ML18022A132
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BFN-25 2.3 METEOROLOGY 2.3.1 General The Browns Ferry site is adjacent to the Tennessee River (Wheeler Lake) which flows northwest at this location. There are no local physiographical features to cause significant climatological anomalies at the site, as the immediate terrain is flat or slightly undulating, with scattered 400- to 600-foot foothills and ridges located 20 to 25 miles to the east through south and southwest. Wheeler Lake adjoins the site and averages 1 to 1-1/2 miles in width. Normally, discontinuities in ambient thermal structure from differential surface heating between land and water should not cause detectable lake breeze circulation at the site area.1 Limited air mass modification may occur within the lower few hundred feet, particularly with southeast winds, when the over-water trajectory may approach 10 miles.
2.3.2 Climatology The site is in a temperate latitude about 300 miles north of the Gulf of Mexico. The area is dominated in winter and spring by alternating cool, dry continental air from the north and warm, moist maritime air from the south. During this period, migratory cyclonic disturbances with numerous thundershowers and thunderstorms pass through the area, with frequent precipitation. Storms, including tornadoes, reach strongest intensity in March and April when maximum air mass contrast generally occurs.
Persistent and unstable maritime air in the summer results in frequent thundershower and thunderstorm activity. Stagnating anticyclones sometimes dominate the area in the fall, with extended periods of low wind speeds and poor dispersion conditions.
Climatological appraisal of the Browns Ferry site is based primarily upon data collected at (1) the plant site during the three-year period, January 1, 1977 through December 31, 1979, (2) Volunteer Weather Observation Stations in Decatur, Alabama, about 13 miles southeast of the Browns Ferry site, for the 80-year period, 1879-1958, and (3) The National Weather Service Station near Huntsville, Alabama, about 20 miles east of the site, for the 13-year period, 1968-1980. Climatological features affecting the atmospheric dispersion of plant emissions are discussed later in this subsection.
2.3.3 Atmospheric Stability Temperature data from the Browns Ferry meteorological tower were used to determine atmospheric stability. The Pasquill seven category (A-G) classification 2.3-1
BFN-25 scheme, based on temperature change with height, was used. Table 2.3-1 gives the percent occurrences of the Pasquill stabilities classified by lapse rates between 33 and 150 feet (10 and 45 meters), and based on wind speeds at 33 feet (10 meters).
Table 2.3-2 gives the percent occurrences of the stabilities classified by lapse rates between 150 and 300 feet (45 and 90 meters), and based on wind speeds at 300 feet (93 meters).
For the lower layer (Table 2.3-1), Classes D and E each occurred about 32 percent of the time. Unstable conditions (Classes A, B, and C) occurred least often, only about l5 percent of the time.
In the upper layer (Table 2.3-2), Classes D and E combined occurred about 88 percent of the time. Unstable classes were much less frequent, occurring less than one percent of the time.
During the three-year period of record, low-level inversion conditions (temperature increases with height) occurred during about 38 percent of the total hours. This compares well with an inversion frequency of about 37 percent obtained from a study by Hosler2 of two years of data from selected NWS stations. Seasonally, the greatest occurrence of inversion conditions is during the fall.
2.3.4 Wind Wind data from the Browns Ferry meteorological tower were used to represent airflow at the site. Tables 2.3-3 through 2.3-9 are joint percentage frequency distributions of wind speed by wind direction for Pasquill stability classes A-G, respectively. These are classified by lapse rates between 33 and 150 feet and based on wind data at 33 feet. Table 2.3-10 is a distribution of wind speed by wind direction based on wind data at 33 feet, disregarding stability class. Tables 2.3-11 through 2.3-22 are monthly distributions of wind data at 33 feet, based on the three-year period. A corresponding set of tables for lapse rates between 150 and 300 feet, and wind data at 300 feet, is given in Tables 2.3-23 through 2.3-42.
2.3.4.1 Wind Direction Lower Level From Tables 2.3-3 through 2.3-10, it can be seen that the highest frequency of winds at the 33-foot level was generally from the southeast sector. The only exception was under Class G stability conditions when the highest frequency was from the north-northeast sector.
The monthly distributions (Tables 2.3-11 through 2.3-22) show a similar high frequency of winds from the southeast sector. Exceptions are the distributions for 2.3-2
BFN-25 January, February, and September, which reveal a high frequency of winds from the north-northwest, north-northeast, and north-northeast sectors, respectively.
Annual and monthly wind direction patterns at the 33-foot level are shown in wind rose plots, Figures 2.3-1 through 2.3-20.
Upper Level At the 300-foot wind sensor level, the distributions (Tables 2.3-23 through 2.3-30) reveal that the maximum frequency of winds is generally from the southeast sector.
Under stabilities A, B, and C, the highest frequencies of winds were from the west or southwest sector, but these combined frequencies occurred less than one percent of the total time. For Class G stability conditions, the highest frequency was from the south-southeast sector.
The monthly distributions (Tables 2.3-31 through 2.3-42) show a high frequency of winds from the southeast and south-southeast sectors.
Exceptions are the distributions for January and February, which reveal a maximum frequency of winds from the northwest and north sectors, respectively.
Annual and monthly wind direction patterns at the 300-foot level are given in wind rose plots, Figures 2.3-21 through 2.3-40.
2.3.4.2 Wind Direction Persistence Persistent wind is defined in this analysis as a continuous wind from one of the 22-1/2 degree sectors (e.g., north-northeast). The persistence is not considered to be interrupted if the wind departs from the sector for one hour and then returns, or if there are up to two hours of missing data followed by a continuation of the same directional persistence.
Tables 2.3-43 and 2.3-44 are summaries of the wind direction persistence durations at the 33 and 300-foot levels, respectively. From these tables, it can be seen that the wind directions which were the most persistent were from the southeast and south-southeast sectors.
At the lower level, about 20 percent of the persistence cases were equal to 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or more, about 4 percent were equal to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or more, and about 0.2 percent were equal to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or more. The four highest persistence durations at this level were 36, 33, 32, and 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br /> with southeast, southeast, south, and north-northwest winds, respectively.
At the upper level, about 22 percent of the persistence cases were equal to 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or more, about 4 percent were equal to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or more, and about 0.4 percent 2.3-3
BFN-25 were equal to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or more. The four highest persistence durations at the 300-foot level were 38, 36, 33, and 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br /> with south-southeast, southeast, southeast and south winds, respectively.
2.3.4.3 Wind Speed Lower Level Average wind speeds at the 33-foot level under different stability conditions (Tables 2.3-3 through 2.3-9) ranged from a low of 3.2 mph under G stability to a high of 7.2 mph under B stability. The highest occurrence of wind speeds was in the 3.5-5.4 mph range under unstable and neutral conditions (Classes A, B, C, and D), and in the 1.5-3.4 mph range under stable conditions (Classes E, F, and G).
The overall mean wind speed, disregarding stability, was 5.7 mph (Table 2.3-10).
The highest occurrence of wind speeds for this distribution was in the 3.5-5.4 mph range with winds primarily from the southeast sector.
From the monthly distributions (Tables 2.3-11 through 2.3-22), it is observed that the highest average wind speeds occurred in the winter and early spring (December through March) and the lowest values occurred in late spring to late fall (May through October). The highest occurrence of wind speeds was in the 7.5-12.4 mph range for January; in the 1.5-3.4 mph range for May, June, and November; and in the 3.5-5.4 mph range for the remaining months.
Annual and monthly wind speed patterns at the 33-foot level are also shown in wind rose plots, Figures 2.3-1 through 2.3-20.
Upper Level Average wind speeds at the 300-foot level, under different stability conditions (Tables 2.3-23 through 2.3-29), ranged from a low of 9.5 mph under A stability to a high of 12.1 mph under D and F stabilities. The highest occurrence of wind speeds was in the 5.5-7.4 mph range under A stability, in the 7.5-12.4 mph range under C, D, and G stabilities, and in the 12.5-18.4 mph range under B, E, and F stabilities.
The overall mean wind speed, disregarding stability, was 12.0 mph (Table 2.3-30).
The highest occurrence of wind speeds for this distribution was in the 7.5-12.4 mph range.
From the monthly distributions (Tables 2.3-31 through 2.3-42), it is observed that the highest average wind speeds occurred in the winter and early spring (December through March) and the lowest values occurred in the late spring and summer (May through August). The highest occurrence of wind speeds was in the 7.5-12.4 mph range for May through September, and in the 12.5-18.4 mph range for the remaining months.
2.3-4
BFN-25 Annual and monthly wind speed patterns at the 300-foot level are also shown in wind rose plots, Figures 2.3-21 through 2.3-40.
A detailed discussion of meteorological diffusion evaluation methods is presented in Section 14.8.5.2.
2.3.5 Temperature and Precipitation 2.3.5.1 Temperature The climate at the Browns Ferry site is interchangeably continental and maritime in winter and spring, predominantly maritime in summer, and generally continental in fall. The mean annual temperature at Decatur3, Alabama, during 1879-1958, was 62.0°F.
In a typical year at Decatur, there are about 70 days with maximum temperatures equal to or greater than 90°F and about 57 days with minimum temperatures equal to or less than 32°F. The most extreme daily temperatures recorded during this 80-year period occurred in June 1914 (108°F) and in February 1899 (-12°F).
Temperature statistics for Decatur (period of record 1879-1958) are given in Table 2.3-45. Table 2.3-46 gives temperature statistics for the Browns Ferry meteorological facility for January 1, 1977 - December 31, 1979. Because of the longer period of record, the Decatur data are considered more representative of normal temperatures in the area.
2.3.5.2 Precipitation Much of the annual precipitation at the Browns Ferry site results from migratory storms in the winter and early spring (December through April).4 Most of the remaining precipitation is in June and July when air mass thundershower activity is common. October usually has the lowest precipitation.
The maximum 1-hour rainfall which may be representative for the Browns Ferry site area was 2.12 inches, recorded in Moulton,5 20 miles southwest of the site, for the 11-year period, 1940-50. The maximum 1-hour rainfall for a 100-year frequency is 3.3 inches.6 The site underground storm drainage system is designed for a maximum rainfall of 4 inches per hour.
Precipitation statistics from Huntsville for the 13-year period, 1968-1980, and normals for 1941-1970 are given in Table 2.3-47. These data are considered more representative of the normal than precipitation data from the Browns Ferry 2.3-5
BFN-25 meteorological facility for January 1, 1977 - December 31, 1979, given in Table 2.3-48.
2.3.5.3 Snowfall Snow does not often occur at the Browns Ferry site and seldom accumulates on the ground for more than a few days. Decatur3 snowfall data in Table 2.3-49 are considered representative of the site area. The maximum 24-hour snowfall7 reported was 17.1 inches in December 1963; next highest were 10.1 and 10.0 inches in January 1940 and February 1895, respectively.
2.3.6 Storms 2.3.6.1 Thunderstorms During 1968-1980, there were about 57 days annually on which thunderstorms were reported in the Huntsville area.4 Thunderstorms occurred most frequently in July, August, June, and May. November and December had the smallest number of thunderstorms, with an average of one thunderstorm day each month.
Windstorms (often associated with thunderstorms) may occur several times a year, particularly in winter, spring, and summer, with winds occasionally exceeding 40 mph. In 1964, 95 mph winds, with rain and hail, were reported at the Redstone Arsenal, 25 miles east-southeast of the site. Also in April 1958 and July 1963, winds were reported in excess of 70 mph in the Huntsville area.
2.3.6.2 Tornadoes There were four tornadoes reported in Limestone County during the 50-year period 1916-65.8, 9 In the adjacent counties, Morgan and Madison, 18 tornadoes were reported during the same period. The bordering Southern Tennessee counties, Giles and Lincoln, reported 13 and 5 tornadoes, respectively, during the 55-year period 1916-70.10 Tornado data compiled by the severe local storms (SELS) unit of the National Weather Service11 for the period 1955-67 were used for evaluating the tornado probability for the Browns Ferry site. In the 1-degree latitude/longitude square containing the site (about 3,930 mi2), there were 31 tornadoes reported during the 13-year period, or about 2.38 tornadoes per year. Thom's value12 for the mean tornado path area (2.82 mi2) was used in calculating an annual point probability for the site of 1.71 x 10-3; this is equivalent to a mean recurrence interval of about 600 years.
The National Severe Storms Forecast Center in Kansas City, Missouri calculated the tornado return probability for the Browns Ferry site based on tornado occurrences 2.3-6
BFN-25 within a 30 nautical mile (nm) radius during 1950-1986.13 A circle of 30 nm radius has an area comparable to a one degree latitude-longitude square. Based on 48 tornado occurrences having path size estimates in the 37-year period, the return probability is 6.979x10-4 and the mean return interval is 1,433 years. The annual tornado occurrence in the 30 nm radius circle is 1.81 (based on 67 tornadoes reported).
2.3.7 Onsite Meteorological Measurement Program 2.3.7.1 Siting and Description of Instruments Collection of onsite meteorological data at the Browns Ferry Nuclear Plant commenced in February 1967 from a meteorological tower located about 0.5 mile north-northeast of the reactor building and about 25 feet above plant grade. This facility was moved in early 1970 to a new location approximately 0.7 mile north-northwest of the reactor building and about 10 feet above plant grade. In March 1973, the facility was moved to its present location about 0.5 mile east-southeast of the reactor building and about 30 feet above plant grade.
The permanent meteorological facility consists of a 91-meter (300-foot) instrumented tower for wind and temperature measurements, a separate 10-meter (33-foot) tower for dewpoint measurements, a ground based instrument for rainfall measurements, and a data collection system in an instrument building (Environmental Data Station or EDS). The data collected include: wind speeds and directions at the 33-, 150-,
and 300-foot levels (wind data collection at 150 feet began on April 23, 1976);
temperatures at the 33-, 150-, and 300-foot levels (temperature data collection at four feet ended on May 24, 1979); and dewpoint temperatures at the 33-foot level (dewpoint data collection at 150 and 300 feet ended on March 6, 1978 and the 4-foot dewpoint data collection ended on November 15, 1978). The dewpoint sensor was moved to a separate tower on September 27, 1994. More exact heights for wind and temperature sensors are given in the EDS Manual.14 Rainfall is monitored from a rain gage located about 70 feet from the tower. The meteorological sensors are connected to the data collection and recording equipment in the EDS.
A system of lightning and surge protection circuitry with proper grounding is included in the facility design.
Instrument Description A description of the meteorological sensors follows. More detailed sensor specifications are included in the EDS manual. Replacement sensors, which may be of a different manufacturer or model, will satisfy Regulatory Guide 1.23 (Revision 1) specifications.15 2.3-7
BFN-25 SENSOR HEIGHT (feet) DESCRIPTION Wind Direction 33, 150, Ultrasonic Wind Sensor and Wind Speed and 300 Temperature 33, 150 Platinum Wire Resistance and 300 Detector (RTD) with aspirated radiation shield Dewpoint 33 Capacitive Humidity Sensor Rainfall 4 Tipping bucket rain gauge 2.3.7.2 Data Acquisition System This data acquisition system is located at the EDS and consists of meteorological sensors, a computer (with peripherals), and various interface devices. These devices send meteorological data to the plant, to the Central Emergency Control Center (CECC), and to enable callup for data validation and archiving offsite. An older data collection system, which included a NOVA minicomputer, was replaced by a new system on September 28, 1988. The previous data collection system, which included a micro-VAX minicomputer, was replaced by a new system on September 10, 2010.
System Accuracies The meteorological data collection system is designed and replacement components are chosen to meet or exceed specifications for accuracy identified in NRC Regulatory Guide 1.23 (Revision 1).
The meteorological data collection system satisfies the Regulatory Guide 1.23 accuracy requirements. A detailed listing of error sources for each parameter is included in the EDS manual.
2.3.7.3 Data Recording and Display The data acquisition is under control of the computer program. The output of each meteorological sensor is scanned periodically, scaled, and the data values are stored.
Meteorological sensor outputs (except rainfall) are measured every five seconds (720 per hour). Rainfall is measured continuously as it occurs. Software data processing routines within the computer accumulate output and perform data calculations to generate 15-minute and hourly averages of wind speed and 2.3-8
BFN-25 temperature, 15-minute and hourly vector wind speed and direction, 15-minute and hourly total precipitation, hourly average dewpoint, and hourly horizontal wind direction sigmas. Prior to April 1987, a prevailing wind direction calculation method was used. Subsequently, vector wind speed and direction have been calculated along with arithmetic average wind speed. Prior to October 20, 2010, temperature and dewpoint were measured every minute (60 per hour).
Selected data each 15 minutes and all data each hour are stored for remote data access.
Data sent to the plant control room every 15 minutes includes 33-, 150-, and 300-foot wind direction, average wind speed, and temperature values. Hourly data sent includes all of these plus the precipitation amount.
Data sent to the CECC computer in Chattanooga every 15 minutes includes 33-,
150-, and 300-foot wind direction, wind speed, and temperature values. All data is sent to the CECC every hour. This data is available from the CECC computer to other TVA and the State emergency centers in support of the Radiological Emergency Plan, including the technical support center at Browns Ferry. Remote access of meteorological data by the Nuclear Regulatory Commission during emergency situations is available through the CECC computer.
Data are sent from the EDS to an offsite computer for validation, reporting, and archiving.
2.3.7.4 Equipment Servicing, Maintenance, and Calibration The meteorological equipment at the EDS is serviced by either engineering aides, instrument technicians, or engineers. Maintenance and calibrations are performed by either instrument technicians, electrical engineering associates, or electrical engineers.
Most equipment is calibrated or replaced at least every six months of service. The methods for maintaining a calibrated status for the components of the meteorological data collection system (sensors, recorders, electronics, DVM, data logger, etc.) include field checks, field calibration, and/or replacement intervals for individual components, on the basis of operational history of the component type. Procedures and processes such as appropriate maintenance processes (procedures, work order/work request documents, etc.) are used to calibrate and maintain meteorological and station equipment.
2.3.7.5 Operational Meteorological Program The operational phase of the meteorological program includes those procedures and responsibilities related to activities beginning with the initial fuel loading and continuing through the life of the plant. The meteorological data collection program is continuous 2.3-9
BFN-25 without major interruptions. The meteorological program has been developed to be consistent with the guidance given in NRC Regulatory Guide 1.23 (Revision 0) and the reporting procedures in Regulatory Guide 1.21 (Revision 1).18 The basic objective is to maintain data collection performance to assure at least 90% joint recoverability and availability of data needed for assessing the relative concentrations and doses resulting from accidental or routine releases.
The restoration of the data collection capability of the meteorological facility in the event of equipment failure or malfunction will be accomplished by replacement or repair of affected equipment. A stock of spare parts and equipment is maintained to minimize and shorten the periods of outages. Equipment malfunctions or outages are detected by personnel during routine or special checks. Equipment outages that affect the data transmitted to the plant can be detected by review of data displays in the reactor control room. Also, checks of data availability to the emergency centers are performed each work day. When an outage of one or more of the critical data items occurs, the appropriate maintenance personnel will be notified.
In the event that the onsite meteorological facility is rendered inoperable, or there is an outage of the communications of data access systems; there is no fully representative offsite source of meteorological data for identification of atmospheric dispersion conditions. Therefore, TVA has prepared procedures to provide for missing or garbled data. These procedures incorporate available onsite data (for a partial loss of data), offsite data, and conditional climatology. The CECC meteorologist will apply the appropriate procedures.
2.3.8 Conclusions The meteorology of the Browns Ferry site provides generally favorable atmospheric conditions for transport and dispersion of plant emissions (see Section 14 and Appendix E). There are no physiographical features in the area to cause local entrapment or accumulation of emissions, particularly during extended periods of anticyclonic circulation or atmospheric stagnation. Limited air mass modification may occur within the lower few hundred feet, particularly with southeast winds when the over-water trajectory may approach 10 miles. Evaluation of the site meteorological information collected since preparation of the Design and Analysis Report confirms earlier judgment that the protective features for provision of routine atmospheric discharge of radioactive material will be adequate.
The Browns Ferry site is located in an area occasionally traversed by cyclonic storms. Wind speeds in excess of 40 mph are occasionally reported, but wind speeds in excess of 75 mph are rare. The estimated probability of a tornado occurrence at the Browns Ferry site in any one year is 6.979 x 10-4, or about one occurrence in 1,433 years should be expected. In spite of the low probability, the plant is designed to withstand tornado forces. (See section 12 for design wind and tornado loadings.)
2.3-10
BFN-25 Because of the suitable physiographical features and adequate atmospheric diffusion conditions, it is anticipated that routine emission rates for atmospheric release of radioactive material will be favorable as compared with calculated maximum permissible emission rates (see Appendix E).
2.3-11
BFN-25 REFERENCES
- 1. Discussion with staff meteorologists. Dr. W. Johnson, W. F. Hilsmeier, and W. M. Culkowski, Atmospheric Turbulence and Diffusion Laboratory, Oak Ridge, Tennessee, April 6, 1966.
- 2. "Low-Level Inversion Frequency in the Contiguous U.S.," Hosler, Charles R.,
Monthly Weather Review, 89, No. 9, 1961, pp. 319-39.
- 3. The Climate of Decatur, Alabama (1879-1958), Long, Arthur R., U.S. Weather Bureau State Climatologist for Alabama, Weather Bureau Office, Montgomery, Alabama, July 1959.
- 4. "Local Climatological Data," Annual Summary with Comparative Data, Huntsville, Alabama, NOAA, National Climatic Center, Asheville, NC, 1980.
- 5. Maximum Station Precipitation for 1, 2, 3, 6, 12, and 24 Hours, Alabama, Technical Paper No. 15, U.S. Weather Bureau, December 1955.
- 6. Rainfall Frequency Atlas of the United States, Technical Paper No. 40, U.S.
Weather Bureau.
- 7. "Summary of Monthly Aerological Records." Huntsville, Alabama (WBAN 03856), Office of Navy Representative, National Weather Records Center.
- 8. Tornado Occurrences in the United States, Technical Paper No. 20, U.S.
Department of Commerce, Weather Bureau, September 1952.
- 9. Monthly Weather Review, Vol. 78 (1950) through Vol. 93 (1965), U.S.
Department of Commerce, Weather Bureau.
- 10. Climatology of Tennessee, NWS Office for State Climatology, NOAA, Environmental Data Service, NCC, Asheville, NC.
- 11. Severe Local Storm Occurrences, 1955-1967, ESSA, Technical Memorandum WBTM 12, U.S. Department of Commerce, September 1969.
- 12. "Tornado Probabilities," Thom, H.C.S., Monthly Weather Review, October-December 1963.
- 13. Tornado data for the Browns Ferry Nuclear Plant site prepared by the National Severe Storms Forecast Center, Kansas City, Missouri, November 1987.
- 14. Browns Ferry Nuclear Plant Environmental Data Station Manual, U.S.
Tennessee Valley Authority 2.3-12
BFN-25
- 15. U.S. Nuclear Regulatory Commission, Regulatory Guide 1.23, Revision 1, Meteorological Monitoring Programs for Nuclear Power Plants, Washington, D.C., March 2007.
- 16. Deleted
- 17. Deleted
- 18. Regulatory Guide 1.21, Revision 1, "Measuring, Evaluating, and Reporting Radioactivity in Solid Wastes and Releases of Radioactive Materials in Liquid and Gaseous Effluents from Light-Water-Cooled Nuclear Power Plants," U.S.
Atomic Energy Commission, Washington, D.C., June 1974.
2.3-13