Those have been researched and tested for decades and the tech still hasn’t caught on. They just don’t put out enough power to be useful for much more than a clock circuit (not even enough to power a full watch, just keep the time).
I have serious doubts they’re going to suddenly become viable anytime soon.
Any useful energy production from nuclear is basically just making steam to run turbines. Same with coal but you know.
I believe they have been used in pacemakers, for example. They are becoming practical for more applications over time and are seemingly on the verge of appearing in consumer electronics. We shall see.
RTGs also do not use water. I suppose the watch batteries are essentially just tiny RTGs.
Conceivably you could use bimetallic strips to produce mechanical energy from the heat generation.
