Modelling the environmental dispersion of radionuclides Jordi Vives i Batlle Centre for Ecology and Hydrology, Lancaster, 1st – 3rd April 2014
Download ReportTranscript Modelling the environmental dispersion of radionuclides Jordi Vives i Batlle Centre for Ecology and Hydrology, Lancaster, 1st – 3rd April 2014
Slide 1
Modelling the environmental
dispersion of radionuclides
Jordi Vives i Batlle
Centre for Ecology and Hydrology,
Lancaster, 1st – 3rd April 2014
Slide 2
What happens if do not have media
concentrations?
Need method of predicting from release rates over a
dilution pathway between source and receptor
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
www.radioecology-exchange.org
Slide 3
1 - Dispersion modelling in ERICA
www.radioecology-exchange.org
Slide 4
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
www.radioecology-exchange.org
SRS-19 is linked to ERICA
help file
Slide 5
Atmospheric dispersion
Gaussian plume
model version
depending on the
relationship between
building height &
cross-sectional area
of the building
influencing flow
Assumes a
predominant wind
direction and neutral
stability class
(=doesn’t enhance
or inhibit turbulence)
Key inputs: discharge rate Q & location of
source / receptor points
www.radioecology-exchange.org
Slide 6
Basic dispersion equation
A Gaussian plume model for an elevated release is as follows:
C x, y, z
Q
2 u 10 z y
2
2
z
H
y
S
exp
2
2
2 z
2 y
where C = the air concentration (Bq/m3) or its time integral Bq.s/m3
Q = release rate (Bq/s) or total amount released (Bq)
u10 = wind speed at 10 m above the ground (m/s)
z = standard deviation of the vertical Gaussian distribution (m)
y = standard deviation of the horizontal Gaussian distribution (m)
HS = effective release height (m)
x, y, z = rectilinear coordinates of the receptors
Importance of Release Height
Effective stack height
www.ceh.ac.uk/PROTECT
Slide 7
Conditions for the plume
(a)
(b)
(c)
a) H > 2.5HB (building height): No building effects
b) H 2.5HB & x > 2.5AB½ (cross-sectional area of building): Airflow in the
wake zone
c) H 2.5HB & x 2.5AB½: Airflow in the cavity zone. Two cases:
source / receptor at same building surface
not at same surface
Not generally applicable at > 20 km from stack
www.radioecology-exchange.org
Slide 8
Key parameters
Wind speed and direction
Release height
Precipitation
10 minute average from 10 m wind vane & anemometer
10 minute total rainfall (mm)
Stability or degree of turbulence (horizontal and vertical
diffusion)
Manual estimate from nomogram using time of day,
amount of cloud cover and global radiation level
Atmospheric boundary layer (time-dependent)
Convective and or mechanical turbulence
Limits the vertical transport of pollutants
www.radioecology-exchange.org
Slide 9
Output
Radionuclide
activity
concentrations in
air (C,H,S & P)
or soil
(everything else)
www.radioecology-exchange.org
Slide 10
Surface water dispersion
Freshwater
Marine
www.radioecology-exchange.org
Small lake
(< 400 km2)
Large lake
(≥400 km2)
Estuarine
River
Coastal
Estuarine
No model for
open ocean
waters
Slide 11
Processes and assumptions
Based on analytical solution of the advection diffusion
equation describing transport in surface water for
uniform flow conditions at steady state
Processes included:
Flow downstream as transport (advection)
Mixing processes (turbulent dispersion)
Concentration in sediment / suspended particles
estimated from ERICA Kd at receptor (equilibrium)
Transportation in the direction of flow
No loss to sediment between source and receptor
In all cases water dispersion assumes critical flow
conditions, by taking the lowest in 30 years, instead of
the rate of current flow
The only difference between RNs in predicted water
concentrations as material disperses is decay by their
different radiological half-lives.
www.radioecology-exchange.org
Slide 12
Rivers and coastal waters
Lz = distance to
achieve full vertical
mixing
The river model assumes that both river discharge of radionuclides such
as water harvesting is done in some of the banks, not in the midstream
The estuary model is considered an average speed of the current
representative of the behaviour of the tides.
Some restrictions related to short receptor discharge point distances
(mixing zone) and length discharge pipe and angle to shoreline receptor
For 10’s of km maximum
Condition for mixing is x > 7D and (y-y0)<< 3.7x
concentration in sediment is assumed to be
concentration in water x Kd
•
www.radioecology-exchange.org
Kd = Activity concentration on sediment (Bq kg-1)
xxxxxActivity concentration in seawater (Bq L-1)
Slide 13
Small lakes and reservoirs
Assumes a homogeneous concentration throughout the water body
Expected life time of facility is required as input
www.radioecology-exchange.org
Slide 14
Large Lake
Surface area >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.’
Some restrictions
related to length
discharge pipe and
angle to shoreline
receptor, short
receptor discharge
point distances
(mixing zone)
Estimates
concentration along
shoreline and along
plume centre line.
www.radioecology-exchange.org
Slide 15
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 crosssection) & flow characteristics (e.g. velocity, water depth)
which do not change significantly with distance / time
End of pipe mixing zones require hydrodynamic models
www.radioecology-exchange.org
Slide 16
2:
PC CREAM as a practical
alternative for dispersion
modelling
www.ceh.ac.uk/PROTECT
Slide 17
Collective dose model PC CREAM
Consequences of Releases to the Environment
Assessment Methodology
A suite of models and data for performing radiological
impact assessments of routine and continuous
discharges
Marine: Compartmental model for European waters
(DORIS)
Seafood concentrations => Individual doses => Collective doses.
Aerial: Radial grid R-91 atmospheric dispersion model
with (PLUME) with biokinetic transfer models
(FARMLAND)
Ext. & internal irradiation => foodchain transfer (animal on
pasture e.g. cow & plant uptake models) => dose
www.radioecology-exchange.org
Slide 18
Marine and aerial dispersion
Radial grid atmospheric model
Compartmental marine model
(continuous
discharge)
Irish S e a
N o rth E a st
Irish S e a
N o rth
S ellafield
L o ca l
co m p a rt.
Irish S e a
N o rth W e st
C u m b ria n
W a te rs
L ive rp o o l
And
M o re ca m b e
B a ys
D u n d alk
Iris h S e a
W est
D u b lin
www.radioecology-exchange.org
Irish S e a
S o u th E a st
Slide 19
R91 aerial dispersion model
Gaussian plume model
Meteorological conditions specified by: Wind speed, Wind
direction, Pasquill-Gifford stability classification
Implemented in PC CREAM and CROM
Model assumes constant meteorological and topographical
conditions along plume trajectory
Prediction accuracy < 100 m and > 20 km limited
Source depletion unrealistic (deposition modelling &
transfer factors are uncertain)
Developed for neutral conditions
Does not include: Buildings, Complex terrain e.g. hills and
valleys, Coastal effects
www.radioecology-exchange.org
Slide 20
Degree of improvement
of the models
Marine model (DORIS) => improvement
Has long-range geographical resolution
Incorporates dynamic representation of water /
sediment interaction
Aerial model (PLUME) => no improvement
Still a gaussian dispersion model unsuitable for long
distances > 20 km
Also assumes constant meteorological conditions
Does not correct for plume filling the boundary layer
www.radioecology-exchange.org
Slide 21
3. Alternative aerial models
www.radioecology-exchange.org
Slide 22
New-generation plume
models
Include deviations from idealised Gaussian plume model
Include turbulence data rather than simplified stability
categories to define boundary layer
Include particulate vs gases and chemical interactions
Model includes the effects on dispersion from:
Complex buildings
Complex terrain & coastal regions
Advanced models: ADMS, AERMOD
Gaussian in stable and neutral conditions
Non-Gaussian (skewed) in unstable conditions
www.radioecology-exchange.org
Slide 23
UK ADMS
Modified Gaussian plume
model
Gaussian in stable and
neutral conditions
Skewed non-Gaussian
in unstable conditions
Boundary layer based on
turbulence parameters
Model includes:
Meteorological pre-processor, buildings, complex terrain
Wet deposition, gravitational settling and dry deposition
Short term fluctuations in concentration
Chemical reactions
Radioactive decay and gamma-dose
Condensed plume visibility & plume rise vs. distance
Jets and directional releases
Short to annual timescales
www.radioecology-exchange.org
Slide 24
4. Alternative marine models
www.radioecology-exchange.org
Slide 25
Geographically-resolving marine
models
Allow for non-equilibrium situations e.g. acute release into
protected site
Advantages:
Resolves into a large geographical range
Results more accurate (if properly calibrated)
Disadvantages:
Data and CPU-hungry (small time step and grid sizes
demand more computer resources)
Run time dependent on grid size & time step
Requires specialist users
Post-processing required for dose calculation (use as
input to ERICA)
www.radioecology-exchange.org
Slide 26
Model characteristics
Input requirements: Bathymetry, wind fields, tidal
velocities, sediment distributions, source term
Type of output: a grid map / table of activity
concentration (resolution dependent on grid size)
All use same advection/dispersion equations, differences
are in grid size and time step
Types of model:
Compartmental: Give average solutions in
compartments connected by fluxes. Good for longrange dispersion in regional seas.
Finite differences: Equations discretised and solved
over a rectangular mesh grid. Good for short-range
dispersion in coastal areas
Estuaries a special case: Deal with tides (rather than
waves), density gradients, turbidity, etc.
www.radioecology-exchange.org
Slide 27
Model characteristics
Finite differences
www.radioecology-exchange.org
Compartmental
Slide 28
Some commonly available models
Long-range marine models (regional seas):
Short-range marine models (coastal areas):
POSEIDON - N. Europe (similar to PC-CREAM model but
redefines source term and some compartments - same sediment
model based on MARINA)
MEAD (in-house model available at WSC)
MIKE21 - Short time scales (DHI) - also for estuaries
Delft 3D model, developed by DELFT
TELEMAC (LNH, France) - finite element model
COASTOX (RODOS PV6 package)
Estuarine models
DIVAST ( Dr Roger Proctor)
ECoS (PML, UK) - includes bio-uptake
www.radioecology-exchange.org
Slide 29
DHI MIKE 21 model
Two-dimensional depth averaged
model for coastal waters
Location defined on a grid - creates
solution from previous time step
Hydrodynamics solved using full
time-dependent non-linear equations
(continuity & conservation of
momentum)
Large, slow and complex when
applied to an extensive region
Suitable for short term (sub annual)
assessments
A post processor is required to
determine biota concentrations and
dose calculations
www.radioecology-exchange.org
Slide 30
Marine Environmental Advection
Dispersion (MEAD)
www.radioecology-exchange.org
Runs on a 2-km 2-dimensional grid
Input: bathymetry, wind field,
sediment distribution maps
Applies advection - dispersion
equations over an area and time
Generates long-range radioactivity
predictions in water and sediment
Has been
combined with
the ERICA
methodology to
make realistic
assessments of
impact on biota
Slide 31
More complex process models
Extra modules for extra processes
More complex issues (eutrophication)
Wave interactions
Coastal morphology
Particle and slick tracking analysis
Sediment dynamics
Discharge
Influx_Pu_III_IV
Influx_Pu_V_VI
Reduction
Seawater_Pu_V_VI
Seawater_Pu_III_IV
OxidationInflux_Pu_particulate
Flushing_oxidised
Adsorption_susp
Desorption_susp
ModelMaker biokinetic
models
Dynamic interactions
with the sediments
Speciation
Dynamic uptake in biota
Flushing_susp
Adsorption_coll
Suspended_load
Pelagic_fish
Adsorption_sed
Desorption_sed
Remobilisation
Deposition
Coagulation
Crustaceans
Surface_sediment
Molluscs
Bioturbation
Sedimentation
Burial
www.radioecology-exchange.org
Flushing_reduced
Benthic_fish
Middle_sediment
Bottom_sediment
Flushing_colloidal
Colloidal
Far_field
Slide 32
5. Alternative river and
estuary modelling
www.radioecology-exchange.org
Slide 33
River and estuary models
Advantages:
Large geographical range
Consider multiple dimensions of the problem (1 - 3D)
Considers interconnected river networks
Results more accurate (if properly calibrated)
Disadvantages - same as marine models:
Data hungry
Run time dependent on grid size & time step
Requires a more specialised type of user
CPU-hungry (as time step and grid size decreases it
demands more computer resources)
Post-processing required for dose calculation (use as
input to ERICA)
www.radioecology-exchange.org
Slide 34
Model characteristics
Input requirements: Bathymetry, rainfall and catchment
data, sediment properties, network mapping, source
term
Type of output: activity concentration in water and
sediment, hydrodynamic data for river
All use same advection/dispersion equations as marine
but differences in boundary conditions
Generally models solve equations to:
Give water depth and velocity over the model domain
Calculate dilution of a tracer (activity concentration)
www.radioecology-exchange.org
Slide 35
Common models
Can be 1D, 2D or 3D models
1D river models: River represented by a line in
downstream direction - widely used
2D models have some use where extra detail is
required
3D models are rarely used unless very detailed
process representation is needed
Off-the-shelf models:
MIKE11 model developed by the DHI, Water and
Environment (1D model)
VERSE (developed by WSC)
MOIRA (Delft Hydraulics)
Research models:
PRAIRIE (AEA Technology)
RIVTOX & LAKECO (RODOS PV6 package)
www.radioecology-exchange.org
Slide 36
Example - MIKE 11
www.radioecology-exchange.org
MIKE11 - Industry
standard code for river flow
simulation
River represented by a line
in downstream direction
River velocity is averaged
over the area of flow
Cross sections are used to
give water depth
predictions
Can be steady flow
(constant flow rate) or
unsteady flow
Use of cross sections can
give an estimate of
inundation extent but not
flood plain velocity
Slide 37
Catchment modelling
Convert rainfall
over the catchment
to river flow out the
catchment
Represent the
processes
illustrated, however
in two possible
ways:
empirical relationship from rainfall to runoff
(cannot be used to simulate changing conditions)
Complex physically based models where all
processes are explicitly represented
Example: DHI MIKE-SHE, HP1 (HYDRUS +
PHREEQC)
SVAT modelling
www.radioecology-exchange.org
Slide 38
Conclusions
ERICA uses the IAEA SRS 19 dispersion models to work
out a simple, conservative source - receptor interaction
SRS 19 has some shortcomings
PC-CREAM can be used as an alternative to the SRS-19
marine model
There are further off-the-shelf models performing
radiological impact assessments of routine and
continuous discharges ranging from simple to complex
Key criteria of simplicity of use and number of
parameters need to be considered – must match
complexity to need
www.radioecology-exchange.org
Slide 39
Effect of using different models
Uncertainty associated with the application of
aquatic SRS models:
Models generally conservative.
From factor of 2 to 10 difference with respect to a dynamic
model.
Uncertainty associated with the application of a
Gaussian plume model for continuous releases:
About a factor of 4 or 10 for a flat and complex terrain
respectively.
At distances < 2.5 times the square root of the frontal area
of the building, the model provides conservative results.
For distances of about 2.5 the above, the model tends to
underpredict for wind speeds above 5-m s-1.
www.radioecology-exchange.org
Slide 40
Effect of using different models (2)
For aerial, PC-Cream is no improvement to SRS 19
For marine, PC cream has a dynamic compartment
model
Effect of using such a fully dynamic model:
In periods where concentrations in compartments increase,
dynamic model estimates of transfer will be lower than for
equilibrium model (‘build-up effect’)
In period where environmental concentrations decrease,
dynamic model estimates higher than equilibrium model
(‘memory effect’)
Diffcult to generalise, but differences could be up to
a factor of 10.
www.radioecology-exchange.org
Slide 41
Summary of key points
SRS19 model
Marine
+ point in coast
PC Cream
DORIS
+ Large compartment box model
+ Dynamic transfer to water and
+ requires very few parameters
sediments
- no offshore dispersion
- requires more parameters
- very simple equilibrium model (Kd - Does not work well at fine
based)
resolution
Orther models
Marine
+ compartmental models for large areas
+ Grid models for fine resolutions (small
areas)
+ Dynamic / time-variable discharges
- parameter hungry (bathimetry,
gridding, etc)
River, lake, reservoir
+ very simple 1D model
- only models riverbanks
River, lake, reservoir
+ 2D - 3D models
+ Full representation of hydrodynamics
+ Can deal with tides, concentration
gradients
N/A
- Simple average flow conditions
- very simple equilibrium model (Kd
based)
- Simple linear river
Aerial
+ limited range 100 m to 20 km
+ constant meteorology
+ Gaussian plume, still conditions
www.radioecology-exchange.org
+ Dynamic / time-variable discharges
+ Complex river networks
- parameter hungry (bathymetry,
gridding, etc.)
PLUME
- Same as SRS19
AERMOD, ADMS, etc.
+ Non Gaussian for unstable conditions
+ Buildings and terrain
+ Solute modelling
+ Complex meteorology
Slide 42
Links to alternative models
M o d el
ADMS 4
AERM OD
O rg a n isa tio n
CERC
EPA
D ELFT 3D
DELFT
H y d rau lics
C ard iff
U n iv ersity
PM L
HEC
(U S A C E )
IA E A
H alcro w
D IV A S T
E co S 3
H E C -R A S
IA E A S R S 1 9
IS IS
M EAD
M IK E 1 1
M IK E 2 1
M IK E 3
M IK E -S H E
M O IR A -P L U S
PC C R EA M 08
P O S E ID O N
P R A IR IE
R 91
RODOS PV6
(C O A S T O X ,
R IV T O X &
LAKECO)
TELEM AC 2 &
3D
VERSE
W SC
DHI
DHI
DHI
DHI
E U M O IR A
p ro g ram m e
HPA
CEPN
AEA
T ech n o lo g y
NRPB
EU RODOS
p ro g ram m e
SOGREAH
L in k
h ttp ://w w w .cerc.co .u k/en v iro n m en tal-so ftw are/A D M S -m o d el.h tm l
h ttp ://w w w .ep a.g o v /scram 0 0 1 /d isp ersio n _ p refrec.h tm # aerm o d
(F reew are)
h ttp ://d elftso ftw are.w ld elft.n l/in d ex .p h p? o ptio n = co m _ co n tent& task = blo g
categ ory & id = 1 3 & Item id = 3 4
h ttp ://h rc.en g in eerin g .cf.ac.u k /
h ttp ://w w w .p m l.ac.u k /
h ttp ://w w w .h ec.u sace.arm y .m il/so ftw are/h ec-ras/h ecras-d o w n lo ad .h tm l (F reew are)
w w w -p u b .iaea.o rg /M T C D /p u b licatio n s/P D F /P u b 1 1 0 3 _ scr.p d f
h ttp ://w w w .h alcro w .co m /isis/isisfree.asp (F reew are)
h ttp ://w w w .h alcro w .co m /isis/d efau lt.asp (P ro fessio n al ed itio n )
h ttp ://w w w .w estlak es.org (in -h o u se m o d el)
h ttp ://w w w .d h ig ro u p .co m /S o ftw are/W aterR eso u rces/M IK E 1 1 .asp x
h ttp ://w w w .d h ig ro u p .co m /S o ftw are/M arin e/M IK E 2 1 .asp x
h ttp ://w w w .d h ig ro u p .co m /S o ftw are/M arin e/M IK E 3 .asp x
h ttp ://w w w .d h ig ro u p .co m /S o ftw are/W aterR eso u rces/M IK E S H E .asp x
h ttp ://u ser.tn in et.se/~ fd e7 2 9 o /M O IR A /S o ftw are.h tm (F reew are)
h ttp ://w w w .h p a.o rg .u k /w eb /H P A w eb & H P A w eb S tan d ard /H P A w eb _ C /1 1
95733792183
h ttp ://w w w .cep n .asso .fr/en 1/lo giciels.htm l
h ttp ://w w w .aeat.co .u k /
h ttp ://w w w .ad m lc.o rg .u k /N R P B -R 9 1 .h tm
h ttp ://w w w .ro d o s.fzk .d e/ro d o s.htm l (F reew are, p assw o rd p rotected )
h ttp ://w w w .telem acsy ste m .co m /in d ex .p h p? o p tio n = co m _ jd o w n lo ad s& Item id = 3 1 & task =
v iew categ o ry & catid = 3 & lan g = en (F reew are)
W SC
www.radioecology-exchange.org
h ttp ://w w w .w estlak es.org (in -h o u se m o d el)
Modelling the environmental
dispersion of radionuclides
Jordi Vives i Batlle
Centre for Ecology and Hydrology,
Lancaster, 1st – 3rd April 2014
Slide 2
What happens if do not have media
concentrations?
Need method of predicting from release rates over a
dilution pathway between source and receptor
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
www.radioecology-exchange.org
Slide 3
1 - Dispersion modelling in ERICA
www.radioecology-exchange.org
Slide 4
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
www.radioecology-exchange.org
SRS-19 is linked to ERICA
help file
Slide 5
Atmospheric dispersion
Gaussian plume
model version
depending on the
relationship between
building height &
cross-sectional area
of the building
influencing flow
Assumes a
predominant wind
direction and neutral
stability class
(=doesn’t enhance
or inhibit turbulence)
Key inputs: discharge rate Q & location of
source / receptor points
www.radioecology-exchange.org
Slide 6
Basic dispersion equation
A Gaussian plume model for an elevated release is as follows:
C x, y, z
Q
2 u 10 z y
2
2
z
H
y
S
exp
2
2
2 z
2 y
where C = the air concentration (Bq/m3) or its time integral Bq.s/m3
Q = release rate (Bq/s) or total amount released (Bq)
u10 = wind speed at 10 m above the ground (m/s)
z = standard deviation of the vertical Gaussian distribution (m)
y = standard deviation of the horizontal Gaussian distribution (m)
HS = effective release height (m)
x, y, z = rectilinear coordinates of the receptors
Importance of Release Height
Effective stack height
www.ceh.ac.uk/PROTECT
Slide 7
Conditions for the plume
(a)
(b)
(c)
a) H > 2.5HB (building height): No building effects
b) H 2.5HB & x > 2.5AB½ (cross-sectional area of building): Airflow in the
wake zone
c) H 2.5HB & x 2.5AB½: Airflow in the cavity zone. Two cases:
source / receptor at same building surface
not at same surface
Not generally applicable at > 20 km from stack
www.radioecology-exchange.org
Slide 8
Key parameters
Wind speed and direction
Release height
Precipitation
10 minute average from 10 m wind vane & anemometer
10 minute total rainfall (mm)
Stability or degree of turbulence (horizontal and vertical
diffusion)
Manual estimate from nomogram using time of day,
amount of cloud cover and global radiation level
Atmospheric boundary layer (time-dependent)
Convective and or mechanical turbulence
Limits the vertical transport of pollutants
www.radioecology-exchange.org
Slide 9
Output
Radionuclide
activity
concentrations in
air (C,H,S & P)
or soil
(everything else)
www.radioecology-exchange.org
Slide 10
Surface water dispersion
Freshwater
Marine
www.radioecology-exchange.org
Small lake
(< 400 km2)
Large lake
(≥400 km2)
Estuarine
River
Coastal
Estuarine
No model for
open ocean
waters
Slide 11
Processes and assumptions
Based on analytical solution of the advection diffusion
equation describing transport in surface water for
uniform flow conditions at steady state
Processes included:
Flow downstream as transport (advection)
Mixing processes (turbulent dispersion)
Concentration in sediment / suspended particles
estimated from ERICA Kd at receptor (equilibrium)
Transportation in the direction of flow
No loss to sediment between source and receptor
In all cases water dispersion assumes critical flow
conditions, by taking the lowest in 30 years, instead of
the rate of current flow
The only difference between RNs in predicted water
concentrations as material disperses is decay by their
different radiological half-lives.
www.radioecology-exchange.org
Slide 12
Rivers and coastal waters
Lz = distance to
achieve full vertical
mixing
The river model assumes that both river discharge of radionuclides such
as water harvesting is done in some of the banks, not in the midstream
The estuary model is considered an average speed of the current
representative of the behaviour of the tides.
Some restrictions related to short receptor discharge point distances
(mixing zone) and length discharge pipe and angle to shoreline receptor
For 10’s of km maximum
Condition for mixing is x > 7D and (y-y0)<< 3.7x
concentration in sediment is assumed to be
concentration in water x Kd
•
www.radioecology-exchange.org
Kd = Activity concentration on sediment (Bq kg-1)
xxxxxActivity concentration in seawater (Bq L-1)
Slide 13
Small lakes and reservoirs
Assumes a homogeneous concentration throughout the water body
Expected life time of facility is required as input
www.radioecology-exchange.org
Slide 14
Large Lake
Surface area >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.’
Some restrictions
related to length
discharge pipe and
angle to shoreline
receptor, short
receptor discharge
point distances
(mixing zone)
Estimates
concentration along
shoreline and along
plume centre line.
www.radioecology-exchange.org
Slide 15
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 crosssection) & flow characteristics (e.g. velocity, water depth)
which do not change significantly with distance / time
End of pipe mixing zones require hydrodynamic models
www.radioecology-exchange.org
Slide 16
2:
PC CREAM as a practical
alternative for dispersion
modelling
www.ceh.ac.uk/PROTECT
Slide 17
Collective dose model PC CREAM
Consequences of Releases to the Environment
Assessment Methodology
A suite of models and data for performing radiological
impact assessments of routine and continuous
discharges
Marine: Compartmental model for European waters
(DORIS)
Seafood concentrations => Individual doses => Collective doses.
Aerial: Radial grid R-91 atmospheric dispersion model
with (PLUME) with biokinetic transfer models
(FARMLAND)
Ext. & internal irradiation => foodchain transfer (animal on
pasture e.g. cow & plant uptake models) => dose
www.radioecology-exchange.org
Slide 18
Marine and aerial dispersion
Radial grid atmospheric model
Compartmental marine model
(continuous
discharge)
Irish S e a
N o rth E a st
Irish S e a
N o rth
S ellafield
L o ca l
co m p a rt.
Irish S e a
N o rth W e st
C u m b ria n
W a te rs
L ive rp o o l
And
M o re ca m b e
B a ys
D u n d alk
Iris h S e a
W est
D u b lin
www.radioecology-exchange.org
Irish S e a
S o u th E a st
Slide 19
R91 aerial dispersion model
Gaussian plume model
Meteorological conditions specified by: Wind speed, Wind
direction, Pasquill-Gifford stability classification
Implemented in PC CREAM and CROM
Model assumes constant meteorological and topographical
conditions along plume trajectory
Prediction accuracy < 100 m and > 20 km limited
Source depletion unrealistic (deposition modelling &
transfer factors are uncertain)
Developed for neutral conditions
Does not include: Buildings, Complex terrain e.g. hills and
valleys, Coastal effects
www.radioecology-exchange.org
Slide 20
Degree of improvement
of the models
Marine model (DORIS) => improvement
Has long-range geographical resolution
Incorporates dynamic representation of water /
sediment interaction
Aerial model (PLUME) => no improvement
Still a gaussian dispersion model unsuitable for long
distances > 20 km
Also assumes constant meteorological conditions
Does not correct for plume filling the boundary layer
www.radioecology-exchange.org
Slide 21
3. Alternative aerial models
www.radioecology-exchange.org
Slide 22
New-generation plume
models
Include deviations from idealised Gaussian plume model
Include turbulence data rather than simplified stability
categories to define boundary layer
Include particulate vs gases and chemical interactions
Model includes the effects on dispersion from:
Complex buildings
Complex terrain & coastal regions
Advanced models: ADMS, AERMOD
Gaussian in stable and neutral conditions
Non-Gaussian (skewed) in unstable conditions
www.radioecology-exchange.org
Slide 23
UK ADMS
Modified Gaussian plume
model
Gaussian in stable and
neutral conditions
Skewed non-Gaussian
in unstable conditions
Boundary layer based on
turbulence parameters
Model includes:
Meteorological pre-processor, buildings, complex terrain
Wet deposition, gravitational settling and dry deposition
Short term fluctuations in concentration
Chemical reactions
Radioactive decay and gamma-dose
Condensed plume visibility & plume rise vs. distance
Jets and directional releases
Short to annual timescales
www.radioecology-exchange.org
Slide 24
4. Alternative marine models
www.radioecology-exchange.org
Slide 25
Geographically-resolving marine
models
Allow for non-equilibrium situations e.g. acute release into
protected site
Advantages:
Resolves into a large geographical range
Results more accurate (if properly calibrated)
Disadvantages:
Data and CPU-hungry (small time step and grid sizes
demand more computer resources)
Run time dependent on grid size & time step
Requires specialist users
Post-processing required for dose calculation (use as
input to ERICA)
www.radioecology-exchange.org
Slide 26
Model characteristics
Input requirements: Bathymetry, wind fields, tidal
velocities, sediment distributions, source term
Type of output: a grid map / table of activity
concentration (resolution dependent on grid size)
All use same advection/dispersion equations, differences
are in grid size and time step
Types of model:
Compartmental: Give average solutions in
compartments connected by fluxes. Good for longrange dispersion in regional seas.
Finite differences: Equations discretised and solved
over a rectangular mesh grid. Good for short-range
dispersion in coastal areas
Estuaries a special case: Deal with tides (rather than
waves), density gradients, turbidity, etc.
www.radioecology-exchange.org
Slide 27
Model characteristics
Finite differences
www.radioecology-exchange.org
Compartmental
Slide 28
Some commonly available models
Long-range marine models (regional seas):
Short-range marine models (coastal areas):
POSEIDON - N. Europe (similar to PC-CREAM model but
redefines source term and some compartments - same sediment
model based on MARINA)
MEAD (in-house model available at WSC)
MIKE21 - Short time scales (DHI) - also for estuaries
Delft 3D model, developed by DELFT
TELEMAC (LNH, France) - finite element model
COASTOX (RODOS PV6 package)
Estuarine models
DIVAST ( Dr Roger Proctor)
ECoS (PML, UK) - includes bio-uptake
www.radioecology-exchange.org
Slide 29
DHI MIKE 21 model
Two-dimensional depth averaged
model for coastal waters
Location defined on a grid - creates
solution from previous time step
Hydrodynamics solved using full
time-dependent non-linear equations
(continuity & conservation of
momentum)
Large, slow and complex when
applied to an extensive region
Suitable for short term (sub annual)
assessments
A post processor is required to
determine biota concentrations and
dose calculations
www.radioecology-exchange.org
Slide 30
Marine Environmental Advection
Dispersion (MEAD)
www.radioecology-exchange.org
Runs on a 2-km 2-dimensional grid
Input: bathymetry, wind field,
sediment distribution maps
Applies advection - dispersion
equations over an area and time
Generates long-range radioactivity
predictions in water and sediment
Has been
combined with
the ERICA
methodology to
make realistic
assessments of
impact on biota
Slide 31
More complex process models
Extra modules for extra processes
More complex issues (eutrophication)
Wave interactions
Coastal morphology
Particle and slick tracking analysis
Sediment dynamics
Discharge
Influx_Pu_III_IV
Influx_Pu_V_VI
Reduction
Seawater_Pu_V_VI
Seawater_Pu_III_IV
OxidationInflux_Pu_particulate
Flushing_oxidised
Adsorption_susp
Desorption_susp
ModelMaker biokinetic
models
Dynamic interactions
with the sediments
Speciation
Dynamic uptake in biota
Flushing_susp
Adsorption_coll
Suspended_load
Pelagic_fish
Adsorption_sed
Desorption_sed
Remobilisation
Deposition
Coagulation
Crustaceans
Surface_sediment
Molluscs
Bioturbation
Sedimentation
Burial
www.radioecology-exchange.org
Flushing_reduced
Benthic_fish
Middle_sediment
Bottom_sediment
Flushing_colloidal
Colloidal
Far_field
Slide 32
5. Alternative river and
estuary modelling
www.radioecology-exchange.org
Slide 33
River and estuary models
Advantages:
Large geographical range
Consider multiple dimensions of the problem (1 - 3D)
Considers interconnected river networks
Results more accurate (if properly calibrated)
Disadvantages - same as marine models:
Data hungry
Run time dependent on grid size & time step
Requires a more specialised type of user
CPU-hungry (as time step and grid size decreases it
demands more computer resources)
Post-processing required for dose calculation (use as
input to ERICA)
www.radioecology-exchange.org
Slide 34
Model characteristics
Input requirements: Bathymetry, rainfall and catchment
data, sediment properties, network mapping, source
term
Type of output: activity concentration in water and
sediment, hydrodynamic data for river
All use same advection/dispersion equations as marine
but differences in boundary conditions
Generally models solve equations to:
Give water depth and velocity over the model domain
Calculate dilution of a tracer (activity concentration)
www.radioecology-exchange.org
Slide 35
Common models
Can be 1D, 2D or 3D models
1D river models: River represented by a line in
downstream direction - widely used
2D models have some use where extra detail is
required
3D models are rarely used unless very detailed
process representation is needed
Off-the-shelf models:
MIKE11 model developed by the DHI, Water and
Environment (1D model)
VERSE (developed by WSC)
MOIRA (Delft Hydraulics)
Research models:
PRAIRIE (AEA Technology)
RIVTOX & LAKECO (RODOS PV6 package)
www.radioecology-exchange.org
Slide 36
Example - MIKE 11
www.radioecology-exchange.org
MIKE11 - Industry
standard code for river flow
simulation
River represented by a line
in downstream direction
River velocity is averaged
over the area of flow
Cross sections are used to
give water depth
predictions
Can be steady flow
(constant flow rate) or
unsteady flow
Use of cross sections can
give an estimate of
inundation extent but not
flood plain velocity
Slide 37
Catchment modelling
Convert rainfall
over the catchment
to river flow out the
catchment
Represent the
processes
illustrated, however
in two possible
ways:
empirical relationship from rainfall to runoff
(cannot be used to simulate changing conditions)
Complex physically based models where all
processes are explicitly represented
Example: DHI MIKE-SHE, HP1 (HYDRUS +
PHREEQC)
SVAT modelling
www.radioecology-exchange.org
Slide 38
Conclusions
ERICA uses the IAEA SRS 19 dispersion models to work
out a simple, conservative source - receptor interaction
SRS 19 has some shortcomings
PC-CREAM can be used as an alternative to the SRS-19
marine model
There are further off-the-shelf models performing
radiological impact assessments of routine and
continuous discharges ranging from simple to complex
Key criteria of simplicity of use and number of
parameters need to be considered – must match
complexity to need
www.radioecology-exchange.org
Slide 39
Effect of using different models
Uncertainty associated with the application of
aquatic SRS models:
Models generally conservative.
From factor of 2 to 10 difference with respect to a dynamic
model.
Uncertainty associated with the application of a
Gaussian plume model for continuous releases:
About a factor of 4 or 10 for a flat and complex terrain
respectively.
At distances < 2.5 times the square root of the frontal area
of the building, the model provides conservative results.
For distances of about 2.5 the above, the model tends to
underpredict for wind speeds above 5-m s-1.
www.radioecology-exchange.org
Slide 40
Effect of using different models (2)
For aerial, PC-Cream is no improvement to SRS 19
For marine, PC cream has a dynamic compartment
model
Effect of using such a fully dynamic model:
In periods where concentrations in compartments increase,
dynamic model estimates of transfer will be lower than for
equilibrium model (‘build-up effect’)
In period where environmental concentrations decrease,
dynamic model estimates higher than equilibrium model
(‘memory effect’)
Diffcult to generalise, but differences could be up to
a factor of 10.
www.radioecology-exchange.org
Slide 41
Summary of key points
SRS19 model
Marine
+ point in coast
PC Cream
DORIS
+ Large compartment box model
+ Dynamic transfer to water and
+ requires very few parameters
sediments
- no offshore dispersion
- requires more parameters
- very simple equilibrium model (Kd - Does not work well at fine
based)
resolution
Orther models
Marine
+ compartmental models for large areas
+ Grid models for fine resolutions (small
areas)
+ Dynamic / time-variable discharges
- parameter hungry (bathimetry,
gridding, etc)
River, lake, reservoir
+ very simple 1D model
- only models riverbanks
River, lake, reservoir
+ 2D - 3D models
+ Full representation of hydrodynamics
+ Can deal with tides, concentration
gradients
N/A
- Simple average flow conditions
- very simple equilibrium model (Kd
based)
- Simple linear river
Aerial
+ limited range 100 m to 20 km
+ constant meteorology
+ Gaussian plume, still conditions
www.radioecology-exchange.org
+ Dynamic / time-variable discharges
+ Complex river networks
- parameter hungry (bathymetry,
gridding, etc.)
PLUME
- Same as SRS19
AERMOD, ADMS, etc.
+ Non Gaussian for unstable conditions
+ Buildings and terrain
+ Solute modelling
+ Complex meteorology
Slide 42
Links to alternative models
M o d el
ADMS 4
AERM OD
O rg a n isa tio n
CERC
EPA
D ELFT 3D
DELFT
H y d rau lics
C ard iff
U n iv ersity
PM L
HEC
(U S A C E )
IA E A
H alcro w
D IV A S T
E co S 3
H E C -R A S
IA E A S R S 1 9
IS IS
M EAD
M IK E 1 1
M IK E 2 1
M IK E 3
M IK E -S H E
M O IR A -P L U S
PC C R EA M 08
P O S E ID O N
P R A IR IE
R 91
RODOS PV6
(C O A S T O X ,
R IV T O X &
LAKECO)
TELEM AC 2 &
3D
VERSE
W SC
DHI
DHI
DHI
DHI
E U M O IR A
p ro g ram m e
HPA
CEPN
AEA
T ech n o lo g y
NRPB
EU RODOS
p ro g ram m e
SOGREAH
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www.radioecology-exchange.org
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