What will the consequences on our CO₂ emissions be of phasing out nuclear power?

If the electricity from our nuclear power plants were replaced by renewable generation, our CO₂ emissions would remain stable. On the other hand, if we replaced our nuclear power with electricity produced by gas-fired power plants in Switzerland or imported electricity, our emissions would increase significantly, but would probably be offset.

All forms of energy production emit greenhouse gases. These emissions can be direct, such as when burning fossil fuels (coal, oil, natural gas, etc.). They can also occur indirectly: during the extraction and processing of fuels (oil refining, for example), or for the development of energy infrastructure: manufacturing, transport and installation of equipment (solar panels, wind turbines, turbines, construction of power plants, etc.).

Nuclear power plants do not release CO₂ during their operation, but uranium mining and processing processes do. The Swiss nuclear industry emits an average of 7 grams of CO₂ for each kWh produced. However, this excellent CO₂ performance of the nuclear industry is subject to considerable uncertainty regarding the extent of future emissions associated with the decommissioning of the plants and the long-term storage of radioactive waste, which is currently very difficult to estimate.

New renewable energy sources also emit greenhouse gases, mainly during the manufacture of this equipment: between 10 and 80 grams of CO₂ per kWh depending on the sources and technologies considered, i.e. slightly more than nuclear energy [→ Q65].

Natural gas-fired power plants are characterised by high direct emissions: roughly 100 grams of CO₂ per kWh for cogeneration units (supplying remote heating networks) and around 400 grams for large power plants for which the heat is not recovered.

Under these conditions, what can happen to our CO₂ emissions when we stop using nuclear power?

If we manage to replace our nuclear electricity entirely with renewable sources, our CO₂ emissions will not increase significantly.

If, on the other hand, we opt for the production of electricity in Switzerland from natural gas, our domestic CO₂ emissions from the energy sector will increase by 5 to 20% depending on the type of production chosen. This would be in conflict with our climate commitments [→ Q4]. This is where the compensation policy, as set out in the Federal CO₂ Act, comes into play. This law requires future operators of gas-fired power plants in Switzerland to "offset" all of their emissions. This means that they will have to invest in renewable-energy or energy-efficiency projects that reduce CO₂ emissions to the same extent as those generated by their own gas plants (Another option would be to capture and sequester emissions from these plants [→ Q95]). The overall balance sheet would then be neutral, with the reduction projects “offsetting”, as it were, the emissions from the power plants.

However, this offsetting rule applies only to greenhouse gas emissions taking place on Swiss territory. It does not apply to the electricity we import.

What would happen if we imported more electricity from neighbouring countries? Europe produces a large proportion of its electricity from coal-fired power plants. Hence the high average fossil CO₂ content of the European electricity mix (296 g/CO₂/kWh). If we were to replace all our current nuclear power generation with imported electricity, our greenhouse gas emissions would therefore increase significantly, not in Switzerland but in Europe. This being the case, the European Union has set a cap on its CO₂ emissions above which emissions will have to be offset. It is therefore likely that the impact of our imports could be climate neutral. But we should not lose sight of the fact that “offsetting” is not quite the equivalent of “not emitting”, as the absence of emissions naturally remains a preferable solution [→ Q83].