Firstly, nuclear power tech is monolithic. It costs a lot and gives a lot. However, I don't really feel like monolithic tech fits in well with Factorio. I don't know if this is something you did on purpose and want to keep but if you're up for some flexibility, I could see the tech being split up into 3 techs.
One tech would be the Steam Turbine. This is obviously an upgrade to the Steam Engine already but due to how it handles heat and gives electricity, it is useless without the nuclear power. As such, I think you should simply let it do its job with lower levels of steam heat so that it is a natural upgrade over the Steam Turbine but at the cost of more steam. In other words, make it less efficient (but at least usable) than a Steam Engine at lower heat levels but at higher heat levels it reaches the efficiency it already has with nuclear power.
Another tech would be the ability to mine and refine uranium. This unlocks the mining equipment and the centrifuge. This allows you to get a head start on building up fuel cells while also being a pre-cursor to the final of the three techs.
The last tech would obviously be the reactor itself and the heat exchanger with it. The other two techs should be a direct requirement to unlock this tech but I think they are parallel in importance. Thus you still have some choice on your way towards nuclear power without forcing it to be such a monolithic task that unlocks so much at once.
Secondly, I feel like there's entirely too much time between the first and second power generation source for your power armor. The tiny solar panels just don't cut it when you've already got the tech for exoskeletons, personal roboports, and laser defense. I think a good halfway point needs to be made. Either a second tier of personal solar panels or maybe some way to plug yourself into your vast electrical network to charge your batteries. Otherwise I find myself having to cut my construction plans short when my roboports can't charge my construction bots anymore.
Thirdly, it feels a little weird that I can put super-heated steam into a silo and it keeps its heat forever. Is that intentional? Makes for a neat backup system if the nuke ever shuts down, though I have no idea for how long it would last because....
Fourth, steam is missing from the fluid production chart. It should be on there, right?
Finally, I was so happy to be able to do this!

I felt like a king being ushered by minions. Thanks for adding ghost-deconstruction of trees! (Someone in chat said this was new to .15 and I had honestly never tried before.)