SPRAY MODEL VALIDATION ON SINGLE DROPLET HEAT AND MASS TRANSFERS FOR CONTAINMENT APPLICATIONS – SARNET-2 BENCHMARK J. Malet 1, T. Gelain 1, S. Mimouni 2, G. Manzini 3, S. Arndt 4, W. Klein-Hessling 4, Z. Xu 5, M. Povilaitis 6, L. Kubisova 7, Z. Parduba 8, S. Paci 9, N.B. Siccama 10, M.H. Stempniewicz 10 1 IRSN, PSN-RES/SCA, Saclay, France 2 Electricité de France, EDF R&D, Chatou, France 3 RSE, Milano, Italy 4 GRS, Berlin/Köln, Germany 5 IKET, KIT, Karlsruhe, Germany 6 LEI, Kaunas, Lithuania 7 UJD SR, Bratislava, Slovakia 8 UJV Rez, Czech Republic, 9 DIMNP, Pisa University, Pisa, Italy 10 NRG, Safety & Power, the Netherlands ERMSAR 2012, Cologne, Germany, March 21 – 23, 2012

Content Introduction Presentation of the experiments Presentation of the benchmark participants Code-experiment comparison exercise Results analysis Conclusions

- 4 Introduction PTR Pump Reactor enclosure Spray nozzles PTR Pump Reactor enclosure Spray nozzles Context Severe accident Mitigation Spray systems in the containment vessel Spray nozzles ~ 500 nozzles 4 different rings/ramps Flow rate: 280 kg/s per ramp Temperature : 20° - 60°C

Spray systems – main effects - 5 Fission products wash-out Hydrogen mixing SPRAY SYSTEMS Pressure reduction

Spray systems – follow-up of SARNET activities separate effect tests in SARNET Fission products wash-out Hydrogen mixing SPRAY SYSTEMS Pressure reduction Condensation on droplet Benchmark #1 Gas mixture entrainment by sprays Benchmark #2 SARNET-2 WP7 : Containment WP7-2, Task 1: Spray activities

- 7 Synthesis of the activities Specification Nov. 2009: Delivery of the specifications Dec. 2009: Specification meeting Calculations Feb. To June 2010: Delivery of the blind and later open calculations (10 institutions, 10 codes, 15 contributions) Benchmark analysis July 2010: Code-experiment comparison meeting July 2010: Delivery of the code-experiment comparison report Final diffusion: March 2011 Presentation at the NURETH 2011 conference

Content Introduction Presentation of the experiments Presentation of the benchmark participants Code-experiment comparison exercise Results analysis Conclusions

- 9 1 st Elementary benchmark - HMT on droplets Single droplet fall (monodisperse size distribution) –Injected droplets: µm m/s °C Air-steam homogeneous and steady mixture –1 - 5 bar – °C –3 - 90% Vd Dd Td Vd_Z2 Dd_z2 Td_z2 Vd_Z1 Dd_z1 Td_z1 Z2 Z1 Initial Tg P RH at rest

Content Introduction Presentation of the experiments Presentation of the benchmark participants Code-experiment comparison exercise Results analysis Conclusions

- 11 Benchmark participants InstitutionCode nameInstitutionCode name KITKIT specific spray modelGRSCOCOSYS v.2.4 IVO EDFNEPTUNE_CFD v GRSCOCOSYS v.2.4 MARCH ERSE (RSE)ECART - standard model 4WUJVMELCOR v YV ECART -"ad hoc" model 4W*UJDCOCOSYS v. 2.3v24 NRGANSYS FLUENT v UJDASTEC v. 2.0 NRGSPECTRALEICOCOSYS v. 2.3 IRSNANSYS CFX v. 12UNIPIFUMO IRSNASTEC CPA v. 1.3 rev3 10 institutions, 10 codes, 15 contributions

Content Introduction Presentation of the experiments Presentation of the benchmark participants Code-experiment comparison exercise Results analysis Conclusions

Overall code-experiment comparison - 13

- 14 Code-experiment comparison – CFD codes

- 15 Code-experiment comparison – ECART, FUMO, MELCOR codes

- 16 Code-experiment comparison COCOSYS and ASTEC codes

- 17 Main conclusions of code-experiment comparion 1.Low user-effect 2.A general good agreement between codes and experiments, but... 3.… large differences obtained for some specific tests 4. To undersand these differences  detailed look on the mass transfer expressions  next section

Content Introduction Presentation of the experiments Presentation of the benchmark participants Code-experiment comparison exercise Results analysis Conclusions

- 19 Mass flux expressions – detailed look Diffusion coefficient Reference temperature « density term » In all codes, the droplet mass flux expression can be expressed with the same general expression below … but different « detailed » choices are made

- 20 « Density term » : different expressions in codes

- 21 Differences in « density terms » From to -100% to + 60% relative differences between the participants « density terms »

- 22 Diffusion coefficient From -20% to over 100% differences between participants for the steam diffusion coefficient in the mixture

- 23 Reference temperature Reference temperature in the participants codes -droplet temperature T d, -bulk temperature T bulk, -the mean value T film1 between droplet and bulk temperature, -so-called 1/3 law temperature T film2, i.e. a value pondered by 1/3 of the bulk temperature and 2/3 of the droplet temperature.

- 24 Reference temperature From -20% to over 100% differences between participants Depending on the way the reference temperature is calculated

- 25 Analysis of benchmark differences between codes/tests The different parameters in the mass flux expressions lead to several « errors » that can compensate together or be enhanced Can we find the reason why these « errors » are small in some tests, and largers in other tests ? The post-processing of partners data has shown 2 relevant parameters (next slide)

- 26 Relevant parameters Vd Dd Td Initial conditions Droplet residence time Relative mass variation compared to droplet mass

- 27 For tests with drops having larger residence time in case of larger mass flux compared to the droplet mass, « errors » in the code expressions are seen more clearly Explanation of the large differences between codes for some tests

Content Introduction Presentation of the experiments Presentation of the benchmark participants Code-experiment comparison exercise Results analysis Conclusions

- 29 Main conclusion  Differences obtained in some specific tests are due to many different choices done by the code developer for the modelling  And are clearly observed for tests with:  Higher droplet residence time  Higher mass transfer rate/compared to droplet mass ratio  Be aware of having validating your model under different conditions if you want to increase your code predictability  1 test is not enough to validate one phenomenon, a range of tests improves the code validation on this phenomena

Consequences for spray calculations in containment analysis It is difficult to say in advance what will be the main effects if wrong choices are made in the droplet HMT modelling, since phenomena are coupled, but… Possible larger errors, if wrong parameters are used in the mass flux expressions, can be assumed : -In case severe accident Thy conditions AND for small droplets -In case of droplet evaporation (H2 when spraying is activated) -In case of larger residence times if saturation is not reached (allowing changes in the droplet size due to mass transfer) - 30

How far is this benchmark from reactor applications ? -same Thy conditions -same range of droplet sizes -no pressure variation, so different droplet thermodynamical equilibrium -different droplet velocities -no gas entrainment, so different droplet dynamical equilibrium -no turbulence

Spray systems – SARNET-2 Benchmarks - 32 Hydrogen mixing SPRAY SYSTEMS Pressure reduction Condensation on droplet Gas mixture entrainment by sprays Benchmark #1 Benchmark #2 SARNET-2 WP7 : Containment WP7-2, Task 1 : Spray activities

- 33 Status of the next elementary benchmark  Tests in the IRSN CALIST facility  Real PWR spray nozzle (2 m « diameter » spray)  Real-scale experiment for spray entrainment  Benchmark specificaions: nov  Partners contributions received  Received in February 2012 (FLUENT, CFX, NEPTUNE, GASFLOW, ECART, FDS)  Last contributions  until March 31 st 2012  Synthesis report in 2012

After SARNET-2, we will be close to be able to calculate real size spray systems in a reactor using accurate CFD tools or advanced spray LP modelling Coupled phenomena The zone of droplet characterisitcs variation is « small » compared to the size of the containment building BUT is the place of strong exchanges: CFD calculations could bring some insights if the reactor meshed zone is reduced to few meters below the nozzles! Hydrogen mixing SPRAY SYSTEMS Pressure reduction Coupled phenomena

Thanks!

st Elementary benchmark - HMT on droplets

Main thermodynamical exchanges for spray occur in a small region: Vertical evolution of the droplet size and temperature Condensation Evaporation Equilibrium temperature Increase of droplet temperature Main variations of droplet sizes due to HMT  in the first meter of droplet fall