1 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Tritium Control A Major Issue for...

23 feb. 04Direction de l’Energie Nucléaire 1Wilfrid Farabolini

Tritium Control

A Major Issue for a Liquid Metal Blanket


Schematic Fluids Circulation in the Reactor

JFWJ3

J5

Tritium extractionfrom LiPb

He purification

QHe

LiPb

He

MHe

QPbLi

J1

J2

J4

Blower

Steam generator

Secondary circuit

Blanket modules

LiPb purification

Pump

air purification

QPbLi

QHe

MLiPb


Analytical Model – Tritium Mass Balance Equations 1/2

LiPb HeJ1

J2 J4

J3 J5 J1 / J5 =140525

day/g385J1 • J1 : Production rate

LiPboutLiPb2 GCJ • J2 : Extraction from LiPb

LiPb : extractor efficiency for LiPbCout : Tritium output concentration in LiPb (mol m-3), GLiPb : LiPb flow rate (m3 s-1)

blanketave3 KCJ • J3 : Permeation towards He coolantCave : Tritium average concentration in LiPb (mol m-3)

Kblanket: Blanket permeation factor (m3 s-1)

HeHeHe4 GCJ • J4 : Extraction from He coolantGHe : He flow rate to detritiation unit (m3 s-1)

)LK(CJ SGSGHe5 ( J5 max = 1 g/year=27 Ci/day , ITER standard )

• J5 : Release to environmentLSG: Steam Generator leak flow (m3 s-1)


Analytical Model – Tritium Mass Balance Equations 2/2

321LiPb JJJt

M

543He JJJt

M

out

inLiPb C

C1

2

CCC outin

ave

LiPb

steelsteel

bblanket Ks

DKs

s

A

PRF

1K

• A, s : respectively wall surface (m2) and wall thickness (m). Need to be evaluated for complex structures (see below)

• Kssteel KsLiPb : Sievert constants (mol m-3 Pa-1/2), respectively in Eurofer and in LiPb• Dsteel Tritium diffusivity in Eurofer (m2 s-1)• PRFb is the Permeation Reduction Factor provided by permeation barrier (if any)

Stationary results (*) :

blanket

LiPb

13

KG

22

1

JJ

LiPb

LiPb

)LK(

G1

JJ

SGSG

HeHe

35

525140J

J

LK

G1

K

G

2

21

MAX,5

1

SGSG

He

blanket

LiPb He

LiPb

LiPb

* Thanks to Italo Ricapito (ENEA consultant) who initiated these computations


Computation of the Blanket Permeation Factor

LiPb

steelsteel

bblanket Ks

DKs

s

A

PRF

1K

Coating

Geometry

Materials and Temperature

Material factor : )TR

Eexp(X)T(X a

0

Geometrical factor :A

sCoating :

T concentration layering in LiPb :(not taken into account in this analytical model: convection)


Materials factor computation

• Significant permeation increase with temperature

• Uncertainties when averaging temperatures

Ks0(mol m-3 Pa-1/2)

Ea(J mol-1)

D0(m2 s-1)

Ea(J mol-1)

LiPb 1.25 10-3 1350 4.03 10-8 19500

Eurofer 1.02 10-1 23810 1.22 10-7 14470


Geometrical factor computation

• HCLL module is composed of many walls (FW, Stiffening grid, Cooling plates) where He circulates inside rectangular channels.

2b

2a2p

e

LN channels

• Permeation formula is relative to plain wall

• How to adapt it to the actual wall structure ?

• Lets A=2a.L.N (surface of He facing LiPb)

and s=e (minimum distance between He and LiPb).

s

NLa2Kgeom

(a, b, p, e) is the correction factor to be used to take into account the actual structure of the HCLL walls ?


Problem identical to heat transfer by conduction

• Temperature (K) tritium concentration (mol m-3)

• Thermal diffusivity (m2 s-1) D.Ks,w / Ks,PbLi material factor (m2 s-1)

• Heat flux (J s-1) tritium flow (mol s-1)

e

b

a p

LiPb

He


Correction Factor for Square Channels

• The thicker the ratio e/a the larger the correction factor

1,0

1,2

1,4

1,6

1,8

2,0

2,2

2,4

0 0,5 1 1,5 2p/a

e/a=0.5

e/a=1.0

e/a=1.5

e/a=2.0


Application to HCLL Walls• The three types of HCLL cooled walls have been modelled to

derive their correction factor

a (mm) b (mm) e (mm) p (mm)

First Wall(LiPb side)

7.0 6.5 4.0 2.0 1.24

Stiffening plates

5.0 1.5 2.5 0.5 1.09

Cooling plates

2.25 2.25 1.0 0.95 1.31

Back plate NA NA 30.0 NA 1


Geometrical Factor Results for the HCLL Module

LiPb facing He surface

(m2)

.A / s (m)

Percentage of total

permeation

First Wall (including side)

4.31 1336 1.06

Stiffening plates (including top and bottom)

37.06 16158 12.8

Cooling plates 82.94 108651 86.0

Back plate (plain) 4.0 133 0.1

• Module Kgeom= 126 278 m• 86 % of the permeation occurs through the cooling plates (and

even more if we consider their higher temperature)


Tritium flow towards He coolant (J3)• Kblanket = 0.89 / PRFb m3 s-1 (Tave = 480 °C, 260 modules)

• LiPb = 0.8 (reasonable efficiency for packed column extractor)

• GLiPb limitation due to LiPb velocity (MHD pressure drops and corrosion)

• Module hydraulic section for LiPb : 0.33 m2

– for whole blanket VLiPb=1 mm/s GLiPb =0.085 m3 s-1 = 790 kg s-1

blanket

LiPb

13

KG

22

1

JJ

LiPb

LiPb


=0.08%

Working Point

• In existing He cooled fission reactor He leakage can be as high as 100% of the total inventory per year

– assumption: He inventory=400 m3 = 2250 kg LSG=1.63 Nm3/h • Tritium permeation through the SG is still to be evaluated.

– present assumption : KSG=0 (optimistic ? Maybe not so much if HTO)

MAX,5

1

SGSG

He

blanket

LiPb

J

J

LK

G1

K

G

2

21 He

LiPb

LiPb

4.3 Ci/kg

43 Ci/kg


Working point with He coolant contamination limit

• The acceptable limit for the He contamination is sometimes reported to be 1Ci/kg = 10-7 kg of T per kg of He.


Tritium extraction strategy

• Oxidize the T in HTO (H2O injection in He coolant, oxidation bed for purge gas)

• Extract tritiated water by zeolithe or cold trap• Advantages : develop natural oxide barriers both in blanket and in SG, much

less permeation for HTO than for T2

• Drawbacks : release limit for HTO is 10 times more stringent than for T2

WaterTrap

Chemical adjust

Heat exchanger

Water Trap

Chemical adjust

HCLL modulegas /

liquid column

= 0.08 %

H2O + HTOH2O + HTO

He coolantHe extraction LiPb

H2O 1000 ppmH2 100 ppmH2 0.1%

He + H2 + HTOxidation

bed


On going studies

• Refinement of the blanket permeation flow computation (J3)– Finite elements modelling (conduction and convection of heat

and of tritium concentration)

– Local temperature,

– LiPb flow (MHD, temperature convection, section variations, pressure drop),

– Soret effect (permeation driven by temperature gradient)

• Evaluate tritium permeation via the Steam Generator• Evaluate reasonable He leak rate for the whole coolant circuit• Evaluate the maximum He purification flow rate capability

– If 4 x 50000 Nm3/h no permeation barrier needed

• Ensure the feasibility of the tritium extraction strategy

Power Plant Conceptual Study (model AB)


Possible 2D modelling of the HCLL module

Tritium production rate (at / cm3.neutron)

0,0E+00

1,0E-03

2,0E-03

3,0E-03

4,0E-03

5,0E-03

6,0E-03

7,0E-03

0 100 200 300 400 500 600 700 800 900

module radial dimension (mm)

Neutron code (Tripoli)Thermal-mechanical code (cast3m)

LiPb flow and Tconvection viacast3m_fluid

T diffusion andpermeation via

cas3m_fluid(heat-like)

Cin

Cout

P

1 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Tritium Control A Major Issue for...

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