tritium transport simulations in pbli breeder blankets
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Tritium transport simulations in PbLi breeder blankets. Hongjie Zhang. UCLA Ph.D. Student. Introduction. Tritium transport, and permeation in fusion blankets are important To contribute achieving tritium self-sufficiency (for given tritium generation rate) - PowerPoint PPT PresentationTRANSCRIPT
Hongjie Zhang
Tritium transport simulations in PbLi breeder blankets
UCLA
Ph.D. Student
Introduction Tritium transport, and permeation in fusion blankets are
important To contribute achieving tritium self-sufficiency (for given tritium generation
rate)
To accurately characterize tritium inventory and losses (for safety concerns)
Issues Tritium behavior in LM blanket involves complicated phenomena consisting of
spatial and time dependent tritium generation profile, tritium permeation, thermo-fluid, nuclear heating, and chemical reactions.
Prediction of tritium transport inside the blanket requires knowledge of MHD for accurate estimations
Low tritium solubility in PbLi leads to high permeation
If chemical reactions are involved, the mathematical description of which may be complex
Being able to treat 3D complicated geometries
Large He concentrations in liquid metal may result in bubble formation
He concentration can modify heat/mass/electrical transfer interfacial exchange coefficients between the liquid metal and the structural material.
Bubbles could act as an effective T sink, affecting T overall inventory and making it difficult for extraction
Scope/Objective Develop 3D computational models to characterize diffusive,
convective and temperature effects on tritium transport in PbLi blankets Integrate the mass transfer model with the thermal-fluid analysis to
account for the velocity (ordinary and MHD flow) and temperature profiles
Account for the tritium generation rate profile and nuclear heating rate profile.
Include complex blanket geometry into analysis domain
Evaluate tritium transport phenomena in PbLi accompanying helium(He) nucleated bubbles and develop relevant transport models to account for He effects
Applications: Obtain Tritium Concentration profile, Tritium permeation flux, and other
parameters of interest for prototypical PbLi Blanket designs (DCLL/HCLL).
Optimize permeator design parameters for tritium extraction.
Assess effect of helium bubbles on permeator extraction efficiency
Relevant Tritium Transport Mechanisms and Issues
PbLi + T
PbLi
Solid
Gas Gas Molecule
atom
Mechanisms Issues
Solution/Diffusion/Convection(MHD velocity profile) of atomic tritium within the PbLi
Requires MHD velocity profile and temperature dependent properties for accurate estimation
Tritium transfer across PbLi/solid interface
1.PbLi + T(L) <-> Solid + T(s)or2.PbLi + T(L) <-> T2(g) T2(g) <-> Wall + T(s)
Low tritium solubility in PbLi lead to high permeation
Diffusion of atomic tritium through the structure
Dissolution-recombination at the solid/gas interface
Convection-diffusion of T2, in the He coolant
Need to account He bubble effectBubbles could act as an effective T sink, affecting T overall inventory and making it difficult for extraction
Solid
Mathematical transport models
(Temperature and convection effects)
1. Convection-Diffusion in PbLi
2. Diffusion in Solid
3. Convection-Diffusion in He coolant
B.C.
At PbLi/Solid and gas/Solid interfaces: 1. Continuity of flux2. Discontinuity of concentration
Notes T transport model1. Velocity u (MHD flow) is obtained
from HIMAG/Stream
2. Solubility and diffusivity database are derived from experiments
3. T generation rate (Qc) is calculated by Neutronics code
4. U: Turbulent velocity
5. Turbulent diffusion coefficient is determined by turbulent viscosity and turbulent Schmidt number
C1
QPb-17Li
CT,S1
CT,S2Pb-17Li
mass transport
He
),()),()((),(),(),(
1111 txtxtxtxu
txcQcTDc
t
c
Tritium concentration profile in PbLi and FS structure (DCLL TBM geometry, turbulent PbLi flow without MHD
effect)
FCI
FS
PbLi
Y - toroidal
Z - poloidal
X - radial
PbLi Inlet
PbLi Outlet
He Inlet
He Outlet
1.6
6m
DCLL Isometric View
Accounting nuclear heating and T
generation profiles
T concentration in PbLi
On the plane z=1.57m T concentration Velocity
T concentration in FS
Velocity profiles affect tritium concentration and permeation characteristics
(Parabolic, Side layer, and Ha layer velocity profile)
PbLi + T
2D Geometry with constant T generation rate(0.035m height, 1m length, 5mm FS thickness)
x
y
parabolic velocity profile
Side layer velocity profile
Tritium concentration in PbLi:
T concentration vs. y at x=0.8m
Velocity distribution vs. y at x=0.8m
Tritium permeation flux through the wall
Note:
• Same mass flow rates, Constant T generation rate• For parabolic velocity profile, T concentration is
higher near wall, however, even closer to the walls, the concentration falls down due to permeation
• For the Side layer velocity, T concentration drops at the highest velocity region of the “M” shape velocity profile.
• M-Shape MHD velocity profiles reduce tritium permeation
Initial results of Tritium Concentration impacted by a 3D MHD flow(3 U-bent duct flow with conducting walls connected through inlet/outlet with manifolds)
Notes:• Higher T concentration near the outlet of up-
flow ducts• MHD M-shape velocity profile alternate T
concentration profile in radial direction, T reductions are observed(red circles A and B).
• T concentration is higher near front walls (red square C) due to the high T generation and low velocity close to the front walls, however, even closer to the walls (D), the concentration falls down again due to permeation
Velocity Profile
T Production rate
T concentration along center line
T concentration in PbLi
A
B
C
D
Summary and Next Steps❖ Summary
3D computational models are initially developed to predict tritium transport in PbLi liquid breeders
Account the effects of convection and the accompanying velocity profile and temperature profile in a complicated geometry
The low tritium concentration layer close to the permeating walls ( due to M-shape side-layer velocity profile or flat-shape Ha-layer velocity profile) has shown a reduced permeation rate.
❖ Next
Evaluate He Bubble effects
Bubble nucleation and interfacial nucleation
Tritium transport between bubble and LM
Applications to DCLL/HCLL with the latest available MHD velocity profiles