A number of months ago, there was a mysterious spike in radiation in the northern region of Russia and the local population were scrambling to get iodine. Nearby was a military research base and they said that there was an "accident" but later admitted that there was an explosion of an experimental missile.
The rumor is that the Russians had been try to develop a nuclear powered missile or cruise missile and it blew up. I believe 4 of their scientists were killed in the explosion. The advantage of a nuclear powered cruise missile is that it effectively has unlimited loitering time so it can fly around indefinitely until it is deployed. Because it is already flying around near its target, the strike can be made very quickly; reducing defensive reaction time. I suspect the Russians are back at it.