Comment by credit_guy

> CFS for example uses FLiBe molten salt

Ok, let's talk about that. For those who are not familiar, CFS stands for Commonwealth Fusion Systems, as startup with links to MIT. CFS aims to build a fusion reactor similar to ITER, but many times smaller, the secret sauce being that they use superconductors to achieve high magnetic fields. Back in 2022 some of the MIT guys got an ARPA-E grant to investigate the use of FLiBe to achieve atritium breeding ratio higher than 1 [1]. The results are in [2], they were published in January 2025. Here are some quotes:

  > The long-term goal of LIBRA is to demonstrate a TBR ⩾ 1 in a large volume (1000 kg ∼ 500 l) of FLiBe molten salt using D–T neutron generators. Note that a full-scale LIB in an ARC-class FPP will require ∼250 000 l of FLiBe, hence the importance of understanding tritium behavior in large salt volumes.

ARC is the fusion reactor designed by CFS. This paper states that it will need 250000 liters of FLiBe. This is an insane amount. To understand how large this amount is, consider this: this ARPA-E project that took 3 years, used a quantity of 100 ml, so 0.1 liters.

Anyway, what breeding ratio was achieved? 3.57 x 10^(-4), or 0.0357%. It's a long way to go from here to 1.

I'm not saying it's impossible, but too many things related to fusion are just "engineering details".

[1] https://arpa-e.energy.gov/programs-and-initiatives/search-al...

[2] https://iopscience.iop.org/article/10.1088/1741-4326/ada2ab/...