes 0
No -+ SKIP to Item 4.5.
4.4 Provide data as reQuested in the table below.1 (See instructions for soecifics.)
Number of Maximum Daily Average Daily Source Parameter or Pollutant Analyses Discharge Discharge (Use codes (If actual data (soeci1 unilsl lsoecit, units\\
per reported)
Mus Cone.
Mass Cone.
Instructions.)
Fecal coliform
'i E.coli Enterococci C
z C
4.5 Is chlorine used (or will it be used)?
0
(.)
rJ Yes 0
No -+ SKIP to Item 4.7.
i 4.6 Provide data as reQuested in the table below.1 (See instructions for specifics.)
- c i Number of Maximum Dally Average Daily Source Parameter or Pollutant Analyses Discharge Discharge (use codes ca (soecil units)
(soeclf unilsl
.c (If actual data per 0
reported)
Mass Cone.
Mass Cone.
instructions)
C CD Total Residual Chlorine
!j 4.7 Is non-contact cooling water discharged (or will it be discharged)?
Yes 0
No -+ SKIP to Section 5.
4.8 Provide data as reQuested in the table below.1 (See instructions for specifics.)
Number of Maximum Daily Average Daily Source Parameter or Pollutant Analyses Discharge Discharge (use codes (If actual data (soeci1 units)
(soeci~ units}
per reported)
Mass Cone.
Mass Cone.
instructions)
Chemical oxygen demand (COD)
SECTION 5. FLOW (40 CFR 122.21 (h)(S))
5.1 Except for stormwater water runoff, leaks, or spills, are any of the discharges you described in Sections 1 and 3 of this application intermittent or seasonal?
D Yes -+ Complete this section.
0 No -+ SKIP to Section 6.
5.2 Briefly describe the frequency and duration of flow.
SECTION 6. TREATMENT SYSTEM (40 CFR 122.21 (h)(6))
6.1 Briefly describe any treatment system(s) used (or to be used).
No treatment will be used.
1 Sampling shall be conducted according to suffictentiy sensitive test procedures (i.e., methods) approved under 40 CFR 136 for the analysis of pollutants or pollutant parameters or required under 40 CFR chapter I, subchapter Nor 0. See instructions and 40 CFR 122.21(e)(3).
EPA Form 3510-2E (revised 3-19)
Page2
EPA Identification Number NPDES Permit Number Facility Name Sequoyah Nuclear Plant (SQN)
Form Approved 03/05/19 0MB No. 2040-0004 Use the space below to expand upon any of the above items. Use this space to provide any information you believe the reviewer should consider in establishing permit limitations. Attach additional sheets as needed.
TVA is requesting no permit limitations; this would mimic the permit requirements for Outfalls 116 and 117 which discharge similar water streams. The discharge will consist of backwash river water that will not go through any plant processes and is unlikely to contain pollutants from the plant.
SECTION 8. CHECKLIST AND CERTIFICATION STATEMENT (40 CFR 122.22(a) and (d))
8.1 In Column 1 below, mark the sections of Form 2E that you have completed and are submitting with your application.
For each section, specify in Column 2 any attachments that you are enclosing to alert the permitting authority. Note that not all applicants are reauired to provide attachments.
Column 1 Column2 0 Section 1: Outfall Location wt attachments (e.g., responses for additional outfalls) 0 Section 2: Discharge Date wt attachments 0 Section 3: Waste Types wt attachments 0 Section 4: Effluent Characteristics wt attachments E
0 i
Section 5: Flow wt attachments 0
C Section 6: Treatment System wt attachments 0 1 0 Section 7: Other Information wt attachments
~
~
Cl)
(,.)
0 Section 8: Checklist and Certification Statement wt attachments "O
C C'G 8.2 Certification Statement u j I certify under penalty of law that this document and all attachments were prepared under my direction or supeNision in
..c accordance with a system designed to assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry of the person or persons who manage the system, or those persons directly responsible for gathering the information, the information submitted is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that there are significant penalties for submitting false information, including the oossibilitv of fine and imorisonment for knowina violations.
Name (print or type first and last name)
Official title Thomas B. Marshall Vice President, SQN Signature Date signed Digitally signed by Marshall, 03t14t2023 Marshall, Thomas EJ: !~omas B.
Oate: 2023.03.1415:08:16-04'00' EPA Form 3510-2E (revised 3-19)
Page3
a-------- 0.75mi TVA Sequoyah Nuclear Plant NPDES Permit No. TN0026450 Hamilton County
Condenser Cooling Water(CCW)
Intake 1447.865 Condenser Circulating System 38.000 Raw Cooling Water System 0.875 Raw Service Water System 0.412 Water Treatment System Make-up Water (DWST)
Outfall 118 Intake Forebay (INACTIVE) 1453.631 Outfall 110 1409.865 Cold Water Return Channel Dredge Pond 1 ennessee K1ver
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Cond. Circulating Water !
! Raw Cooling Water i Diesel fuel recover trench l i
High Press Fire water l
i Potable water i
1447.014..
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Closed Mode Cooling Towers Units 1 &2 I Helper Mode 42.320 ERCWlntake 40.306 Cooling Water i Steam Generator ******.... ;
0.030 Slowdown 1-* ---------------==:......i Cooling Tower Slowdown Basin (CTB) i ERCW System 0.050
! Condensate Oemin.
,........ System (AH).***..**...*** )
1,,,,,. :.1~~;?;:ou: :::~*-.. 1 Laundry, Shower, and Chemical Drains CCS Wastewater Condensate Oemin.
l System Wastewater Miscellaneous 0.463 Equipment Cooling TBS Raw Water Leaks & Draindowns YDP Liquid Radwaste Treatment System (LRW)
Neutral Waste Sump Unlined Metal Cleaning Waste Pond Low Volume Waste Treatment Pond (LVP)
Lined Metal Cleaning Waste Pond 0.014 Outfall 117 ERCW Screen &
Strainer Backwash Raw Water Treatment 1 CCW Discharge Channe; 1
! CCS Wastewaters l
i Primary System Waste
[
!........................................ }
Diffuser Pond (DP)
Makeup Water Process wastewaters r------*
Filter Backwash and WTP Wastewaters Primary System Component Cooling System Steam Generator Fill 0.030 TBS DP 0.0~
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0.100 Condensate Dem in Regeneration Waste I
I Turbine Building Sump (TBS) 1.~7 Miscellaneous Low Volume Wastewaters Miscellaneous Equipment Cooling Water Essential Raw Cooling Water Maintenance Oraindown Component Cooling System Wastewater Process waters and wastewaters Steam Generator Slowdown Condensate Oemin Regen Waste Secondary System leaks and Draindowns Ice Condenser waste Laboratory wastewaters Turbine Buikling floor and Equipment drains Alum Sludge Pond Yard Drainage Pond (YDP)
Miscellaneous Low Volume Wastewater & Yard Drainage Service Building Sump Office Bldg Floor & Equip Drains Diesel Gen Bldg Sump & O&G Interceptor (o/w separator)
Backup Security Diesel O&G Interceptor (o/w separator)
Solar Bldg Sump Air Cooling Water Switchyard Bus Cooling Water Miscellaneous line leaks, flushes and draindowns ERCW system maint. draindowns Electrical Sumps East Valve Vault Room drains Pressure washing & vehicle rinses Switchyard stormwater runoff Landfill Runoff
§ CCW Discharge Channel
§ Cooling Tower Basin n
Negligible flow Alternate path Chemical Additive Tennessee Valley Authority Sequoyah Nuclear Plant Wastewater Flow Schematic NPDES Permit No. TN0026450 March 2023 8 Liquid Radwaste Treatment System
§ Turbine Building Sump 8 Low Volume Waste Treatment Pond 8 Yard Discharge Pond 3 Diffuser Pond Net Stormwater Flow (runoff, precipitation, less evaporation)
Pump Rated Capacity All flows shown in million gallons per day (MGD)
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Table of contents TVA requested Deltares to evaluate alternative outfall locations of the SQN F to the risk of re-impingement of lethargic fish. For this purpose simulations ar hydrodynamic model of the Chickamauga Reservoir and the Delft3D-PART p summarises this initial assessment and includes the following content:
Introduction to the initial assessment of the SQN Fish Return Channel OL Objective of the present assessment Modelling approach Modelling scenarios and assumptions:
Alternative locations for the fish return channel outfall Ambient hydrodynamic conditions Modelling assumptions Modelling results Discussion on results and limitations of the modelling Conclusions and recommendations Deltores
Introduction Sequoyah NPP (SQN) is planning to replace their travelling water screens at the cooling water intake with a more fish friendly design. This upgrade includes a fish return channel for which an existing structure might be refurbished. The outlet of this considered return channel discharges approximately 150m from the mouth of a small embayment which is located about 500m upstream of the intake structures (skimmer wall) in the reservoir (red circle), but this return channel could be relocated if this would be more effective. During the decision-making process for this investment, the question came up whether returned fish might be lethargic for a while and in such state move only with the ambient currents towards the intake again (i.e. re-impingement).
TVA asked Deltares whether an initial quick evaluation could be performed with the existing numerical flow model and particle tracking methods to see if re-impingement of fish is a potential risk and should be considered in more detail. In this assessment, TVA asked Deltares to assess 4 potential fish return channel outfall locations for the potential re-impingement of fish in the intake.
Deltores
Objective The objective of this first assessment is to assist TVA and SQN in their selection of the most appropriate and effective location for the proposed fish return channel outfall by providing indicative model computations of the dispersion of particles (representing lethargic fish) from different discharge locations.
Delta res
Modelling approach To simulate the potential re-impingement of lethargic fish to the SQN intake for different outfall locations, the existing three-dimensional Delft3D-FLOW model of the Chickamauga Reservoir is used. This model was validated in detail for water levels, currents and temperature and is presently used to forecast Chickamauga Reservoir temperatures at SQN.
For the purpose of this assessment the Delft3D-FLOW model is refined in the area of the proposed fish return channel locations to a grid cell resolution of about 6m.
The Delft3D-FLOW model ( coupled to COSUMO to simulate the SQN outfall) is used to compute the hydrodynamic conditions for different ambient scenarios.
D-PART, the offline particle tracking model of the Delft3D suite of models, is used to simulate the dispersion of lethargic fish.
At each fish return channel outfall location, large number of particles (i.e. 10.000) are released simultaneously at the start of each simulation which subsequently disperse by the currents in the Chickamauga Reservoir.
Model results (i.e. particle tracks) are analyzed for key indicators like the re-impingement rate (i.e. percentage of the particles that reaches the intake) and travel time of the particles.
Deltores
Modelling scenarios Alternative locations for the fish return channel outfall In consultation and agreement with TVA, the following alternative fish return channel outfall locations are assessed:
Location 1: Proposed location by TVA Location 2: Closer to the main channel Location 3: Directly downstream of the SQN intake Location 4: Further downstream of the SQN intake Fish return channel outfall Location 1 is proposed by TVA. Location 2 is an alternative location closer to the main channel which aims to let lethargic fish by-pass the intake. Location 3 is directly downstream of the intake to minimise the risk of re-impingement.
Location 4 is further downstream compared to Location 3 to avoid re-impingement of lethargic fish also under adverse current conditions.
Deltores
Modelling scenarios Ambient hydrodynamic conditions To assess the dispersion of lethargic fish, 3 different periods around the SQN field survey campaign May/June/July 2017 are simulated. The field survey included water level, current and temperature measurements which were used to validate the SQN Delft3D-FLOW model. The 3 simulation periods are selected to be representative for normal and adverse ambient conditions. Since the hydrodynamics near SQN are largely determined by the dam discharges of the Wattsbar Dam (upstream) and Chickamauga Dam (downstream), the 3 selected simulation periods are selected based on differences in these discharges.
The following periods are simulated:
Start period 1: 12 June 2017 12:00. A period with relatively low dam discharges (i.e. a relatively large percentage of the reservoir water is drawn in by SQN).
Start period 2: 20 July 2017 12:00. A period with normal dam discharges. This period is considered representative for average conditions.
Start period 3: 2 June 2017 12:00. A period with relatively high dam discharges.
The total duration of each simulation is 4 to 10 days depending on the ambient flow scenarios to ensure sufficient time to determine if re-impingement of fish in the intake occurs.
The hydrodynamic conditions (i.e. currents) at the start of each period are presented in the next slides.
Deltores
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Modelling scenarios - Low discharg 1 The simulated near-surface and near-bottom currents by Delft3D-FLOW during low dam discharges (12 June 2017 12:00)
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Modelling scenarios - Normal disch The simulated near-surface and near-bottom currents by Delft3D-FLOW during normal dam discharges (20 July 2017 12:00)
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Modelling scenarios - High discharg The simulated near-surface and near-bottom currents by Delft3D-FLOW during high dam discharges (2 June 2017 12:00)
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Modelling scenarios Model assumptions For the hydrodynamic and particle modelling the following modelling assumptions are made:
The intake flow of SON is constant under normal operation of SON with a flowrate of about 67 m3/s. Lower SON intake flow rates are expected to reduce the re-impingement of lethargic fish from the fish return channel to the intake.
For the fish return channel outfall Location 1, 3 and 4 the particles are released near the water surface. For outfall Location 2 particles are released near the bottom. At all locations 10.000 particles are released simultaneously in a horizontal radius of 1 OOm at the start of each simulation to ensure sufficient variation in possible particle tracks.
The lethargic fish are assumed to be neutrally buoyant.
Sensitivity tests are performed with the particle tracking model for different time steps, horizontal and vertical diffusion parameters, number of particles and total simulation time.
Deltores
Modelling scenarios To summarize, the simulated scenarios include 3 modelling periods,
4 alternative fish return channel locations. In total 12 simulations are performed simulations is presented below:
Dam discharges Fish Return Channel location Low Location 1 - surface Low Location 2 - bed Low Location 3 - surface 4
Low t ocation 4 - surface 5
Normal Location 1 - surface 6
Normal Location 2 - bed 7
Normal Location 3 - surface 8
Normal Locati:on 4 - surface 9
High Location 1 - surface 10 High Locat,ion 2 - bed 11 High Location 3-surface 12 High Location 4 - surface Delta res
Results There are two ways to minimize the risk of re-impingement of returned lethargic fish into the SQN intake:
Minimize the number of returned lethargic fish that will move with the current back to the intake, i.e. avoid re-impingement.
Provide the returned lethargic fish sufficient time to recover and become mobile before they could reach the intake again.
To evaluate the modelling outcomes for each of the location alternatives, the following indicators are therefore used:
Re-impingement rate (i.e. percentage of particles that end up in the SQN intake channel).
Travel time (i.e. minimum and average time the particles needed to reach the intake.
The following slides summarize the modelling results for the above indicators. Map plots of the particle tracks are presented for each scenario with different ambient flow conditions and fish return channel outfall location. Note that for visualization purposes only a select number of particle tracks is plotted. In addition, a table is provided with the percentage of particles that end up in the intake and the minimum and average travel time of these particles for each scenario. The intake is defined here as the area behind the skimmer wall. It is estimated that the travel time from the skimmer wall to the actual intake is less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, but since it is unclear if fish could exit the intake channel via the skimmer wall again this definition of the intake is used for the re-impingement rate and travel time.
Deltores
Results Simulated particle tracks for the different fish return channel locations during low dam discharges Deltores
Results Simulated particle tracks for the different fish return channel locations during normal dam discharges Delta res
Results Simulated particle tracks for the different fish return channel locations during high dam discharges Delta res
Results Below table summarizes the outcome of the 12 model simulations fo impingement rate and travel time. The re-impingement rates are pro*
indicative nature of this assessment.
2 3
4 5
6 7
8 9
10 11 12 Deltores Dam discharges Low Low Low Low Normal Normal Normal Normal High High High Fish Return Channel location Location 1 Location 2 Location 3 Location 4 Location 1 Lo tion 2 Locatio Location 4 Loca ion 1 Location 2 Location 3 Location 4 Re-impingement rate
[%]
50-75 50-75
-10 0
25-50
'5-50 0-10 0
25-50 25-50 0-1'0 0
Minimum travel particles to the in 2
1 1
1 1
1 1
t 1
Results Main findings Based on the modelling results of the 12 simulations presented in previous slides, the following observations are made:
Fish Return Channel Outfall Locations 1 and 2 (i.e. upstream of the SQN intake) are expected to result in re-impingement rates of 25%-75% if returned fish remain lethargic.
Fish Return Channel Outfall Location 1 (in comparison with Location 2) provides the returned lethargic fish more time to recover and to become mobile again before they could reach the intake again. For outfall Location 1 the average expected travel time is in the order of 6-12 hours depending on the ambient conditions.
The potential re-impingement rate of lethargic fish decreases with increasing dam discharges for all return channel locations.
If lethargic fish are returned at Location 3 the lethargic fish generally will move with the currents downstream of the intake. Only during adverse low dam discharges part of the returned lethargic fish may reach the SQN intake again (i.e. 0 -10%).
When lethargic fish are returned at Location 4, under all ambient conditions no significant re-impingement of lethargic fish is expected.
Deltares
Discussion on results and limitation~
This initial assessment provides a first indication of the effectiveness of different locations of the propo!
impingement of the fish. This assessment is supported by indicative model results from a limited numb of the model and modelling approach are discussed and their potential impact on the results presentec Limited number of simulations/ambient scenarios. This assessment only simulated the disper conditions. These conditions are chosen such that it provides a representative picture how letharg modelling results show that the re-impingement rate decreases with increased dam discharges. H scenario assessed here are expected to further decrease the re-impingement rate. Lower dam di~
very rare. It is therefore concluded that if different or more ambient scenarios would be assessed 1 change.
Buoyancy of the lethargic fish. In this assessment the lethargic fish are assumed to be neutral!~
If the lethargic fish are positively buoyant, the lethargic fish are expected to float with the curr impingement.
If the lethargic fish are expected to be negatively buoyant, the fish will move with the (genera bottom. This would increase the travel time and thus the time to recover. If lethargic fish mov, likely to be drawn into the intake channel. Although re-impingement rates may change when the effectiveness of different outfall locations are still expected to hold.
Model settings. Several model parameters (that need to be based on expert judgement in the ab tests. In particular the re-impingement rate of lethargic fish from outfall locations upstream of the i particles in the numerical model. However, for all (reasonable) values for the vertical diffusion int~
Location 1 and 2. This indicates that the risk of re-impingement of fish remains substantial for the~
parameters for vertical diffusion. The provided indicative travel times for the particles/fish are less diffusion. Other model parameters showed no significant impact on the modelling results.
Assumption of fish being lethargic. For the present assessment of selecting preferred locatiorn fish being lethargic is appropriate. No information is available how many and how long returned f non-lethargic fish responds to the flow (gradients) near the intake and skimmer wall (i.e. are they recommended to seek advice from a fish biologist to discuss whether it could be beneficial to hav wall and avoid impingement of fish, in addition to the return system.
Deltores
Conclusions and recommendation The objective of this first assessment is to assist TVA and SQN in their selection of the most appropriate and effective location for the proposed fish return channel outfall by providing indicative model computations of the dispersion of particles (representing lethargic fish) from different discharge locations. Based on the results of this assessment the following conclusions and recommendation are made:
Alternative fish return channel outfall locations upstream of the intake (Location 1 and 2) are
- expected to have re-impingement rates behiveen 25% and 75% depending on the ambient conditions.
Since re-impingement rates are similar but the travel times from Location 2 to the intake are less compared to Location 1 (and the fish return channel/pipeline should be extended to the edge of the main channel, which is more costly), Location 1 could be preferred over Location
- 2.
It is recommended to also consider the embayment near Location 1 (area in the green circle) as a possible outfall location. It is expected that this location may provide the lethargic fish more time to recover compared to Location 1(i.e. order of 1-2 days compared to 6-12 hours.)
No significant re-impingement of lethargic fish is expected when fish are returned downstream of the intake at Location 3 and 4. Only under adverse low dam discharges 0-10% of the returned fish may re-impinge at the SQN intake when returned at Location 3. Returning fish at Location 4 is unlikely to result in any re-impingement. Locating the fish return channel outfall further downstream of Location 4 is therefore not needed from a risk of re-impingement point of view.
Deltores
TENNESSEE VALLEY AUTHORITY River Operations SEQUOYAH NUCLEAR PLANT STATION 14 RELOCATION STUDY WR2023-7-45-920-01 Prepared by Colleen R Montgomery Jessica Brazille Knoxville, Tennessee January 2023
[Ifil
EXECUTIVE
SUMMARY
The National Pollutant Discharge Elimination System (NPDES) Permit No. TN0026450 for Sequoyah Nuclear Plant (SQN) identifies the water temperature limits for thermal compliance of the plant discharge from Outfall l0l's mixing zone (a virtual box surrounding the discharge diffusers), additional restrictions on the temperature rise (Delta-T) between an ambient river station several miles upstream of the plant (Station 14), and the water temperatures at the downstream end of the mixing zone (2). The plant has struggled with great volatility in the Delta-T (temperature change from upstream to downstream temperature sensors) for decades, which has lead to frequent cooling tower use, even in the winter. Winter use has significantly damaged the cooling towers due to ice formation.
Multiple water temperature field studies and biological evaluations of aquatic species occurred in the vicinity of SQN from the 1980's through the mid 2000's, demonstrating no adverse impact from several proposed temperature limit changes, and as a result, TDEC (TN Department of Environment and Conservation) agreed to allow the following changes to the water temperature limits in the SQN NPDES permit:
(1) Increase the Delta-T limit from 5.4 F 0 to 9.0 F 0 from November 1 to March 31 for the icing issue (1989)
(2) Adopt 24-hour (instead of hourly) averaging on most of the temperature limits (2001)
(3) Move the ambient (upstream) temperature station from the intake skimmer wall (Station
- 13) six miles upstream of the plant, after recirculation studies demonstrated that Station 13 was pulling in water from the mixing zone when the river flow was low (2006).
But the Delta-T struggles have persisted, despite these permit changes. A 2020 modeling study determined that a significant reason for this is the existence of an underwater dam in the river just downstream of the SQN intake. This structure, which creates an emergency cooling water reservoir for safe plant shutdown in the extremely rare event of the loss of Chickamauga Dam, also prevents cooling, mixing and destratification that would naturally occur downstream of the plant's discharge, and forces the plant to have an unnaturally high delta-T. Because this structure is a plant safety element, it cannot be removed to improve water temperatures.
Since physical changes cannot be made downstream, and temperature limits cannot be adjusted more than they already have been, focus was turned to evaluating alternative locations for Station 14 (the upstream station). The placement of Station 14was not studied in great detail originally. Therefore, field data was collected at two alternative locations seasonally for two years to determine if there is a location that provides less volatile upstream data.
Results demonstrate that a better location for the upstream station would be about one mile downstream of the existing station, generally producing delta-T values about a degree lower than those from the existing upstream station.
Delta-T reductions from relocation of the upstream station have the potential to save the plant a significant amount of cooling tower use hours in the fall and the spring, and thus provide an economic benefit to TVA.
TABLE OF CONTENTS Page No.
Table of Contents EXECUTIVE
SUMMARY
............................................................................................................. i INTRODUCTION.......................................................................................................................... 1 INSTREAM Data Collection at Two Alternative Station 14 sites................................................. 5 CONCLUSIONS AND RECOMMENDATIONS......................................................................... 8 REFERENCES............................................................................................................................... 9 LIST OF FIGURES Figure 1 SQN Location Map........................................................................................................... 1 Figure 2 Location of SQN Station 14............................................................................................. 3 Figure 3 Impacts of Underwater Dam on SQN Upstream and Downstream Water Temperatures3 Figure 4 Locations of Station 14 Alternative Sites......................................................................... 5 Figure 5. Measured Water Temperatures at WBH, SQN Station 14, and the alternative Ambient Temperature Sites in a November 2020 cold front and flow change..................................... 6 Figure 6 SQN Delta-T Calculations for Station 14 and the two Alternative Station 14 Sites from October 20-November 6, 2020............................................................................................... 7 Figure 7 SQN Delta-T Calculations for Station 14 and the The "Soddy US" site from May through October of 2021......................................................................................................... 8 LIST OF TABLES Table 1. Sequoyah Nuclear Plant Thermal Compliance Parameters.................................. 2 11
INTRODUCTION Sequoyah Nuclear Plant (SQN) is located on Chickamauga Reservoir at Tennessee River Mile (TRM) 484.5, on the inside of a river bend. The plant is 45.4 miles downstream of Watts Bar Dam
& 13.5 miles upstream of Chickamauga Dam.
The intake for SQN is located at approximately TRM 485.8 and the discharge diffusers (Outfall 101) are located at TRM 483.67. A site location map is shown in Figure 1, along with current NPDES monitoring stations.
SQN Site Location Map
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Figure 1 SQN Location Map and Water Temperatur Stations G
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For environmental compliance, SQN has three water temperature monitoring stations that measure water temperatures at multiple depths at a 15-minute interval, to comply with four different water temperature limits outlined in the plant's NPDES permit. The diffuser discharge itself is not monitored directly; however, there is a mixing zone (a virtual box) around the diffusers and extending about 1200 feet downstream of them and a small distance upstream.
Temperature compliance calculations apply at the downstream edge of the mixing zone. Table 1 summarizes the NPDES instream temperature limits for Outfall 101, the diffuser discharge.
Initially, the temperature limits for SQN were all hourly, but SQN had frequent struggles complying with these limits. Numerous field studies ultimately demonstrated that upstream reservoir conditions are so variable and significantly influenced by both changes in the weather and changes in dam releases and not caused by plant operations. With this information, TVA was able to petition TDEC in 2001 to request changing the monitoring period from hourly to 24-hours.
The petition was granted for all temperature limits except for the Temperature Rate of Change.
Another factor that aided in obtaining these changes from TDEC was the fact that when the SQN cooling towers were used in the winter, it damaged the fill material inside the towers that helps disperse the water. Ice buildup on the plastic fill material caused it to break in numerous places and decreased the cooling efficiency of the towers. This problem helped TVA successfully petition TDEC for the 9.0 F 0 Delta-T limit over the winter months.
Table 1. Sequoyah Nuclear Plant Thermal Compliance Parameters Compliance Parameter NPDES Limit Averaging Period Ambient River Temperature (Sta. 14) 86.9 °F Running 24-hr avg Downstream Temperature (at 86.9 °F Running 24-hr avg downstream mixing zone boundary)
Delta-T (Ambient-Downstream) 5.4 F 0 4/1 to 10/31 Running 24-hr avg 9.0 F 0 11/1 to 3/31 Temperature Rate of Change (TROC) 3.6 F 0 /hr Running 1-hr avg Unfortunately, SQN still frequently battles Delta-Tissues from rapid water temperature changes and destratification in the reservoir, induced by dam release changes to manage rainfall events, and significant air temperature changes (especially in the spring and fall or after thunderstorms).
SQN must operate cooling towers because of Delta-T spikes from these non-plant-related events, despite all of the temperature limit changes that have occurred.
Before March of 2006, the upstream / ambient water temperature station was Station 13, located at the intake skimmer wall. However, data analysis of river temperatures demonstrated that under low river flow conditions (which typically occur in the spring and summer), water from the mixing zone recirculates upstream and reaches Station 13, making the station not truly representative of ambient river conditions when the flow is low.
Station 14 became the new ambient river temperature station in spring of 2006. It is located at TRM 490.5, about 6 miles upstream of the plant, and it is very close to the right bank. Its location near the shore was necessary because the station had to be kept outside of the navigation 2
channel so it would not obstruct boat travel. Figure 2 shows the location of Station 14 and the main river
~
channel. Although moving the ambient river temperature station farther upstream was ethically the right thing to do, it also increased SQN's delta-T compliance issues by collecting data where no recirculation occurs, and its placement was not actually evaluated in detail initially.
Another part of the reason for SQN's Delta-T compliance struggles is that an underwater dam exists in the river just downstream of the SQN intake. This structure (actually an old road bed) creates an emergency cooling water reservoir to allow safe plant shutdown in the extremely rare event of the loss of Chickamauga Dam. But the 1
underwater dam also blocks the coolest water on the bottom of the reservoir from flowing down the river and Figure 2 Location ofSQN Station 14 mixing with and cooling the diffuser discharge, causing the plant to have an unnaturally high Delta-T. This impact has been demonstrated by field studies in the 1980's and more recently by Ce-Qual-W2 (1) modeling of Chickamauga Reservoir with and without the ur.derwater dam.
Model results, shown in Figure 3, clearly show hotter water in the mixing zone as a result of the underwater dam in the left plot.
Water Temperatures with underwater dam
~5r---
OAY: 158-5 St8 St 14 190 Diffuser 18515 1G 17 18 19 20 ~ 22 23 2, 25 26 27 28 29 30 31 32 33 3' :is lticlllNt**
fi
- 27. :I Water Temperatures without underwater dam 215r----------------,
MY: 161.5 Dlffu:;er 1851s 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 3-4 35 Kiloaetets Figure 3 Impacts of Underwater Dam on SQN Upstream and Downstream Water Temperatures Based on inquiries TVA made in 2019 (3), TDEC is averse to extending the time frame ofthe nine-degree Delta-T variance to encompass periods of weather changeability in April and October because it is perceived as allowing degradation of water quality conditions.
All of these issues led to another field study that was conducted to assess the placement of Station 14 and to evaluate two alternative sites that could have the potential to make the plant's Delta-T readings lower.
3
The foundation behind this study is that the upstream station stratifies and destratifies much more rapidly and more easily than the downstream station does. Destratification of the upstream station is an important factor in the plant's Delta-T increases that require cooling tower use.
Below is an example of a summer destratification event that impacted Station 14 but did not impact Station 8 (the downstream temperature station). This is a typical result of a strong thunderstorm in the summer.
SQN Station 14 (upstream) Water Temps, 2015 90,--------,-----,-------
Upstream Destratlflcatlon caused by 88 +------+----+--
- Strong lhundersto,ms
~ 86 a
Wind events preceding storms Heavy rainfall (causes mixing)
( Mr--J~~i+--~~~ - -t---,,---+--ti J s2 -fy:-:+/-J~
Ii i 80 78 +------+----+----1-----+----+-----+----l 76 +------+----1------1-----+----+-----+----l 8/3 8/4 90 88 I"
~86 e
.. r 84
~
~ 82
- i 80.
78 8/3 8/4 5
8/5 8/6 8/7 8/8 SQN Station 8 (DS) Water Temps, 2015 8/5 No Immediate temperature reduction downstream from the weather event 8/6 8/7 8/8 SQN Delta-T (Sta 8 to 14), 2015 8/9 8/10 8/9 8/10
-6inch
-3ft
-5ft
-7 ft 9ft
-ll ft
-15ft
-2ott
-25ft
-30ft
-3ft
-5ft
-7ft 673ft
-667ft
-656ft
-646ft
-637ft 4.5 +------+----1------1-----+-~--+-----+----l --Meas 1-hr DT 4
3.5 I"
3 i 2.5 0
2 1.5 0.5 0 s Figure 4 A Typical Summer Destratification Event at Station 14 that increases the Delta-T Relocating the upstream station could potentially decrease the magnitude of the destratification by collecting water temperature data in a location that is that is more stable and representative of the water flowing in the river, rather than water influenced by localized phenomena.
4
INSTREAM DATA COLLECTION AT TWO ALTERNATIVE STATION 14 SITES Station 14 is at most 200 feet from shore, and it was postulated that its temperature readings may be influenced by changes to the temperature of the land during summer heat events, strong thunderstorms (which induce mixing), and also when a strong cold front comes through the region (since weather changes will alter the land temperature much more quickly than the water temperature). Station 14 has significant stratification during summer heat that is easily mixed away by heavy wind or rain events in summer thunderstorms. These rapid temperature changes increase the Delta-T between this location and the mixing zone and causes the plant excessive cooling tower use in the spring and fall to mitigate conditions created by weather (not the plant).
The river bathymetry was carefully studied (4) in the area of Station 14, as well as the area within about two miles downstream and one mile upstream of the station, in order to choose two trial sites to evaluate for the relocation of Station 14. Water temperature floats with sensors at five depths (3', 5', 7', 10' and 15') were placed at the chosen locations, shown in Figure 5. Data from these monitoring stations were analyzed, along with data from Station 14, to compare the Delta-T computed from the alternate sites to the Delta-T computed from Station 14.
The temporary stations recorded water temperatures by using HOBO Weather Station temperature monitors, which 1
transmit data via satellite to a server where it can be monitored in almost real-time and downloaded. Data was collected at the two alternate locations in October and November of 2019, then 5 Lo.;ati,.is of Station 14 Alterna from April to November of 2020, and the sa"'1e t rn.
'J n *n ~ 021. Test Site pstream of Soddy Creek, is at TRM 488.7 (five mile:. upstr" m of the tiusers), and Test Site 2 is located downstream of Soddy Creek at TRM 487.9. Anal* ;is of the " :;ita, along with water temperature 5
data from Watts Bar Dam, demonstrated that in the fall after a strong cold front, water temperatures at Station 14 become cooler than the release temperatures from Watts Bar Dam (WBH). This reinforces the theory that the temperature station is too close to shore and easily influenced by brief weather events. This phenomenon did not occur at one of the alternative sites, and it occurred at a lesser degree at the second alternative site. Figure 6 shows November 2020 data, demonstrating the impacts of a strong cold front on the water temperatures.
In Figure 6, WBH release temperature data is in orange, Station 14 data is in black, and the two alternative site stations are in different shades of blue. Through the entire time period shown, the alternative site referred to Test Site 1 or "Soddy US" had the warmest water temperatures and generally had a smaller temperature range between top and bottom temperature readings compared to Station 14. When a cold front arrived on November 15, 2020, data at the existing Station 14 became cooler than the data at WBH, whereas the data at Soddy US remained slightly warmer than the WBH data. This cooling of Station 14 seemed unnatural, given that SQN is 45 river miles south of Watts Bar Dam. In general, the air and water temperatures around Chattanooga are usually several degrees warmer than those occurring farther north in the Tennessee Valley. The water temperatures at the Test Site 2, or the "Soddy DS" site, were also warmer than those at Station 14. However, this site is closer to shore than the Soddy US station and is likely influenced from the land temperatures as well.
SQN Sta 14 alt Temps, 2020 vs Sta 14 3-5-7 avg US of Soddy Cr
- = *= WBH taildeck 5, 'F 5-7 avg-DS of Soddy Cr CHH Dam Releases, cfs
-Sta 14 3-5-7 T 66 *,--------------;-=*."C'C'"--.C--~----7'",~---,~.-,-.,.,_-_,..,-_
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,,_ ~-cJ--r------,* 70000 65 +--------~----~----------' ------+-------< 60000 64 50000 63 +"o':lll--=,_c.__;_;;_:a.v--=c:=----4-- --'---
'5 40000 !
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30000 a 61 }---------"-------------""""'"il.,"'r-----l
- c 0 20000 59 ~~*-------------------------1----i 10000 11/6 11/7 11/8 11/9 11/10 11/11 11/12 11/13 11/14 11/lS 11/16 11/17 11/18 11/19 11/20 Figure 6. Measured Water Temperatures at WBH, SQN Station 14, and the alternative Ambient Temperature Sites in a November 2020 cold front and flow change.
A warmer upstream temperature measurement in the fall will translate to a lower Delta-T calculation between the ambient station and the downstream station at SQN. After the mid-6
November cold front, the Chickamauga Dam releases jumped to 70,000 cfs. Even at this higher flow rate, there was still a significant difference in the temperature data between the sites.
Delta-T calculations from a few weeks earlier in 2020 when the river flows were lower also demonstrated that the Delta-Tusing the "Soddy US" site as the ambient temperature station was generally at least 0.5 degrees lower than the value computed from Station 14. Figure 7 illustrates these differences for a multi-week period from late October to early November of 2020. The station downstream of Soddy Creak also produced a slight improvement over the existing Station 14 location; however the location upstream of Soddy Creek appears to be the most beneficial.
s 4.5 0.5 0
0 N
c3' OT Sta l4-plume N
m
-:I'
,n N
N N
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c3' c3' c3' c3' c3' Delta-T comparison OT sta 14 US Soddy-plume or sta.14 DS Soddy-plu e
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rl
.-i
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.-i
.-i Figure 7 SQN Delta-T Calculations for Station 14 and the two Alternative Station 14 Sites from October 20-November 6, 2020 Data from the spring and summer months in 2021 demonstrates a similar or even greater benefit at times. Figure 8 presents the data from spring through fall of 2021, along with the Chickamauga Dam releases, which varied from about 15,000 cfs to over 30,000 cfs during the season. Nearly 100% of the time, the Soddy US station produced a delta-T that was 0.5 to 1 degree lower than the Delta-T from Station 14.
7
5.5 4.5 t... 2.5 i 1.5 0.5
-0.5 CHH Q and DT reduction from Alternate Station 14, 2021 24-hr avg of DT Soddy US-Plume 24-hr avg of Sta 14 DT
- - - -
- CHH flow 40000 35000 30000.,,
't; 25000 oi 20000 J Ill 15000 ~
- c 10000 V 5000
-1.5 0
5/1 5/15 5/29 6/12 6/26 7/10 7/24 8/7 8/21 9/4 9/18 10/2 10/16 10/30 Date Figure 8 SQN Delta-T Calculations for Station 14 and the "Soddy US" site from May through October of 2021 CONCLUSIONS AND RECOMMENDATIONS Given the data collected over a wide range of flows and months, it appears that the Soddy US location produces more stable and slightly lower Delta-T values nearly all of the time, compared to the Station 14 data. Typical Delta-T reductions ranged from 0.5 to 1 Fahrenheit Degrees, which is significant when the limit is 5.4 Fahrenheit Degrees in the spring, summer and fall.
The physical barrier of the underwater dam just upstream of the diffusers impedes natural mixing that would reduce the delta-T if the structure did not exist, and it also impacts the water temperature profile for many miles upstream of the dam. The underwater dam cannot be removed because it is an essential structure for safe emergency shutdown; therefore, it is in TVA's best interest to collect upstream temperature data that is most representative of river conditions and the least influenced by external phenomena. The Soddy US station appears to better meet this criterion and provides a better representation of river conditions than the existing Station 14 location.
The data collected thus far at the Soddy US location looks promising and more stable, and the NPDES Permit for SQN has already been adjusted in the latest permit to generalize the ambient water temperature station's location as "approximately 5 miles upstream of the plant."
Therefore, it is recommended that the next time the station needs significant maintenance, it should be moved to TRM 488. 7 at the edge of the channel on the right bank.
8
REFERENCES (1) Wells, S. A., "CE-QUAL-W2: A two-dimensional, laterally averaged, hydrodynamic and water quality model, version 4.2, user manual part 1, introduction," Department of Civil and Environmental Engineering, Portland State University, Portland, OR, 2020.
(2) TDEC, State of Tennessee NPDES Permit No. TN0026450, Tennessee Department of Environment and Conservation, Issued August 18, 2020.
(3) Cheek, T. E., Response Letter to TDEC Regarding Amended NPDES Permit Application for Sequoyah Nuclear Plant 316(a) demonstration Denial, January 17, 2020.
(4) Navionics.com, https://webapp.navionics.com/#boating@8&key=emguEzhlfO, a website providing underwater bathymetry and navigation hazards and aids 9