It goes completely against what most believe, but out of all major energy sources, nuclear is the safest

Our World in Data presents the empirical evidence on global development in entries dedicated to specific topics.

This blog post draws on data and research discussed in our entry on Energy Production and Changing Energy Sources.

Energy production and consumption is a fundamental component to economic development, poverty alleviation, improvements in living standards, and ultimately health outcomes. We show this link between energy production and prosperity here, where we see a distinct relationship between energy use and gross domestic product per capita.

The unintentional consequences of energy production can, however, also result in negative health outcomes. The production of energy can be attributed to both mortality (deaths) and morbidity (severe illness) cases as a consequence of each stage of the energy production process: this includes accidents in the mining of the raw material, the processing and production phases, and pollution-related impacts. We have recently explored this trade-off with respect to development and air pollution.

If we want to produce energy with the lowest negative health impacts, which source of energy should we choose? Here we limit our comparison to the dominant energy sources—brown coal, coal, oil, gas, biomass and nuclear energy; in 2014 these sources accounted for about 96% of global energy production.1 While the negative health impacts of modern renewable energy technologies are so far thought to be small, they have been less fully explored.2 We also acknowledge that there are numerous metrics which could be considered (even in consideration of health impacts only) for such comparisons. Here we focus on death rates.

There are two key timeframes to consider when attempting to quantify potential fatalities from energy production. The first is the short or generational timespan, which covers deaths related to accidents in the mining, processing or production phase of energy sources as well as the outdoor air pollution impacts from the production, transport and combustion of fuels. The second is the long-term or intergenerational impacts (and resultant deaths) from climate change.

Deaths from accidents and air pollution

In the chart below we see the results of the analysis by Markandya and Wilkinson (2007) published in the medical journal The Lancet.3 This is the rate of short-term deaths from accidents and air pollution related to energy production. Since we want to compare the relative safety of producing energy from various sources, this data has been standardised to the deaths resultant from the production of one terawatt-hour (TWh) of energy in each case. One terawatt-hour is roughly equivalent to the annual energy consumption of 12,400 US citizens. Although deaths from accidents and air pollution have been combined, it’s important to note that air-pollution related deaths are dominant. In the case of brown coal, coal, oil and gas, they account for greater than 99% of deaths, as well as 70% of nuclear-related deaths4, and all biomass-related deaths.

We can see that brown coal and coal rate the worst when it comes to energy-related fatalities. Coal-fired power plants are a key source of sulphur dioxide and nitrogen oxides, key precursors to ozone and particulate matter (PM) pollution, which can have an impact on human health, even at low concentrations.5

At the other end of the scale as the safest source of energy we have nuclear energy, resulting in 442 times fewer deaths relative to brown coal per unit of energy. Note that these figures also account for estimated cancer-related deaths as a result of radioactive exposure from nuclear energy production.

In the second chart below we have estimated the hypothetical number of global deaths which would have occurred as a result of energy production if all energy was produced from a given source, by multiplying respective death rates (per TWh) by IEA estimates of global energy production in 2014 of 159,000 TWh.6 If global energy demand in 2014 was met solely through brown coal, we estimate global deaths as a result of energy production to be more than five million. In contrast, if global energy demand was met through nuclear sources, the number of deaths would have been only 11,800 (442-times less).

What would our worst-case probabilities suggest about risk?

It’s important to note that we may consider the values of death rates and hypothetical number of deaths from nuclear power quoted above to be worst-case projection of risk and mortality. The figures for death rates per TWh from Markandya and Wilkinson (2007) are calculated on a theoretical basis using a method called the ‘linear, no-threshold model’.7 The basis of this model assumes that the number of deaths is directly and linearly proportional to the dosage of radiation; additionally it assumes there is no lower limit or “safe” level of exposure, meaning individuals are at risk even at very low doses.

However, this model for estimating mortality risk from radiation exposure is particularly controversial, with suggestions that it leads to an overestimation of probable risk.8 Furthermore, as James Hansen argues in his 2011 paper, our empirical evidence of mortality risk based on historical nuclear events (of which, there has been only three large-scale incidents: Three Mile Island, Chernobyl, and Fukushima) is several orders of magnitude lower than those we would predict from theoretical linear, no-threshold models of probability.9 As a result, we may consider these models (and the quoted figures used in the charts above) to be an upper, worst-case estimate of risk rather than one based on historical evidence (which may fail to accurately reflect worst-case conditions).

Managing nuclear waste

An additional concern for nuclear energy, beyond direct attributed deaths from accidents is the challenge of radioactive waste management. Waste produced from the nuclear fission process (and facility) varies in levels of radioactivity, as well as the period of time for which it poses a risk to human health. This period of concern extends anywhere from 10,000 to one million years. We therefore segregate waste into three categories: low, intermediate, and high-level waste. Our ability to deal with low and intermediate levels of waste (LLW and ILW) are typically well-established. LLW can be compacted, incinerated and buried safely at a shallow depth. ILW, containing higher amounts of radioactivity, needs to be shielded in concrete or bitumen before disposal.10

Dealing with high-level waste (HLW) is more challenging. The long lifetime and high amounts of radioactivity in spent nuclear fuel means waste must not only be appropriately shielded, but also be in a stable environment over long timescales. To achieve this, most propose storage in deep geological sites. The difficulty therefore lies in ensuring chosen sites would be geologically stable (including temperature and water fluctuations) over this period of time. To date, the majority of our HLW is stored in multi-barrier repositories at surface sites. However, to deal with them appropriately, long-term deep geological solutions must be developed.11 Sweden and Finland are arguably the furthest forward in the development of long-term storage solutions.12

Deaths from climate change

Energy production not only has short-term health impacts related to accidents and air pollution; it also contributes to the long-term impact of global warming, the impacts of which (e.g. extreme weather, sea level rise, reduced freshwater resources, crop yields, heatstroke) are likely to be fatal for some.13 It’s particularly challenging to predict how many climate change related deaths we might experience decades from now, and how much we could attribute to a specific energy source. This makes it difficult to compare specific figures related to long-term deaths.

We can, however, use a proxy (a related or substitute indicator) to compare the potential contribution of energy sources to climate change. For this, we use the carbon intensity of energy, which measures the grams of carbon dioxide (CO2) emitted in the production of a kilowatt-hour of energy (gCO2e per kWh). Using this proxy, we can assume that energy sources with a higher carbon intensity would have a larger impact on mortality rates from climate change for a given level of energy production. In the chart below we see both measures of fatality: on the y-axis we have the death rates (per TWh) from accidents and air pollution as we discussed in the previous chart; on the x-axis we have each energy source’s carbon intensity, measured in gCO2e per kWh.

We see a strong correlation between both measures, energy sources that are unhealthy in the short-term are also unhealthy in the long-term. And those that are safer for the current generation are safer for future generations.

Coal rates poorly for both variables (and especially brown coal) has both a high death rate from local air pollution, as well as having a high carbon intensity. Oil is also associated with high short- and long-term health impacts. At the other end of the scale, both nuclear and biomass have a low carbon intensity (with nuclear lowest at 12gCO2e/kWh and biomass at 18gCO2e/kWh). This is 83 and 55 times lower than coal, respectively.

Nuclear energy therefore scores lowest on both short- and long-term mortality related to energy production. It’s estimated that up to 1.8 million air-pollution related deaths were avoided between 1971-2009 as a result of producing energy with nuclear power plants rather than available alternatives.14

Conclusions on energy safety

Discussions with regards to energy safety often incite the question of: how many died from the nuclear incidents at Chernobyl and Fukushima? We addressed this question in a separate blog post. In summary: estimates vary but the death toll from Chernobyl is likely to be of the order of tens of thousands. For Fukushima, the majority of deaths are expected to be related to induced stress from the evacuation process (standing at 1600 deaths) rather than from direct radiation exposure.

As stand-alone events these impacts are large. However, even as isolated, large-impact events, the death toll stands at several orders of magnitude lower than deaths attributed to air pollution from other traditional energy sources—the World Health Organization estimates that 3 million die every year from ambient air pollution, and 4.3 million from indoor air pollution.15 As so often is the case, single events that make headlines overshadow permanent risks that result in silent tragedies.

Based on historical and current figures of deaths related to energy production, nuclear appears to have caused by far the least harm of the current major energy sources. This empirical reality is largely at odds with public perceptions, where public support for nuclear energy is often low as a result of safety concerns. This is shown in the chart below which measures the share of survey respondents in a given country who are opposed to nuclear energy as a means of electricity production. At a global level, opposition to nuclear energy stood at 62 percent in 2011.

Public support for renewable energy production is much stronger than for nuclear or fossil fuels. Why are we therefore concerned with the comparison between the latter two? Whilst the share of energy production from renewable technologies is slowly growing, 96 percent of global energy production is produced from fossil fuels, nuclear and traditional biomass sources. Our global transition to renewable energy systems will be a process which takes time—an extensive period during which we must make important choices on bridging sources of energy production. The safety of our energy sources should be an important consideration in designing the transitional pathways we want to take.