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