Changing any configs and then loading a save results in a crash with the following message:

The mod Bluetonium (2.5.4) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Bluetonium::on_configuration_changed
Bluetonium/control.lua:15: attempt to index field 'kovarex-enrichment-process' (a nil value)
stack traceback:
Bluetonium/control.lua:15: in function <Bluetonium/control.lua:2>

This occurs because the kovarex-enrichment-process technology no longer exists. Are you using a mod that deletes it?

Yes; I am using Nuclear Fuel, which is listed as an optional dependency.

Nuclear Fuel (like this mod) does not delete the kovarex-enrichment-process technology, but rather just hides it. It doesn't matter anyway because Bluetonium overrides Nuclear Fuel's settings if you're using both. Some other mod must be deleting the technology which is breaking both Nuclear Fuel and Bluetonium.

it seems you are correct; is there a way to figure out what mod caused this and/or recover the save?

The easiest way (though it takes time) is to just disable a bunch of mods and see if it breaks. If it does, then re-enable a few and try to narrow it down. If it doesn't, then try disabling a different bunch of mods and repeat the process. You might want to start with mods that seem like they'd affect uranium related technology, or big overhauls that might delete it. If you want, you could post your list of mods and I'll see if anything stands out to me.

I found it, it was Radioactive science.
I don't see an easy way to fix the problem other than for the mod to not delete Kovarex, so I'm gonna find myself an alternative that I like.
Thanks for your help!