Oxygen control systems and impurity purification in lead:

1. Oxygen control systems and impurity purification in lead: Partners : CEA: L. Brissonneau,

2. Summary • Context • Oxygen control systems • Experiments • Scale up • Handling of impurities • Experiments • Scale up • Conclusion

3. Need for oxygen control • Avoid PbO formation • LBE thermohydraulics • Risks of plugging • Formation of protective oxide layers • To prevent metallic element release • To control oxide layers growth kinetics

4. Formation of PbO (upper limit)‏ • Quite a good agreement between Gromov (1998) and Ganesan (2006) 350 and 550°C

5. Upper limit • Too high oxygen content can lead to PbO precipitation at cold stop ( 350°C) • For 4000 t Pb with 5.10-1 ppm oxygen a cold stop at 350°C (solub limit 1.10-1 ppm) yields 22 kg of PbO • The higher acceptable limit for oxygen content in operation is 8.10-2 ppm.

6. Formation of magnetite Fe3O4 • 3Fe + 4PbO = Fe3O4 + 4Pb • 3Fes + 2O2 = Fe3O4 = 3/2 DGf(Fe3O4) • 4PbOs = 2Pbs + 2O2 = 2 DGf(PbO) • 3FeL = 3 Fes = - 3RT ln aFe(L) • 4Pbs = 4 PbL = 4 RT ln aPb(L)=0 • 4OL = 4 PbOL = 4 PbOS = -4 RT ln aO(L) • Raoult law : aFe= CFe/C*Fe ; aO= CO/C*O • Or aO(Fe3O4)=a0 Pb-Bi • Ganesan : • Fe3O4 RT lnP(O2) = -551.99.103+156.9T

7. Operating domain • Large domain in stable operating conditions •  3 orders of magnitude • Narrower domain in transient; cold stop, to limit oxidation kinetic • One order of magnitude, 10-3 <[O]<10-1 ppm

8. Extension of operating domain • One major limit is PbO precipitation at cold stop • 8.10-2 ppm maximum of oxygen. • The dissolution of protective oxides is the lower limit : Fe3O4 at more or less high temperature depending on surface protection • 10-4 ppm if claddings are protected • 10-5 ppm if hot leg is protected( by Ta?) • Protection of the hot surfaces by Ta could also lead to very low oxygen strategy if no dissolution of Ta occurs • Then Ta oxidation should be avoided ! ? • Ta oxidation at oxygen content higher than 10-15 ppm • Initial oxygen will be trapped by hot Ta, then colder surfaces will oxidize • Any “extra” oxygen must be trapped : • hot traps Mg, Al ? • Reduction by H2 in a dedicated loop ??

10. Accidental conditions • Air ingress • Leak in the argon cover gas circuit • 52 kg of oxygen in sodium in Superphénix (1990) • In lead, very low solubility of O in lead (>103 times at 500°C compared to Na) should lead • to surface oxidation : slow o dissolution by vortices • Rather easy detection in gas phase (N2 or O2 by MS, GPC…) or by oxygen probe in Pb • Water ingress • Leak in SG tubes • Few dissolution of H2O in Pb • Detection in cover gas (GPC, IRS, oxygen probe). • Oxides formed must be reduced • H2 loop • Filtering

12. Circuit purification : filtering • Several types of liquid filters was tested • Metallic mesh ; dynalloy, Poral (CEA) • Filtration efficiency depends on : • Liquid metal properties (viscosity, density,..) • Particles : nature, form, size, concentration • Temperature • Flow velocity • Filters medium characteristics (geometry, porosity, pressure drop...) • Its location in system • Temperature max : 400°C • Flow velocity :  0.5 m/s, but filtration rate 0.2 cm/s (related to filter area, <2 cm/s recommended by manufacturers) • Far from elbows… • Need of a auxiliary « loop » or cartridge to have flow rate compatible with filters characteristics

13. Poral Dynalloy Atomic ratio Cr:1 ; Fe: 2, Pb:8, Bi :10 Other impurities : In, Sb, Si, Al, Pall cartridge

14. Filtration characteristic • Magnetite part of the duplex layer might be removed by the LBE flow • magnetite formation  10 kg/year • Stella few grams ( 8g on 250 cm²) are trapped on classical filters for DP  1 bar • About 30 m² (three cartridge filter 10m² EFIT Type) • Need of high level of maintenance with radiocontamination problems (54Mn, 60Co…) • Impurity in LBE : In, Sb, Al, Si • Might lead to high quantity depending on their initial content • Use of H2 to reduce lead oxide • 1 kg of PbO ( +1% / saturation at 400°C / 6000 t) needs min. 110l H2 • 1 kg Fe3O4 needs 410 l H2 : But H2 efficient enough ? • H2 , H2O management (T, Po…)? • Bubbling is necessary to reduce the larger oxides

15. Purification strategy

17. Oxygen supply devices implementation

20. Oxygen supply : gas phase • H2/H2O equilibrium • = 1/11 at 550°C for 10-6 wt% (NRI) • 1 month, 5 litres • Less success in CORRIDA (FZK) • 1000 kg LBE • Poor solid/gas mass transfer • Ar/O2 or Ar/O2/H2O injection • Manual control • Main parameters • Gas flow rate • PO2 pressure (0.1-1% in Ar) • LBE flow rate • LBE temperature • Seems to work by local injection • Better stability achieved with H2O

21. Oxygen supply by gas phase • Advantages • Same device for O2 control and purification by H2. • No operation on the device in normal operation • Quite easy to control automatically • Drawbacks • Rely on sensors if non equilibrium gases are used • Need for exchange coefficient if equilibrium gases are used • Risks of oxide formation • Large flow rates • (Dilution) Gas purification (FP, AP, T, Po,) and recycling • Risk of contamination exposure for operators

22. Oxygen supply for large scale facilities, gas phase An auxiliary loop, type CORRIDA, to supply oxygen in the pool ? • XT-ADS 0.45 g/h, T =400°C • Q(O2)=5.8 cm3/min • Q(Ar/O2)≈600 cm3/min • Min. LBE flow to avoid PbO precipitation : 6 kg/min • EFIT 9 g/h, T =400°C • Q(O2)=116 cm3/min • Q(Ar/O2)≈12 l/min • Min. LBE flow to avoid PbO precipitation : 360 kg/min • No pumping problems • Exchange coefficient in kg/m².h tested in CORRIDA • Not too far from what is required for XT-ADS • two orders of magnitude lower than what would be required for EFIT : • Higher flow rates need experimental validation LBE mass flow : 318 kg/ min in CORRIDA

23. Test interpretations : • Stella experiments performed to estimate fundamental parameters of PbO dissolution were not successful • Oxygen content evolution observed in other parts of the test line show that the oxygen sensors deliver a local measure of oxygen concentration • reflect the heterogeneous oxygen distribution in the system. • Tests highlight various mechanisms in competition : • Oxygen supply by dissolution of PbO pellets • Reduction of oxygen by hydrogen from the cover gas (Ar 5% H2) • Dissolution of Fe3O4 protective layers in low range of oxygen concentration (<10-7 wt%) or of the residual particles present in the coolant • consumption of oxygen by oxidation of the walls or of the metallic corrosion products coming from dissolution of metal walls.

24. Solid phase supply for large scale facilities • Need of fluid saturated deviation to prevent Fe-Cr oxides reaction with the pellets • O supply driven by flow rate and temperature • Large device  15-50 kg PbO(1 - 3.5 kg O) • EFIT 9 g O /h • One filling per 4 – 16 days • Several devices are needed per auxiliary loops or cartrides • Several filling operations per year even for oxidation rate one order of magnitude lower • Use of the mass exchanger on an auxiliary loop • Maintenance : problem of activated products in cold areas (54Mn, 60Co)  150cm IPPE MX, Martynov, ICONE 17

25. Solid mass exchange • Advantages • No gas management • No risks of plugging (oxide formation) • Quite easy control by flow rate and temperature • Drawbacks • More complex design for MXp • More maintenance : pellets filling • Personal exposure • Risks of oxide precipitation on pellets • Sluggish kinetic for dissolution

26. Conclusion • Oxygen supply seems difficult at large rates in classical devices • Gas phase supply would need further experiments to demonstrate the ability of large exchange coefficient • Solid phase supply was not clearly demonstrated • More complex design to be tested • Automatic filling of the device ? • Personal exposure problems • Purification techniques have been defined • Filter characteristics, cold trap • Longer experiments are needed • Maintenance problem

27. Thanks for your attention

28. Open questions • Sensors location • At the entrance of the core • At the entrance of each heat exchanger • In each secondary loop • Oxygen supply • Gas phase or solid phase • One auxiliary loop per heat exchanger ? • Independant oxygen delivery • Solid mass supply in the pool ? • High oxygen supply rate / steel passivation • Maintenance or filtration operation • Filtration • In the auxiliary loop or large filter cartridge ? • Maintenance operations

29. Recommandations for Sensors locations • Because of non homogeneous concentration, it is necessary to use at least three sensors. They shall be placed in the coolant flow in the zones with maximum, minimum and intermediate temperatures (supposedly, in the range from 460 to 540 С). • If there are zones with low rate of coolant temperature variation at their outlet, it is reasonable to install additional sensors. • Before each zone with large exchange area • In each secondary loop to check the good working of the oxygen supply device

30. Oxygen control process studiesby solid mass exchange method • Solid PbO dissolution test N°2 in STELLA 3 pellets at T=500 °C for only 90 hours with a flow rate Q=1 m3/h (u=0.12 m/s) and [O]~10-5–10-8 wt% No more pellets in the dissolution device after test !