One open issue is still what the cost will be for magnetic flasks to encapsulate the reacting materia. And how much energy will be needed, in relation to produced energy to confine the core? Such questions are very important when discussing possible and/or practical sizes.


And if it's local, then it isn't really a problem?

With 33% total efficiency, a 500MW power plant would not only produce 500MW of electricity but also 1GW of heat. If sent out into a river or the sea, that heat will add "on top of" the normal heat and can lead to environmental changes for several kilometers. I'm not convinced that it would be much better to use huge cooling towers boiling off a lot of water.

So in the end, you still need to think about both the global warming (which is a question of heat retention), and the extra heat produced by the power plant.