AtmosphericDispersion

Gaussian-plume dispersion of stack releases: dilution factor, time-integrated air concentration, dry and wet ground deposition, and resuspension, over Pasquill–Gifford stability classes and a wind rose.

The solver core is nuclide-agnostic. A species enters only through its decay constant and its deposition velocity, so tritium from a heavy-water reactor — the case the original work addressed — is a parameterisation rather than an assumption.

A worked run

using AtmosphericDispersion

source = StackSource(;
    height = 50.3, diameter = 2.33, exit_velocity = 10.0,
    exit_density = 0.6, exit_temperature = 324.0,
)
atmosphere = Atmosphere(;
    reference_speed = 4.0, temperature = 287.0, density = 1.2,
    lapse_rate = 0.02, surface = SURFACE_AGRICULTURAL,
    roughness = ROUGHNESS_PASTURE,
)
site = Site(; source, atmosphere)

# A wind rose must declare which way its directions are read.
grid = SectorGrid(16)
rose = WindRose(grid, fill(1/16, 16), BlowingFrom(); stability = fill(1/6, 6))

# Long-term dilution 5 km due south of the stack, with tritium depletion.
dilution_long_term(0.0, -5000.0, site, rose; nuclide = TRITIATED_WATER)

Or from a configuration file:

config = load_configuration("config/reference.toml")
dilution_long_term(0.0, -config.extent, config.site, config.rose;
                   nuclide = config.nuclide)

Conventions

Receptor positions are given in the geographic frame as displacements from the stack, east first then north, in metres. Bearings are in radians clockwise from north. A wind direction is the direction the wind blows from, as in meteorological practice and in ADMS.

Sectors are indexed clockwise from north with sector 1 centred on north, so that for sixteen sectors the index runs N, NNE, NE and so on. Centring rather than starting at north puts the cardinal directions at sector centres, where binning cannot be decided by floating-point round-off.

The long-term dilution formula weights by the frequency of wind blowing towards the receptor's sector, which is the opposite reading. WindRose therefore takes the convention as a required argument and stores blowing-towards internally, so the formulae cannot be fed the wrong sense. Getting this wrong rotates the whole field by half a turn while leaving every magnitude and sum rule intact.

The module

AtmosphericDispersion

Pages

• Conventions
• • The wind-direction convention
  • What the convention costs
  • Depletion composes by multiplication
• Validation
• • Against the published literature
• The 2021 thesis code
• • How far the 2021 results move
• Sectors, stability and the wind rose
• • Sector geometry
  • Stability classes
  • Wind rose
• Site and dispersion parameters
• • Surface categories
  • Tabulated coefficients
  • The mixing layer
  • Wind profile and dispersion parameters
  • Source and ambient state
  • Plume rise
  • Buildings
  • Site
• Dilution, depletion and deposition
• • Dilution
  • Nuclides
  • Depletion
  • Ground deposition and resuspension
• Configuration
• • The [model] table
  • The [mixing_layer] table
  • The [nuclide] table
  • The [buildings] table
  • The [wind_rose] table
  • Reference
• References