It’d be difficult. Not theoretically impossible, but difficult. The problems are power-to-weight and power-to-bulk.
Whether a tank is powered by a big stonking gasoline engine, diesel engine or gas turbine, it is a heat engine. Heat engines generate useable power from a heat differential. You need to have a “reservoir” of high temperature to take heat from and run it through the engine, and a “reservoir” of low temperature to dump heat into. The last is important, and I’ll come back to it.
Most heat engines use a working fluid that is heated and expands to convert heat into work.
Diesel, gasoline and gas turbine engines are internal combustion engines. The combusting fuel acts as the high temperature reservoir. The gases generated by the combustion act as the working fluid. The outside world acts as the low temperature reservoir, and heat is dumped into it simply by exhausting the hot combustion gases.
A water boiler and steam expander (turbine/piston/other), whether heated by combustion or nuclear energy, constitute an external “combustion” engine. That means that heat has to be transferred to the working fluid by conduction. The more power you want, the more heat-transfer area you need. This gives you bulk problems - tanks are heavy and need a lot of power. Internal combustion engines don’t have this limitation - heat is generated within the working fluid itself, there is no need for heat-transfer by conduction.
The other problem is the cold reservoir, which again has to be the outside world. You could simply exhaust the steam to the outside world, but this means that you have to carry water and take on more over time, lessening the advantage of using nuclear power in the first place. It also marks your position with a steam plume, which I guess your average tank crew would take a dim view of.
The alternative is to run the steam through a radiator (effectively a condenser) to dump the heat, recondensing the water so it can be recirculated. Again, this requires heat transfer across the walls of the radiator, and a big radiator is bulky and heavy. Also, where do you put the radiator? The thinner the walls, the better a radiator it is, but you can’t stick a delicate thin-walled structure on the outside of a tank where piffling small arms can perforate it. Instead you have to have the radiator inside the tank, and use fans to suck air in, blow it over the radiator and blow the hot air out again. Fitting this lot inside a current tank is a tall order, and I haven’t even started on radiation shielding…
A large, non-armoured structure like the Antarctic nuclear tank Astro linked to gets around many of these problems. Plus in the Antarctic you have an infinite source of clean make-up water. Similarly, nuclear ships can run seawater over their condensers, and have energy to spare to purify seawater if they need a top-up.