1. Radionuclide dispersion modelling
Radiation Protection of the Environment (Environment Agency Course, July 2015)

2. By the end of the presentation and practical you should….
Radiological protection of the Environment: CEH Lancaster November 2010
By the end of the presentation and practical you should….
Understand the purpose of dispersion models
Know the origin of the dispersion models used in ERICA
Be able to use some of the basic dispersion models provided in ERICA
Radiation dosimetry 2 2

3. Radiological protection of the environment: CEH Lancaster 24th - 26th November 20103

4. What happens if do not have media concentration?
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
What happens if do not have media concentration?
Need method of predicting from release rates
If have dispersion model can run and input predictions
If not then ERICA has some screening level models built-in to enable this in Tiers 1 and 2 4

5. Taken from IAEA SRS Publication 19
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Taken from IAEA SRS Publication 19
Designed to minimise under-prediction (conservative generic assessment): ‘Under no circumstances would doses be underestimated by more than a factor of ten.’
A default discharge period of 30 y is assumed (estimates doses for the 30th year of discharge)
Models - atmospheric, freshwater (lakes and rivers) and coastal water models available 5

6. SRS-19 is linked to ERICA help file
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Taken from IAEA SRS Publication 19
Designed to minimise under-prediction (conservative generic assessment): ‘Under no circumstances would doses be underestimated by more than a factor of ten.’
A default discharge period of 30 y is assumed (estimates doses for the 30th year of discharge)
Models - atmospheric, freshwater (lakes and rivers) and coastal water models available
SRS-19 is linked to ERICA help file 6

7. Atmospheric dispersion
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Atmospheric dispersion
Simple atmospheric dispersion model incorporating downwind transport (advection), mixing (turbulent diffusion) and effects of buildings
For continuous, long-term release (not accidents)
Gaussian plume model (=normal distribution in vertical and lateral axis)
Not applicable >20 km from release
in ERICA assume 20 km if >20 km
Assumes a predominant wind direction and neutral stability class (=doesn’t enhance or inhibit turbulence)
If you (really) want all the equations – see SRS-19 7

8. Atmospheric dispersion
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010 8

9. Atmospheric dispersion
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Importance of Release Height
Effective stack height 9

10. Conditions for the plume
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010 10

11. Conditions for the plume
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010 11

12. Output
Radionuclide activity concentrations in air (C,H,S & P) or soil (everything else)

13. Surface water dispersion
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Surface water dispersion
Freshwater
Small lake (< 400 km2)
Large lake (≥400 km2)
Estuarine
River
Marine
Coastal
No model for open ocean waters 13

14. Processes and assumptions
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Processes and assumptions
Processes included:
Flow downstream as transport (advection)
Mixing processes (turbulent dispersion)
Concentration in sediment estimated from ERICA Kd at receptor (equilibrium)
No loss to sediment between source and receptor
Half-life drives difference between RN in water
River flow conditions – 30 y low assumed 14

15. Small lakes and reservoirs
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Small lakes and reservoirs
Assumes a homogeneous concentration throughout the water body
Expected life time of facility is required as input 15

16. Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Large Lake
>400 km2
‘....as a rough rule a lake can be considered to be large when the opposite side of the lake is not visible to a person standing on a 30 m high shore.’ 16

17. Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Large Lake
Some restrictions related to short receptor discharge point distances (mixing zone)
Some restrictions related to length discharge pipe and angle to shoreline receptor
Estimates concentration along shoreline
Estimates concentration along plume centre line 17

18. Rivers (& Estuaries) Estuaries model similar to rivers
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Lz = distance to achieve full vertical mixing (=7D)
Estuaries model similar to rivers
Some tidal parameters used 18

19. Coastal waters Some restrictions related to:
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Some restrictions related to:
short receptor discharge point distances (mixing zone)
length discharge pipe and angle to shoreline receptor
Dispersion along the coast
Shoreline or ‘in sea’ receptors
For 10’s km (not >100 km) 19

20. Summary limitations of IAEA SRS 19
Radiological protection of the environment: CEH Lancaster 24th - 26th November 2010
Summary limitations of IAEA SRS 19
Simple environmental and dosimetric models as well as sets of necessary default data:
Simplest, linear compartment models
Simple screening approach (robust but conservative)
Short source-receptor distances
Equilibrium between liquid and solid phases - Kd
More complex / higher tier assessments:
Aerial model includes only one wind direction
Coastal dispersion model not intended for open waters e.g. oil/gas marine platform discharges
Surface water models assume geometry (e.g. river cross-section) & flow characteristics (e.g. velocity, water depth) which do not change significantly with distance / time
End of pipe mixing zones require hydrodynamic models 20