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Progress on Ruthenium Release and Transport under Air Ingress Conditions

European Review Meeting on Severe Accident Research Karlsruhe, Germany, 12-14 June 2007. Progress on Ruthenium Release and Transport under Air Ingress Conditions. A. Auvinen 8 , G. Brillant 6 , N. Davidovich 4 , R. Dickson 1 , G. Ducros 2 , Y. Dutheillet 3 ,

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Progress on Ruthenium Release and Transport under Air Ingress Conditions

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  1. European Review Meeting on Severe Accident ResearchKarlsruhe, Germany, 12-14 June 2007 Progress on Ruthenium Release and TransportunderAir Ingress Conditions A. Auvinen8, G. Brillant6, N. Davidovich4, R. Dickson1, G. Ducros2, Y. Dutheillet3, P. Giordano6, M. Kunstar7, T. Kärkelä8, M. Mladin5, Y. Pontillon2, C. Séropian6, N. Vér7 1 AECL, Chalk River (Can) 2 CEA DEN/DEC/SA3C, Cadarache (Fr) 3 EDF R&D, Clamart (Fr) 4 ENEA, Roma (I) 5 INR, Pitesti (Rom) 6 IRSN DPAM/SEMIC, Cadarache (Fr) 7 KFKI AEKI, Budapest (Hun) 8 VTT, Espoo (Fin)

  2. Outline 1. Air ingress scenario calculations • Modelling of flow with ASTEC and SATURNE • Effect of air ingress in the core ICARE/CATHARE 2. Release of ruthenium from the fuel • Experiments with fuel fragments and cladded fuel samples • Modelling of ruthenium release with ELSA module of ASTEC code 3. Ruthenium release and transport experiments 4. Conclusions and future work

  3. Air ingress scenario calculations with ASTEC • French 900 MWe PWR containment modelled • Containment building nodalization > 50 zones • Hot leg break (12”) followed by LHF • Typical air flow through RPV 10 mol/s continues several hours

  4. Reactor meshing for CFD calculation (Saturne) Coarse meshing in the dome 40.000 to 60.000 cells Refined meshing in the annulus zone

  5. CFD results • Small breach in the hot leg 99% 1 % 0.07 kg/s Air + steam : 7 kg/s Boundary conditions MAAP + Tolbiac aBreach size is the predominant factor

  6. Conditions resulting from air-ingress • Calculated with ICARE/CATHARE v2 using TMI2 input deck • Boundary conditions, flow rates and gas composition from ASTEC and SATURNE results • Effect of air on core degradation and availability of oxygen in the core region State of the core after 1 hour 12” break (left) and 29” break (right) Oxygen mass fraction after 1 hour 12” break (left) and 29” break (right)

  7. Experiments on ruthenium release from fuel MCE1 Experiment • UO2 fragments (burnup 10.7 MWd/kgU) • heated to test T in Ar/2%H2 • Tests 1,2,3,4,7:  air added for 900 s at test T • Tests 5, 6 and 8:  no added air, but some oxygen ingress in Test 8 • significant UO2 volatilization in all air tests and Test 8 HCE3 Experiment • 25-mm segments of clad CANDU fuel element • press-fitted Zircaloy end-caps • Steam: Tests H01, H03 and H06 • Air:  Tests H02 and H05 • Ar/H2 with oxygen ingress:  Test H04

  8. MCE1 HCE3 1 2 3 4 5 6 7 8 1 2 3 4 5 6 Peak T (K) 1973 2073 2173 2273 2073 2273 2350 2350 2200 2160 2110 2100 1780 1810 Atmos. Air Air Air Air Ar/H2 Ar/H2 Air Ar/H2 H2O Air H2O Ar/H2O Air H2O Exp. (%) 100 100 100 100 0 10 100 90 5 87 4 0 0 0 Calc (%) IRSN 100 100 100 100 0 0 100 46 0 0 0 0 0 0 Calc.(%) ENEA - - - - - - - - 8.7 0 - - - - Modelling of Ru release in ELSA module of ASTEC code v1.3 • Volatilization from Ru(s) or RuO2(s) (depending on fuel oxygen potential) • Gaseous species are RuOx with x = 0 to 4 • Validation • De-cladded fuel samples MCE1 tests from AECL • Cladded fuel samples HCE3 tests from AECL

  9. Kinetic release of ruthenium: MCE1-4 and HCE3-H02 • Test HCE3-H02: • ruthenium kinetic release is under- estimated by ELSA calculations for cladded samples (IRSN) • Test MCE1-4: • ruthenium kinetic release is well estimated by ELSA calculations for decladded samples (IRSN) • modelling of ruthenium release is validated for de-cladded fuel samples in air • a better understanding and estimation of the gas/fuel surface will be engaged for cladded samples for a better modelling of ruthenium release in that conditions

  10. Release of ruthenium: HCE3-H01 and –H02 (ENEA)

  11. Release kinetics: HCE3-H01 and –H02 (ENEA) • FP release well estimated in steam flow (H01) • Ru release underestimated in air flow (H02)

  12. Exhaust Pyrex glass tube Flow meter Inner quartz tube Ceramic rod Ice bath 1 M NaOH – 0,05 M NaOCl absorber solution Furnace Reaction chamber with sample Quartz tube Absorber Air Setup of RUSET-5 experiments Air injection (171 cm3/min) was started when furnace with sample was heated up to the required temperature. Isothermal experiments were performed at 1000 and 1100oC. The released ruthenium was collected in two places: • in an inner quartz tube placed into the outlet tube of reaction chamber to determine the amount of deposited RuO2 in the decreasing temperature area • in an ambient temperature absorber solution at final outlet air to quantify the gaseous ruthenium oxide components in the outlet gas after cooling down.

  13. Partial pressures of RuO4 in RUSET-5 outlet air The concentrations of RuO4 in the ambient temperature escaping air in case of pure Ru are about one order of magnitude lower than in case of alloy or alloy with other FPs. The total amount of Ru collected in alkaline hypochlorite solution was greater in case of tests performed at 1000oC than at 1100oC, maybe due to the longer sampling time.

  14. Facility for ruthenium transport experiments

  15. Results from ruthenium transport experiments Ruthenium release rate Ruthenium aerosol transport Gaseous Ru transport

  16. Scaled ruthenium deposition profiles

  17. Aerosol transport kinetics at 1300 K

  18. Gaseous RuO4 experiment 4 – SS plates Location 30 cm Metallic Metallic + RuO2 Oxidised + RuO2 Oxidised Location 55 cm Oxidised + RuO2 Oxidised Metallic Metallic + RuO2

  19. Conclusions • Air-ingress flows following hot leg break and LHF were evaluated in two independent studies. • Natural circulation loop could bring air to RPV for several hours. • It seemed highly likely that the fuel would come into contact with oxygen. • Ruthenium release can be significant in gas mixtures containing air in pure steam and in steam-hydrogen mixture. • Release fraction and kinetics greatly influenced by burn-up and degradation state of the fuel as well as cladding. • The influence of cladding especially in air-ingress conditions needs to be studied further. • Ruthenium is transported in primary circuit either as RuO2 aerosol particles or gaseous RuO3 and RuO4. • Transport mainly influenced by reactions of gaseous Ru-oxides on the surface. • Fission products and other materials seems to suppress autocatalytic surface reactions and increase transport of gaseous ruthenium. • Due to their small size RuO2 particles agglomerate with larger aerosol particles and are transported with them.

  20. Future work • The data base on Ru release under air ingress conditions from irradiated PWR fuel rods is still scarce. • VERDON programme will include a specific air ingress test on a genuine irradiated UO2 fuel sample in its original cladding. • The release of fission products • Deposition of FPs on thermal gradient tubes • Potential re-volatilisation of FPs induced by air injection • Models developed for UO2 oxidation and Ru release will be validated against independent experimental data such as from VERDON and VERONIKA programs. • Behaviour of ruthenium species in the reactor containment building studied by IRSN and by Chalmers University. • Trapping of ruthenium on containment surfaces • Stability of RuO4 in the containment • The production of gaseous ruthenium inside the reactor containment This work is performed in the frame of a Network of Excellence, SARNet, of the 6th FWP sponsored by the European Commission.

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