Advancing Tritium Self-Sufficiency in Fusion Power Plants:
Insights from the BABY Experiment
Remi Delaporte-Mathurin, Nikola Goles, Colin Dunn, Emily Edwards, Samuele Meschini, Stefano Segantin, Sara Ferry, Ethan Peterson, Dennis Whyte, Edward Lamere, Colin Weaver, Kevin Woller and LIBRA collaborators
HWS 2024 conference, Chamonix
\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
❓How ❓
Lithium is used to breed tritium
\mathrm{D} + \mathrm{T} \rightarrow \mathrm{He} + \mathrm{n}
\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}
The tritium issue
\mathrm{D} + \mathrm{T} \rightarrow \mathrm{He} + \mathrm{n}
1 \ \text{GWth} \approx 10^{20} \ \text{reactions/s} \approx 50\ \text{kg/year}
Cost: $30,000 per gram
Half-life: 12 years
\mathrm{T} \rightarrow \mathrm{He} + \mathrm{e}^-
☢
⚛️Breeding tritium
🛡️Shield from neutrons
🔥Extract heat
Liquid Immersion Blanket
FLiBe
ARC power plant
Sorbom et al, Fus Eng Design, Volume 100, November 2015, Pages 378-405
LIBRA: demonstrating the LIB
What is the smallest blanket that can demonstrate a \(\mathrm{TBR} \geq 1\) ?
LIBRA
Liquid Immersion Blanket tritium Robust Accountancy
Objectives
🎯T self-sufficiency with DT neutrons
🎯Experience with molten salt handling
🎯Tritium extraction from molten salts
Ferry, S. E. et al. (2023), Fusion Science and Technology, 79(1), pp. 13–35. doi: 10.1080/15361055.2022.2078136.
The BABY experiment 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
neutron generator
Tritium collection
reentrant heater
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
The LIBRA experiment
He
Tritium detection
LIBRA was designed to achieve TBR ≈ 1
\mathrm{TBR} = \mathrm{\frac{T \ produced}{T \ consumed}}
= \mathrm{\frac{T \ produced}{neutron \ produced}}
Neutronics simulations
Let's start smaller
- 14 MeV neutron generator \( 10^{10} \) n/s
- 500 L of FLiBe
→ Never done at MIT ⚠️
The BABY programme
The BABY experiment breeds tritium at a smaller scale
① neutrons are generated
② tritium is created from nuclear reactions
③ tritium is transported in the salt
④ tritium is released into the gas phase
⑤ tritium is collected and counted
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!
Neutrons are detected with a combination of techniques
3.35\times10^{13}\ \mathrm{n}
Niobium activation foils
Diamond detector
Over 24 h
\( (n,\alpha)\) peak provide information on DT neutron rate
Neutron detection
Tritium was measured with 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
21 Bq of tritium have been collected
~100 % of the tritium as HT!
Making the salt more oxidising drives the speciation towards soluble forms
The TBR measurement somewhat agrees with neutronics simulations
Where did the tritium go?
\mathrm{TBR} = \frac{1.17\times10^{10} \ \mathrm{T}}{3.35\times10^{13}\ \mathrm{n} }
= {3.57\times10^{-4}}
Modelled TBR (OpenMC)
Measured TBR
OpenMC model
OpenMC model
Comparison of TBR calculations with different breeders
At the 100 mL scale
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 different releases
\(k\) mass transport coefficient
\(A\) surface area
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 different releases
Cumulative release
Neutron generators on
Salt T inventory
T fluxes
Cumulative release
Varying the mass transfer coefficients only affects the dynamics
Reproducibility
Higher fidelity FESTIM¹ model
\frac{\partial c}{\partial t} = \nabla \cdot (D \nabla c) + S + v\cdot \nabla c
¹ 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
Hypotheses
- Advection not correctly taken into account?
- Permeation barrier: oxide layer?
- Complex chemistry?
Top release
Wall release
\varphi = \int_{\partial \Omega} -D \nabla c \cdot \mathbf{n} \ dS
The flux is computed from the concentration field
\mathrm{cumulative \ release} = A \int_0^t \varphi \ dt
Diffusivities of FLiBe and FLiNaK
1L of salt
Top release gas sweep
Outer-vessel for capturing permeated tritium
The next design will collect the permeated tritium
Conclusions and next steps
So much more we can do
- Continue to improve neutron detection and source characterisation
- Larger volume of salt
- Collect permeated tritium
- FLiBe
- Road to LIBRA and \(\mathrm{TBR} \sim 1 \)
100 mL
1 L
100 L
500 L
BABY
LIBRA
- BABY is the first TBR measurement in molten salts
- Theoretical and technical knowledge on tritium breeding technologies
- Paper submitted to Nuclear Fusion
- Data: github.com/LIBRA-project/insights-from-BABY-experiment-paper
Thank you!
Any question?
remidm@mit.edu
Advancing Tritium Self-Sufficiency in Fusion Power Plants (HWS talk)
By Remi Delaporte-Mathurin
