Should we replace nuclear power plants by gas-fired power plants?

A nuclear reactor (there are generally several reactors in a plant) of 1000 MW (1 MW = 1.000 kW) of nominal power (in France reactors go from 900 to 1400 MW) produces 1000 x 24 x 365 = roughly 8.700 GWh (1 GWh = 1.000.000 kWh) per year. Actually the reactor does not function all the time, because a small fraction is devoted to maintenance, and sometimes fixing problems. The best possible availability ratio, in the facts, is therefore closer to 90% or 95%.

NB : in France the “availability ratio” is closer to 80%. It is not the result of failing systems, just the reflect that production is not at its maximum.

If we produce electricity with natural gas (methane), we emit roughly 400 grams of CO2 per kWh (it actually varies because all plants are not equally efficient).

Therefore to produce 8.700 GWh (that is 8.700.000.000 kWh) of electricity out of gas, we will emit roughly 3 million tonnes of CO2, or 900.000 tonnes carbon equivalent. This means that substituting just one nuclear reactor by natural gas turbines creates the same emissions than those of a city of 400.000 inhabitants (in France).

Some other considerations on the fact that drawing massively on gas can be found here.

Let’s extrapolate

When we produce on kWh of electricity, the CO2 emitted varies greatly depending on the primary energy (the primary energy is the “initial” energy) used (Some complementary explanations on the “greenhouse gas content” of the electric kWh can be found here) :

France consumed 480 TWh (one TWh = 1.000.000.000 kWh, that is pretty much !) of electricity in 2002 (From Observatoire de l’Energie), that is 480.000.000.000 kWh, of which 75% roughly, that is 360 TWh, came from nuclear plants.

On the other hand our country has emitted roughly 630 million tonnes CO2 equivalent (that is 170 millions tonnes carbon equivalent) of greenhouse gases (without sinks) in 2001 (we will take that figure as the 2002 emissions as well).

The following table presents what additionnal emissions we would have if we substituted all nuclear energy by another primary energy (this is totally irrealistic for wood or hydro power, but it is possible for gas or coal) :

We can thus see that replacing all nuclear reactors by gas would lead to an increase France’s emissions by 25%,

Replacing all nuclear energy by coal (that will be the last available fossil fuel) increases the emissions by more than 50% ! Let’s note also that this substitution would generate 20 to 30 million de m3 of ash per year, that is 20.000 times more than the nuclear waste, and these ashes contain lots of toxic elements, including nuclear waste also (it is not pure chance if Marie Curie discovered radium in materials coming from a coal mine !) and that, when washed by rain, can lead to aquifer pollution.

We understand here that just by substituting coal by gas for electricity generation Germany can decrease its national emissions by 25% roughly, but Germans will still remain much larger greenhouse gases emitters per person than French: replacing coal by nuclear would let them gain another 25%.

We can also see that solar or wind generation offer no gain compared to nuclear, but they offer one compared to oil or gas : therefore praising to pull out of nuclear energy to replace it by solar and/or wind generation, is to be mistaken regarding the problem : it’s fossil fuels that must be replaced by renewables if we want to mitigate climate change, not nuclear energy !

Let’s go the opposite way

Let’s now suppose that all electricity production in the world presently made with fossil fuels goes nuclear, or almost. It is of course an academic exercise, but the result leaves thoughtful.

In 1995, the world production (equivalent to the world consumption, since it is not possible to store large quantities of electicity) totalized 13.520 TWh, of which 17% came from nuclear reactors, and 17% also from hydroelectricity, another “CO2 free” electricity generation. I considered as eligible for full nuclearization of the rest all countries that already have the bomb (because it is a strong argument for the people opposed to the multiplication of nuclear reactors) or that already have nuclear reactors, or could have some because they have a sufficient level of technical culture (for example any country of the EU, even if it does not have reactors today, like Italy or Denmark, is in this category for my calculation).

Here is the electricity production that would be concerned :

Of course the above table shoud undergo little adjustments : I have been severe with Latin America, and on the opposite there are some far eastern countries – Afghanistan ? – where I would not be enchanted to see some nuclear power plants, but let’s say that these large masses are suited for a calculation of rough figures. We thus have about 14.000 Twh on the world 15.684 that are produced in countries that either already have the bomb (what can be regretted, and that personnally I regret, but we won’t rewrite history), or a sufficient culture of security to have nuclear reactors.

A rough 65% of this electricity is now produced with coal or gas (the remainder is constituted with nuclear, precisely, and hydroelectricity, solar and wind power being perfectly negligible for the time being). Let’s take an average emission of 700 grams of CO2 par kWh (or 190 grams carbon equivalent), an intermediate value beteween the 900/1000 grams of coal and 430 of gas (knowing that coal has a higher share than gas today) : replacing all fossil fuel electricity generation by nuclear power in the “eligible” zones would allow an annual saving of 1,7 billion tonnes carbon equivalent, that is 25% to 30% of the overall human CO2 emissions coming from fossil fuels.

Just for USA, that produced 3.968 TWh in 2001 among which 810 were nuclear and 213 came from hydro power, going nuclear for 100% of the remaining priduction would allow a saving of 470 million tonnes carbon equivalent, that is close to 30% of their emissions, or the equivalent of the whole russian emissions.

Assuming technologies that enable to extend the time horizon for reserves, from 1 century today (for 20% of the world’s electricity, that is 6% of the global energy consumption) to thousands years tomorrow (for 100% of electricity) are tuned one day (breeders of all kinds, and more generally Generation IV reactors) such a saving is still not sufficient to stabilize the perturbation of the climate (such a stabilization requires a 50% decrease of emissions at least), but it would be a significant component if the world objective was to bring back emissions under 3 billion tonnes as fast as possible.

But if our objective is perpetual growth as long as it can be sustained, going nuclear for the eligible electricity production today only shifts the emission curve by 20 years or so : it is not enough to avoid trouble. It is indeed in a context where energy savings is a top priority that nuclear is a good element of solution for mitigating climate change. Without such a will to stabilize or reduce the energy consumption, it “gives us” a couple of decades, but nothing more.