You're conflating two things and applying them to a third unrelated situation. High enriched U is a proliferation risk because it's easier to enrich to weapons

You're conflating two things and applying them to a third unrelated situation. High enriched U is a proliferation risk because it's easier to enrich to weapons grade. Fuel rods that have been through a full fuel cycle are 'useless' because of the Pu 240. Fuel rods that have been in a reactor for 1-2 years (present in every 'civilian' reactor at all times) are neither of these things. And contain weapons grade Pu that can be used if you have Pu separation facilities.