BSF’s molten salt laser fusion concept envisions a spherical reactor filled with a molten salt coolant that functions as a laser gain medium. Tentatively, a rare-earth element such as neodymium (Nd) or ytterbium (Yb) will enable laser activity, making the medium suitable for use as a heat-capacity laser operating at temperatures exceeding 700 K. Prior to fusion, an intense optical pump excites the doped molten salt, storing energy in the lasing ions. When the fusion fuel is acoustically compressed and begins to emit thermal radiation, this emission seeds laser amplification. The resulting laser cascades are amplified by the doped medium and reflect from the chamber’s polished interior, converging back on the fuel. This category addresses the feasibility of using molten FLiBe as a laser gain medium.
Several fusion startups think that a lithium containing molten salt like flibe would be the perfect material for a fusion blanket. I’m not so sure. The eutectic (53:47) mixture of BeF2:LiF (see phase diagram below) has a favorable melting point (364 C / 637 K), but using it would consume an enormously huge supply of berrylium, an expensive and rare element.
For example, the blanket of DEMO (ITER’s succesor) is projected to be ~1.5 meter thick and have a volume of ~1800 cubic meters. If it was filled with a 53:47 flibe mixture, it would contain ~500 metric tons of beryllium, which is, according to Wikipedia, more than the current global annual production of berrylium (~200-300 tons).
Current fusion reactors are an engineering joke, truly deserving of all the mockery we can muster. One especially ridiculous (yet common) feature is the so-called “stand-off blanket”. Seriously, calling it a stand-off blanket is basically saying, “Let’s put the blanket so far from the action that we need a mountain of material to catch the neutrons — and let’s make sure there’s a giant empty hole in the middle.” So much of that blanket material just sits out there, far from the source, completely wasted. These stand-off blankets are so large and material-hungry that one might wonder whether the goal is to generate electricity or to single-handedly bankrupt the periodic table.
I too am scratching my head at what’s required for these huge reactors. The absurdity doesn’t stop at the materials (gold & diamond ICF targets) — it extends to the sheer scale of these things as well. The current breed of fusion plant concepts are gigantic — as if bigger automatically means better.
Honestly, “stand-off blankets” are the most inefficient geometric setup you could imagine. They’re essentially a giant spherical (or doughnut-shaped) shell of material with a big hole in the middle where nothing gets bred or absorbed. It’s like using a hula-hoop to catch rain.
Presumably, the blanket needs to maintain some distance (a “stand-off”) from the plasma, basically cowering from the intense heat and radiation. But regardless of how far away it stands, it still requires the same thickness — otherwise it won’t capture neutrons or absorb their heat. It honestly makes me wonder if the designers are secretly competing in an extreme engineering contest to use up 100% of the world’s beryllium in one fell swoop.
Stand-off blankets are ridiculous, and it’s comical that anyone thinks they are the optimal path to fusion power. It’s high time we embrace compact, contact-blanket designs — the kind that touch (or nearly touch) the reaction zone. A contact blanket uses only a tiny fraction of the material (orders of magnitude less), so there’s no need to strip-mine the Earth or deplete it of rare elements. For example, a contact blanket one meter thick requires about 4.19 cubic meters of material, whereas a stand-off blanket positioned ten meters out needs around 1,386 cubic meters — over 300 times as much material.
FLiBe is several orders of magnitude better at preventing neutron leakage than pure lithium. For example, a natural lithium blanket 1.5 meters thick would still allow 30% of its neutrons to escape, compared to just 0.001 (0.1%) escaping from a 2:1 (LiF):(BeF2) = @0.2843% Li blanket.
The plot (above), based on 7.59% ^6Li (natural lithium), shows leakage per source neutron.
The plot (below), based on 100% ^6Li, shows pure Li6 blocks more neutrons from escaping.
Assuming we stick to unenriched lithium (7.59% Li6), a one meter thick blanket would have the same TBR = 1.2, whether it is made of pure lithium or a 2(LiF):(BeF2) mixture of flibe.
The plot (above) is based on 7.59% ^6Li (natural lithium)
The plot (below) is based on 100% ^6Li
Instead of a blanket that’s far away from the action, contact-blanket designs place the blanket right up against the fusion zone — snuggling it like a boa constrictor. The result? You end up needing far less blanket material to do the same (or even better) job, and this approach doesn’t require cornering the world’s beryllium market.
Let’s clear this up: the beryllium in a FLiBe blanket isn’t just there for decoration — it’s serving an important job as a neutron multiplier. So yes, some of it (a small fraction) does get consumed during normal tritium breeding operations. But “enormously huge”? Not so much.
Here are some OpenMC simulation results showing how 14.1 MeV fusion neutrons interact inside a 1-meter-thick FLiBe blanket:
- In 2:1 LiF:BeF₂ (mol ratio), about 18% of source neutrons undergo a ⁹Be(n,2n) reaction.
- In 1:1 LiF:BeF₂, that rises to 26% of source neutrons undergoing ⁹Be(n,2n).
So, if each fusion neutron has an 18%–26% chance of triggering one of those reactions (and effectively “consuming” a beryllium atom), what does that mean for a real plant?
For a 1 GW thermal DT fusion plant, the beryllium consumption would be around:
- 6.2 kg/year for 2:1 FLiBe
- 8.9 kg/year for 1:1 FLiBe
That’s it. Not 500 tons. Not hundreds of trucks. Just a few kilograms per year — more like a suitcase full, not a supply chain crisis.
So no, that’s not an “enormously huge” supply. That’s a rounding error in industrial terms.