Overview and progress updates on the LIBRA tritium breeding project
Remi Delaporte-Mathurin, Nikola Goles, Davide Pettinari, Collin Dunn, Emily Edwards, Sara Ferry, Ross MacDonald, Stefano Segantin, Weiyue Zhou, Kevin Woller
LIBRA: derisking fusion power plants
What is the smallest breeding blanket that can demonstrate a TBR of 1?
🎯Demonstrate T self-sufficiency with DT neutrons
🎯Validating neutronics and tritium transport models
🎯Investigate tritium extraction from liquid breeders
LIBRA experiment
Ferry, Sara E., et al. ‘The LIBRA Experiment: Investigating Robust Tritium Accountancy in Molten FLiBe Exposed to a D-T Fusion Neutron Spectrum’. Fusion Science and Technology 0, no. 0 (17 June 2022): 1–23. https://doi.org/10.1080/15361055.2022.2078136.
Half-life: 12 years
\mathrm{T} \rightarrow \mathrm{He} + \mathrm{e}^-
☢
Consumption of a 1 GWth fusion reactor (1 year)
50 kg
The breeding blanket
\mathrm{n} + ^6\mathrm{Li} \rightarrow \mathrm{T} + \mathrm{He} + 4.8 \ \mathrm{MeV}
\mathrm{n} + ^7\mathrm{Li} \rightarrow \mathrm{T} + \mathrm{He} + \mathrm{n} - 2.5 \ \mathrm{MeV}
\mathrm{TBR} = \mathrm{\frac{tritium \ produced}{tritium \ consumed}} > 1
\mathrm{D} + \mathrm{T} \rightarrow \mathrm{He} + \mathrm{n}
FLiBe
14 MeV neutron source
Li + n → T + He
Neutron multiplier
The LIBRA experiment
~1 m
Tritium transport
Transport mechanisms:
- Diffusion
- Advection
Release pathways:
- Release gas/liquid interface
- Permeation through walls
The LIBRA experiment
Sweep/sparge gas
Tritium detection
The LIBRA experiment
The BABY programme studies tritium breeding at a small scale
- \(14 \ \mathrm{MeV}\) neutrons generated
- tritium created from nuclear reactions
- tritium transport in the salt
- tritium released into the gas phase
- tritium collection and accountancy
Molten salt @ 700C
neutron generator
Tritium collection
reentrant heater
How to measure TBR?
\mathrm{TBR} = \mathrm{\frac{T \ produced}{T \ consumed}}
= \mathrm{\frac{T \ produced}{n \ produced}}
We need to measure these two numbers!
The BABY 100 mL experiment
Delaporte-Mathurin, Rémi, et al. ‘Advancing Tritium Self-Sufficiency in Fusion Power Plants: Insights from the BABY Experiment’. Nuclear Fusion, 2024. https://doi.org/10.1088/1741-4326/ada2ab.
Neutron generator
Bubblers
Molten salt capsule
Gas handling system
Temperature control
Tritium was measured using
Liquid Scintillation Counting
HTO, TF and TCl
(soluble in water)
HT, T2
(insoluble)
More details in Nikola Goles' talk tomorrow...
Liquid Scintillation Counting
Counts between 0-18.6 keV for tritium detection
Neutrons are detected with a combination of techniques
Nb/Zr activation foils
provides real-time neutron rate
A8 Diamond proton recoil telescope
Neutrons are detected with a combination of techniques
A8 Diamond proton recoil telescope
supported by Cividec
DD peak
(2 MeV)
DT peak
(14 MeV)
Upgrade: BABY 1 L
Autumn 2024
1 L of salt
More ports for diagnostics
Outer-vessel for permeated tritium
New crucible
Only one neutron generator below the crucible
One bubbler per gas line
×6
The previous TBR record has been broken again!
Tritium Breeding Ratio
Note: only HT even when purging with pure He
- Increased solid angle of salt 100 mL: 2%, 1L: 7%
- Now we just need x500...
\Omega = 0.25 \ \mathrm{sr}
\Omega = 0.9 \ \mathrm{sr}
All the BABY 1L runs
LIBRA to validate models
OpenMC model
Is our neutronics model an accurate representation?
support lead bricks
?
Romano, Paul K., et al. ‘OpenMC: A State-of-the-Art Monte Carlo Code for Research and Development’. Annals of Nuclear Energy, 82 (1 August 2015): 90–97. https://doi.org/10.1016/j.anucene.2014.07.048.
DT generator
Salt
Epoxy
Tritium Breeding Ratio
Measured
Modelled
Our measurements agree very well with neutronics models
- ~ 10% uncertainty on neutron fluence measurement
- discrepancy on 100 mL attributed to permeation losses
- Ongoing effort on uncertainty quantification
Neutron dose rates
Gamma dose rates
<𝟐 𝐦𝐫𝐞𝐦/𝐡
outside the vault ✅
\(3.2 \times 10^{6}\) 𝐦𝐫𝐞𝐦/𝐡
\(5.3 \times 10^{3}\) 𝐦𝐫𝐞𝐦/𝐡
\(10^{-2}\) 𝐦𝐫𝐞𝐦/𝐡
\(10^{-2}\) 𝐦𝐫𝐞𝐦/𝐡
The BABY experiment was modelled in OpenMC
ClLiF salt gives the highest TBR at the 100 mL scale
Using natural Li
V \frac{d c_\mathrm{salt}}{dt} = S - \textcolor{#438343}{Q_\mathrm{OV}} - \textcolor{#2a7eb8}{Q_\mathrm{IV}}
Q_i = A_i \ k_i \ (c_\mathrm{salt} - c_\mathrm{external}) \\ \approx A_i \ k_i \ c_\mathrm{salt}
S = \mathrm{TBR} \cdot \Gamma_n
A transient 0D model is used to simulate the tritium release
\(k_i\) mass transport coefficient (m/s)
neutron rate
Salt volume
Inner vessel
Outer vessel
- \( \mathrm{TBR} = 4.71 \times 10^{-4} \) (from OpenMC)
- \( \Gamma_n = 3.88 \times 10^8 \) n/s (from measurement)
- Mass transport coeffs. \( k_i \) (fitted)
100 mL
salt
Top release
Wall release
A transient 0D model is used to simulate the tritium release
Cumulative release (Bq)
Neutron generators on
Reproducibility
Varying the mass transfer coefficients only affects the dynamics
Redox potential affects the release dynamics
Cumulative release (Bq)
Redox potential affects the tritium speciation
Total tritium release
The 0D model reproduces the experimental data
Irradiation
Cumulative T release (Bq)
Model
Measurements
The results agree with the model
Very long experimental time
Cumulative T release (Bq)
No permeated T was detected
J_\mathrm{permeation} = K_r \ c_T ^ 2
Inert atmosphere (He) so low recombination rate
8 months ago, SOFT, Dublin:
W Shmayda recommended to put some H2 in the purge gas.
We had not.
Cumulative T release (Bq)
Run #3: adding H2 to the sparge gas
J_\mathrm{permeation} = K_r \ c_T ^ 2 + K_r' \ c_T \ P_\mathrm{H_2}
\mathrm{H_2 + T (ad)} \rightleftarrows \mathrm{ HT +H (ad)}
Releasing T trapped in piping from previous runs
Pure He:
- No permeation
- Previous parameterisation is predictive ✅
Adding 1000 ppm H2:
Salt volume
IV metal surfaces
OV metal surfaces
IV bubbler
OV bubbler
S = \Gamma_n \cdot \mathrm{TBR}
A_\mathrm{OV} \ k_\mathrm{OV} \ c_\mathrm{salt}\ c_\mathrm{H2}
(1-f) \ A_\mathrm{IV} \ k_\mathrm{IV} \ c_\mathrm{salt}
f \ A_\mathrm{IV} \ k_\mathrm{IV} \ c_\mathrm{salt}
k_\mathrm{exchange,IV} \ I_\mathrm{piping, IV} \ c_\mathrm{H2}
k_\mathrm{exchange,OV} \ I_\mathrm{piping, OV} \ c_\mathrm{H2}
Run #4: H2 from the start
Conclusion:
listen to Walter!
×10
From 60 days to 4 days!
Mass transport coefficient
LIBRA produces validation data for multiphysics models
See FESTIM details in James Dark's talk this afternoon
Tritium production map from neutronics (OpenMC)
Tritium concentration field (FESTIM)
Max conc. 1.4E13 T/m3
[T/n/cm3]
Natural convection neglected
LIBRA will help validate FESTIM models
Delaporte-Mathurin et al, International Journal of Hydrogen Energy 63, 2024, 786-802
Temperature
(steady state)
Velocity
(steady state)
Tritium concentration
The FESTIM model highlights a qualitative discrepancy
- Very sensitive to diffusivity
- Wall release > Top release
Different than measured
Hypotheses
- Advection not correctly taken into account?
- Permeation barrier: oxide layer?
- Complex chemistry?
Top release
Wall release
Diffusivities of FLiBe and FLiNaK
Where will we go from here?
A staged approach to \(\mathrm{TBR} \approx 1\) ...
Tritium Breeding Ratio
LIBRA ONE (700 L)
LIBRA ONE
Measured
Expected
LIBRA-Pi
BABY
100 mL
1 L
ClLiF
FLiBe
More science experiments
May 2025
Our roadmap
100 mL
1 L
ClLiF
FLiBe
LiPb
LiOx
Tritium production map in LiOx packed bed
Irradiate LiPb and LiOx
100 mL
1 L
LIBRA Pi
ClLiF
FLiBe
LiPb
LiOx
manufacturing
coating
operation
BABY informs the design and operation of LIBRA-Pi
~100 L of ClLiF
100 mL
1 L
LIBRA Pi
LIBRA ONE
ClLiF
FLiBe
LiPb
LiOx
manufacturing
coating
operation
design
LIBRA ONE
FESTIM model
~700 L of FLiBe
100 mL
1 L
LIBRA Pi
LIBRA ONE
Modelling
ClLiF
FLiBe
LiPb
LiOx
manufacturing
coating
operation
design
validation data
informs design & operation
2025
LIBRA-toolbox
Experimental analysis
Tritium release models
Neutron detection
Neutronics models
Parametric optimisation
Tritium detection LSC counting
Modelling
Materials
Activation foil analysis
Diamond detector analysis
PRT analysis
spectrum analysis
Open-science and reproducibility are core values of LIBRA
- GitHub organisation:
github.com/LIBRA-project
- Zenodo community:
zenodo.org/communities/libra-project
- FAIR principles, open-science, 100% reproducible
Thank you!
Any question?
✉️ remidm@mit.edu
TFG 2025
By Remi Delaporte-Mathurin
