We need to separate the idea of taxing CO2 from the idea of making nuclear viable.

There are many, many good reasons to tax CO2. It's just that even if you do, it's likely that nuclear will still not fare very well in the overall generation picture. If you consider China, which kneecaps CO2 generating technologies in fairly draconian fashion, those technologies still dominate China's generation sources. Nuclear comes in way behind sources like hydroelectric and wind. (And that's even with the Chinese government propping it up.)

Nuclear is simply a very costly technology to implement compared to throwing up some windmills in Texas and Oklahoma or something. It's just much cheaper. And the infrastructure is already in place for a lot of the CO2 generating sources, so investments don't have to be as large. I suspect you would need a fairly huge tax to make nuclear beat natural gas for instance. And even if it did, what about all the other sources? Wind/pumped storage hydro? Solar where appropriate? Geothermal or hydroelectric? It's just not as easy a thing as it seems.

But taxing CO2 has numerous other benefits, even if saving nuclear is not one of them.