[philipkglass]

Right, that's true in the actual world. I'm trying to imagine a world where a startup is developing nuclear power for the very first time, which includes developing/building any enrichment technologies their reactor might depend upon.

I don't think that a reactor requiring enriched fuel is a good Very First Reactor design -- and the actual first reactors did not require enriched fuel -- but enrichment came up in the course of answering whether a startup could invent a modern reactor in the absence of an existing nuclear industry.

[DennisP]

Possibly a nuclear industry kicked off by startups would use different technology. It may be no coincidence that we used a gigantic price-insensitive entity to develop the early technology, and ended up with expensive reactors.

Molten salt reactors, for example, were known back in the 1950s, and appear to have a number of major cost advantages.

[philipkglass]

Molten salt reactors might be the second generation of reactors in an alternative history with nuclear-by-startups. They require a higher fissile material concentration than found in natural uranium. To start operating a MSR you need some reactors fueled with natural uranium and moderated by graphite or heavy water in order to breed fissile plutonium from uranium, or uranium 233 from thorium, to get concentrated fissile material for starting molten salt reactors.

Or you could start a MSR with U-235 enriched from natural uranium, but that would require developing complex and expensive enrichment technology before you get your first watt of nuclear power generation.

[DennisP]

True, and maybe a CANDU would be best at first if enrichment is a huge barrier. But MSRs don't necessarily need especially high enrichment. The IMSR for example only needs 5% U235, which is the upper end of what light water reactors use. https://en.wikipedia.org/wiki/Integral_Molten_Salt_Reactor