Tritium transfers evaluation on ITER HCLL TBM O' GASTALDI, P' AIZES, F' GABRIEL, J'F' SALAVY, L' GIA

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Tritium transfers evaluation on ITER HCLL TBMO.
GASTALDI, P. AIZES, F. GABRIEL, J.F. SALAVY, L.
GIANCARLI
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Context and objectives

• Context
• For future fusion reactor, tritium in-situ
  production is needed (breeding systems)
• Large amount of tritium will be handled
• A dedicated tritium management strategy is needed
  to avoid important release
• ITER Test Blanket Module will allow to test among
  others the tritium breeding and the recovery of
  tritium systems
• Objectives of the presented work
• Develop a dynamic modeling of tritium mass
  transfer in HCLL TBM
• Estimate the fluxes (incl. release) and
  inventories in dynamic ways
• Analyze the consequences of the results

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Design of HCLL TBM and associated circuits

• The HCLL concept characterized by a two-loops
  architecture
• A first loop where flows the liquid
  tritium-breeding material lithium-lead eutectic
  (with 6Li enrichment)
• A second loop where flows pressurized helium (80
  bars) acting as coolant
• Associated systems
• TES Tritium extraction system allowing to
  recover tritium from the PbLi
• CPS Coolant purification system allowing to
  purify He and recover transferred tritium on a
  by-passed fraction of He flow
• Heat exchanger between water and He

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Design of HCLL TBM and associated circuits
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Design of HCLL TBM and associated circuits
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Basis of the modelling system description

• Systems description

• Main identified tritium fluxes
• F1 Production of Tritium by neutron
  bombardment
• F2 Extraction of Tritium from the PbLi
  loop (TES)
• F3 Transfer of Tritium to the Helium by
  permeation
• F3FW transfer through the First Wall
• F3SP transfer through the Stiffening Plates
• F3CP transfer through the Cooling Plates
• F4 Extraction of Tritium from the helium
  loop (CPS)
• F5 Transfer to cooling water

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Basis of the modeling main assumptions

• Uniform tritium concentration in the PbLi of the
  blanket
• Effect of a limit layer at the transfer surface
  is not taken into account
• Hydraulic effects and MHD effects are not taken
  into account
• Transfer is considered diffusion limited
• Mass transfer fluxes are based on Ficks law
  without taking into account other phenomena
  Soret effect, electric field effect,
• Surface of tritium transfer is considered as plan
  wall. Use of corrective shape factor ? to
  obtain a realistic exchange area
• The concentration of Tritium in the water circuit
  is considered to be nil
• The transfer of Tritium from the reactor core to
  the PbLi loop is negligible compared to the
  other terms
• Limitation of tritium transfer due to different
  chemical form (particularly in He) is not taken
  into account
• Isotopic swamping in the materials is not modeled

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Basis of the modelling Main equations

• Main mass fluxes (mol.s-1)
• Mass balance on each loop (non linear
  differential equations system)

(mol.m-3)
(m3.s-1)
(mol.m-1.s-1.Pa-n)
(mol.s-1.Pa-n)
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Basis of the modelling used data

• Materials
• Permeablity and Sieverts constant in eurofer is
  relatively well known
• Not the case for Sieverts constant in Pb-Li
  large discrepancies

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Basis of the modelling used data

• TBM design (temperature level, size, based on
  DDD 2006 description)
• Exchange areas calculated with channels
  characteristics and shape factor (transposition
  from 2D geometry for permeation to plan wall)

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Results

• The results of dynamic (at infinite time) and
  stationary are similar
• In the case of short pulses with SOLE data
  (SP_SOLE), pseudo-steady state is long to reach
  (more than 30 pulses)

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Results

• With Reiters data the pseudo steady state is
  more rapidly reached (few pulses), the tritium
  concentration in PbLi is much lower, but
  variation at each pulse are in the same order of
  magnitude

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Results

• Fraction of tritium in He is very low with
  realistic set of parameters
• Variations differ a lot in function of Ks, but
  same o.m

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Results

• Inventories are very limited (many o.m. below
  tritium inventory of other systems in ITER)
• Permeated tritium to water (integration of F5
  flux (g per year))
• Very low contribution to release by permeation
  (contribution of leak is 3 o.m. higher)

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Conclusion

• According to these calculations
• TBM will not represent a particular difficulty
  towards
• Tritium inventories
• Potential tritium release
• Concentration in each loop is rather limited but
  variations can be important
• Needs to define specific measurement tools in
  order to follow these variations and analyze the
  physical phenomena
• And/or needs to reach pseudo equilibrium (depends
  on what must be analyzed) by large number of
  successive pulses (in the worst case)

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Conclusion for the future

• But many points are still open
• Basic data uncertainties (mainly for PbLi)
• Integration in the models of all phenomena
  (neglected in this first approach) which could
  impact mass transfer
• Impact of velocity profile,
• Impact of He bubbles contained in PbLi (transfer
  to gas phase)
• Boundary layer resistance
• Diffusion under irradiation
• Interface phenomena (sorption desorption)
• Isotopic swamping effect, chemical interactions,
  
• Discriminate and evaluate them by dedicated
  experiments
• Develop modeling tools at two levels
• System tools
• Multiphysic analyses tools