BABY 1L: First Tritium Breeding Campaign Results

TL;DR

The paper addresses the challenge of achieving tritium self-sufficiency in fusion by benchmarking tritium breeding and release in a molten-salt breeder at 1 L salt volume under 14 MeV DT irradiation. It combines a detailed experimental setup (BABY 1L) with OpenMC-based neutronics modelling and a 0D tritium-release framework, unified through the open-source libra-toolbox. The results show a sixfold increase in Tritium Breeding Ratio (TBR) relative to the 100 mL baseline and good agreement between measured TBR and OpenMC predictions, while revealing diffusion-limited tritium transport and significant isotopic-exchange effects when hydrogen is added to the sweep gas. These findings validate the BABY platform as a mature testbed for tritium-breeding studies and guide future modelling and experimental directions toward more predictive, integrated tritium transport simulations.

Abstract

Achieving tritium self-sufficiency is a critical challenge for future fusion power plants. The BABY 1L experiment, part of the LIBRA project at MIT, aims to benchmark tritium breeding and release in molten salt breeder systems under deuterium-tritium (DT) neutron irradiation. Building on the initial \SI{100}{mL} campaign, BABY 1L introduces a tenfold increase in breeder volume, improved thermal and gas handling systems, and enhanced neutron diagnostics, including a proton recoil telescope. We report on results from four irradiation experiments using sealed-tube DT neutron generators, with tritium collected by water bubblers measured via liquid scintillation counting. Experimentally determined Tritium Breeding Ratios (TBRs) were compared to OpenMC neutronics simulations, showing very good agreement. The measured TBR values demonstrate a six-fold improvement over the \SI{100}{mL} experiments, largely attributed to the increased solid angle and improved measurement fidelity. We also investigate tritium release dynamics and identify diffusion-limited transport as the dominant regime in the salt volume in the temperature range 630-750 \si{\celsius}. Additionally, we observe that the introduction of hydrogen in the helium carrier gas significantly accelerates tritium release, consistent with an isotopic exchange mechanism. All analysis is conducted through the open-source \texttt{libra-toolbox} \cite{libra-toolbox}, which streamlines simulation, data processing, and validation across experimental campaigns. These results provide critical insights into the design and operation of future liquid breeder systems and demonstrate the maturity of the BABY platform as a testbed for tritium breeding studies.

Figures (11)

• Figure 1: Simplified diagram of the experimental system, consisting of the vessel assembly, neutron generator, and gas handling system with bubblers for tritium collection.
• Figure 2: Cross-section diagram of the vessel assembly showing system components and the temperature distribution, not to scale.
• Figure 3: P&ID diagram of the 1L BABY gas system.
• Figure 4: Schematic representation of the number of radioactive nuclei (e.g., ^92mNb) in the foil over time. The build-up during neutron irradiation is followed by exponential decay. The shaded regions indicate the periods over which decays are counted.
• Figure 5: Geometry of the OpenMC neutronics model.