Spray systems in French PWR
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ICHS, 11-13 September 2007
On The Use Of Spray Systems: An Example Of R&D Work In Hydrogen Safety For Nuclear
Applications
C. Joseph-Auguste1, H. Cheikhravat2, N. Djebaïli-Chaumeix3 and E. Deri1
1 CEA 2 IRSN
3 CNRS-ICARE
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Spray systems in French PWR
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Spray systems in French PWRo Argument against: ◦ may generate flammable mixtures or enhance flame
propagation through turbulence induced by sprays
o 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
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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
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Spherical bomb
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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
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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
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LP analysis: hypotheseso conservation of mass and
energy (impermeable and adiabatic walls)
o ideal gaseso constant volumeo complete combustion o the whole energy liberated
by the combustion vaporizes the liquid water
o air is considered as a binary mixture (N2-O2)
o hydrogen combustion is a single-step reaction
o Tgas(t0) = 413K o Tliq(t0) = 298K
Before After
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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)
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Final temperature vs initial H2 mole fraction for ≠ initial volume fractions of
liquid water
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Final pressure vs initial H2 mole fraction for ≠ initial volume fractions of liquid water
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Conclusions
o First results of the experimental study devoted to characterize the spray in terms of size distribution
o LP analysis: 1) heat sink as expected in the presence of liquid
water2) 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
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Future work
o Experimental: study of the influence of the spray on a hydrogen-air flame
o CFD: current coupling of 1D spherical combustion model with a two-phase flow model
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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