Presentation on theme: "Hydrogen-tritium transfer in SFR Concepts"— Presentation transcript:
1 Hydrogen-tritium transfer in SFR Concepts K. LIGER, T. GILARDITél : 33 (0)
2 OUTLINES Theory of diffusion and mass transfer phenomena Fick’s law, parameters, steady state...Data’s for liquid Na and stainless steel: Sievert constants, permeation, diffusionPermeation Na/Metal/Na and Na/Metal/gasEquilibrium between Na and cover gasCold trap and cristalisationLinks between H and T transfersMass transfer in a reactorSystem definitionPollution sourcesModelingEstimation of the fluxes of Hydrogen and tritium
3 General goal for tritium transfer estimation 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 trapsSO THAT:During operationThe release does not exceed release authorisationDuring conceptionA suitable release limit authorisation could be asked
4 Theory: Mass transfer through a wall Hydrogen permeation includes severall phenomenaMolecule dissociation at the interphase between metal and mediumAdsorption, AbsorptionDiffusion in the metalDe-absorption, De-adsorptionAtoms combinationIn general, mass transfer is controlled by diffusion (combination is the second predominant phenomena)Hence, permeation can be represented by Fick’s law
5 Theory of Diffusion : Fick ’s law j : fluxD : diffusivityC : concentratione : thicknessÉquations de Fick Fick’s law - Mass conservation’s lawFor a simple geometryE.g.: Evolution of concentration in a plan wall after a step of concentration from C = C2 to C1xeo
6 Steady state vs transient state ? When steady state and transient meet each other…Assumption : plan wallTime to reach 99,99% of the steady state flow depends on:D, diffusivity of material (function of temperature and nature of the material)e, thicknesstp does not depends on the concentration gradientTime to reach 98,5% of the steady state flow: tp /2Over the lifespan of a reactor, steady state can be assumed!
7 Theory: Diffusion depends on… Nature of material: Austenic steel versurs ferritic steel, ....factor 100 for D at 250°C, and only 10 at 500°CTemperature:D = A exp( -E / T(K) ) , m² /sSS316 : factor 105 between room temperature and 500°CSurface state : Oxidised layer is a permeation barrierHydrogen trapped in the metallic structure
8 Diffusion : Hydrogen/tritium trapped in metallic structure Gaseous adsorption on metallic surfaceexternal on surfaceinternal on small fissuration and defect structureIn the matrixImpuritiesGrain boundariesdislocations...Some of these mechanisms are irreversiblesE.g.: during heating of metal in a vacuum oven, hydrogen release is observed up to melting temperatureBehaviour of T similar to 1H, but isotopic exchange may modify macroscopic behaviour of TIn presence of hydrogen trapped in the structure:Shorter transient state for T diffusionLower diffusion flux under steady state
9 Theory: H/T equilibrium between cover gaz and Na Sievert constant Hydrogen equilibrium between Na (liquid or solid) and the cover gas
10 Theory: equilibrium between gas and metal Sievert constant Hydrogen equilibrium between metal and the cover gasSimilar solubility of H and T in steelDiffusion depends on atomic massHence, diffusion is « easier » for H
12 Theory: Diffusion through a wall immersed in Na Plan wallSimilar equations for T
13 Theory: Diffusion through a wall immersed in Na and gas Similar equations for T
14 Theory: Diffusion through pipes In that case, diffusion flux through the surface is:
15 Cold traps : C*: Solubility of H in Na Flux of hydrogen to the cold trap:Flux of Tritium to the cold trap:Co-cristallisation of tritium with HIsotopic exchange and T decay neglectedCold trap efficiency:C*: Solubility of H in Na
16 Theory: Isotopic exchange in gas phase hydrogen - tritium Isotopic exchange reaction:Equilibrium constant is:
17 Tritium transfer in a Reactor Assumptions:Steady state calculationHomogeneity of concentrations in the circuitsIsotopic exchange in cold traps neglected as well as T decaySource of T:In primary circuit:Ternary fission reactionsControl rod reactionsActivation of impurities: B, LiEstimation of the source on the base of Superphenix and Phenix past experienceSource of H:In primary circuit: fission reactions.In secondary circuit:Gaz in the ternary circuit: source = 0Water in the ternary circuitAqueous corrosion of GVThermal decomposition of N2H4 used in water to limit presence of O : N2H4 = 2 NH3 + 2 N2 + 3 H2 for T>250°C
18 Schematic view of the reactors RURNa/NaArGVTurbineIIIIIINa/AirPF IBPR~PF IISPX:reference caseImprovement of the models for Tritium transfer in other SFR conceptsAnd for other fission reactors (EPR, HTR, VHTR…)Y- H2O- He-N2- SCO2
19 SFR: Mass balance for Hydrogen: for Tritium: Diffusion through heat exchangersDiffusion through GVDiffusion through pipes and volumesTrapping in cold traps (for H in Na) / Sources in the circuitsH exchange with covering gasfor Tritium:Diffusion through heat exchangersDiffusion through GVDiffusion through pipes and volumesTrapping in cold traps (for T in Na) / Sources in the circuitsH/T exchange with covering gas
20 Localisation of exchange in the different concepts SFR Na/Na/H2OSFR Na/Na/SCO2SFR 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/sRelease of T for other concepts: nearly 1200 kBq/sPresence of:secondary cold traps of great importance for Na/Na/H2O conceptprimary cold traps of great importance for other conceptsPermeation through GV:is of great importance for Na/Na/H20 concept. Great PE lowers gaseous releasehas no effect for other conceptsAddition of secondary hydrogen source minimises T release
22 Conclusion ... Diffusion Modeling Improvement needed: T release depends on the conceptImportance of cold trapsImportance of Hydrogen sourceWays of limitation of diffusion: nature of metal, oxydised layer, thickness, temperatures, aerasModeling partially validated on Phenix and Superphenix former resultsModeling Improvement needed:Colds traps modeling should be improvedTransient state should be implementedMeasurement of H/T diffusivity through metals
23 References  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 K.S. FORCEY ; D.K. ROSS ; J.C.B. SIMPSON ;D.S. EVANSHydrogen transport and solubility in 316L and steels for fusion reactor applications.Journal of Nuclear Materials 160 (1988), North Holland, Amsterdam. D.M.GRANT ;D.L. CUMMINGS and D.A. BLACKBURNHydrogen in 316 steel ; diffusion, permeation and surface reaction.Journal of Nuclear Materials 152 (1988), North Holland, Amsterdam.
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