Perhaps things would have been different if more countries had been like France and built a large network of nuclear power stations to fuel their weapons program; but even France is regretting it and had not built a new one for decades.
https://www.ft.com/content/c7421fbe-f326-11e8-9623-d7f9881e7...
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It's not environmental groups that are against a price on carbon, until you can convince conservatives to get on board with one then nuclear can't even get passed the first hurdle.
And as far as I know, conservatives are pro-competition and not against nuclear at all in the States.
For existing plants? The problem with expanding nuclear, at least in Europe, is not the operational costs but that the cost of building new nuclear power stations is so high that they'll never pay for themselves without massive subsidies.