Grid electricity is only about a third of primary energy consumption. Renewables and nuclear power only make up about 10% and 6% of primary energy consumption worldwide [1]. In the coming years we have to ramp those fractions up globally A LOT in order to become CO2-neutral. Also from the low fraction of 6% we can see that nuclear could be switched off today without making a big difference for CO2 output, renewables already generate more power.

[1]: http://en.wikipedia.org/wiki/Primary_energy