Exelon has stated that for new nuclear plants in the US to compete with NG CC, CO2 taxes would have to be $300-400/ton. To compete with NG for filling in around renewables, CO2 taxes would have to be much higher than that.
Other projections have the economy basically decarbonizing (without needing nuclear) at a CO2 tax of just $200/ton.
There's a good reason Exelon is tryin to spin off all its NPPs.
“The cost of new nuclear is prohibitive for us to be investing in,” says Crane. Exelon considered building two new reactors in Texas in 2005, he says, when gas prices were $8/MMBtu and were projected to rise to $13/MMBtu. At that price, the project would have been viable with a CO2 tax of $25 per ton. “We’re sitting here trading 2019 gas at $2.90 per MMBtu,” he says; for new nuclear power to be competitive at that price, a CO2 tax “would be $300–$400.” Exelon currently is placing its bets instead on advances in energy storage and carbon sequestration technologies.
I don't think we really know what a fair CO2 tax should be since it is hard to say what are the long term societal costs of an extra ton of CO2 in the atmosphere. (Though we will likely find out in the next 50 years.)
I am not sure the amount of subsidies that are given to wind, but the rationale for the CO2 tax idea seems to come from that:
>...Crane blamed the regulators of wholesale power markets for failing to give credit to nuclear generators for the social benefits of their carbon-free output. He and other executives say that it’s unfair to not provide nuclear generators a subsidy comparable to the tax credit that wind turbine operators receive for every kilowatt-hour of electricity they produce.
