I'd be highly surprised if the thought of tactical nukes even crossed Putin's mind over the hail-Mary Kursk thing which has no very conceivably durable outcome for UA/NATO.  But it's possible that I am over-estimating him, or that he is neo-con-ish enough to have convinced himself that introducing tactical nukes will of lasting positive benefit for Russia.  I don't see the man as being that much of a risk-taker, nor needing to take such risks as Russia is destined to come out of this thing in much better shape than they probably dreamed possible without resorting to anything very risky.  Doing so only introduces the possibility of snatching defeat from the jaws of victory from the Russian perspective.