ML22049B317
| ML22049B317 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 10/04/2021 |
| From: | Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML21286A574 | List:
|
| References | |
| Download: ML22049B317 (1) | |
Text
BFN-25 2.4 HYDROLOGY, WATER QUALITY, AND AQUATIC BIOLOGY 2.4.1 General The various uses of water in the Browns Ferry area have been investigated. Ground and surface hydrology has been studied to determine the characteristics of both ground and surface water flow in the immediate plant area and the surrounding regional area. Water quality and biological monitoring programs have been developed and implemented to monitor water quality and biological life of Wheeler Reservoir during plant operation.
2.4.2 Hydrology 2.4.2.1 Ground Water Ground water at Browns Ferry is derived from precipitation. Some of the precipitation evaporates, some runs off into streams, and some seeps into the soil.
A portion of the water entering the soil is used by vegetation and some of it seeps downward to become ground water.
2.4.2.1.1 Regional Area Studies of subsurface waterflow in the area indicate that ground water flows from the structural highs toward the structural lows. Elevations range from 556 at Wheeler Reservoir to 880 in the east Central part of Limestone County. Rock strata have a regional dip of about 20 ft/mile to the south and southwest, locally altered by minor anticlines and synclines. Both topography and drainage reflect the geologic structure of the area.
Rocks exposed in Limestone County are, from oldest to youngest, the Chickamauga limestone, Chattanooga shale, Fort Payne chert, and Tuscumbia limestone. The principal aquifer for Limestone County is the Mississippian Carbonate Regional Aquifer. At this site, the aquifer consists of the Tuscumbia Limestone and the Fort Payne Chert.
A mantle of residuum overlies the Fort Payne and Tuscumbia formations. Wells deriving their supply from the residuum are of low capacity. The residuum in the area consists of a mixture of silt, clay, chert, and discontinuous zones of chert gravel. The residuum is capable of storing large amounts of water, which are released at a slow rate to wells, springs, and solution channels in the underlying bedrock.
Ground water occurrence is restricted to fractures and solutional cavities in the bedrock. Generally large yields can be anticipated from Tuscumbia and Fort Payne formations.
2.4-1
BFN-28 2.4.2.1.2 Site Area Ground water movement from the regional area into the Browns Ferry site area is controlled by topography and geologic structure. Recharge is also derived from local precipitation that has percolated through the residuum. Natural ground water movement in the area is from the plant site to the Tennessee River.
2.4.2.2 Surface Water Surface water is derived from precipitation remaining after losses due to infiltration and evapotranspiration. It can be generally classified as local surface runoff or streamflow.
2.4.2.2.1 Surface Runoff Surface runoff in the area flows down Poplar Creek, Douglas Branch, and Round Island Creek to the Tennessee River.
2.4.2.2.2 Streamflow Regulatory Guide 1.27, Ultimate Heat Sink for Nuclear Power Plants, Revision 3, was used as the basis for evaluating the BFN UHS.
Per Regulatory Guide 1.27, Sections B, the BFN UHS must be capable of withstanding each of the most severe natural phenomena expected, other site-related events, appropriate combinations of natural phenomena or site-related events, and a single failure of manmade structural features without loss of capability of the UHS to accomplish its safety functions. The most severe phenomena may be considered to occur independently and not simultaneously (e.g., a tornado and an earthquake). In addition, the single failure of manmade structural features need not be considered to occur simultaneously with severe natural phenomena or site-related events unless the severe natural phenomena can cause failure of a manmade structural feature.
Per Regulatory Guide 1.27, Sections C.2.a, the BFN UHS must be capable of withstanding, without loss of the UHS safety functions, all of the following events:
(1) The most severe natural phenomena expected at the site in accordance with General Design Criteria (GDC) 2, (2) The site-related events (e.g., transportation accident, river diversion) that historically have occurred or that may occur during the plant lifetime, (3) Appropriate combinations of less severe natural phenomena and/or site-related events, 2.4-2
BFN-28 (4) Failure of reservoirs, dams, and other manmade water retaining structures both upstream and downstream of the site including the potential for resultant debris to block water flow; and (5) Potential changes in ocean, river, or lake levels as a result of severe natural events, or possible changes in climatological conditions in the site region resulting from human or natural causes, that may occur during the plant lifetime.
- a. Description of UHS The Browns Ferry UHS is the Wheeler Reservoir, which was formed by the damming of the Tennessee River by the Wheeler Dam, located downstream of Browns Ferry, and the Guntersville Dam located upstream of Browns Ferry. This water area has been monitored since 1939. The Wheeler Reservoir provides water flow to the RHRSW system through the plant intake structure.
- b. Inflow Since 1939, streamflow records have been maintained at the Guntersville Dam on the Tennessee River. The average daily discharge flow for the period 1939 to 2015 has been 33,500 cfs. The maximum streamflow occurred on March 19, 1973, and was 304,400 cfs. The minimum daily average streamflow, 100 cfs, occurred several times during the period of record, due to regulation of Guntersville Dam. Generally, minimum daily flows are much higher.
Flow duration data for the period 1939 to 2015 were provided by the TVA River Management. This period of record, 76 years, represents a significant period of time (i.e. - much greater than 30 years) and results in highly reliable data.
A review of the flow duration data observed during the time period between 1939 and 2015 shows that streamflow equal or exceed the following values for the indicated percentages of the time:
2.4-3
BFN-28 Regulatory Guide 1.27, Section C.2.a(2) - The site-related events (e.g.,
transportation accident, river diversion) that historically have occurred or that may occur during the plant lifetime As specified earlier, the most severe regulation of outflow from Guntersville Dam during the period of record limited the flow to 100 cfs. The actual flow past the Browns Ferry site will be larger than this as a result of inflow from numerous incoming branches between Guntersville Dam and the site. However, the 100 cfs flow rate alone is sufficient to meet the 80 cfs accident and shutdown requirements of the plant. During this time, the water level in the Wheeler Reservoir would be expected to be at its average normal level of 553.5, but would be no lower than its minimum normal level of 550.0, both of which exceed the minimum required level for adequate flow and NPSH to the RHRSW pumps and provide a significant volume of water available to the plant.
Additionally, a 30 day low Guntersville Dam discharge flow was determined during a period of several low flow days. The average discharge flow was still approximately 6,000 cfs, which more than supports the flow requirements of RHRSW.
Obstruction of the intake pumping station channel resulting from a river transportation accident is discussed in Section 12.2.7.6. At the normal minimum pool level of 550.0, there is sufficient pool depth to ensure that adequate flow and NPSH to the RHRSW pumps is available to the plant.
Regulatory Guide 1.27, Section C.2.a(3) - Appropriate combinations of less severe natural phenomena and/or site-related events, From an historical perspective, the inflow from the upstream Guntersville Dam and the Wheeler Reservoir levels combine in a myriad of ways throughout the year based on climatic conditions in the region. However, there are no reasonable combinations of reservoir level and inflow that would invalidate the ability of the reservoir to perform its safety function. The intake structure has been designed for both flooding and seismic events and is therefore capable of performing its safety function for all natural phenomena. The reasonable combination of the minimum normal Guntersville Dam flow of 1,319 cfs and the minimum normal Wheeler Reservoir level of 550.0 feet ensures the ability of the BFN UHS to perform its safety function.
Regulatory Guide 1.27, Section C.2.a(4) - Failure of reservoirs, dams, and other manmade water retaining structures both upstream and downstream of the site including the potential for resultant debris to block water flow.
2.4-7
BFN-28 2.4.2.2.3 Floods The Browns Ferry site is located on the right bank of Wheeler Reservoir at approximately Tennessee River mile (TRM) 294. The lowest natural ground elevation in the site vicinity is about 560 feet above mean sea level and the average ground elevation is about 580.
The probable maximum flood (PMF) at Browns Ferry is calculated to reach El.
571.7. However, the site PMF level is being maintained at elevation 572.5. This is the flood which defines the upper limit of potential flooding at the plant. A concise definition of PMF is given in Section 1.2, while the determination of PMF is described in Appendix 2.4A.
2.4.3 Water Quality Information reflecting the water quality, water temperature, and aquatic biota conditions in the vicinity of the Browns Ferry Nuclear Plant (BFN) were incorporated into the Final Environmental Statement, Browns Ferry Nuclear Plant, Units 1, 2, and 3, Volumes 1, 2, and 3, TVA Office of Health and Safety, Chattanooga, Tennessee, September 1, 1972. Results of the preoperational water monitoring program for the period 1968 through 1973 are included in the report "Water Quality and Biological Conditions in Wheeler Reservoir Before Operation of Browns Ferry Nuclear Plant - 1968-1973." Results of the operational monitoring program for the period 1974 through 1980 were included in a series of five semiannual reports followed by five annual reports. The last report including the 1980 monitoring results was "Water Quality and Biological Conditions in Wheeler Reservoir During Operation of Browns Ferry Nuclear Plant January 1, 1980-December 31, 1980," Volumes I and II.
These monitoring and reporting requirements under the jurisdiction of NRC were determined to be duplicative of the requirements imposed by the Browns Ferry NPDES permit (AL 0022080) issued on June 30, 1977. In response to TVA's letter dated July 27, 1981, NRC notified TVA of their concurrence with this determination by letter dated December 10, 1981, and accepted TVA's recommendation to delete these monitoring requirements from the Browns Ferry Environmental Technical Specifications. All subsequent water quality, biological, and thermal monitoring and reporting have been and will continue to be in accordance with the requirements of the Browns Ferry NPDES permit (Permit No. AL 0022080) and/or TVA policy.
The most recent comprehensive evaluation of the aquatic conditions of Wheeler Reservoir is contained in the report "A Supplemental 316 (a) Demonstration For Alternative Thermal Discharge Limits For Browns Ferry Nuclear Plant, Wheeler Reservoir, Alabama," TVA, February 1983.
2.4-9
BFN-25 2.4.4 Water Use The public and industrial water supplies which withdraw surface water from the Tennessee River in the 61-river mile reach from Decatur, Alabama to Colbert Steam Plant, not including Browns Ferry Nuclear Plant, are listed in Table 2.4-4.
2.4.4.1 Industrial Major industrial water users are located both upstream and downstream of the Browns Ferry project. These users withdraw water from Wheeler Reservoir each day for process and cooling needs. Most of this water is subsequently returned to the reservoir.
2.4.4.2 Public The major public uses of the reservoir are for water supplies, recreation, and waste disposal. Six public water supplies are taken directly from the Tennessee River portion of Wheeler, Wilson, and Pickwick Reservoirs within the reach from Decatur, Alabama, about 12 river miles upstream from the plant, to Colbert Steam Plant, about 49 river miles downstream from the plant. Eleven industrial supplies also withdraw water from the reservoirs in this same reach, and some use a portion of their withdrawal for potable water within the plant.
2.4.4.3 Browns Ferry Nuclear Plant The Browns Ferry Nuclear Plant will use a large volume of water. When all three units are in operation, river water will be pumped through the plant at the rate of about 4,400 cfs. The temperature of this water will be elevated above its natural temperature. Heated condenser cooling water will be diffused into the main channel flow of the Tennessee River by a Diffuser System consisting of three perforated pipes laid side by side on the bottom of the channel near TRM 294. The Diffuser System is detailed in paragraph 12.2.7.5.
The containment, treatment, storage (including quantities), and pathways for release of liquid radiological effluents at BFN are detailed in Section 9.2 Liquid Radwaste System.
The nearest community surface water supply is at Decatur, Alabama, on Wheeler Reservoir 12 miles upstream from the Browns Ferry site. With normal operation of Guntersville and Wheeler Dams, there would be no flow upstream from Browns Ferry that would reach Decatur. Should a slug release (i.e., a finite volume of contaminant released nearly instantaneously into a receiving waterway) occur at a time when upstream flow to Decatur could conceivably occur, the river control system could be operated to prevent the upstream flow.
2.4-10
BFN-25 The first downstream water intake is the West Morgan-East Lawrence Water Authority intake located at TRM 286.5 on the left bank of Wheeler Reservoir. An analysis was made to determine the minimum dilution to be expected between the diffusers and the intake at West Morgan-East Lawrence for both accidental slug and continuous plane source releases. The following assumptions were used in the analysis.
- 1. Because the water intake is located on the bank opposite the plant, minimum dilution would occur when the release is fully mixed over the cross section of the reservoir. This is accomplished by configuring the release as a plane source placed vertically across the width of the channel.
- 2. Mixing calculations are based on steady flow conditions in the reservoir. River flow is assumed to be 33000 ft3/sec. This is the flow which is equaled or exceeded in the reservoir approximately 50 percent of the time.
- 3. The concentration profile from an instantaneous (i.e. slug) release of contaminant is assumed to be Gaussian in the longitudinal direction.
- 4. The calculated contaminant concentration is conservative. Material discharged into the river does not degrade through radioactive decay, chemical or biological processes, nor is contaminant removed from the reservoir by adsorption to sediments or by evaporation.
All results are given in units of relative concentration, expressed as C/C0 where C represents the concentration of contaminant at the point of interest, and C0 is the concentration of contaminant at the point where it enters the reservoir. Dilution is the reciprocal of relative concentration.
The maximum relative concentration at the West Morgan-East Lawrence Water Authority intake due to a continuous plane source release rate Q (ft3/sec) of contaminant is 3.0 Q x 10-5. The maximum relative concentration at this location due to an instantaneous plant source release of a volume V (ft3) of contaminant is 3.2 V x 10-10. For the instantaneous relative concentration, the following parameter values were used:
channel width = 6000 ft, channel depth = 35 ft, longitudinal dispersion parameter = 200, mixing coefficient (manning's n) = 0.03.
At the time of initial plant licensing, there were no private ground water wells located within one mile of the reactor building, and there were only eight houses located within one mile of the site perimeter which relied on groundwater as a source of 2.4-11
BFN-25 water supply. Because all local groundwater in the plant site area flows directly to Wheeler Reservoir (see Section 2.4.2.1), it is improbable that any liquid released from the site could contaminate these sources of water supply through contamination of groundwater. Furthermore, with the containment provided for the liquid radwaste system (see Section 9.2), there is little likelihood of the release of liquid radwaste to the groundwater. In the event of any unusual release of radwaste liquid which could contaminate groundwater at the site, special local monitoring will be carried out in accordance with the Radiological Monitoring Plan, Browns Ferry Nuclear Plant, to ensure that the use of these wells will not result in undue hazards to any person, even though there is little likelihood of the wells becoming contaminated.
With the very unlikely event that the private wells located within one mile of the site perimeter could become contaminated, the public and industrial groundwater supplies in the site vicinity (all of which are located well beyond one mile from the site) would not be expected to be affected by plant operation. Consequently, the contamination of public and industrial groundwater supplies is not a concern at Browns Ferry requiring the monitoring and/or inventorying of such supplies.
However, a periodic inventory of the private wells located within one mile of the site reactor building will be conducted. Table 2.4-6 contains a list of the private wells as inventoried in 1989. Figure 2.4-3 shows the location of the private wells within one mile and two miles of the plant.
2.4.5 Aquatic Biota The historic aquatic biological conditions and their associated routine monitoring and reporting are identified in Section 2.4.3 Water Quality.
2.4.6 Monitoring Programs All Browns Ferry related radiological water quality and aquatic biological monitoring programs are being conducted and reported in accordance with the Browns Ferry Nuclear Plant Radiological Environmental Monitoring Program as described in the Browns Ferry Offsite Dose Calculation Manual.
Since 1981, all nonradiological water quality, aquatic biological, and water temperature monitoring programs have been and will continue to be conducted and reported in accordance with the Browns Ferry NPDES permit (Permit No. AL 0022080) and/or TVA policy. (See Section 2.4.3 Water Quality for a discussion of these monitoring programs prior to 1981.)
2.4-12
BFN-25 2.4.7 Conclusions Ground water movement in the area is from the plant site to the Tennessee River.
The principal aquifer in the area is overlain by a mantle of residuum that retards the movement of shallow ground water. Migration of radionuclides in the residuum would be quite slow. It is highly unlikely that the private groundwater wells located within one mile of the site perimeter could be contaminated by operation of BFN.
Special local groundwater monitoring of these wells would be implemented in the event of a liquid radioactive release to the groundwater at BFN. Consequently, the potential for contamination of the public and industrial groundwater systems in the BFN area is not a concern which requires monitoring or inventorying of these systems. A periodic inventory of private wells within one mile of the site area will be implemented. Surface water runoff from the plant site is to the Tennessee River.
Surface water runoff from the plant site is to the Tennessee River. Regulated by the TVA flood control system, the probable maximum flood would result in increasing Wheeler Reservoir level to 572.5 feet above sea level at the site. Safety-related structures are protected against all flood conditions up to El. 578 as discussed in response to Question 2.6 and would not be endangered by the probable maximum flood.
All nonradiological water quality, biological, and thermal monitoring and reporting related to BFN has been and will continue to be conducted in accordance with the requirements of the NPDES permit and/or TVA policy.
2.4-13