ermsar 2012, cologne, germany, march 21 – 23, 2012 aerosol retention in containment leak paths:...

ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012

Aerosol Retention in Containment Leak Paths: Indications for a Code Model

in the Light of COLIMA Experimental Results

Sonia Morandi, Flavio Parozzi, Emilio Salina (RSE) Christophe Journeau, Pascal Piluso (CEA)


COLIMA Experiment : Transport of the aerosol through the concrete crack sample

In the framework of SARNET of FP6

CEA and RSE managed an ad-hoc experiment, with prototypic aerosol generated from the facility COLIMA and a sample of cracked concrete with defined geometry


COLIMA Experiment : Transport of the aerosol through the concrete crack sample

Aerosol: prototypic aerosol (COLIMA)

Thermite mixture Concrete degradation productsElements simulating the fission products

Concrete crack (RSE)

ΔP: 1 bar 0.3 m-piece of a crack 1.5 meter-length (assuming then a total pressure drop of 5 bars along a whole real crack)


COLIMA Results

Zone Collected mass

Mass fraction

0-5 cm 210 mg 70%5-10 cm 68 mg 23%10-20 cm 21 mg 7%

In the 5-20 cm range, some preferred flow path traces are visible

Intense aerosol deposition in the first 5 cm of the crack

Almost no deposit after 20 cm

Total of about 270-300 mg of aerosols directed to the sample


Eulerian approach – Deposition Model

Gravitational settling Inertial deposition from turbulent flow Centrifugal deposition from bent pipes

and curved pathways Diffusional deposition from turbulent flow Diffusional deposition from laminar flow Thermophoretic deposition Diffusiophoretic deposition Pool scrubbing

VMA

dtdM

d


Eulerian approach – Resuspension Model

dtdM

M1

ΔtA0MAΔM

0ΔtlimΛ

bFa F Resultant force acting on the particle

a, b Constant based on experimental data

Aerodynamic Forces

Fcoh Cohesive ForceFfric Frictional Adhesive ForceFcen Centrifugal Force

Adhesive Forces

Fgra Gravitational Force Aerodynamic/Adhesive Force

Fdrag Drag ForceFburst Bursting Force

graFcenFfricFcohFburstFdragFF

Faero < Fadhe → Deposition

Faero > Fadhe → Resuspension

Deposition inhibited


Analysis of the Experiment with Eulerian Approach

AMMD 0.97 µm

σg 2.05

Aerosol mass flow 5·10-7 kg/s

Density 7350 kg/m3

Porosity 20–80 %

Crk1 Crk2 Crk3 Crk4 Crk5 Crk6Inlet Outlet

Crack Length 0.30 m

ΔP 1 bar

Gas flow 400 Nlit/min

Temperature 383.15 K

Curvature radius 0.01-0.02 m

Concrete crack


Comparison with the experimental results

The adhesive forces strongly prevail over the lift forces

Main mechanism of deposition: Centrifugal sedimentation because of the crack tortuosity


Comparison with the experimental results

0

50

100

150

200

250

300

Aer

osol

dep

osite

d m

ass

[mg]

EXPPorosity 80%Porosity 60%Porosity 40%Porosity 20%

rbend 0.01 m

rbend 0.01 mrbend 0.01 m

rbend 0.01 m

rbend 0.02 m

rbend 0.02 mrbend 0.02 m

rbend 0.02 m

0 - 5 cm 5 - 10 cm 10 - 20 cm 20 - 30 cm

Best Fit:Curvature Radius: 0.02 mPorosity: 60-40%


Lagrangian Approach

Lagrangian approach: Fast-running and numerically stable Performed only when the boundary conditions change significantly

(i.e. crack geometry, carrier gas and aerosol properties) Mechanistic approach congruent with the other aerosol deposition

models in Source Term Codes

Eulerian approach : heavy calculation when coupled to a containment analysis under accident conditions

Very short time steps required to analyze the crack (~ 10-4 s)

Time step required for containment volumes related to nodalizations and model stability (~ s )


Lagrangian Approach - Aerosol

Decontamination factor

)k(rjDFjkrTOTDF Removal mechanisms Particle size Local gas flow conditions.

Assumptions :No variations:

Crack geometric characteristicsThermodynamic conditions Particle size, shape and density

Condensation/evaporation of radionuclide species is neglected

No resuspension of particles


1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03rp [m]

Faer

odyn

amic

/ F ad

hesiv

e

0.05 m

0.02 m

Straight path

Tortuous path0.005 m0.01 m

0.001 m

0.03 m

Deposition inhibited

Deposition allowed

CURVATURE RADIUS


No resuspension of particles



Airborne concentration decay because of deposition mechanisms along a path

Assumption:All the particles of a given size class have equal deposition velocityThe thermal-fluid dynamic conditions are homogeneous (well-mixed conditions)Only tranverse mixing occursNo interactions among the particles

)x(ndxxdn



dAdvncAv0ncAvn

cAvdAdvexp)k(rjDF

bendACvfloorASvtotADvTHvLvTDvTlvdAdv

Deposition velocity of particles vd is calculated as the combination of the different removal mechanisms

Deposition Mechanisms:•Turbulent flow•Diffusional deposition •Thermophoresis •Diffusiophoresis•Gravitational settling•Centrifugal deposition

Balance inside a generic spatial step


Lagrangian Approach – Thermal Hydraulic

0.E+00

2.E+05

4.E+05

6.E+05

8.E+05

1.E+06

1.E+06

0 0.5 1 1.5 2Crack abscissa [m]

Pres

sure

[Pa]

ECART Eulerian calculationsimplifying correlation

pressure inside containment

pressure outside containment

Assumptions: Constant pressure and temperature along the crack pathway

during the considered time interval

Estimate ofPressure profile = f (PCont, PEnv)

Darcy–Weisbach Blasius Equation

2

xL4A20p0pxp

L

2cp0pcpA


Comparison between Lagrangian and Eulerian predictions

0

50

100

150

200

250

300

Aer

osol

dep

osite

d m

ass

[mg]

EXP

Eulerian model (with resuspension)

Eulerian model (without resuspension)

Lagrangian model (without resuspension)

rbend : 0.015 mPorosity: 60 %

0 - 5 cm 5 - 10 cm 10 - 20 cm 20 - 30 cm

Eulerian vs Lagrangian:ComparableRetention efficiency :

Lagrangian >Eulerian

Eulerian no-res vs Lagrangian:Similar distribution deposited mass

Note: Eulerian Model : 6 Control Volume Lagrangian Model : 4800 Spatial Steps

Aerosol transported throughout the crack: the smallest particles are less influenced by the centrifugal force


Conclusions Typical Eulerian approach: good agreement with the experimental data

Lagrangian approch: – Fast running, numerically stable, including typical retention mechanism of Source Term Codes– Can be performed only when boundary conditions change significantly

Discrepancies between experimental results and simulation:– Simulation : aerosol parameters were assumed as constant with time– Experiment: aerosol parameters deduced from integral measurements made after the

experiment (i.e. particle concentrations and size distributions), or affected by uncertainties (i.e. particle shape and density).

The simulations underline that resuspension conditions are likely to occur along the crack, probably in terms of inhibition of deposition, involving the smallest aerosol particles.


Thank you!

ermsar 2012, cologne, germany, march 21 – 23, 2012 aerosol retention in containment leak paths:...

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