The concern isn't that they are producing nuclear fuel. It's that the plutonium needed for nuclear weapons is a by-product of those reactors. Plutonium isn't

The concern isn't that they are producing nuclear fuel. It's that the plutonium needed for nuclear weapons is a by-product of those reactors. Plutonium isn't naturally occurring on earth - the only place to get it is from a reactor - either yours, or buy it from someone else who has one.