Atmospheric Dispersion in Nuclear Power Plant Siting IAEA Safety Series 50-SG-S3
Introduction <ul><li>The atmosphere is an important pathway for the transport of radioactive releases from a nuclear power...
Meteorological investigation at different stages <ul><li>Site Survey </li></ul><ul><li>Meteorological characteristics alon...
Site Evaluation <ul><li>During the design and licensing of a nuclear power pant, evaluations shall be made of the concentr...
Need of Meteorological Data <ul><li>Meteorologica l  characteristic of the site should be well understood preceding the li...
Limitation of Meteorological Measurements <ul><li>The actual dispersion is of  Lagrangian characteristics in which each pa...
Terrain Consideration <ul><li>Meteorological measurement are oftenly determined by the terrain due to the reasons. </li></...
Type of Meteorological data required <ul><li>The precision, nature and scope of meteorological data to be collected should...
<ul><li>Indicators for Turbulence: </li></ul><ul><li>Air temperature and temperature laps rate. </li></ul><ul><li>Sky cove...
Instrumentation for data collection <ul><li>The meteorological instrumentation system should have performance within the l...
Terrain Complexity <ul><li>Wind and air temperatures are affected by terrain irregularities and the presence of large wate...
<ul><li>Coastal Sites </li></ul><ul><li>Sites near large water bodies are subject to distinct following local wind system....
Atmospheric Dispersion <ul><li>A radioactive gas once become airborne travels and disperses in a manner that is influenced...
<ul><li>The effluent movement is also affected by wind during and after rise which is called Guide transport.  </li></ul><...
Types of Dispersion Models <ul><li>Selection of models and input data to fit  a specific situation depends upon the charac...
The Effluent Behavior <ul><li>The effluent undergoing plume rise may subject to processes such as: </li></ul><ul><li>Radio...
Indicators of Turbulence <ul><li>While using dispersion models it is necessary to specify atmospheric stability as functio...
<ul><li>Adiabatic condition:  If the rate of change in temperature is per unit altitude then it is called the adiabatic la...
<ul><li>Inversions:   When the temperature increases over some range in altitude and some where not then the condition exi...
<ul><li>3. Insolation, cloudiness and wind speed: </li></ul><ul><li>Insolation, cloudiness and wind speed are also used to...
Stability Classes <ul><li>Following are the six stability classes using solar radiation and net night radiation with wind ...
Note: 1 langley= 1 cal.cm -2 =4.187 J.cm -2 STABILITY CLASSIFICATION TABLE, USING SOLAR RADIATION AND  NIGHTNET RADIATION,...
Atmospheric Dispersion Calculations  Approaches <ul><li>Theoretically following approaches may be adopted to treat atmosph...
Nature of Sources <ul><li>In atmospheric dispersion calculations different kinds of sources are usually classified in term...
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Atmospheric Dispersion in Nuclear Power Plant Siting

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  • The stability conditions in two regions will usually be different in the two regimes. The dispersion of pollutants will therefore differ in rate and direction in each regime.
  • Atmospheric Dispersion in Nuclear Power Plant Siting

    1. 1. Atmospheric Dispersion in Nuclear Power Plant Siting IAEA Safety Series 50-SG-S3
    2. 2. Introduction <ul><li>The atmosphere is an important pathway for the transport of radioactive releases from a nuclear power plant to the environment and there by to man. Meteorological phenomenon and mechanism is involved in the dispersion of the released effluent in the atmosphere. To calculate the concentration and deposition in a region, different models may be used. Specific inputs data is required to for such type of calculation. Meteorological data is one of the inputs. This guide emphasis Selection of models and input data to fit a specific situation for accurate measurement of dispersed radionuclide. </li></ul>
    3. 3. Meteorological investigation at different stages <ul><li>Site Survey </li></ul><ul><li>Meteorological characteristics along with population density and land use in a region are important factors while determining the suitability of a site for power plant siting. At the stage of site survey climatic information may be gathered from nearby synoptic weather station. Adverse meteorological characteristics i.e. channeled flow, unfavorable wind prevailing wind direction or stability conditions should be studied in combination with population distribution. IAEA safety series No. 50-SG-S4 is also helpful in site selection and evaluation for Nuclear Power Plant. </li></ul>
    4. 4. Site Evaluation <ul><li>During the design and licensing of a nuclear power pant, evaluations shall be made of the concentrations due to effluent which may release from the plant in operational states and accidental conditions. Therefore significant meteorological variables are determined for input into dispersion calculations for statistical analysis, which might be helpful to obtain probability distribution of concentration of radioactive material released from the plant. </li></ul>
    5. 5. Need of Meteorological Data <ul><li>Meteorologica l characteristic of the site should be well understood preceding the licensing stages. However need of meteorological data during the routine operation is not much extensive These information will be helpful to determine: </li></ul><ul><li>The short and long-term routine radioactive releases to the environment. </li></ul><ul><li>To take countermeasures after an accidental release (contingency Planning). </li></ul><ul><li>A programme for meteorological measurement along with forecast is essential for implementing of emergency measures </li></ul>
    6. 6. Limitation of Meteorological Measurements <ul><li>The actual dispersion is of Lagrangian characteristics in which each parcel of fluid during its travel may be subjected to the following conditions very different from the source. </li></ul><ul><li>Physical and chemical state of effluents </li></ul><ul><li>Terrain and height of the source </li></ul><ul><li>Meteorological condition </li></ul><ul><li>Variation in plume w.r.t distance and time </li></ul><ul><li>Consideration of the above conditions can permit a proper evaluation of the dispersion using dispersion models. </li></ul>
    7. 7. Terrain Consideration <ul><li>Meteorological measurement are oftenly determined by the terrain due to the reasons. </li></ul><ul><li>Hill side meteorological measurements provide data that is applicable only to its immediate surrounding. </li></ul><ul><li>Plant structure in particular cooling towers may effect atmospheric dispersion. </li></ul><ul><li>While collecting meteorological data, such local effects should be considered such that these may not affect the values of the variables to be measured. </li></ul>
    8. 8. Type of Meteorological data required <ul><li>The precision, nature and scope of meteorological data to be collected should be compatible with the methods and models in which they may be used. </li></ul><ul><li>The bases of such programme are: </li></ul><ul><li>General Meteorological Data: </li></ul><ul><li>Air Temperature </li></ul><ul><li>Air flow ( wind direction and speed with duration) </li></ul><ul><li>Thickness if mixing layer </li></ul><ul><li>Precipitation </li></ul><ul><li>Humidity </li></ul><ul><li>Cont….. </li></ul>
    9. 9. <ul><li>Indicators for Turbulence: </li></ul><ul><li>Air temperature and temperature laps rate. </li></ul><ul><li>Sky cover during day ,night or net radiation </li></ul><ul><li>Wind direction fluctuations </li></ul><ul><li>Wind speed at different heights </li></ul><ul><li>It is useful to have good knowledge of the space and time distribution of such variables to understand and determine effluent trajectory. The inaccurate information collected about turbulence indicators may lead to wrong estimates of the concentrations. </li></ul>
    10. 10. Instrumentation for data collection <ul><li>The meteorological instrumentation system should have performance within the limit described in the manual. The instruments systems should be protected, maintained, serviced and calibrated. Latest instruments available in the market for the collection of this type of data should be preferred. </li></ul>
    11. 11. Terrain Complexity <ul><li>Wind and air temperatures are affected by terrain irregularities and the presence of large water bodies. There are two main types of complex terrains. </li></ul><ul><li>Uneven terrain e.g. ridges and valleys </li></ul><ul><li>Coastal areas, or an area near large water bodies </li></ul><ul><li>Uneven Terrain </li></ul><ul><li>In uneven terrain the mean atmospheric flow comprises of </li></ul><ul><li>Lower regime where wind are locally effected by structures, hills and valleys. </li></ul><ul><li>Upper regime where winds are not affected. </li></ul>
    12. 12. <ul><li>Coastal Sites </li></ul><ul><li>Sites near large water bodies are subject to distinct following local wind system. </li></ul><ul><li>In fair weather wind direction depends on the position of the sun i.e. towards land during day and toward water during night. </li></ul><ul><li>The on-shore and off-shore winds experience a change of surface roughness and temperature gradient patterns which under appropriate condition may result in recirculation of fumigation. </li></ul>
    13. 13. Atmospheric Dispersion <ul><li>A radioactive gas once become airborne travels and disperses in a manner that is influenced by its own physical properties and those of ambient atmosphere into which it is released. </li></ul><ul><li>The effluent once released into the atmosphere with certain velocity and temperature are generally different that of the ambient atmosphere. The effluent motion has vertical component due to the effects of vertical velocity and difference of temperature until they are dissipated. </li></ul><ul><li>The vertical rise of the effluent is called the plume rise and it changes the effective height of the release point. </li></ul><ul><li>Cont…. </li></ul>
    14. 14. <ul><li>The effluent movement is also affected by wind during and after rise which is called Guide transport. </li></ul><ul><li>The turbulent motion of the atmosphere causes random movement of the effluent resulting in a progressive lateral and vertical spreading by mixing with air called Guide atmospheric dispersion. </li></ul><ul><li>The combination of transport and diffusion is called atmospheric dispersion . </li></ul>
    15. 15. Types of Dispersion Models <ul><li>Selection of models and input data to fit a specific situation depends upon the characteristics of the site and its region and conditions of release. Some typical uses of atmospheric dispersion models are: </li></ul><ul><li>To derive shot-term concentration and deposition values. </li></ul><ul><li>To determine long-term time integrated concentration and deposition </li></ul><ul><li>The model we will discuss are applicable to the situation where the meteorological parameters are reasonably uniform in time and space. </li></ul>
    16. 16. The Effluent Behavior <ul><li>The effluent undergoing plume rise may subject to processes such as: </li></ul><ul><li>Radioactive decay and buildup of daughter products. </li></ul><ul><li>Wet deposition (Rainout/snow out by water droplets as precipitation or Washout by falling precipitation) </li></ul><ul><li>Dry deposition (Gravitational settling) </li></ul><ul><li>Formation of aerosols and coalescence of aerosols. </li></ul><ul><li>Re-suspension of material deposited on surface </li></ul>
    17. 17. Indicators of Turbulence <ul><li>While using dispersion models it is necessary to specify atmospheric stability as function of meteorological parameters such as: </li></ul><ul><li>1.Temperature laps rate: The rate of decrease of temperature with height i.e. -dT/dZ. The temperature distribution in the atmosphere frequently differs from normal adiabatic behavior and may have any of following conditions: </li></ul><ul><li>Cont…. </li></ul>
    18. 18. <ul><li>Adiabatic condition: If the rate of change in temperature is per unit altitude then it is called the adiabatic lapse rate. This lapse rate is about 1 o C/100 m as shown in fig. </li></ul><ul><li>Super adiabatic condition: Over certain ranges in altitude the rate of temperature decrease may be more rapid than the adiabatic rate, and in this case, the stratum of air is said to exhibit super adiabatic behavior. </li></ul><ul><li>Stable condition: In stable condition at the altitude the rate of temperature decrease is less rapid as compared to adiabatic rate and the stratum. </li></ul><ul><li>Cont… </li></ul>
    19. 19. <ul><li>Inversions: When the temperature increases over some range in altitude and some where not then the condition exist called an inversion. </li></ul><ul><li>Isothermal condition: When the temperature remains constant across a stratum, it is then known as isothermal. </li></ul><ul><li>2 . Wind direction Fluctuation: The wind direction fluctuation is also used to characterize the atmospheric stability. The standard deviation of the wind direction is obtained by electronic devices or by wind direction records. The wind direction record shows different width of trace for different stability conditions </li></ul><ul><li>Cont… </li></ul>
    20. 20. <ul><li>3. Insolation, cloudiness and wind speed: </li></ul><ul><li>Insolation, cloudiness and wind speed are also used to determine the stability classes. </li></ul><ul><li>Thermal turbulence is related to heat flux. The cloud cover reduces the heat losses or heat gain tending to make the stability neutral. </li></ul><ul><li>Strong winds increase mixing and lead to neutral stability. </li></ul><ul><li>Clear skies at night with low winds make for stable atmosphere. Whereas, the similar conditions in day time make for an unstable atmosphere. </li></ul><ul><li>During the day solar radiation measurement or estimates are useful in determining the stability classes . </li></ul><ul><li>4. Richardson and Bulk Richardson Number: </li></ul><ul><li>These reflect the imbalance between thermal or convective turbulence. </li></ul>
    21. 21. Stability Classes <ul><li>Following are the six stability classes using solar radiation and net night radiation with wind speed. </li></ul><ul><li>A Extremely stable </li></ul><ul><li>B Moderately stable </li></ul><ul><li>C Slightly unstable </li></ul><ul><li>D Neutral </li></ul><ul><li>E Slightly stable </li></ul><ul><li>F Moderately stable </li></ul><ul><li>The incoming solar radiation may be measured by pyrheliometer. At night net radiation flux is measured by net radiometer. </li></ul>
    22. 22. Note: 1 langley= 1 cal.cm -2 =4.187 J.cm -2 STABILITY CLASSIFICATION TABLE, USING SOLAR RADIATION AND NIGHTNET RADIATION, WITH WIND SPEED (Pasquill-Gifford Table) D - - D E F D D E D D D D D D A A-B B D A-B B C D B B-C C D C C-D D D C D D D U<2 2≤U<3 3≤U<4 4≤U<5 5≤U R N > -1.8 -1.8≥ R N ≥-3.6 -3.6>R N R D ≥50 50> R D ≥ 25>R D ≥12.5 12.5> R D Stability class, day, with solar radiation R D (langleys/h) Stability class, day, with solar radiation R D (langleys/h) Wind speed U(m/s) At 10 m
    23. 23. Atmospheric Dispersion Calculations Approaches <ul><li>Theoretically following approaches may be adopted to treat atmospheric dispersion with their own limitations: </li></ul><ul><li>The gradient transfer or K-theory approach </li></ul><ul><li>The statistical theory approach </li></ul><ul><li>The dimensional analysis approach </li></ul><ul><li>The K-theory approach is mainly used for such type of calculations which can take space-time variations of wind and stability conditions and terrain complexity into account. </li></ul>
    24. 24. Nature of Sources <ul><li>In atmospheric dispersion calculations different kinds of sources are usually classified in terms of spatial configuration and duration of release which are: </li></ul><ul><li>Point sources </li></ul><ul><li>Line and area sources </li></ul><ul><li>Volume sources </li></ul><ul><li>Actual sources of radioactive effluent are not point sources but may be considered for mathematical simplicity. Line and area sources may be treated by subdivision into a number of effective point sources. For large volume sources a virtual point source may be considered. </li></ul>

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