Even a low-yield nuclear weapon used on the battlefield, aside from killing troops in the immediate vicinity, would still contaminate a broad area and expose large numbers of civilians in densely-populated Ukraine and neighbouring countries to radiation risks. In fact, Russia and its ally Belarus would face the highest contamination risk because of prevailing winds.
So what's holding Putin back?
The resolve shown by the US and its western allies in supporting Ukraine since the Russian invasion on February 24 has shocked Putin.
And the Russian president realises deploying nuclear weapons in the war is a big leap in the dark, Blaxland says.
"You cross that threshold and you don't know what happens next.
"He cannot be sure such an escalation will be successful."