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STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.1RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Engineering & Projects Organization
RESTRICTED AREVAThe information in this document is AREVA property and is intended solely for the addressees.
Reproduction and distribution are prohibited. Thank you
B. Farges, P. Brocheny, C. Thelier, N. GoreaudAREVA NP
CFD for atmospheric dispersion prediction in close range
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.3RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Outline of the presentation
1. Context
2. Methodology setup and validation
2a. Hydraulics
2b. Dispersion
3. Industrial application
4. Conclusion and outlook
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.4RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
1. Context (1/2)
Some accidental or incidental scenarios can lead an i ndustrial site to release gases or particules in the atmosphere
Depending on the concentration, of the weather condit ions and of the quantity, it will form a plume of a give n size / concentration
Utilities must demonstrate that these scenarios are p roperly handled and that the consequences are acceptable� For the public outside the facility fences => long range
� More and more : for the workers on site => close ra nge
Some tools exist on the market dedicated to these is sues, but� No or very limited capacity for detailed representa tion of a given
industrial site (buildings, complex obstacles…)
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.5RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
1. Context (2/2)
AREVA has a long history in using CFD
� Variety of problems� Trained engineers� Computation power available� Validation file on numerous
applications� CFD used as a support to safety
analyses
For this reason : choice to use CFD for the modelling of near-field atmospheric dispersion
� Detailed representation of site geometry (buildings…)
� Recirculations, turbulence, buoyancy,… taken into account
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.6RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
2. Methodology setup Approach
Step by step : growing complexity
a. Hydraulics only :• On an empty domain• With a single building• Benchmark against litterature
b. Addition of dispersion :• On an empty domain first• Validation against the Prairie Grass experiment
c. Addition of reacting flows (not part of presentation t oday) :• Possibilities to account for chemical reactions / power decay during dispersion
Illustration on the sizing of protection on an AREVA facility
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.7RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
2.a. Methodology setup Hydraulics on empty domain
Assumptions� Surface boundary layer� Perfect gas� Stationnary wind profile : Assumtion that meteo variation are slow compared to
dispersion transient
Computation assumptions� In accordance with best practicesIdentified through a litterature survey� Large domain dimensions in order to prevent side effects .� Turbulence model : standard (was found to be the best compromise)
� Dispersion in neutral conditions (classical
choice : Richards & Hoxey, Hargreaves, Vendel)B.Blocken et al, 2007
ε−k
Equations of velocity , temperature and turbulent qua ntities profile relative to a neutral atmosphere prescribe at inlet.
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.8RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Profiles prescribed at domain inlet (from similitude theory from Monin-Obukhov)
Acceptable situation on empty domain
2.a. Methodology setup Hydraulics on empty domain
Turbulent kinetic energy
Turbulent dissipation
Velocity
Temperature
Atmosphéric profiles
)(
*
0
3
zz
u
+=
κε
µC
uk
²*=
)ln(*
0
0
z
zzuu
+=
κ
( ) zTzT ⋅−= 0098,00
Profiles maintained
Local anomalytypical for standard CFD codes
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.9RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Behaviour of flow around an obstacle (square building)� Presence of turbulent structures
� Classical k-epsilon limitations (consistent with litt erature) :
Results are consistent with the state of the art and judged acceptable
Slightsurestimation of turbulent kinetic
energy upstream
Slightunderestimation of recirculation zone
Slightsurestimation of the recirculation zone downstream
2.a. Methodology setup Hydraulics with a single building
10 m
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.10RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Reference experiment : Projet Prairie Grass (1956)� SO2 release in an open plain
� 68 tests about 10 of them in neutral conditions• Three configurations chosen to validate the methodology
Two means to calibrate the results :� Calibration of a parameter : S ct => fast, provides order of magnitudes at the plume
centerline
� Statistical correction => more complex, more reliabl e
2.b. Methodology setup Dispersion
Vervecken et al. 2013
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.11RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Simulation of the Prairie Grass experiment� Calibrating Sct enables to get the right concentration in the axis of the
plume
But the shape of the plume is incorrect : overestimation in the axis of the plume and underestimation of its width . (Known phenomenon : Vervecken, Riddle )
Acceptable for an order of magnitude determination.
2.b. Methodology setup Dispersion
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.12RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Simulation of the Prairie Grass experiment� Accounting of wind oscillations (litterature : Verveck en)
• Statistical fluctuations around the average wind direction : a statistical fluctuation with standard deviation σ
αhas been measured :
• Turbulence modelling already accounts for some deviation σm� definition of an additive deviation σe to reach σ
α
• Performance of several computations for several angles• Gaussian ponderation of the results
2.b. Mise en place de la mod élisation Dispersion
Fluctuations de la direction du vent (essai n°57)
0
0,02
0,04
0,06
58 90 122Angle en degré
Den
sité
de
prob
abili
té
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.13RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
Simulation of Prairie Grass experiment� Results with second method
• Shape of the plume and concentration of the plume are better predicted• Drawback : several computations are necessary
Correction statistique sur les capteurs à 50 m
0
100
200
300
400
500
600
60 70 80 90 100 110 120
Angle en degré
conc
entr
atio
n de
SO
2 en
mg/
m3
Mesures test 57
Simulation 57 -Sct0,7
Simulation 57 -Sct 0,7 - correctionstatistique
2.b. Mise en place de la mod élisation Dispersion
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.14RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
3. Industrial application
Milling facility
Industrial problem� Ammonia stored on site under
pressure
� If a leakage happens, need to ensureacceptable doses are not overcome
First step� CAD repair inside STAR-CCM+ from
site data
� Large domain generation
� Meshing• Less than 5 million cells for the total
volume• Enabling a fast and smooth transient run
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.15RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
3. Industrial application
Results� Instantaneous velocity profiles on
site for a given wind direction• First indication of zones of potential
hazard
� Instantaneous concentration profiles everywhere on the plant
• Information that enables to quantify the dilution of the release and the size of the plume
� Derived into the quantification of the zones where reglementary thresholdcan be overcome
• Used for demonstration to regulators and design optimisation
STAR Global conference AREVA - dispersion – March 17-19th 2014 - p.16RESTRICTED AREVA
The information in this document is AREVA property and is intended solely for the addressees.Reproduction and distribution are prohibited. Thank you
4. Conclusion and outlook
AREVA has developped a method to assess the consequences of atmospheric dispersion in close range� Based on its expertise on CFD
� For its own purpose
This method is operational and proved to provide usefulresults on an industrial case
Beyond safety demonstration, this method has a lot of potential :� Site layout verification / optimisation
� Strong wind sizing
� Wind power generation
� …
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