This blog post draws on data and research discussed in our entry on Energy Production & Changing Energy Sources.
When it comes to the safety of nuclear energy, discussion often quickly turns towards the nuclear accidents at Chernobyl in Ukraine (1986) and Fukushima in Japan (2011). These two events were by far the largest nuclear incidents in history; the only disasters to receive a level 7 (the maximum classification) on the International Nuclear Event Scale.
How many deaths did each of these events cause?
When it comes to nuclear accidents there are really two fatal impacts to consider: the first being the number of direct deaths which occurred either at the time of incident, or in the days which followed (i.e. the acute impacts); the second being the long-term (chronic) impacts of radiation exposure, which has known links to the incidence of several forms of cancer.
Deaths from Chernobyl
In the case of Chernobyl, 31 people died as a direct result of the accident; two died from blast effects and a further 29 firemen died as a result of acute radiation exposure (where acute refers to infrequent exposure over a short period of time) in the days which followed. The number of people who were impacted over long-term radiation exposure is more difficult to discern and remains highly contested. The difficulty lies in the fact that the relationship between low-level radiation exposure and cancer incidence can be challenging to decouple from other environmental and lifestyle factors; cancers can in many cases be multi-causal, and not solely correlated with factors such as radiation exposure.
In an assessment titled ‘Chernobyl’s Legacy: Health, Environmental and Socio-Economic Impacts’ the World Health Organisation (WHO) estimated that the total number of deaths of the population in close proximity to Chernobyl will be around 4,000. Estimating the numbers of people affected across Europe by radiation is more contested. A study in the International Journal of Cancer by Cardis et al. (2006) estimates another 16,000 deaths across the former USSR. If we extend this to total attributed deaths across Europe, radiation scientists Fairlie and Sumner suggest this total rises to between 30,000-60,000 deaths. The highest estimate to date comes from a 2006 Greenpeace report which estimates an eventual death toll of 93,000. Although uncertain, the total number of deaths attributed to the Chernobyl disaster is likely to be in the range of tens of thousands. The upper and lower estimates are shown in the chart below.
Deaths from Fukushima
In the case of Fukushima, although 40-50 people experienced physical injury or radiation burns at the nuclear facility, the number of direct deaths from the incident are quoted to be zero. However, mortality from radiation exposure was not the only threat to human health: it’s estimated that around 1,600 people died as a result of evacuation procedures and stress-induced factors. This affected mostly older people; more than 90 percent of these deaths occurred in individuals over the age of 66.
How many are projected to suffer in the long-term from low-level radiation exposure? In its Health Risk Assessment of the nuclear disaster, the World Health Organization (WHO) note exposure levels too low to affect human health for the national population, with exception to a few communities in closest proximity. In these localities, it is those who were infants at the time of exposure who are at greatest risk of cancer—at the two closest sites, the incidence of cancer in this demographic is projected to be between 4-7 percent higher than baseline cancer rates for both males and females (with the exception of thyroid cancer in females, which is 70 percent higher). The WHO project the number of deaths from low-level exposure to be close to zero, and up to 400 in upper estimates (as represented in the chart below).
In more recent evaluations of rates of perinatal mortality (that is, stillbirths or deaths within the first week of life) in areas closest to the Fukushima site, there were no statistical indications of increased incidence. In fact, rates of perinatal mortality showed an overall decline with time—the general trend we see through improved healthcare and healthier lifestyles.
The death toll of the Fukushima nuclear accident dominated headlines for weeks after the event and overshadowed the much larger tragedy that happened at the same time and place: the Tsunami killed 15,893 people, around eight times (if we assume the upper estimate of the long-term death toll from the nuclear incident) the number of the nuclear accident.
Why was the death toll from Chernobyl so much higher than Fukushima?
Chernobyl and Fukushima are the only two disasters to receive a level 7 (the maximum classification) on the International Nuclear Event Scale. But why is the upper estimate of deaths from Chernobyl almost fifty times higher than that of Fukushima?
There are a couple of factors which are likely to have played a key role here. The first of these concerns the technical functionality and safety measures of the respective nuclear facilities. Chernobyl occurred 25 years prior to Fukushima; it was the first instance of a nuclear accident at this scale. From a technical perspective, the nuclear reactors at Chernobyl were poorly designed to deal with such a scenario. Its fatal RBMK reactor had no containment structure, allowing radioactive material to spill into the atmosphere (in contrast, Fukushima’s reactors had steel-and-concrete containment structures, although it’s likely that at least one of these were also breached). Crucially, the cooling systems of both plants worked very differently; at Chernobyl, the loss of cooling water as steam actually served to accelerate reactivity levels in the reactor core, creating a positive feedback loop towards fatal explosion (the opposite is true of Fukushima, where the reactivity reduces as temperatures rise, effectively operating as a self-shutdown measure).
These technical differences undoubtedly played a role in the relative levels of exposure from both events. However, the governmental response to both events is also likely to have played a crucial role in the number of people who were exposed to high levels of radiation in the days which followed. In the case of Fukushima, the Japanese government responded quickly to the crisis with evacuation efforts extending rapidly from a three kilometre (km), to 10km, to 20km radius whilst the incident at the site continued to unfold. In comparison, the response in the former Soviet Union was one of denial and secrecy.
It’s reported that in the days which followed the Chernobyl disasters, residents in surrounding areas were uninformed of the radioactive material in the air around them. In fact, it took at least three days for the Soviet Union to admit an accident had taken place, and did so after radioactive sensors at a Swedish plant were triggered from dispersing radionuclides. It’s estimated that the delayed reaction from the Soviet government and poor precautionary steps taken (people continued to drink locally-produced, contaminated milk, for example) led to at least 6,000 thyroid cancer cases in exposed children.
Whilst prevention, and ultimately containment (which are predominantly technical issues), are crucial to the safety of nuclear energy production, these two events also highlight the importance of political governance and response in the aftermath of such disasters.
Risk of nuclear in context
The potential risks of nuclear energy are real: in both Chernobyl and Fukushima, deaths occurred as a result of direct nuclear impacts, radiation exposure and psychological stress. Nonetheless, of the two largest nuclear disasters, the death toll was of the order of tens of thousands in one, and thousands in the latest. Arguably still too many, but far fewer than the millions who die every year from impacts of other conventional energy sources.
As covered in a separate blog post on the relative safety of energy sources, the comparatively low death toll from nuclear energy (resulting in 442 times fewer deaths relative to brown coal per unit of energy, even with radioactive exposure deaths included) is largely at-odds with public perceptions, where public support for nuclear energy is often low as a result of high safety concerns. The key distinction here is that nuclear risk is generally focused within low-probability, high-impact single events in contrast to air pollution impacts which provide a persistent background health risk.