500,000 tons of heavy fuel oil, per year, directly from the US, during the Clinton administration. By "executive treaty" or something, meaning congress had no say in the deal. Bush put a stop to it, and Pyong Yang restarted a Nuclear Reactor designed specifically to enrich uranium. Obama adopted the "strategic patience" policy, and had no talks with NK, while analysts predicted the bomb, and a ballistic missile, within a decade.
They got it done a little faster than that.
To the best of my knowledge they only have the one reactor, but the genie is out of the bottle at this point. If we bombed the reactor with a conventional warhead, it's a good bet Kim Jong whatever would drop a Nuke on South Korea.
IMO, the only solution is regime change, as much as I hate to say it. Even if Kim agreed to UN inspections, NK is a decent sized, rough terrain country. Plenty of places to stash one or two nukes, and still have that to hold over SK's head, while allowing inspections and getting sanctions lifted.
So either ignore it, and let the sanctions take their toll until there is maybe a civil war, or push hard to create one.
This is why I'm glad I'm not President. Pretty much no good options at this point.