Overview of the LIBRA project
The LIBRA plan:
let's test it before ARC
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
500L FLiBe
14 MeV neutron source
Inconel
double wall
Li + n → T + He
Neutron multiplier
The LIBRA experiment
Tritium transport
Transport mechanisms:
- Diffusion
- Advection
Release pathways:
- Release gas/liquid interface
- Permeation through walls
The LIBRA experiment
He
Tritium detection
The LIBRA experiment
A staged approach to \(\mathrm{TBR} \approx 1\) ...
Tritium Breeding Ratio
LIBRA full-scale
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
The BABY experiment was modelled in OpenMC
ClLiF salt gives the highest TBR at the 100 mL scale
Neutrons are detected with a combination of techniques
Niobium activation foils
Diamond detector
\( (n,\alpha)\) peak provides real-time data
Neutrons are detected with a combination of techniques
A8 Diamond proton recoil telescope
supported by Cividec
DD peak
(2 MeV)
DT peak
(14 MeV)
Neutron detection
Tritium was measured using
Liquid Scintillation Counting
HTO, TF and TCl
(soluble in water)
HT, T2
(insoluble)
Liquid Scintillation Counting
Counts between 0-18.6 keV for tritium detection
The TBR measurement somewhat agreed with neutronics simulations
Hypothesis: tritium was lost to permeation
\mathrm{TBR} = \frac{1.17\times10^{10} \ \mathrm{T}}{3.35\times10^{13}\ \mathrm{n} }
= {3.57\times10^{-4}}
Modelled TBR (OpenMC)
Measured TBR
V \frac{d c_\mathrm{salt}}{dt} = S - \textcolor{#438343}{Q_\mathrm{wall}} - \textcolor{#2a7eb8}{Q_\mathrm{top}}
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
\(k\) mass transport coefficient
neutron rate
100 mL
salt
Top release
Wall release
- \( \mathrm{TBR} = 4.71 \times 10^{-4} \) (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
LIBRA-toolbox
Contains tools to streamline our experimental analysis:
- LSC counting
- Tritium modelling
- Parametric optimisation
- Neutronics models (OpenMC)
- Neutron detection
- Activation foil analysis
- Count manipulation
- Proton Recoil Telescope (coincidence)
Everything (98%...) we do is open-source
- GitHub organisation:
github.com/LIBRA-project
- Zenodo community:
zenodo.org/communities/libra-project
- FAIR principles, open-science, 100% reproducible
Upgrade: BABY 1 L
1 L of salt
Top release gas sweep
Outer-vessel for permeated tritium
New crucible
Only one neutron generator below the crucible
One bubbler per gas line
×6
New world record! 🥇
The previous TBR record has been broken again!
Tritium Breeding Ratio
Now we need ×500...
Measured
Modelled
The BABY 1L results also agree with the model
But:
- Is the 0D assumption valid?
- Tritium production not homogeneous
- Temperature not homogeneous
- Why is there no permeation?
- Is this reproducible?
BABY 1L run 2 (as of 24 Feb 2025)
Impact of H2 in the purge gas
- Adding H2 released tritium from previous runs
- Isotopic exchange H2 + T -> HT + H
- "Enabled" wall permeation (never seen before)
Where will we go from here?
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
LIBRA-ONE
BABY-1L
OpenMC model
Is our neutronics model an accurate representation?
4 lead bricks → +11 % TBR
?
BABY will inform the design and operation of LIBRA-Pi (100 L)
Irradiate FLibe, LiPb, and LiOx
Neutronics simulations LiOx
- Collaboration with UKAEA
- Led by Ross MacDonald (secondee at MIT)
Take aways
- Tritium self sufficiency is the next big risk item on the fusion roadmap
- \( Q_\mathrm{plasma} = 40+ \) is useless without fuel for the reaction
- Safety factor is 9.5 %, but the real uncertainty may be larger...
- Up to now, R&D was mostly (only?) focused on computational studies
- Some initiatives give us hope
- LIBRA: world record measured TBR
- LIBRTI: UK-led programme for tritium breeding
- VNS: 2.5 m major radius tokamak (see Giannini et al 2024 10.1109/TASC.2024.3365097)
Will it be soon enough to build a successful FOAK fusion power plant by 2030-2040?
Thank you!
Any question?
✉️ remidm@mit.edu
LIBRA presentation (Edinburgh U visit)
By Remi Delaporte-Mathurin
LIBRA presentation (Edinburgh U visit)
The tritium fuel cycle presents one of the most critical challenges for achieving sustainable fusion power. Tritium, a key fuel for fusion reactions, is both scarce and radioactive, requiring efficient production, handling, and recycling to support the operation of future fusion power plants. This seminar will explore the scientific and engineering hurdles associated with the tritium fuel cycle, including production, transport, storage, and recovery, as well as the stringent safety and environmental considerations. We will highlight ongoing research at the Plasma Science and Fusion Center (PSFC) aimed at addressing these challenges, with a focus on the development of tritium breeding blankets. These blankets are designed to produce tritium in situ by leveraging neutron interactions with lithium-containing materials. Our work includes experimental investigations, such as the LIBRA project, and advanced modeling efforts using the open-source hydrogen transport code FESTIM. Key topics will include the optimisation of tritium production and recovery, the role of material selection, and the integration of tritium systems with fusion reactor designs. By advancing these technologies, we aim to pave the way toward achieving tritium self-sufficiency, a cornerstone of viable fusion energy systems.
