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What are the CO2 emissions of nuclear power?

Jean-Pierre Pervès
Jean-Pierre Pervès
Former President of CEA and French Nuclear Energy Society (SFEN)
Key takeaways
  • Many people in France think that nuclear power emits CO2, whereas the reality is quite different.
  • To understand CO2 emissions, we must differentiate between the emissions of a technology during its operation as well as its overall carbon footprint, which includes those resulting from all phases of construction, operations, and decommissioning.
  • Nuclear power has a very low carbon footprint, but it cannot meet peak demand on its own. It must therefore be complemented by renewable energies.
  • Total emissions from each country's electricity mix is therefore important and in that respect France, as long as its nuclear power is strong, is very efficient.
  • By way of comparison, in 2020, the emissions of France, Denmark, Spain, Holland and Germany were, respectively, 45, 102, 144, 290 and 300 g CO2eq/kWh.

In pro­por­tion to its pop­u­la­tion, France has the largest nuclear park in the world. Indeed, accord­ing to 2019 fig­ures, 72% of French elec­tric­i­ty comes from nuclear ener­gy, 20% from renew­able ener­gy and 8% from fos­sil fuels. Nuclear ener­gy enables France to be 50% ener­gy inde­pen­dent, while allow­ing it to export elec­tric­i­ty for profit.

Today, France’s objec­tive is to reduce its green­house gas (GHG) emis­sions by 40% by 2030, com­pared to 1990 lev­els. It may have to decrease these even more, how­ev­er, since Europe has decid­ed to accel­er­ate its decar­bon­i­sa­tion pro­gramme with its “Fit for 55” objec­tive (55% reduc­tion by 2030) that takes into account car­bon capture.

Accord­ing to opin­ion polls, many French peo­ple still think that nuclear pow­er emits CO2, but the real­i­ty is quite dif­fer­ent. This mis­con­cep­tion is under­stand­able, how­ev­er, since the ener­gy tran­si­tion pro­gramme states that GHG emis­sions need to be reduced but our reliance on nuclear pow­er also.

What is nuclear energy?

Nuclear ener­gy is the fis­sion of a fuel, ura­ni­um, which releas­es heat. This heat is used to heat water in the reac­tor to a high tem­per­a­ture of 330°C and a high pres­sure of 155 bars. A sec­ondary cir­cuit then pro­duces steam at 220°C and 70 bars, which dri­ves the tur­bine and the tur­bo generator.

How is the carbon footprint of nuclear energy calculated?

We need to dif­fer­en­ti­ate between two concepts:

  • CO2 emis­sions of a tech­nol­o­gy dur­ing oper­a­tion: as for wind or solar ener­gy, nuclear ener­gy emits hard­ly any CO2.
  • The car­bon foot­print, which includes emis­sions dur­ing the entire life of the instal­la­tion, known as “from well-to-wheel”, that is, those result­ing from all phas­es of con­struc­tion, oper­a­tion and dismantling.

There are two units of impor­tance here: car­bon diox­ide emis­sions, expressed in grams of CO2 per kWh, or gCO2/kWh, and GHG emis­sions, which include all green­house gas­es in gCO2eq./kWh. The impacts of oth­er GHGs are stan­dard­ised as “CO2 equivalent”. 

For exam­ple, in the case of nuclear pow­er, in addi­tion to con­struc­tion, there is extrac­tion of ore, enrich­ment of ura­ni­um by ultra­cen­trifu­ga­tion, trans­port, pro­duc­tion and dis­tri­b­u­tion of elec­tric­i­ty and, of course, decom­mis­sion­ing and waste man­age­ment must be con­sid­ered, too.

Although such an analy­sis seems sim­ple, these para­me­ters are in real­i­ty extreme­ly com­plex to assess, since they must direct­ly take into account mea­sur­able activ­i­ties as well as indi­rect con­tri­bu­tions, pos­si­bly out­side our bor­ders. For exam­ple, for nuclear pow­er France imports its ura­ni­um from mines in Cana­da, Aus­tralia, Niger and Kaza­khstan, and must trans­port it after trans­for­ma­tion to our ports. On the oth­er hand, a sig­nif­i­cant part of the mate­ri­als and equip­ment is avail­able nationally.

If we look at oth­er means of elec­tric­i­ty gen­er­a­tion, there is a mas­sive amount of equip­ment that comes from abroad, such as wind tur­bines and solar pan­els, so we have to include their foot­print in our own.

Nuclear power has a very low carbon footprint 

The three tech­nolo­gies hydropow­er, wind and solar are very cli­mate effi­cient. Even an error in assess­ment of a fac­tor of two or three would not change this con­clu­sion. Solar pan­els, although a lit­tle less effi­cient, still rank well. But, each coun­try will ben­e­fit more or less from each of these technologies:

  • Solar PV will be very effi­cient in a dry, low lat­i­tude cli­mate, and cer­tain­ly much less so near the Arc­tic Circle.
  • Inter­mit­tent elec­tric­i­ty will have to rely on back­up capac­i­ty, which will very often be a nat­ur­al gas plant, thus reduc­ing its performance.
  • Nuclear pow­er itself will not be able to meet peak demand and will be sup­ple­ment­ed by renew­able ener­gies, but also part­ly by fos­sil fuel pow­er plants.

This is why we use the emis­sion fac­tor of each coun­try’s elec­tric­i­ty mix. From this point of view, as long as its nuclear pow­er remains strong, France per­forms very well, if com­ple­ment­ed by hydro and oth­er renew­ables. By way of com­par­i­son, in 2020, the emis­sions of EU coun­tries were the fol­low­ing (in g/kWh): Swe­den (13), France (55), Aus­tria (83), Den­mark (102), Spain (190), Bel­gium (192), Italy (212), Ger­many (301), Hol­land (318) and Poland (724)1.

How do nuclear, renewable and fossil fuels compare?

We will lim­it our­selves to two ref­er­ence doc­u­ments, that of the ADEME (the agency of the Min­istry of the Envi­ron­ment), and that of the IPCC (the Inter­gov­ern­men­tal Pan­el on Cli­mate Change), the for­mer being rather hos­tile to nuclear ener­gy and the lat­ter neutral.

These fig­ures are very com­pa­ra­ble to those of the IPCC, with the notable excep­tion of nuclear pow­er, which has half the car­bon foot­print in France. This low fig­ure comes from the fact that the Georges Besse 2 plant (for iso­tope sep­a­ra­tion), which enrich­es ura­ni­um, is pow­ered by French elec­tric­i­ty, which is remark­ably car­bon-free (unlike oth­er coun­tries that have mas­tered this tech­nol­o­gy and which still rely heav­i­ly on fos­sil fuels to pro­duce their electricity).

Between oppo­nents and sup­port­ers of this or that ener­gy, the fig­ures may dif­fer, espe­cial­ly as the cal­cu­la­tions them­selves are tech­ni­cal­ly com­plex, and may even be the sub­ject of polit­i­cal choic­es: how can steel pro­duced in each coun­try be com­pared accord­ing to the lev­el of tech­nol­o­gy and the use of coal of more or less good quality?

It is in this sense that the two assess­ments by ADEME and the GHG are inter­est­ing because they are very sim­i­lar. The IPCC data have the advan­tage of being multi­na­tion­al, and the fig­ures obtained are eval­u­at­ed by experts from all over the world accord­ing to a high­ly struc­tured process, with peer reviews.

But action is needed

To meet the objec­tives of the 2015 COP21 – which led to the Paris Agree­ment, signed by 195 coun­tries com­mit­ting to act to con­tain the rise in tem­per­a­ture below 2°C by 2100 – France must, like oth­er nations, reduce its GHG emis­sions. This goal, which requires France to reduce its GHG emis­sions by 40% by 2030 (or even more with the new Euro­pean tar­gets, as men­tioned), can only be achieved if it makes a rad­i­cal shift towards a low-car­bon economy.

An analy­sis of our coun­try’s emis­sions clear­ly reveals the areas where action is urgent­ly need­ed: in 2019, trans­port and build­ings were respon­si­ble for 63% of emis­sions and it is repeat­ed­ly stat­ed that we will have to rein­dus­tri­alise our coun­try if we want to reduce our car­bon foot­print. The solu­tion can only come from an elec­tri­cal vec­tor which, accord­ing to the Inter­na­tion­al Ener­gy Agency (IEA), could car­ry 80% of the world’s ener­gy needs by the end of the cen­tu­ry (fos­sil fuels still pro­vide three quar­ters of glob­al con­sump­tion today).

Nuclear pow­er, with its low car­bon foot­print and pro­duc­tion flex­i­bil­i­ty, will nec­es­sar­i­ly play an impor­tant role, com­bined with hydropow­er and sol­id bio­mass (lim­it­ed) to pro­duce elec­tric­i­ty when it is need­ed. These con­trol­lable pro­duc­tions will be sup­ple­ment­ed by inter­mit­tent elec­tric­i­ty, pos­si­bly based on a mass stor­age of elec­tric­i­ty but they have yet to be demon­strat­ed. This switch from a “fos­sil » soci­ety to an “elec­tric” one is a real chal­lenge, how­ev­er, and will require huge invest­ments. Being long term and high­ly cap­i­tal inten­sive (this is true for both nuclear and renew­able ener­gies), our ener­gy future depends on clear, robust and long-term strategies.

Polit­i­cal whims and often unfruit­ful quar­rels have unfor­tu­nate­ly weak­ened France’s posi­tion, as clear­ly evi­denced by the surge in prices in the coun­try this autumn. With a view to shut­ting down all our coal-fired pow­er sta­tions by 2024, hav­ing refused to launch new nuclear pow­er sta­tions for 15 years and for­bid­ding the con­struc­tion of nat­ur­al gas-fired pow­er sta­tions, our con­trol­lable pro­duc­tion fleet no longer has the nec­es­sary pow­er. It is urgent to act, because even if nuclear pow­er is relaunched, this will take more than a decade and we will not be able to avoid the con­struc­tion of a few nat­ur­al gas pow­er plants as a tran­si­tion­al ener­gy source.

In France, EDF has embarked on a major refur­bish­ment of its reac­tors to extend their oper­a­tion under the safe­ty con­di­tions recog­nised by the Nuclear Safe­ty Author­i­ty. With the EPR2, it is also devel­op­ing a new mod­el that is more effi­cient in terms of both pro­duc­tion and cli­mate, with a gain of around 15 to 20%. We are still wait­ing on deci­sions, but the tide is turn­ing and we can hope for a real relaunch of nuclear pow­er in France and in Europe.

In par­al­lel, many oth­er efforts will have to be made to improve ener­gy effi­cien­cy and reduce our cli­mate foot­print by repa­tri­at­ing indus­tri­al activities.

Interview by Isabelle Dumé

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Jean-Pierre Pervès

Jean-Pierre Pervès

Former President of CEA and French Nuclear Energy Society (SFEN)

Former deputy director of the CEA research center in Cadarache, then director of the CEA research centers in Fontenay aux Roses and Saclay. Areas of experience: operation and design of research reactors, nuclear instrumentation, design of small and medium power reactors, isotope separation, operation of research centers (waste, radiation protection, infrastructure, nuclear safety).

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