1. 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)

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

3. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 COLIMA Experiment : Transport of the aerosol through the concrete crack sample Aerosol: prototypic aerosol (COLIMA) Thermite mixture Concrete degradation products Elements 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)

4. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 COLIMA Results Zone Collected mass Mass fraction 0-5 cm210 mg70% 5-10 cm68 mg23% 10-20 cm21 mg7% 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

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

6. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Eulerian approach – Resuspension Model F Resultant force acting on the particle a, b Constant based on experimental data Aerodynamic Forces F coh Cohesive Force F fric Frictional Adhesive Force F cen Centrifugal Force Adhesive Forces F gra Gravitational Force Aerodynamic/Adhesive Force F drag Drag Force F burst Bursting Force F aero < F adhe → Deposition F aero > F adhe → Resuspension Deposition inhibited

7. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Analysis of the Experiment with Eulerian Approach AMMD0.97 µm σgσg 2.05 Aerosol mass flow 5·10 -7 kg/s Density7350 kg/m 3 Porosity20–80 % Crk1Crk2Crk3Crk4Crk5Crk6InletOutlet Crack Length0.30 m ΔPΔP1 bar Gas flow 400 Nlit/min Temperature383.15 K Curvature radius 0.01-0.02 m Concrete crack

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

9. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Comparison with the experimental results Best Fit: Curvature Radius: 0.02 m Porosity: 60-40%

10. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 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 )

11. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Lagrangian Approach - Aerosol Decontamination factor Removal mechanisms Particle size Local gas flow conditions. Assumptions : No variations: Crack geometric characteristics Thermodynamic conditions Particle size, shape and density Condensation/evaporation of radionuclide species is neglected No resuspension of particles

12. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Lagrangian Approach - Aerosol No resuspension of particles

13. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Lagrangian Approach - Aerosol Airborne concentration decay because of deposition mechanisms along a path Assumption: All the particles of a given size class have equal deposition velocity The thermal-fluid dynamic conditions are homogeneous (well-mixed conditions) Only tranverse mixing occurs No interactions among the particles

14. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Lagrangian Approach - Aerosol Deposition velocity of particles v d 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

15. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Lagrangian Approach – Thermal Hydraulic Assumptions: Constant pressure and temperature along the crack pathway during the considered time interval Estimate of Pressure profile = f (P Cont, P Env ) Darcy–Weisbach Blasius Equation

16. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Comparison between Lagrangian and Eulerian predictions Eulerian vs Lagrangian: Comparable Retention 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

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

18. ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012 Thank you!