Yes, the Russian forces will use a tactical nuclear weapon at some point. I'd say within a month, actually. They still have to keep their front lines stable until that 300k new troops are online and in the personnel replenishment system.
That weapon will most likely be used on or around the
Zaporizhzhia nuclear power plant complex. Zaporizhzia is around 310 miles/ 11 hours northwest of the beginning of the Chernobyl exclusion zone.
Zaporizhzhia to Chernobyl Exclusion Zone - 8 ways to travel via , and train
Everyone seems to forget Chernobyl was in Ukraine. When it went, western Europe was blanketed by a huge cloud of radiation from it.
Zaporizhzia is 6 times larger than Chernobyl; and is in the same wind pattern.
When Russia uses a tactical nuke on the place; not only will Ukraine suffer from ground contamination. Much of Eastern Europe gets their power from that plant complex. In addition; western AND eastern Europe (with a number of NATO members now in Eastern Europe)will both get huge radiation doses.
If that happens; would Poland, Romania or any of the Baltic countries invoke Article 5 due to rad dosages? Would NATO respond? I'd bet the answers to both questions is a resounding Yes.
Russian forces would get a two for one win if they used a tactical nuke on that power plant. They would get back at Ukraine AND NATO.