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

2 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Schematic Fluids Circulation in the Reactor J FW J3J3 J5J5 Tritium extraction from LiPb He purification  Q He  LiPb  He M He Q PbLi J1J1 J2J2 J4J4 Blower Steam generator Secondary circuit Blanket modules LiPb purification Pump air purification  Q PbLi Q He M LiPb

3 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Analytical Model – Tritium Mass Balance Equations 1/2 LiPb He J1J1 J2J2 J4J4 J3J3 J5J5 J 1 / J 5 = J 1 : Production rate J 2 : Extraction from LiPb  LiPb :extractor efficiency for LiPb C out :Tritium output concentration in LiPb (mol m -3 ), G LiPb :LiPb flow rate (m 3 s -1 ) J 3 : Permeation towards He coolant C ave :Tritium average concentration in LiPb (mol m -3 ) K blanket :Blanket permeation factor (m 3 s -1 ) J 4 : Extraction from He coolant G He :He flow rate to detritiation unit (m 3 s -1 ) ( J 5 max = 1 g/year=27 Ci/day, ITER standard ) J 5 : Release to environment L SG :Steam Generator leak flow (m 3 s -1 )

4 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Analytical Model – Tritium Mass Balance Equations 2/2 A, s : respectively wall surface (m 2 ) and wall thickness (m). Need to be evaluated for complex structures (see below) Ks steel Ks LiPb : Sievert constants (mol m -3 Pa -1/2 ), respectively in Eurofer and in LiPb D steel Tritium diffusivity in Eurofer (m 2 s -1 ) PRF b is the Permeation Reduction Factor provided by permeation barrier (if any) Stationary results (*) : * Thanks to Italo Ricapito (ENEA consultant) who initiated these computations

5 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Computation of the Blanket Permeation Factor Coating Geometry Materials and Temperature Material factor : Geometrical factor : A s Coating : T concentration layering in LiPb : (not taken into account in this analytical model: convection)

6 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Materials factor computation Significant permeation increase with temperature Uncertainties when averaging temperatures K s0 (mol m -3 Pa -1/2 ) E a (J mol -1 ) D 0 (m 2 s -1 ) E a (J mol -1 ) LiPb Eurofer

7 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Geometrical factor computation HCLL module is composed of many walls (FW, Stiffening grid, Cooling plates) where He circulates inside rectangular channels. 2b 2a 2p e L N 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).  (a, b, p, e) is the correction factor to be used to take into account the actual structure of the HCLL walls ?

8 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Problem identical to heat transfer by conduction Temperature (K)  tritium concentration (mol m -3 ) Thermal diffusivity (m 2 s -1 )  D.K s,w / K s,PbLi material factor (m 2 s -1 ) Heat flux (J s -1 )  tritium flow (mol s -1 ) e b ap LiPb He

9 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Correction Factor for Square Channels The thicker the ratio e/a the larger the correction factor 

10 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire 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) Stiffening plates Cooling plates Back plateNA 30.0NA 1

11 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Geometrical Factor Results for the HCLL Module LiPb facing He surface (m 2 ) .A / s (m) Percentage of total permeation First Wall (including side) Stiffening plates (including top and bottom) Cooling plates Back plate (plain) Module K geom = m 86 % of the permeation occurs through the cooling plates (and even more if we consider their higher temperature)

12 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Tritium flow towards He coolant (J 3 ) K blanket = 0.89 / PRF b m 3 s -1 (T ave = 480 °C, 260 modules)  LiPb = 0.8 (reasonable efficiency for packed column extractor) G LiPb limitation due to LiPb velocity (MHD pressure drops and corrosion) Module hydraulic section for LiPb : 0.33 m 2 –for whole blanket  V LiPb =1 mm/s G LiPb =0.085 m 3 s -1 = 790 kg s -1

13 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire  =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 m 3 = 2250 kg  L SG =1.63 Nm 3 /h Tritium permeation through the SG is still to be evaluated. –present assumption : K SG =0 (optimistic ? Maybe not so much if HTO) 4.3 Ci/kg 43 Ci/kg

14 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Working point with He coolant contamination limit The acceptable limit for the He contamination is sometimes reported to be 1Ci/kg = kg of T per kg of He.

15 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Tritium extraction strategy Oxidize the T in HTO (H 2 O 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 T 2 Drawbacks : release limit for HTO is 10 times more stringent than for T 2 Water Trap Chemical adjust Heat exchanger Water Trap Chemical adjust HCLL module gas / liquid column  = 0.08 % H 2 O + HTO He coolant He extraction LiPb H 2 O 1000 ppm H ppm H 2 0.1% He + H 2 + HT Oxidation bed

16 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire On going studies Refinement of the blanket permeation flow computation (J 3 ) –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 Nm 3 /h  no permeation barrier needed Ensure the feasibility of the tritium extraction strategy  Power Plant Conceptual Study (model AB)

17 Wilfrid Farabolini 23 feb. 04Direction de l’Energie Nucléaire Possible 2D modelling of the HCLL module Neutron code (Tripoli) Thermal-mechanical code (cast3m) LiPb flow and T convection via cast3m_fluid T diffusion and permeation via cas3m_fluid (heat-like) C in C out P