IEA Implementing Agreement on Nuclear Technology for Fusion Reactors

1. IEA Implementing Agreement on Nuclear Technology for Fusion Reactors Liquid Breeder Blankets Subtask Coordinating Meeting on R&D for Tritium and Safety Issues in Lead-Lithium Breeders11-12 June 2007, Idaho Falls, ID, USA How could be foreseen the tritium mass transfer F. Gabriel1, O. Gastaldi1(presenter), L. Sedano2 (1 CEA, 2 CIEMAT) O. GASTALDI

2. The TBM objectives • Demonstrate the capacity of tritium extraction while masteringits inventory • efficient technological components • efficient remote control • understanding the physical and chemical phenomena and their interactions • capitalize these knowledge in software tools • Knowledge modelling is required in order to represent in a reliable way the different phenomena (in particular T mass transfer phenomena) O. GASTALDI

3. Recall of the needs in term of tritium management • Prediction capabilities of tritium transport modeling tools for tritium transport simulation analyses is a major scientific technical goal of fusion nuclear technology for ITER-TBM: • To help the designer and optimize the technical choices • To better understand future experimental tests • To answer to safety concerns : • Inventories prediction (help for accountancy methods) • Tritium release estimation O. GASTALDI

4. Understanding of T transport phenomena • Many phenomena could have an impact on tritium mass transfer from LLE to helium coolant: • Level of solubility • MHD impact of velocity profile, • Impact of He bubbles contained in PbLi (transfer to gas phase) • Boundary layer resistance • Diffusion under irradiation • Interface phenomena (sorption – desorption) • Isotopic swanping effect • … O. GASTALDI

5. Understanding of T transport phenomena • Many phenomena could have an impact on tritium mass transfer from LLE to helium coolant O. GASTALDI

6. Different levels of modeling • Two complementary type of tools • System analyses (ODE system – component = 2 inlets, 2 outlets and a transfer function) • loop control (main tritium rates, inventory) • global sensitivity analysis • Component analysis (PDE system – multiphysics analyses) • qualification of the transfer function • local analysis and component optimization • model validation • Development of reliable system tools, a good knowledge of phenomena is needed • In case of lack of knowledge, refined models associated with analytical experiments are needed O. GASTALDI

7. System approach tools developed in EU • Development of engineering tool (system approach) based on • Steady state • Fick’s law • Simplified components description • Using mean values • It allows to: • Lead sensivity studies • Determine what are the major parameters (on which priority must be put in term of R&D) O. GASTALDI

8. System approach tools developed in EU • Example of result: • Except at the beginning of the range, quite progressive gain O. GASTALDI

9. System approach tools developed in EU: TRICICLO • TRICICLO: system tool • Non –linear, (self)-coupled, multiparametric problem. (at a larger scale) O. GASTALDI

10. System approach tools developed in EU: TRICICLO • “Moving-slab” technique for tritium transport transient computation in HCLL channel (unit symmetry from BB segmentation) SOURCE DIFF. BALANCE LOCAL FLUX EXPRESSION O. GASTALDI

11. System approach tools developed in EU: TRICICLO • Simplified (reliability of the MODEL?) but TRANSIENT. • Main hypothesis: • Diffusion (Fick’s law). • No bubbles in Pb-Li (possible to be taken into account by an apparent Pb-Li higher T solubility in Pb-Li). • MHD drag transport take in a very simplified way (apparent i.e.: reduced radial diffusivity). • Interfacial resistance (He-film) can be endorsed in the model (as a PRF of a barrier). • Radiation effects in the steel (as factors in Diff. & Solub.). • Accounting of isotopic swamping possible (Walbroek theory). • Dynamic accounting of gas chemistry criteria (oxidation threshold) on EUROFER and INCOLOY for surface characteristics. • Precise sizing of INCOLOY 800 Steam Generator and dynamic transfers (in surface limiting regimes through). • CPS, TES, TRS transfers in/out with system efficiencies (DF factors) O. GASTALDI

12. System approach tools developed in EU: TRICICLO • Example of results: • assessment of macroscopic behaviour • But also sensitivity analysis O. GASTALDI

13. H-p.p. H´-p.p. System approach tools developed in EU: TRICICLO • Illustration of potential discussions on hypothesis: basic controversial (unknowns ?) to write to express some fluxes. ISOTOPIC SWAMPING: T-p.p. BB HCS T-FLUX Does T-flux vary with H-pp. or H´-pp. ? Quantit. dependences on T., H, H’ pp ? Isotopic effects would play on BBPC and PCSG fluxes Experimental data on isotopic swamping is poor. Dependencies from the Theory on Isotopic effect on transport in [F. Waelbroek, Jül 1966, Dez. 1984 ] for gas-gas problems assumed. O. GASTALDI

14. System approach tools developed in EU: TRICICLO  ISOTOPIC SWAMPING EFFECTS: DIFFERENT SITUATIONS HCPB [F. Waelbroek, Jül 1966, Dez. 1984 ] pp. 109 HCLL CO-STREAM ISOT. SWAMP. • Low permeation numbers • (surface-limited regimes) • forT & large for H • Large permeation numbers • (diffusion-limited regimes) • for H and T T-FLUX T-FLUX swamped a factor GAS T-FLUX swamped a factor GAS • Large permeation numbers • (diffusion-limited regimes) • for H and T COUNTER-STREAM ISOT. SWAMP. T-FLUX swamped factor T-FLUX swamped a factor T-FLUX GAS GAS • Low permeation numbers (surface-limited regimes) for H and T co-/counter-stream No effect  STEADY STATE ISOT. SWAMP. MODEL IMPLEMENTED IN TRICICLO O. GASTALDI

15. System approach tools developed in EU: TRICICLO • Uncertainties on Isot. Swamp. for TRICICLO • Basic theory and experimental database for gas-gas mixtures. • It is uncertain how a low solubility media (LM) in (f) position can reduce H flux- back minimizing isotopic swamping effects. • Isotopic swamping effects if taken into account should be coupled with presence of permeation barriers and/or EUROFER oxidation conditions (as it is tentatively done in TRICICLO tools) . O. GASTALDI

16. Refined models – an illustration General issue: The tritium concentration in the He and in the Pb-15.7Li are evaluated by solving partial differential equations governing the tritium balance, the thermal field and the velocity field in a simplified 2D geometrical representation of the breeder unit at the mid equatorial plan. Objective: evaluate the sensitivity effect of the Pb-15.7Li velocity profile on engineering outputs F3, and Cf for the inboard and outboard equatorial modules O. GASTALDI

17. Refined models – an illustration • Heat source and tritium source from Monte Carlo analysis, • Boussinesq approximation, • Inductionless MHD approximation, • Inboard magnetic field = 10 T, • Outboard magnetic field = 5 T, • Toroidal magnetic field, • Perfect conductor side walls, • Limited diffusion regime for the tritium, • Permeation Reduction Factor = 1, • Steady state. Engineering Outputs: O. GASTALDI

18. Refined models – an illustration Sensitivity analysis based on the identification of the parameters of the response surface XBC = choice of the fluid boundary condition XNC = choice of the natural convection Temperature distribution (°C) – B = 10 T Tritium concentration (at m-3) – B = 10 T Concentration profile Radial velocity O. GASTALDI

19. Refined models – an illustration • Results: • In the inboard and outboard equatorial HCLL modules within the above listed assumptions, the permeation rate towards the He circuit, the mean outlet tritium concentration and the ratio of the permeation rate to the production rate are almost insensitive to the magnetic field • A concentration boundary layer is developed and could be regarded as an equivalent Permeation Reduction Factor of 30 (which was not considered in the previous tritium permeation estimations). • Such results can be integrated in the system approach tools as PRF • But even with refined model it is needed to solve some persistent lacks of knowledge and uncertainties by experimental campaign O. GASTALDI

20. Many uncertainties and persistent lacks • Data lacks (persistent) • Materials databases: • Pb-15.7Li properties (like T solubility), • Radiation spectral effects on T-transport properties in EUROFER (& coatings) • Base phenomena with large potential effect on T-transfers in IBTC • He-cavitation issues (bubble nucleation impact on tritium) • Validation (or not) of isotopic swamping mechanisms • Soret effect quantification • Trapping models • Coatings impact and associated representation • (He chemistry effects) O. GASTALDI

21. Many uncertainties and persistent lacks • Data lacks (persistent) • Systems definition and system parameter unknows. • Key technological choices: Power Conversion System (SG) for the IBTC • Unknown dependencies: Do TES/LM efficiencies depend on T p.p. ? - H-dopping effect ??? - (CPS, TRS) scaling & DFs dependencies on (Q2, Q2O) stream p.p. ? O. GASTALDI

22. Many uncertainties and persistent lacks – illustration (Ks) • Pb-Li eutectic alloy proposed in the 70´s with intensive characterization of base properties work during 80´s in EU labs (JRC, CEA, KfK) on eutectic (assumed as 83at%Pb-17at %Li). • Practical experience determining H-isotope´s solubility in Pb-Li alloys shows how the measurement is potentially full ofparasitic effects: (1) wall impact on solubility () (2) uncertainty in the eutectic composition () (3) impact of eutectic disproportioning () (4) role of M-impurities (¿ ?) (5) Other ? LM hydrodynamics (¿-?) Li vapors and pressure gauge performances (-) O. GASTALDI

23. Many uncertainties and persistent lacks – illustration (Ks) (1) wall impact on solubility() - confirmed for some early data (corrected > 90´s measure: by coating capsules: Al2O3, W,..), - [ 2 o.o.m. values ] & wall material solution activation -Es (2) uncertainty in the eutectic composition () - See previous presentation (3) eutectic disproportioning () • not systematically checked & driving potentially to incorrect overestimated solubility (in connection with Li-aggregation by clustering) Deviation from theoretical eutectic composition [15.7(2)at%Li] at liquid phase and solubility impact with Li aggregation. O. GASTALDI

24. Many uncertainties and persistent lacks – illustration (Ks) (4) role of M-impurities (¿?) Steel corrosion products show high solubility limits in Pb15.7Li (Ni > Mn > Fe > Cr). However, tritium solubility in dominant (Fe) is comparable (10-8 at.fr. Pa-1/2) to lower reference solubility data in Pb15.7Li [Reiter], i.e.: amount of impurity comparable to that of measured eutectic. In this sense, even for unprotected samples and conservatively high corrosion rate values for (cm s-1) thermo-convection velocities (10-100 mg m-2 h-1), impurity impact can be assumed as negligible. Solubility limits for FM corrosion components (Fe, Ni, Mn, Cr) in Pb-Li O. GASTALDI

25. Many uncertainties and persistent lacks – illustration (Ks) • Two kinds of techniques have been used: • Hot Absorption (HA) techniques: gravimetric (HA-g) or pressure drop (HA-p) versions, • Isovolumetric Desorption (ID) (desorbed gas pressure evolution after absorption) • Results: • HA-g (o.o.m higher than actual solubility values and no Sievert´s law) ABANDONED. • First HA-p measurements shown first Sievert´s dependencies and lower values (> 1 o.o.m) • ID techniques seem to be as most performant methode for measuring Sievert´s constant and a refinement of HA-p methodes. • Allows checking reversibility between absortion & desorption (key issue) • can neutralize possible role of LM hydrodynamics O. GASTALDI

26. Development plan • First step: • Exchange on the way to represent the main transport phenomena of tritium in LLE • Establish a common basis of knowledge • Prioritize the main issues in order to cover the lacks of knowledge • Develop experimental program in order to solve them (using shared procedure and/or using cross checking) • Second step : • Develop one (or several (depending on the objectives)) open tool(s) for T transfer modeling O. GASTALDI

27. Development plan of the tool – What is the need? • Potential users : • Design Engineer • component simulation (validated models) • sensitivity analysis • complex meshing • important CPU time • user-friendly interface • Physicist • model validation • experiment design • interpreted language (easily model implementation) • numerical tools access • Numerician • software improvement • basic programming level • object-oriented language O. GASTALDI

28. Development plan of the tool- How could we built it? • Basic facts • not really a commercial tool • not that much users • quite complex physics • Shared development • open access CFD based tools • development divided among partners • A team will integrate all developments in a QA version O. GASTALDI

29. Development plan - Preliminary road map for the 1st tool • needs specification • analysis of needs • specification of criteria • selection of a software • research of potential software • assessment of bests • development of our application • model implementation • benchmark evaluation • Experimental program • in order to reduce data lack • qualification of codes O. GASTALDI

30. Conclusion (1/2) • Main issues to solve are: • Permeation modeling • isotopic swamping • surface model • trapping model • coating and interface models • He chemistry effects • experimental validation • Multiphysic analysis and validation • He bubbling effect • Constitutive law [C = f(P)] O. GASTALDI

31. Conclusion (1/2) • Main issues to solve are: • Permeation modeling • isotopic swamping • surface model • trapping model • coating and interface models • He chemistry effects • experimental validation • Multiphysic analysis and validation • He bubbling effect • Constitutive law [C = f(P)] With or without irradiation O. GASTALDI

32. Conclusion (2/2) • Main points to treat within the collaboration program: • Definition of common way to describe phenomena in modeling tools (benchmarking of the different available codes) • Definition of specific experimental tests in order to obtain main parameters of models O. GASTALDI

33. O. GASTALDI

34. Support to the discussion • Fundamental points: • Establishment of a common database • Definition of common LLE specifications with QA procedure for its manufacturing – EU can propose some specifications (to be discussed) O. GASTALDI

35. Support to the discussion • For each issues what could proposed: • Permeation modelling • isotopic swamping • surface model • trapping model • coating and interface models • He chemistry effects • experimental validation • Multiphysic analysis and validation • He bubbling effect • Constitutive law [C = f(P)] – Sievert constant determination • What are the reference laws for these phenomena? • What is the level of reliability? • Which kind of experiments do we need to complete it? • Is there existing facility or analytical bench able to do so? O. GASTALDI