Hydrogen-tritium transfer in SFR Concepts

1. Hydrogen-tritium transferin SFR Concepts K. LIGER, T. GILARDI Tél : 33 (0)4 42 25 49 08 e-mail : karine.liger@cea.fr

2. Theory of diffusion and mass transfer phenomena Fick’s law, parameters, steady state... Data’s for liquid Na and stainless steel: Sievert constants, permeation, diffusion Permeation Na/Metal/Na and Na/Metal/gas Equilibrium between Na and cover gas Cold trap and cristalisation Links between H and T transfers Mass transfer in a reactor OUTLINES • System definition • Pollution sources • Modeling • Estimation of the fluxes of Hydrogen and tritium

3. Estimate : The distribution of H and T in the circuits and then the gaseous and liquid release of T as well as the accumulation of T in the cold traps SO THAT: During operation The release does not exceed release authorisation During conception A suitable release limit authorisation could be asked General goal for tritium transfer estimation

4. Hydrogen permeation includes severall phenomena Molecule dissociation at the interphase between metal and medium Adsorption, Absorption Diffusion in the metal De-absorption, De-adsorption Atoms combination In general, mass transfer is controlled by diffusion (combination is the second predominant phenomena) Hence, permeation can be represented by Fick’s law Theory: Mass transfer through a wall

5. Équations de Fick - Fick’s law - Mass conservation’s law For a simple geometry E.g.: Evolution of concentration in a plan wall after a step of concentration from C = C2 to C1 j : flux D : diffusivity C : concentration e : thickness Theory of Diffusion : Fick ’s law x e o

6. When steady state and transient meet each other… Assumption : plan wall Time to reach 99,99% of the steady state flow depends on: D, diffusivity of material (function of temperature and nature of the material) e, thickness tp does not depends on the concentration gradient Time to reach 98,5% of the steady state flow: tp /2 Steady state vs transient state ? Over the lifespan of a reactor, steady state can be assumed!

7. Nature of material:Austenic steel versurs ferritic steel, .... factor 100 for D at 250°C, and only 10 at 500°C Temperature: D = A exp( -E / T(K) ) , m² /s SS316 : factor 105 between room temperature and 500°C Surface state : Oxidised layer is a permeation barrier Hydrogen trapped in the metallic structure Theory: Diffusion depends on…

8. Gaseous adsorption on metallic surface external on surface internal on small fissuration and defect structure In the matrix Impurities Grain boundaries dislocations... Some of these mechanisms are irreversibles E.g.: during heating of metal in a vacuum oven, hydrogen release is observed up to melting temperature Diffusion : Hydrogen/tritium trapped in metallic structure • Behaviour of T similar to 1H, but isotopic exchange may modify macroscopic behaviour of T • In presence of hydrogen trapped in the structure: • Shorter transient state for T diffusion • Lower diffusion flux under steady state

9. Hydrogen equilibrium between Na (liquid or solid) and the cover gas Theory: H/T equilibrium between cover gaz and NaSievert constant

10. Theory: equilibrium between gas and metal Sievert constant • Hydrogen equilibrium between metal and the cover gas • Similar solubility of H and T in steel • Diffusion depends on atomic mass • Hence, diffusion is « easier » for H

11. Solubility in metal : Sievert constant E.g.: SS316, mol(H)/m3(acier)/pa1/2 • KTISON (1983) = 0,9123 exp( -1352,1 / T(K) ) • KFORCEY (1988) = 0,9424 exp( -2229 / T(K) ) • KGRANT (1988) = 2,2191 exp( -1890 / T(K) ) • DFORCEY(1988) = 3,82 10-7 exp( -5472,4 / T(K) ) , m² /s

12. Theory: Diffusion through a wall immersed in Na Plan wall Similar equations for T

13. Theory: Diffusion through a wall immersed in Na and gas Similar equations for T

14. In that case, diffusion flux through the surface is: Theory: Diffusion through pipes

15. Cold traps : • Flux of hydrogen to the cold trap: • Flux of Tritium to the cold trap: • Co-cristallisation of tritium with H • Isotopic exchange and T decay neglected Cold trap efficiency: C*: Solubility of H in Na

16. Isotopic exchange reaction: Equilibrium constant is: Theory: Isotopic exchange in gas phasehydrogen - tritium

17. Steady state calculation Homogeneity of concentrations in the circuits Isotopic exchange in cold traps neglected as well as T decay Source of T: In primary circuit: Ternary fission reactions Control rod reactions Activation of impurities: B, Li Estimation of the source on the base of Superphenix and Phenix past experience Source of H: In primary circuit: fission reactions. In secondary circuit: Gaz in the ternary circuit: source = 0 Water in the ternary circuit Aqueous corrosion of GV Thermal decomposition of N2H4 used in water to limit presence of O : 3 N2H4 = 2 NH3 + 2 N2 + 3 H2 for T>250°C Estimation of the source on the base of Superphenix and Phenix past experience Tritium transfer in a Reactor Assumptions:

18. PF I Ar III I II ~ GV Turbine RUR Na/Na BPR RUR Na/Air Schematic view of the reactors PF II SPX:reference case Improvement of the models for Tritium transfer in other SFR concepts And for other fission reactors (EPR, HTR, VHTR…)

19. Diffusion through heat exchangers Diffusion through GV Diffusion through pipes and volumes Trapping in cold traps (for H in Na) / Sources in the circuits H exchange with covering gas SFR: Mass balance for Hydrogen: for Tritium: • Diffusion through heat exchangers • Diffusion through GV • Diffusion through pipes and volumes • Trapping in cold traps (for T in Na) / Sources in the circuits • H/T exchange with covering gas

20. Localisation of exchange in the different concepts SFR Na/Na/H2O SFR Na/Na/SCO2 SFR Na/Na/He-N2

21. Concepts comparison • SFR Na/Na/H2O, Na/Na/SCO2, Na/Na/He-N2 • Presence of H2O in the ternary circuit leads to a source of H, which is benefit to reduce gaseous leakage: • Release of T for Na/Na/H2O: 65 kBq/s • Release of T for other concepts: nearly 1200 kBq/s • Presence of: • secondary cold traps of great importance for Na/Na/H2O concept • primary cold traps of great importance for other concepts • Permeation through GV: • is of great importance for Na/Na/H20 concept. Great PE lowers gaseous release • has no effect for other concepts • Addition of secondary hydrogen source minimises T release

22. Diffusion T release depends on the concept Importance of cold traps Importance of Hydrogen source Ways of limitation of diffusion: nature of metal, oxydised layer, thickness, temperatures, aeras Modeling partially validated on Phenix and Superphenix former results Modeling Improvement needed: Colds traps modeling should be improved Transient state should be implemented Measurement of H/T diffusivity through metals Conclusion ...

23. [1] Paul TISON Influence de l’hydrogène sur le comportement des métaux. Rapport CEA-R-5240 ; Thèse présentée à l’université Paris 6 le 9 Juin 1983 [2] K.S. FORCEY ; D.K. ROSS ; J.C.B. SIMPSON ;D.S. EVANS Hydrogen transport and solubility in 316L and 1.4914 steels for fusion reactor applications. Journal of Nuclear Materials 160 (1988), North Holland, Amsterdam. [3] D.M.GRANT ;D.L. CUMMINGS and D.A. BLACKBURN Hydrogen in 316 steel ; diffusion, permeation and surface reaction. Journal of Nuclear Materials 152 (1988), North Holland, Amsterdam. References