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Steam Condensation Effect in Hydrogen Venting from a BWR reactor building

Steam Condensation Effect in Hydrogen Venting from a BWR reactor building. University of Tokyo Masahiro Kondo, Nejdet Erkan , Koji Okamoto. Background. In Fukushima- daiichi NPP accident, hydrogen explosion effected the following mitigation measures.

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Steam Condensation Effect in Hydrogen Venting from a BWR reactor building

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  1. Steam Condensation Effect in Hydrogen Venting from a BWR reactor building University of Tokyo Masahiro Kondo, NejdetErkan, Koji Okamoto ICHS 2015 Oct. 19-21

  2. Background • In Fukushima-daiichi NPP accident, hydrogen explosion effected the following mitigation measures. • Hydrogen ventingwas considered in Japan. • CRIEPI evaluated its efficiency using a CFD (computational fluid dynamics) and a LP (lumped parameter) model [1-4] • No steam condensation model was included, although it might effect the building atmosphere [1-4] Kondo M. Yoneda K. Nishi Y. and Inada F. “Reasearch on the hydrogen venting from the BWR reactor building at severe accident”, Proceedings of JSME annual meeting 2012, S083012-S083015 ICHS 2015 Oct. 19-21

  3. Steam Condensation Effect • Concentration effect • Vent-enhancing effect Steam Air Steam Hydrogen Air Hydrogen condensation Hydrogen might be concentrated due to condensation. Condensation heat might enhance the venting. heat-up Q. There exist both negative and positive effect. Which is dominant? ICHS 2015 Oct. 19-21

  4. Objective • To study steam condensation effect in hydrogen venting • CFD calculation • The case where hydrogen-steam mixture flows into the building (hydrogen-steam case) • The case where hydrogen nitrogen mixtureflows into the building (hydrogen-nitrogen case) • LP evaluation • Evaluation results and evaluation time are compared to the CFD calculation. • A Parameter study is conducted with the LP model. comparison ICHS 2015 Oct. 19-21

  5. Calculation Geometry water film on inner wall surface evaporation/condensation model adopted concrete wall 2240kg/m3, 750 J/kgK, 0.53 W/mK 40 m 50 m reference section 18 m wall width : 0.3m window(2m x 2m) outer space gas mixture inlet pressure boundary 303K, O2:N2=0.21:0.79,101325 Pa velocity inlet boundary 473K (please correct proceeding page 4 line 3) H2:H2O=0.5:0.5 (hydrogen-steam case) or H2:N2=0.5:0.5 (hydrogen-nitrogen case) 0.72 m3/s (equivalent to 1600kg hydrogen / 24 hours) ICHS 2015 Oct. 19-21

  6. Calculation Model and Parameters • Transient calclulationusing STAR-CCM+ • Δt = 1.0 sec • gravity = 9.81 m/s2 • gas mixture • multi-component gas • H2,O2,H2O,N2 • k-e turbulent model • water film • density: 997.6 kg/m3 • specific heat: 4181 J/kgK • thermal conductivity: 0.62 w/mK • latent heat: 2500 kJ/kg • concrete wall • density: 2240kg/m3 • specific heat: 750 J/kgK • thermal conductivity: 0.53 W/mK • external heat transfer coefficient: 4.0 W/mK ICHS 2015 Oct. 19-21

  7. Mesh Configuration 2 layer meshes + 6 wall meshes window mesh size: 1 m outer space meshes on the reference section meshes around the window ICHS 2015 Oct. 19-21

  8. Hydrogen Distribution Small difference in hydrogen concentration t = 2.0 hour t = 2.0 hour 0.00 0.04 0.08 0.12 t = 4.0 hour t = 4.0 hour t = 6.0 hour t = 6.0 hour t = 8.0 hour t = 8.0 hour Hydrogen Concentration (mol/mol) t = 10.0 hour t = 10.0 hour (b) hydrogen-nitrogen case (a) hydrogen-steam case ICHS 2015 Oct. 19-21

  9. Temperature Distribution t = 2.0 hour Large differencedue to condensation heat t = 2.0 hour t = 4.0 hour Temperature (C) t = 4.0 hour t = 6.0 hour t = 6.0 hour t = 8.0 hour t = 8.0 hour 30.0 40.0 50.0 t = 10.0 hour t = 10.0 hour (b) hydrogen-nitrogen case (a) hydrogen-steam case ICHS 2015 Oct. 19-21

  10. History of Hydrogen Concentration and Temperature Temperature rise in hydrogen-steam case was larger after condensation started, because of condensation heat. Hydrogen concentration was slightly lower in the hydrogen-steam case,because condensation heat enhanced venting. In this calculations, main difference was due to condensation heat ICHS 2015 Oct. 19-21

  11. LP (Lumped Parameter)model • condensation model[5] • Stefan’s law • model for vertical opening [6] • Counter-current flow z w zout_h outflow uout(z) zout_l zin_h inflow uin(z) zin_l The history of hydrogen concentration and temperature are predicted using these models and compared with the CFD results. [5] Kondo M., Yoneda K., Furuya M., Nishi Y., JNST (2015) doi:10.1080/00223131.2014.1000993. [6] Proceedings of 2015 annual meeting of AESJ (2015) I12. ICHS 2015 Oct. 19-21

  12. CFD vs LP With LP model, the results equivalent to the CFD’s were obtained much faster. ICHS 2015 Oct. 19-21

  13. Parameter Study using LP model Impact on area of the window Hydrogen concentration in hydrogen-steam case is higher. ”concentration effect” is dominant Hydrogen concentration in hydrogen-steam case is lower. ”vent enhancing effect” is dominant Both “concentration effect” and “vent-enhancing effect” are observed, but dominant effect changes depending on the opening conditions. ICHS 2015 Oct. 19-21

  14. Conclusion • To study steam condensation effect in hydrogen venting • CFD calculation • hydrogen-steam case and hydrogen-nitrogen are compared • In the calculated case, difference in hydrogen concentration was small, but the large temperature difference was observed. • comparison between LP and CFD • LP could obtain equivalent results to CFD in much smaller prediction time. • parameter study using LP • Both “concentration effect” and “vent-enhancing effect” is observed, depending on the opening conditions. ICHS 2015 Oct. 19-21

  15. Thank you ICHS 2015 Oct. 19-21

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