Both Sendai reactors (unit 1 and unit 2) have now been restarted. Sendai unit 1 has just started providing electricity to the grid. (August 14th)
So how will this affect Japans Carbon Dioxide emissions? And how would renewables (say wind) compare?
When nuclear was shut down in Japan it was replaced with an unholy mix of coal and gas (with about 7% oil) A rough estimate of the amount of Carbon Dioxide from the generation that replaced nuclear would be around 750Kg of Carbon Dioxide for every MegaWatt Hour of energy generated (750KG/MWh)
Sendai, during its last year of full operation generated just short of 13TWh of electricity (13000 GigaWatt Hours) So today, the first day of generation, Sendai unit one (half of the power plant) will have generated around 18GWh of energy. This will displace energy that would have otherwise been generated from the coal/gas/oil mix
So a rough estimate of the amount of Carbon Dioxide prevented from being dumped into the atmosphere by this single day of generation from half a nuclear power plant amounts to 18000 x 750 = 13.5 million Kg of Carbon Dioxide or 13500 Tonnes.
A single day of operation from half a nuclear power plant prevents the emission of 13500 Tonnes of carbon Dioxide.
Amazing isn't it?
How would a renewables option compare?
An 150m high 2MW wind turbine with a typical 25% capacity factor would intermittently produce 12MWh in a day. Or using same units as Sendai - 0.012GWh
So to match the single day output from half of Sendai nuclear power plant (and ignoring the problems of intermittency) would would need 1500 turbines.
Or to put it another way, for a single turbine to match a single days energy generation from half of Sendai nuclear power plant would take that turbine four years, one month and nine days.
Don't figures like that just knock you out?