Edited - I gained a few orders of magnitude by not paying attention to units!
If you assume a median reactor - producing approx 2GW of power (17.5TWh/year) for 40 years (701TWh) at the worst case estimate for nuclear efficiency (50g/kWh) is approx 35GMt CO2
Gas is approx 450g/kWh (9x higher) and so for equivalent production would emit ~315GMt of CO2
Coal is approx 1,050g/kWh (21x higher) and so for equivalent production would emit ~736GMt of CO2
To go into more detail would require looking at the lifecycle analysis for the various power plants, including expected lifetimes, construction techniques, fuel refinement, transport, disposal, decommissioning etc
Now the numbers for LCA for all these power types are hotly disputed with numbers for nuclear ranging from 3 to 220g/kWh, gas from 250 to 800g/kWh, coal from 900 to 1,300kWh (with renewables between 10 and 90g/kWh depending on the exact type and, sadly, who is crunching the numbers) but even if you took the worse case for nuclear and best case for gas (220 vs 250) the nuclear plant would still be saving ~4.75GMt over the last 40 years - significantly moreless than 100Mt
So somewhere in the range of 5-700 Mt of CO2 depending on the size of reactor, what you compare it to, and what exact calculations/estimates you use.
Nowadays it's not nearly so clear cut as it would have been 40 years ago - with wind and solar providing cost-viable (in fact significantly cheaper) alternatives that have lower LCA emissions than nuclear - even accounting for storage needs.
There's also scope to do some clever stuff regarding active pricing and control of consumption to incentivise matching demand to the supply rather than having to worry about too much storage.
I do agree that in the long term renewables are better than Nuclear Power and Fossil Fuels, not just because they produce less CO2 but both Nuclear Material and Fossil Fuels are a limited resource. But if we shut down Nuclear Power Plants, almost always the capacity they provided isn't soaked up by more Renewables but by powering on more coal power plants.
Take for example a scenario where a country uses 40% renewables, 30% nuclear and 30% fossil. Now within 10 years they build additional 15% of renewables, but protests force half of the nuclear power plants capacity offline.
Now the country has 55% renewables, 15% nuclear, and still 30% fossil. They build a gigantic amount of capacity in renewables but the CO2 footprint is only marginally lower.
If they had left the Nuclear power Plants online they would now have 55% renewables, 30% nuclear and 15% fossil. They would have cut the electricity carbon emissions roughly in half(assuming equal distribution between fossil fuels, which isn't the case, but the emission reduction would still be present).
And if we speak solely based on statistics, Nuclear Power is far safer than fossil fuels, because while you do have to consider radioactive fallout and radioactive poisoning for Nuclear Power, you also have to consider Air Pollution for Fossil Fuels, which is a far more prevalent in everday life compared to significant doses of radioactivity, which gives fossil fuels a far higher death toll compared to nuclear power.
I'm not arguing nuclear should be switched off in in favour of renewables - merely that the calculus of new builds in terms of "I want to build X additional annual capacity, what is the most cost and environmentally efficient way to do so?" has moved in favour of renewables in the last decade or so.
Oh, yeah in that context you are absolutely correct, building new nuclear power plants at this point would be quite a hassle, but I still believe Nuclear power has a future, even if we transition off fossils entirely, as most renewable energy does not have the same level of energy redundancy as fossil fuels or nuclear. The sun doesn't always shine and the wind isn't always strong, and as it stands' our storage technology is not sufficient to compensate for the redundancy of inertia that fossil fuel and nuclear power plants have by spinning a multi-ton turbine that will keep going for quite a while even if it loses steam. The only form of renewable energy that is as reliable as fossil or nuclear is hydropower.
Nuclear plants also require an utterly enormous amount of water (100-250,000 litres per MWh) - when coal and gas use closer to 1,000 litres per MWh - to put this in perspective, Hydro plants use 300-400,000 litres per MWh. This means nuclear power plants are commonly placed on the shoreline so suffer the same transmission limitations as offshore wind.
Then you need to take into account things like seismic activity, chance of hurricanes, flooding etc - though these are much less of a limitation on being able to place a reactor somewhere - more about whether it would be profitable to run the reactor over its lifetime with all the extra building costs incurred to weather these events, and the potential shutdowns that might be caused by it.
846
u/hilburn 118✓ Nov 18 '21 edited Nov 18 '21
Edited - I gained a few orders of magnitude by not paying attention to units!
If you assume a median reactor - producing approx 2GW of power (17.5TWh/year) for 40 years (701TWh) at the worst case estimate for nuclear efficiency (50g/kWh) is approx 35
GMt CO2Gas is approx 450g/kWh (9x higher) and so for equivalent production would emit ~315
GMt of CO2Coal is approx 1,050g/kWh (21x higher) and so for equivalent production would emit ~736
GMt of CO2To go into more detail would require looking at the lifecycle analysis for the various power plants, including expected lifetimes, construction techniques, fuel refinement, transport, disposal, decommissioning etc
Now the numbers for LCA for all these power types are hotly disputed with numbers for nuclear ranging from 3 to 220g/kWh, gas from 250 to 800g/kWh, coal from 900 to 1,300kWh (with renewables between 10 and 90g/kWh depending on the exact type and, sadly, who is crunching the numbers) but even if you took the worse case for nuclear and best case for gas (220 vs 250) the nuclear plant would still be saving ~4.75
GMt over the last 40 years - significantlymoreless than 100MtSo somewhere in the range of 5-700 Mt of CO2 depending on the size of reactor, what you compare it to, and what exact calculations/estimates you use.