[Accujack]

It's the other way around. Highly enriched uranium has been easy to use as a fuel source for decades. Using less enriched material has always been a problem, actually. CANDU (Canadian design) did a pretty good job making it work, though.

Nuclear weapons didn't use much uranium, they manufactured and processed plutonium.

By the way, a lot of nuclear fuel in the past few decades has been reprocessed material from weapons that were decommissioned. I believe the US even traded with the Russians for their spare plutonium.