tl;dr: They're taking the warheads out of precision guided nukes and launching them without explosives to hit targets in Ukraine, presumably because they're running out of missiles.
https://www.bbc.com/news/world-europe-63826082
Russia is now using nuclear-capable missiles with non-explosive warheads to exhaust Ukraine's air defences, the Ukrainian military has said.
It displayed what it said were fragments of Soviet-made X-55 cruise missiles - designed for nuclear use - found in Ukraine's two western regions.
Moscow is now resorting to using blunt projectiles that still cause devastation, they say. A
UK intelligence report
in November came to similar conclusions.
He said the projectiles were designed in Soviet times to hit "strategic targets with predetermined co-ordinates".
The UK said the missiles were designed "exclusively as a nuclear delivery system".
However, it is believed the Russian military removed the nuclear warheads from the missiles fired at Ukraine and replaced them with an inert system.