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Thorium was originally proposed to fix the proliferation issues. But U-233 works pretty well for making “Big Boom”.

And Thorium reactors make it, just like Uranium reactors make Plutonium.

I prefer the Uranium cycle. At least until we run out of it. Then I will prefer the Thorium cycle.

Ideally, at some point, we have fusion mastered, long before we dig all the heavy metals out of the ground, and burn it up in fission reactors.

Also, many people don’t realize that Chernobyl was running on “dirt”, which is to say, unenriched natural U238. Though some reports still say it was (at a level of 1 to 2%).

But you can do that with Graphite or Heavy Water. But when you do it with graphite, and you boil away all of your water, the reaction doesn’t stop, until the reactor undergoes self disassembly and the fuel assembly geometry is disturbed. There are reports that indicate Chernobyl may have been operating in uncooled, fully exposed, criticality for at least a few seconds after the lid came off (fishermen told stories of seeing actinic light beaming upward, just after the explosion, before they died a few days later).

At least in Heavy Water reactors, like the Candu reactors, they slow down from lack of water, or when they boil their coolant. They won’t even rupture since they can’t exceed a maximum power output, since when voids form in the heavy water, the reaction also slows down.

To be clear:

“unenriched natural U238”

should be...

“unenriched uranium metal”

Which means, they did chemical/physical processes to extract the metal from the ore.

They did not boost the amount of U235 (called enrichment).

They just used graphite to moderate the neutrons from the very small amount of neutrons generated from the natural decay of U235 atoms in the metal.