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Comment by est31 | Hacker News Reader

> There are advanced reactor designs that don’t rely on the fission of U-235, but rather use the far more abundant isotope U-238. Some of these reactors can burn “spent” fuel, or “depleted” uranium left over from the enrichment process—extracting something like 60 times as much energy from uranium as traditional nuclear reactors.

Does anyone have links for such reactors?

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Breeder reactors, as others have pointed out. Oklo is a modern design based on the concept: https://www.nrc.gov/reactors/new-reactors/col/aurora-oklo.ht...

Also see “Problem free nuclear power and global change”: https://www.osti.gov/biblio/614877

And “Nuclear fission power for 21st century needs”: https://www.sciencedirect.com/science/article/abs/pii/S01491...

> Does anyone have links for such reactors?

https://en.wikipedia.org/wiki/Breeder_reactor you also need https://en.wikipedia.org/wiki/Nuclear_reprocessing to remove https://en.wikipedia.org/wiki/Neutron_poison which would stop the reaction.

If we did that, there would be no nuclear waste left. (Or more specifically all the waste would decay very fast, and not be a long term problem.)

> if we did that

Some "we" and/or some "they". Russia seems to be intent and making advances toward closing the fuel cycle, in efforts IMHO severely underreported on HN. (It might be better that way. I have seen reticence to stir up jealousy or something in the Anglosphere. Let them [ignorantly] go about their business.)

The most famous of these is the Chernobyl reactor design, the RBMK. It could be run on natural uranium rather than enriched uranium and would self enrich the uranium via neutron bombardment inside the reactor.

https://en.wikipedia.org/wiki/RBMK

Of course there are some flaws in a reactor that breeds it's own enriched uranium. There's states that the neutron flux is too low so the enriched elements aren't burnt off quickly as intended. This leads to a state where the whole reactor is a highly enriched weapons grade bomb.

That‘s wrong. The RBMK is not a fast reactor, it’s a pressure-channel boiling water reactor.

Fast reactors are/were for example the:

- French Superphenix - Russian BN-600/800 - German SNR-300 - Japanese Monji - American EBR II

The BN reactors are still operational.

A reactor that runs on natural uranium is still fissioning 235U (and some of the 239Pu that has been bred, but that's true of reactors that run on low enriched U as well.)

I believe breeder reactors can create fuel from U-238.

https://en.wikipedia.org/wiki/Breeder_reactor

Heavy water reactors can run on natural uranium. https://en.m.wikipedia.org/wiki/Pressurized_heavy-water_reac...

Aren't heavy water reactors the most popular way that new countries have built nuclear weapons? Basically everyone but North Korea?

You don't need a reactor to make a uranium based nuclear weapon at all (you just need to enrich natural uranium to a high enough percentage of U-235).

American and Soviet plutonium production reactors were largely (perhaps even entirely? not sure) graphite moderated.

Yeah, but that graphite has to have zero boron in it, which is not easy to accomplish. You have to go to fairly crazy extremes, like regulating what kind of laundry detergent your factory workers are allowed to use.

https://en.m.wikipedia.org/wiki/Nuclear_graphite

Heavy water is simpler to get; you basically just need a lot of electricity.

And these are still fissioning 235U. 238U by itself does not sustain a chain reaction.

https://en.wikipedia.org/wiki/CANDU_reactor

This design has a lot of practical advantages, but seems to be suffering in the market from the same capital cost disease as other reactors.

This is a bit nit-picky, but a CANDU reactor does not fission U-238. Neutrons in a CANDU reactor are still thermal neutrons, and if you put pure U-238 in a CANDU reactor it won't run. A CANDU reactor does run on uranium with a lower amount of U-235 than a standard PWR design, and it does transmute some of that U-238 into Pu-239 which it then does fission, but it doesn't directly fission U-238 and it does require some baseline ratio of U-235 to operate.

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