Final Environmental Statement

Related to the Operation of 

Watts Bar Nuclear Plant, Unit 2

Supplement 2

Final Report

Office of Nuclear Reactor Regulation

NUREG-0498

Supplement 2, Vol. 1
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Final Environmental Statement 

Related to the Operation of 

Watts Bar Nuclear Plant, Unit 2

Supplement 2

Final Report

Manuscript Completed: May 2013

Date Published: May 2013

Office of Nuclear Reactor Regulation

 

NUREG-0498

Supplement 2, Vol. 1
Plant Description 

May 2013 3-3 NUREG-0498, Supp 2 

3.2 Plant Structures and Operations 

This section describes each major WBN plant structure, including the reactor system and 

structures that would interface with the environment during WBN Unit 2 operation. 

Understanding the operational aspects of these structures is important in assessing the 

environmental impacts from WBN Unit 2 operation (Chapter 4). 

The reactor system includes the reactor vessel, where nuclear fission takes place to generate 

heat that converts water to steam. The steam passes through one or more turbines that spin an 

electrical generator resulting in the flow of electricity. After leaving the generator, the steam is 

converted back into water in the main condenser that is part of the power plant cooling system 

(NRC 2002). Additional information on the WBN Unit 2 reactor system and cooling system is 

provided in the following sections. 

3.2.1 Reactor System 

For WBN Unit 2, TVA proposes to operate a four-loop PWR Nuclear Steam Supply System 

(NSSS) using the Westinghouse Electric Corporation design. The NSSS consists of a reactor 

and four closed-reactor coolant loops connected in parallel to the reactor vessel. Each loop 

contains a reactor coolant pump, a steam generator, loop piping, and instrumentation. The 

NSSS also contains an electrically heated pressurizer and auxiliary systems. The reactor 

design resembles WBN Unit 1, which has operated since 1996. The NSSS for Unit 2 is rated at 

3,411 MW(t) and, at this core power, the NSSS would operate at 3,425 MW(t). The additional 

14 MW(t) results from the contribution of heat to the primary coolant system from nonreactor 

sources, primarily reactor coolant pump heat. The net electrical output is 1,160 MW(e), and the 

gross electrical output is 1,218 MW(e) (TVA 2009a). 

3.2.2 Cooling System 

To condense the steam into water, the cooling system removes heat from the steam and 

transfers that heat to the environment. To do this, the cooling system pumps water through 

thousands of metal tubes in the plant’s condenser. Steam exiting the plant’s turbine is cooled 

and condensed into water when it comes in contact with the cooler tubes. The tubes provide a 

barrier between the steam and the environment so there is no physical contact between the 

plant’s steam and the cooling water. The condenser operates at a vacuum so any leakage in 

this system will produce an “inflow” of water into the condenser rather than an “outflow” of water 

to the environment (NRC 2002). 

At WBN Unit 2 water is taken from the Tennessee River to cool plant components and to be 

pumped through the cooling tubes in the condenser. The heated water that exits from the 

condenser goes to a natural-draft cooling tower where heat is transferred to the atmosphere 

through evaporation and conductive cooling. The cooled water is cycled back into the 

condenser to cool additional steam. This type of cooling system is called a closed-cycle cooling 

system. 
Plant Description 

NUREG-0498, Supp 2 3-4 May 2013 

The NRC considered normal operating conditions and emergency shutdown conditions as the 

operational modes for WBN Units 1 and 2 in its assessment of operational impacts on the 

environment (Chapter 4 of this SFES). The NRC considers these conditions to be those under 

which maximum water withdrawal, heat dissipation, and effluent discharges occur. Cooldown, 

refueling, and accidents are considered alternative modes to normal plant operation. During 

these alternative modes, water intake, cooling-tower evaporation, water discharge, and 

radioactive releases may change from those observed during normal operating or emergency 

shutdown conditions. However, the heat fluxes during normal operation at full load are maximal 

and the following subsections consider flows and effluents during normal operations at full load. 

WBN Unit 1 uses a unique system based on a closed-cycle system with natural-draft wetcooling towers and a supplemental cooling system. WBN Unit 2 would use the same system. 

The original cooling system constructed for the WBN units was a closed-cycle system to 

transfer heat from the main condenser of each unit to the atmosphere through a natural-draft 

cooling tower associated with that unit. TVA identifies this system as the condenser cooling 

water (CCW) system in the 2008 ER (TVA 2008). During normal plant operation, the CCW 

system for each unit would dissipate up to 7.8 × 109 Btu/hr of waste heat (TVA 1972; TVA 

2009a). Additional heat is removed from plant components by the essential raw cooling water 

(ERCW) system and the raw cooling water (RCW) system. Water from both of these systems 

discharges to the cooling-tower basins for the CCW. 

Most excess heat in the cooling water transfers to the atmosphere by evaporative and 

conductive cooling in the cooling tower. In addition to evaporative losses, a small percentage of 

water is lost in the form of droplets (drift) from the cooling tower. The water that does not 

evaporate or drift from the tower is routed back to the cooling-tower basin. 

Evaporation of cooling-water-system water from the cooling-tower increases the concentration 

of dissolved solids in the cooling-water system. In most closed-cycle wet-cooling systems, a 

portion of the cooling water is removed and replaced with makeup water from the source (for 

WBN, the Tennessee River), to limit the concentration of dissolved solids in the cooling system 

and in the discharge to the receiving water body. 

Because the WBN cooling towers cannot remove the desired amount of heat from the 

circulating water during certain times of the year, TVA added the supplemental condenser 

cooling water (SCCW) system to the cooling system for the WBN reactors (TVA 1998). The 

SCCW draws water from behind Watts Bar Dam and delivers it, by gravity flow, to the coolingtower basins to supplement cooling of WBN Unit 1. This cooling system would also be used for 

Unit 2. The temperature of this water is usually lower than the temperature of the water in the 

cooling-tower basin and, as a result, lowers the temperature of the water being used to cool the 

steam in the condensers. Slightly less water enters the cooling-tower basins through the SCCW 
Plant Description 

May 2013 3-5 NUREG-0498, Supp 2 

intake than leaves the cooling-tower basins and is discharged to the Tennessee River through 

the SCCW discharge structure (TVA 2010a). Figure 3-2 shows the major components of the 

cooling system. 

3.2.2.1 Intake Structures 

Intake Pumping Station 

TVA originally designed the intake pumping station (IPS) to supply water to both WBN Units 1 

and 2. Since 1996, it has supplied water to WBN Unit 1. It is located about 3.1 km (1.9 mi) 

below Watts Bar Dam at Tennessee River Mile (TRM) 528.0. The IPS is located at the end of 

an intake channel approximately 240 m (800 ft) from the shoreline of the reservoir (TVA 2009a). 

The IPS has two sump areas, each with two intake openings. The channel leading from the 

intake opening to the well containing the traveling screen is 1.58 m (5.17 ft) wide at the traveling 

screens and 5.3 m (17.5 ft) high. Each traveling screen is 1.2 m (4 ft) wide and the height of the 

water column passing through the screens ranges from 8.8 m (29 ft) in the summer to 7.6 m 

(25 ft) in the winter due to the fluctuations in the pool elevation for Chickamauga Reservoir. The 

traveling screens have a fractional open area of 0.503 (50.3 percent open area) (TVA 2011a). 

The open area through the trash racks at each bay opening in the IPS is approximately 8.84 m2

(95.1 ft2), for a total of 35.2 m2 (380 ft2) open for the passage of water through the trash racks 

(TVA 2010a). 

The water flows through the trash racks, then through the traveling screens, where it 

subsequently enters the sump areas within the IPS. Each sump contains four ERCW pumps 

that pump water into a common header to serve plant components. Typical summertime 

operation for two units would have two ERCW pumps operating in each sump (TVA 2011a). 

Once the water passes through the ERCW system and cools the components, it generally 

discharges to the cooling-tower basins to provide makeup water to offset evaporative losses. 

The system also can discharge to the Yard Holding Pond (YHP). The two sumps and their 

associated pumping units provide redundant systems for providing cooling water to both units at 

the WBN site (TVA 2009a). 

The IPS also contains seven RCW pumps. Three RCW pumps are located in one side of the 

IPS and four are located in the other side. Six of these are sufficient to meet the non-safetyrelated cooling needs of WBN Units 1 and 2. In general, three pumps in each side of the IPS 

will be used to meet cooling needs; however, at times, four pumps in one side of the IPS and 

two in the other side may be used (TVA 2011a), resulting in higher intake velocity in the side of 

the IPS with four pumps in operation. Water from the RCW system discharges to the outlet 

flume of the cooling-tower basin for the unit being served. This water also serves as makeup 

water for the condenser cooling system (TVA 2009a). In addition, the IPS houses high-pressure 

pumps for the fire-protection system. 
Plant Description 

NUREG-0498, Supp 2 3-6 May 2013 

(To convert feet [ft] to meters [m], multiply by 0.3048 m/ft) 

Figure 3-2. Major Components of the Cooling System for WBN Units 1 and 2 (TVA 2008)
Plant Description 

May 2013 3-7 NUREG-0498, Supp 2 

Currently, Unit 1 withdraws between 1.92 m3/s (68 cfs) of water in winter and 2.06 m3/s (73 cfs) 

of water in summer from the Chickamauga Reservoir for normal operations (TVA 2011a). 

Normal operations for two units would require the withdrawal of between 3.20 m3/s (113 cfs) of 

water in winter and 3.79 m3/s (134 cfs) of water in summer from the reservoir (TVA 2011a). 

Under normal conditions, while drawing water through all four bays in the IPS and operating four 

RCW pumps located together in one side of the IPS, the water velocity through the openings in 

the traveling screens would be 0.21 m/s (0.67 ft/s) in winter and 0.19 m/s (0.62 ft/s) in summer 

for the portion of the intake structure with four RCW pumps operating (TVA 2011a). 

The withdrawal of 3.79 m3/s (134 cfs) through the IPS would represent 0.5 percent of the mean 

annual flow of the Tennessee River as measured at Watts Bar Dam (778 m3/s [27,500 cfs]; see 

Table 2-2). 

Supplemental Condenser Cooling-Water Intake 

The intake facility for the SCCW is located above Watts Bar Dam at TRM 529.9. The SCCW 

has six intake bays, and three are currently used for the operation of WBN Unit 1. No additional 

bays would be used during the operation of both units. Each intake bay is 2.17 m (7.13 ft) wide 

at the traveling screens and 9.4 m (31 ft) high at a summer pool elevation of 225.8 m (741 ft) for 

Watts Bar Reservoir. This results in an opening of 20.5 m2 (221 ft2). The traveling screens and 

their support structures occupy a portion of the opening leaving 8.41 m2 (90.5 ft2) open to the 

passage of water in each bay or a total of 25.2 m2 (271.5 ft2) for the passage of water through 

the screens into the SCCW intake. The open area through the trash racks at each bay opening 

in the SCCW intake structure is approximately 16.7 m2 (180 ft2), for a total of 50.2 m2 (541 ft2) 

(TVA 2012a). Figure 3-2 shows the locations of the IPS and SCCW intakes. 

The SCCW system operates by gravity flow, and as such, the flow through the intake structure 

fluctuates in response to changes in the elevation of the water level in Watts Bar Reservoir. 

Flow into the SCCW system has not been measured, but is estimated based on the dimensions 

of system components and calculations based on water levels or plant operations. Losses due 

to evaporation are also estimated, although discharge from the SCCA is measured (TVA 

2012a). TVA estimates the average monthly flow through the SCCW intake for the operation of 

WBN Units 1 and 2 will be 7.9 m3/s (278 cfs) of water from the Watts Bar Reservoir (TVA 

2012a). This is slightly less than the flow through the SCCW while operating Unit 1 only, 

however the difference is within the uncertainty in the estimate for flow while operating one or 

two units. 

The normal intake flow rates are higher in the summer months when Watts Bar Reservoir levels 

are maintained at 225.8 m (740.75 ft). Normal flow rates during summer months with both units 

operating are expected to be approximately 8.6 m3/s (303 cfs). Flow through the intake 

structure can be as high as 8.9 m3/s (313 cfs) and intake at this rate would result in a water 

velocity through the open areas in the trash racks in the SCCW of 0.18 m/s (0.58 ft/s) (TVA 
Plant Description 

NUREG-0498, Supp 2 3-8 May 2013 

2012a). The maximum water velocity through the SCCW intake structure occurs as the water 

enters the wet well for the traveling screens. This velocity is 0.66 m/s (2.18 ft/s) for the summer 

pool (TVA 2012b). The water velocity through the openings in the traveling screens at the 

SCCW would be 0.35 m/s (1.15 ft/s) under these conditions (TVA 2012a). 

Table 3-1 lists flow rates for operating two units or a single unit at the WBN site. 

Table 3-1. Anticipated Water Use 

Service Normal Two-Unit Operation Single-Unit Operation 

Heat discharged 1.5 × 1010 Btu/hr(a) 7.8 × 109 Btu/hr(a)

CCW 

Evaporation rate 1.8 m3/s (62 cfs)(b) 0.82 m3/s (29 cfs)(a)

Drift rate 5.6 L/s (0.2 cfs)(c) 2.8 L/s (0.1 cfs)(c)

Blowdown rate 1.9 m3/s (67 cfs)(b) 1.5 m3/s (53 cfs)(a)

Blowdown rate when diffusers are 

discharging from cooling towers and YHP 

4.81 m3/s (170 cfs)(d) 3.82 m3/s (135 cfs)(d)

IPS makeup flow 

Summer 

Winter 

3.79 m3/s (134 cfs)(e) 

3.20 m3/s (113 cfs)(e)

2.06 m3/s (73 cfs)(f)

1.92 m3/s (68 cfs) (f)

SCCW(b)(g) 

Intake flow rate 6.5 to 8.6 m3/s (230 to 303 cfs) 6.5 to 8.6 m3/s (230 to 

303 cfs) 

Discharge flow rate 6.8 to 7.9 m3/s (240 to 279 cfs) 6.8 to 7.9 m3/s (240 to 

279 cfs) 

YHP overflow weir(d) 0 0 

(a) TVA 2010a 

(b) TVA 2012a 

(c) 1972 FES-CP (TVA 1972). 

(d) TVA (2008). 

(e) Normal withdrawal is 3.20 m3/s (113 cfs) of water in winter and 3.79 m3/s (134 cfs) of water in summer (TVA 

2011a); Average annual withdrawal is 3.28 m3/s (116 cfs) (TVA 2012a) 

(f) TVA 2011a. 

(g) Flow in the SCCW system is variable, dependent on parameters such as reservoir elevation and cooling tower 

basin surface elevation (TVA 2012a). 

3.2.2.2 Cooling Towers 

The WBN cooling-water system uses natural-draft cooling towers to dissipate waste heat from 

the plant. Two cooling towers, one dedicated to each unit, would serve the WBN site. Each 

tower is 108 m (354 ft) in diameter and 146 m (478 ft) high (TVA 1972). 

3.2.2.3 Temporary Blowdown Storage 

TVA uses the unlined YHP (Figure 3-1), which is approximately 8.9 ha (22 ac) in size (TVA 

2005a) for temporary storage of cooling-tower blowdown when the flow from the hydroturbines 
Plant Description 

May 2013 3-9 NUREG-0498, Supp 2 

at Watts Bar Dam drops below 99 m3/s (3,500 cfs). When hydroturbine operation resumes with 

releases of at least 99 m3/s (3,500 cfs), valves on the discharge line allow the YHP to discharge 

into Chickamauga Reservoir through the diffusers (TVA 2008). 

3.2.2.4 Discharge Structures 

Outfall 101 – Discharge Diffusers 

TVA plans to discharge cooling water from the main cooling-water system for WBN Units 1 and 

2 to Chickamauga Reservoir through a diffuser system located approximately 3.2 km (2 mi) 

below Watts Bar Dam at TRM 527.9 (TVA 2008). The National Pollutant Discharge Elimination 

System (NPDES) permit for the WBN site identifies the diffuser discharge as Outfall 101 (TVA 

2011b). Harper (1997) describes this diffuser system as consisting of two pipes branching from 

a central conduit at the right bank of Chickamauga Reservoir and extending perpendicular to the 

river flow of the Tennessee River. Each pipe is controlled by a butterfly valve located a short 

distance from the junction with the central conduit. 

The downstream leg of the diffuser consists of 49 m (160 ft) of 1.37-m (4.5-ft)-diameter 

corrugated steel diffuser pipe at the end of approximately 91 m (297 ft) of corrugated steel 

approach pipe of the same diameter. The diffuser pipe is half buried in the river bottom and has 

two 2.54-cm (1-in.)-diameter ports per corrugation. The centroid of the ports is angled up at 45

degrees from horizontal in a downstream direction (Harper 1997). 

The upstream leg of the diffuser system consists of 24 m (80 ft) of 1.07-m (3.5-ft)-diameter 

corrugated steel diffuser pipe at the end of approximately 136 m (447 ft) of corrugated steel 

approach pipe of the same diameter. The upstream diffuser pipe section is half buried in the 

river bottom and extends its entire length beyond the dead end of the downstream diffuser pipe 

section. The port diameter, spacing, and orientation of the upstream leg are the same as those 

of the downstream leg (Harper 1997). Figure 3 from the TVA analysis of the SCCW thermal 

plume (Ungate and Howerton 1977) illustrates the diffuser configuration. TVA does not plan to 

make any upgrades or changes to the diffusers in preparation for operating Unit 2 (TVA 2010b). 

TVA maintains operational procedures for this system to ensure the plant effluent is adequately 

diluted. The 2008 TVA ER explains the process as follows: 

To provide adequate dilution of the plant effluent, discharge from the diffusers is 

permitted only when the release from Watts Bar Dam is at least 3,500 cubic feet 

per second (cfs). To ensure this happens, an interlock is provided between the 

dam and WBN that automatically closes the diffusers when the flow from the 

hydroturbines at Watts Bar Dam drops below 3,500 cfs. To provide temporary 

storage of water during these events, the blowdown discharge conduit also is 

connected to a yard holding pond. When the flow from Watts Bar Dam drops 

below 3,500 cfs, thereby closing the diffuser valves, the blowdown is 

automatically routed to the yard holding pond. When hydro operations resume 
Plant Description 

NUREG-0498, Supp 2 3-10 May 2013 

with releases of at least 3,500 cfs, the interlock is ‘released’ and the diffuser 

valves can be opened. When this occurs, the discharge from the diffusers would 

contain blowdown from the cooling towers and blowdown from the yard holding 

pond. To protect the site from the consequences of exceeding the capacity of 

the yard holding pond, an emergency overflow weir is provided for the pond, 

which delivers the water to a local stream channel that empties into the 

Tennessee River at TRM 527.2. The operation of Watts Bar Dam and the WBN 

blowdown system are very carefully coordinated to avoid unexpected overflows 

from the yard holding pond (TVA 2008). 

A flow of 3,500 cfs is approximately 99 m3/s. 

Outfall 113 SCCW Discharge 

The SCCW system discharges water through a discharge structure originally constructed for the 

Watts Bar Fossil Plant (also called the Watts Bar Steam Plant). The NPDES permit for the 

WBN site identifies the SCCW discharge as Outfall 113 (TVA 2011b). Water leaving the 

cooling-tower basins is piped to the discharge structure approximately 1.8 km (1.1 mi) upstream 

of the IPS. TVA describes the discharge structure as an “open discharge canal, an overflow 

weir drop structure, and a below water discharge tunnel” (TVA 1998). The discharge tunnel is 

described as “a rectangular culvert 7 feet wide by 10 feet high at the discharge point” 

(TVA 1998). The elevation of the culvert outlet is 205.7 m (675 ft). To reduce the impact of the 

discharge on the river bottom, TVA installed a concrete incline to direct flow toward the river 

surface as it leaves the outfall (TVA 1998; PNNL 2009). 

TVA designed and constructed the SCCW system so it could operate the cooling system for 

WBN Units 1 and 2 with or without the SCCW. If the temperature of the discharge water 

exceeds allowable release limits, TVA can shut down the SCCW system. TVA also included a 

crosstie and control valve in the system that allows part of the flow from the SCCW intake to 

bypass the cooling-tower basins and mix with the effluent in the discharge pipeline. When there 

is a possibility of exceeding the NPDES river temperature limit, TVA opens a bypass valve to 

allow cooler water in the intake pipeline to mix with water in the discharge line, cooling the 

effluent before it discharges to the reservoir (TVA 2008). The bypass is generally needed 

during winter months when the water temperature in the Tennessee River is cooler, and a 

possibility exists of exceeding the in-stream temperature rate-of-change limit in the NPDES 

permit. TVA opens the crosstie around November 1, and it remains open until the end of April 

(PNNL 2009). 

Outfall 102 YHP Emergency Overflow 

The YHP has an emergency overflow weir at 215.3 m (706.5 ft) of elevation designed to prevent 

the capacity of the pond from being exceeded. If water goes above the height of the weir, it 

flows into a local stream channel that empties into Chickamauga Reservoir at TRM 527.2 
Plant Description 

May 2013 3-11 NUREG-0498, Supp 2 

(TVA 2008). The NPDES permit for the WBN site identifies this discharge as Outfall 102 

(TVA 2011b). 

3.2.3 Landscape and Stormwater Drainage 

Landscaping and the stormwater drainage system affect both the recharge to the subsurface 

and the rate and location that precipitation drains into adjacent creeks and streams. Impervious 

areas eliminate recharge to aquifers beneath the site, while pervious areas maintained free of 

vegetation experience considerably higher recharge rates than adjacent areas with local 

vegetation. The stormwater drainage system, including site grading, ditches, and swales 

provides a safety function by ensuring a locally intense precipitation event would not flood 

safety-related structures. 

Figure 3-3 shows drainage for the WBN site. The surface-water drainage system directs water 

away from safety structures and into ditches and drainways, which ultimately feed into drainage 

ditches and creeks. 

3.2.4 Other Plant Systems 

Diesel Generators 

TVA installed five diesel generators on the WBN site. Missile and fire barrier-type shelter walls 

separate four diesel generators and their associated support equipment from each other. 

A separate building houses the fifth diesel generator (TVA 2009a). 

Roads 

The workforce and a portion of the materials needed for plant operations will enter and exit the 

site via roads. TVA expects to transport solid waste and radwaste from the WBN site via 

roadways. The nearest land transportation route, Tennessee State Route 68, is located about 

1.6 km (1 mi) north of the site (TVA 2009a). 

Wells 

No water supply wells are located on the WBN site. The 1995 SFES-OL-1 notes that the Watts 

Bar Utility District supplies groundwater to the WBN site potable water system. The Watts Bar 

Utility District uses groundwater wells located about 6.4 km (4 mi) (TVA 2009b) northwest of the 

site to provide potable water to its customers and the WBN site. The utility currently has the 

capacity to deliver approximately 6.8 million L/d (1.8 million gal/d) of water to customers 

(TVA 2010c). TVA expects the site will use 91,000 L/d (24,000 gal/d) during normal operations 

of both units and that peak demand during the completion of Unit 2 and an outage at Unit 1 will 

be 300,000 L/d (80,000 gal/d) (TVA 2010c).