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Spray systems in French PWR

On The Use Of Spray Systems: An Example Of R&D Work In Hydrogen Safety For Nuclear Applications C. Joseph-Auguste 1 , H. Cheikhravat 2 , N. Djebaïli-Chaumeix 3 and E. Deri 1 1 CEA 2 IRSN 3 CNRS-ICARE. Spray systems in French PWR. Spray systems in French PWR. Argument against:

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Spray systems in French PWR

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  1. On The Use Of Spray Systems: An Example Of R&D Work In Hydrogen Safety For Nuclear ApplicationsC. Joseph-Auguste1, H. Cheikhravat2, N. Djebaïli-Chaumeix3 and E. Deri11 CEA 2 IRSN 3 CNRS-ICARE ICHS, 11-13 September 2007

  2. Spray systems in French PWR

  3. Spray systems in French PWR • Argument against: ◦ may generate flammable mixtures or enhance flame propagation through turbulence induced by sprays • Arguments for: ◦ reduce overpressures in the containment ◦ remove any scattered radioactive aerosols ◦ could cause heat sinks and mixtures homogenization Experimental set-ups and numerical modelling

  4. Experimental set-up: spherical bomb measure of flame velocity • stainless steel sphere (i.d. 500 mm) equipped with 4 opposites quartz windows (100 mm optical diameter, 40 mm thick) • black polished surface in order to suppress multiple diffusion

  5. Spherical bomb

  6. Modelling strategy (2007-2009) • Main experimental objective: study of the effect of droplets on a hydrogen-air flame in a humid atmosphere by measuring flame velocity • Use of the measured flame velocity to obtain more detailed CFD models but study of thermodynamics aspects is also needed • Lumped-Parameter analysis

  7. Principle of the Lumped-Parameter (LP) modelling • Based on heat and mass transfers • Assymptotic analysis: final state Preliminary work for a future CFD modelling the CFD results must correspond to the LP ones after vaporization

  8. conservation of mass and energy (impermeable and adiabatic walls) ideal gases constant volume complete combustion the whole energy liberated by the combustion vaporizes the liquid water air is considered as a binary mixture (N2-O2) hydrogen combustion is a single-step reaction Tgas(t0) = 413K Tliq(t0) = 298K Before After LP analysis: hypotheses

  9. LP analysis: computation • Calculation of amount of energy released due to complete combustion E1(Tfin) • Calculation of amount of energy necessary to heat and evaporate liquid water and heat steam E2(Tfin) • Final thermal equilibrium: solving of the equation E1(Tfin) = E2(Tfin) Tfin • Calculation of the final density • Calculation of the final pressure (ideal gas relation)

  10. Final temperature vs initial H2 mole fraction for ≠ initial volume fractions of liquid water

  11. Final pressure vs initial H2 mole fraction for ≠ initial volume fractions of liquid water

  12. Conclusions • First results of the experimental study devoted to characterize the spray in terms of size distribution • LP analysis: 1) heat sink as expected in the presence of liquid water 2) the steam due to vaporization becomes important as the amount of initial hydrogen reaches a certain value (between 12% and 15% with our data) so that the final pressures are higher than the AICC pressure 3) this first study is a preliminary work for the full CFD modelling taking into account the reaction rate and a polydisperse spray

  13. Future work • Experimental: study of the influence of the spray on a hydrogen-air flame • CFD: current coupling of 1D spherical combustion model with a two-phase flow model

  14. Appendice: work in progress • Several two-phase flow models exist => which one? • Current study of drop residence time and evaporation time to choose the best one

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