Hydrogen-tritium Hydrogen-tritium transfertransfer

in SFR Conceptsin SFR Concepts

K. LIGER, T. GILARDITél : 33 (0)4 42 25 49 08

e-mail : karine.liger@cea.fr

2

OUTLINESOUTLINES

• 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 System definition Pollution sources Modeling Estimation of the fluxes of Hydrogen and tritium

3

General goal for tritium transfer estimationGeneral 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 traps

• SO THAT:• During operation

– The release does not exceed release authorisation• During conception

– A suitable release limit authorisation could be asked

4

Theory: Mass transfer through a wallTheory: Mass transfer through a wall

• 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

5

Theory of Diffusion : Fick ’s law Theory of Diffusion : Fick ’s law

• 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

t=infinite t t=0

C2 C2 C2

C1 C1 C1

o

x

j D C

div jC

t

0

j : fluxD : diffusivityC : concentratione : thickness

j DC

x

DC

x

C

t

2

2 0

e

6

Steady state vs transient state ?Steady state vs transient state ?

• 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

p

e

D

2

Over the lifespan of a reactor, steady state can be assumed!

7

Theory: Diffusion depends on…Theory: Diffusion depends on…

• 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

8

Diffusion : Hydrogen/tritium trapped in metallic structureDiffusion : Hydrogen/tritium trapped in metallic structure

• 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

• 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

Theory: H/T equilibrium between cover gaz and NaTheory: H/T equilibrium between cover gaz and Na Sievert constantSievert constant

• Hydrogen equilibrium between Na (liquid or solid) and the cover gas

P. = H2H

NaSHK

)(gas2

H 2

1 Na

H

NasT

NasH KK 73,1

)(gas2

T 2

1 TNa

P. = T2T

NaSTK

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Theory: equilibrium between gas and metal Theory: equilibrium between gas and metal Sievert constantSievert constant

steel

ST

steel

SHKK

P. = H2H

AcSHK )(gazeux

2H 2

1 Hmetal in

)(gazeux2

T 21 T

metal in

P. = T2T

AcSTK

• 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

1

3steel

T

steelH

D

D

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Solubility in metal : Sievert constant 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) )

0

0,05

0,1

0,15

0,2

0,25

200 250 300 350 400 450 500 550 600T, °C

mol

(H)/m

3/P

a1/2

Forcey [7]Tison [6]Grant [8]

DFORCEY (1988) = 3,82 10-7 exp( -5472,4 / T(K) ) , m² /s

1,E-15

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

25

150

250

350

450

550

T, °C

D, m

²/s

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Theory: Diffusion through a wall immersed in NaTheory: Diffusion through a wall immersed in Na

Plan wall

C Na1 = SH

Na1K P and C Na

2 = SHNa

2K P

Cac1 = SH

ac1K P and Cac

2 = SHac

2K P

then 1ac SH

ac

SHNa 1

NaCK

KC and 2

ac SHac

SHNa 2

NaCK

KC

Fick’s law :

= DA

eC Cac ac

1 2 ( C in at/m3)

CCK

K NaNaNa

SH

ac

SH

e

A = D 21 (C in at/m3)

then CCNaNa

e

A= PE 21

PE = D. = pe

. SHac

SHNa

SHNa

K

K K

C1Na

C2Na

C1ac

C2ac

e

Na

Na

where : at/s PE : kg/m/s

CiNa : at/kg

: kg/m3 KSH

Na, KSHac : at/m3/Pa1/2

Similar equations for T

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Theory: Diffusion through a wall immersed in Na and gasTheory: Diffusion through a wall immersed in Na and gas

1ac SH

ac

SHNa 1

NaCK

KC

2ac

2C P KSHac

= DA

eK

KC K P

SHac

SHNa 1

NaSHNa

2 (C in at/m3 ; P2 in Pa)

P.C

K

K2

NaSHNa

1Na

SH

ac

SH Ke

AD. =

... (C in at/kg)

with PE = D. = pe

.SHac

SHNa

SHNa

K

K K

and KU. C Pgas22 SH

NaK

thus = PEA

eC KU. C1

Na2gas

with C1Na: at/kg

C2gas : at/kg

M : kg/molP : Pa

C1

C2

C1ac

C2ac

e

gas

Na

Similar equations for T

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Theory: Diffusion through pipesTheory: Diffusion through pipes

• In that case, diffusion flux through the surface is:

2

2

1

1 2 1 2

Lrr

D C C DA

eC Cml

ln

rr1 r2o

A

L r rrr

ml 2 2 1

2

1

ln

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• 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

)(3 trapcoldT

CCqf

5.0*

)(

trap cold T

s

CC

CC

Cold traps :Cold traps :

Cold trap efficiency:

Na

H

Na

T

trapcoldT

Na

H

Na

H C

CCCqf

)(3

0,01

0,1

1

10

100

1000

10000

100130

160190

220250

280310

340370

400430

460490

520550

580

Te m pe rature , °C

[O], ppm

[H], ppm

C*: Solubility of H in Na

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Theory: Isotopic exchange in gas phaseTheory: Isotopic exchange in gas phasehydrogen - tritiumhydrogen - tritium

• Isotopic exchange reaction:

• Equilibrium constant is:

H T HTgaz gaz gaz2 2 2( ) ( ) ( )

kP

P PHT

H T

2

2 2

Ln kT K

1 4966133

,( )

0

1

2

3

4

5

100 300 500 700T, °C

k

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Tritium transfer in a ReactorTritium transfer in a Reactor

1. Steady state calculation

2. Homogeneity of concentrations in the circuits

3. Isotopic exchange in cold traps neglected as well as T decay

4. 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

5. 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

Assumptions:

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RURNa/Na

Ar

GV Turbine

I IIIII

RURNa/Air

PF I

BPR

~

Schematic view of the reactorsSchematic view of the reactors

Y - H2O

- He-N2

- SCO2

SPX:reference case

Improvement of the models for Tritium transfer in other SFR concepts

And for other fission reactors (EPR, HTR, VHTR…)

PF II

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SFR: Mass balanceSFR: Mass balance

• 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

for Hydrogen:for Hydrogen:

• 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

for Tritium:for Tritium:

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Localisation of exchange in the different conceptsLocalisation of exchange in the different concepts

Localisation T flux% H flux % Primary cold traps 41 46 Secondary cold traps 19 23 GV 3 7 Intermediate heat exchanger 26 9 Pipes and volumes 7 10

Localisation T flux% H flux % Primary cold traps 28 6 Secondary cold traps 35 89 GV Intermediate heat exchanger 36 5 Pipes and volumes

SFR Na/Na/H2O

SFR Na/Na/SCO2

Localisation T flux% H flux % Primary cold traps 31 35 Secondary cold traps 14 16 GV 30 30 Intermediate heat exchanger 19 8 Pipes and volumes 3 7

SFR Na/Na/He-N2

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Concepts comparisonConcepts 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

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Conclusion ...Conclusion ...

– 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

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ReferencesReferences

[1] Paul TISONInfluence 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. EVANSHydrogen 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. BLACKBURNHydrogen in 316 steel ; diffusion, permeation and surface reaction.Journal of Nuclear Materials 152 (1988), North Holland, Amsterdam.