Speaking only about U233, produced in the thorium fuel cycle: it's been used in composite fission cores in several tests by USA and (then-) USSR. There may have

Speaking only about U233, produced in the thorium fuel cycle: it's been used in composite fission cores in several tests by USA and (then-) USSR. There may have been one small test of an unmixed U233 device by India. [1] So maybe U233 could be used to make a weapon. I don't know whether that possibility makes it a big proliferation risk or not. [1] https://en.wikipedia.org/wiki/Uranium-233 https://en.wikipedia.org/wiki/Uranium-233