Nuclear and Carbon: How Low is Low?

23rd June 2022

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James Tucker, Soben’s Director of Transport and Infrastructure, takes an in-depth look at the emerging power source of nuclear energy…

The volatility of gas prices due to the conflict in Ukraine has underlined the need to reduce our dependence on natural gas for power generation. But of equal importance is the urgent imperative to cut carbon emissions.

According to the International Energy Agency, worldwide emissions of carbon from burning fossils fuels were around 33.5 billion tonnes in 2021, 46% of that from coal, 32% from oil and 22% from natural gas. Currently nuclear power accounts for around 10% of power generation globally; the US is the world’s biggest producer, generating around 20% of its electricity through nuclear.

However, is nuclear power seen as a viable carbon friendly alternative or one to be ignored and phased out? Judging by the build programmes underway in several countries including China, India, South Korea and the UK it would seem the former. That said, we know that nuclear power generation has a lower carbon footprint than fossil fuels which I am sure is of no surprise to those countries considering a build programme or indeed those already committed but there are differing views as to exactly how much lower it is.

Indeed, this is true for all types of power generation so it is important to understand where the carbon is and how the footprint varies so that we can re-examine and improve the way we build, maintain, operate, and decommission our power plants to ensure the least harm to our environment and give the generations to come a fighting chance of reducing carbon.

Comparing sources

Although we often talk about absolute values in response to carbon emissions from different power sources, it is important to remember that – as with most whole life carbon calculation – there are many moving parts and assumptions to take into consideration. There are the emissions produced when mining, manufacturing, transporting, and constructing the plant; emissions for extracting, processing and transporting the fuel for the plant throughout its life; emissions to maintain and operate the plant; and, finally, the emissions produced when that plant is decommissioned and dismantled.

With fossil fuel-powered stations, there will always be the need to extract and supply natural gas, coal or oil. With nuclear, there is the impact of mining uranium ore and processing it into fuel rods not forgetting transportation costs involved in getting it to plants. However, once in operation, the nuclear fission process produces no carbon dioxide. Fossil fuel-powered plants, of course do. Carbon capture and storage (CCS) could deal with some, though probably not all, of these emissions in operation, although there is a lot of development work still to be done on CCS technologies.

Renewable energy, such as solar or wind power, emits no carbon due to fuel extraction or supply and no carbon in operation. The variables involved in carbon footprint calculations for these types of power generation are location and environmental conditions. For instance, there are huge variations in the footprint of photo voltaic (PV) power generation, depending on the position of panels and the intensity of the sun.

The other uncertainties in whole-life carbon calculations involve what will happen in the future. As we decarbonise electricity supplies around the world, the carbon emitted to create building materials and enrich uranium will fall. Manufacturing processes for PV panels or wind turbines are likely to become more energy efficient. And there is the uncertainty about how good we will get at CCS and how long that will take.

Devil in the detail

An often-quoted source of lifecycle carbon data for different energy sources comes from the World Nuclear Association. It says that coal produces 820g of carbon per kWh, natural gas 490, solar PV 28, nuclear 12 and offshore wind 12.

A 2017 study by Germany’s Potsdam Institute for Climate Impacts Research (PIK) takes into account CCS and the decarbonisation of the grid and suggests that both nuclear and renewable power is actually lower in carbon than previously calculated. It says that nuclear lifetime carbon emissions are 4g of carbon per kWh, solar is 6g and wind 4g. Coal with CCS has a footprint of 109g per kWh and gas with CCS has 78g.

Looking at various sources and pieces of research, calculations of emissions for nuclear power vary hugely, from as little as 3g per kWh up to over 200g per kWh. Reasons for this wide variation include uncertainty over how nuclear power stations will be dismantled and the long-term carbon cost of storing radioactive waste and other elements. In the UK, for example, there are plans for a vast underground depository or Geological Disposal Facility made up of tunnels and vaults, covering an area of around 20 square kilometres.

Another uncertainty is the amount of carbon that will be required to process the uranium. The concentration of the ore impacts on the amount of energy needed to create the rods, and we don’t know yet what the concentration of future uranium reserves will be or how difficult it will be to extract them.

Greater transparency

What these differences in carbon footprint estimations do tell us is that there is a need for greater uniformity in the way that we carry out carbon accounting. The good news is that carbon accounting practices and carbon management are advancing fast.

That said, although carbon estimates are mixed there does seem to be a consensus nuclear plants produce less carbon than their fossil fuel equivalents however, other variables such as how quickly new power sources are needed, local climate, and available land will inevitably dictate a mixed bag of power generation.

How we manage and measure carbon will effect these decisions, therefore greater transparency on carbon emissions and measurement for all types of energy will help governments, especially in the short to medium term,  make informed decisions about how the best mix of energy sources will work for their country – and ultimately, the planet.

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