US intelligence

US intelligence agencies determine that North Korea is constructing new missiles
They’re dismantling the factories to make better ones. They couldn’t fit the new bigger missiles in those sheds they were using.
He'll probably sign a secret pledge that Russia is the sole arbiter of their nuclear capabilities and try to throw the first reporter who writes about it in jail.
One only really needs to look at Saddam Hussein and Muammar Gaddafi to start laughing at the idea that NK would denuclearize. Both gave up their nuclear weapons programs, and both were killed either directly by the US or indirectly by the US aiding opposing forces.

Nukes aren't there to be used as weapons, they're there as a deterrent to conflict. They're there to keep Kim's fat ass in power.