Nuclear energy is an important source of low-carbon energy. But, there is strong public opposition to it, often because of concerns around safety.
These concerns are often sparked by memories of two nuclear accidents: the Chernobyl disaster in Ukraine in 1986, and Fukushima in Japan in 2011.1
These two events were by far the largest nuclear accidents in history; the only disasters to receive a level 7 (the maximum classification) on the International Nuclear Event Scale.
How many people died in these nuclear disasters, and what can we learn from them?
How many died from the nuclear accident in Chernobyl?
In April 1986, the core of one of the four reactors at Chernobyl nuclear plant, in Ukraine, melted down and exploded. It was the worst nuclear disaster in human history.
There are several categories of deaths linked to the disaster – for some we have a good idea of how many died, for others we have a range of plausible deaths.
30 people died during or very soon after the incident.
Two plant workers died almost immediately in the explosion from the reactor. Overall, 134 emergency workers, plant operators, and firemen were exposed to levels of radiation high enough to suffer from acute radiation syndrome (ARS). 28 of these 134 workers died in the weeks that followed, which takes the total to 30.2
A point of dispute is whether any more of the 134 workers with ARS died as a result of radiation exposure. In 2008, several decades after the incident, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) published a large synthesis of the latest scientific evidence.3 It reported that a further 19 ARS survivors had died by 2006. But many of these deaths were not related to any condition caused by radiation exposure. Seven were related to diseases not related to cancers including tuberculosis, liver disease, and stroke; six were from heart attacks; one from a trauma incident; and five died from cancers.4 It’s difficult to say how many of these deaths could be attributed to the Chernobyl accident – it’s not implausible it played a role in at least some of them, especially the five cancer deaths.
Most of the population was not exposed to levels of radiation that would put them at risk of negative health impacts. However, the slow response to the disaster meant that some individuals were exposed to the short-lived radionuclide Iodine-131 (131I) through the contamination of milk. Radioactive fallout settled on pasture grass across the region; this contaminated milk supplies and leafy vegetables that were consumed in the days immediately after the incident.
This exposure to 131I has not been linked to increased cancer risk in the adult population, but several studies have shown an increased incidence of thyroid cancer in those who were children and adolescents around this time. Figuring out how many cases of thyroid cancer in this young population were caused by the accident is not straightforward. This is because there was a large increase in screening efforts in the aftermath of the disaster. It’s not uncommon for thyroid cancer cases to go undetected – and have no negative impact on an individual’s life. Increased screening, particularly in child populations, would result in finding many cases of cancer that would normally go undetected.
In 2018, UNSCEAR published its latest findings on thyroid cancers attributed to the Chernobyl disaster. Over the period from 1991 to 2015, there were 19,233 cases of thyroid cancer in patients who were younger than 18 at the time of the disaster across Ukraine, Belarus, and exposed regions of Russia. UNSCEAR concluded that around one-quarter of these cases could be linked to radiation exposure. That would mean 4,808 thyroid cancer cases.5
By 2005, it was reported that 15 of these thyroid cancer cases had been fatal.6 However, it was likely that this figure would increase: at least some of those still living with thyroid cancer will eventually die from it.
It’s therefore not possible to give a definitive number, but we can look at survival rates and outcomes to get an estimate. Thankfully the prognosis for thyroid cancer in children is very good. Many patients that have undergone treatment have seen either a partial or complete remission.7 Large-scale studies report a 20-year survival rate of 92% for thyroid cancer.8. Others show an even better prognosis, with a survival rate of 98% after 40 years.9
If we combine standard survival rates with our number of radiation-induced cancer cases – 4,808 cases – we might estimate that the number of deaths could be in the range of 96 to 385. This comes from the assumption of a survival rate of 92% to 98% (or, to flip it, a mortality rate of 2% to 8%).10 This figure comes with significant uncertainty.
Finally, there has been significant concern about cancer risks to the wider population across Ukraine, Belarus, Russia, and other parts of Europe. This topic remains controversial. Some reports in the early 2000s estimated much higher death tolls ranging from 16,000 to 60,000.11 In its 2005 report, the WHO estimated a potential death toll of 4,000.12 These estimates were based on the assumption that a large number of people were exposed to elevated levels of radioactivity, and that radioactivity increases cancer risk, even at very low levels of exposure (the so-called ‘linear no-threshold model’ of radiation exposure).
More recent studies suggest that these estimates were too high. In 2008, the UNSCEAR concluded that radioactive exposure to the general public was very low, and that it does not expect adverse health impacts in the countries affected by Chernobyl, or the rest of Europe.13 In 2018 it published a follow-up report, which came to the same conclusion.
If the health impacts of radiation were directly and linearly related to the level of exposure, we would expect to find that cancer rates were highest in regions closest to the Chernobyl site, and would decline with distance from the plant. But studies do not find this. Cancer rates in Ukraine, for example, were not higher in locations closer to the site14 This suggests that there is a lower limit to the level at which radiation exposure has negative health impacts. And that most people were not exposed to doses higher than this.
To summarize the previous paragraphs:
- 2 workers died in the blast.
- 28 workers and firemen died in the weeks that followed from acute radiation syndrome (ARS).
- 19 ARS survivors had died later, by 2006; most from causes not related to radiation, but it’s not possible to rule all of them out (especially five that were cancer-related).
- 15 people died from thyroid cancer due to milk contamination. These deaths were among children who were exposed to 131I from milk and food in the days after the disaster. This could increase to between 96 and 384 deaths, however, this figure is highly uncertain.
- There is currently no evidence of adverse health impacts in the general population across affected countries, or wider Europe.
Combined, the confirmed death toll from Chernobyl is less than 100. We still do not know the true death toll of the disaster. My best approximation is that the true death toll is in the range of 300 to 500 based on the available evidence.15
How many died from the nuclear accident in Fukushima?
In March 2011, there was an accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. This accident was caused by the 2011 Tōhoku earthquake and tsunami – the most powerful earthquake recorded in Japan’s history.
Despite it being such a large event, so far, only one death has been attributed to the disaster. This includes both the direct impact of the accident itself and the radiation exposure that followed. However, it’s estimated that several thousand died indirectly from the stress and disruption of evacuation.
No one died directly from the disaster. However, 40 to 50 people were injured as a result of physical injury from the blast, or radiation burns.
In 2018, the Japanese government reported that one worker has since died from lung cancer as a result of radiation exposure from the event.
Over the last decade, many studies have assessed whether there has been any increased cancer risk for local populations. There appears to be no increased risk of cancer or other radiation-related health impacts.
In 2016, the World Health Organization noted that there was a very low risk of increased cancer deaths in Japan.16
A more difficult question is how many people died indirectly through the response and evacuation of locals from the area around Fukushima. Within a few weeks of the accident more than 160,000 people had moved away, either from official evacuation efforts or voluntarily from fear of further radioactive releases. Many were forced to stay in overcrowded gyms, schools, and public facilities for several months until more permanent emergency housing became available.
The year after the 2011 disaster, the Japanese government estimated that 573 people had died indirectly as a result of the physical and mental stress of evacuation.17 Since then, more rigorous assessments of increased mortality have been done, and this figure was revised to 2,313 deaths in September 2020.
These indirect deaths were attributed to the overall physical and mental stress of evacuation; being moved out of care settings; and disruption to healthcare facilities.
It’s important to bear in mind that the region was also trying to deal with the aftermath of an earthquake and tsunami: this makes it difficult to completely separate the indirect deaths related to the nuclear disaster disruptions, and those of the tsunami itself.
Combined, the confirmed death toll from Fukushima is therefore 2,314.
What can we learn from these nuclear disasters?
The context and response to these disasters were very different, and this is reflected in what people died from in the aftermath.
Many more people died from Chernobyl than from Fukushima. There are several reasons for this.
The first was reactor design. The nuclear reactors at Chernobyl were poorly designed to deal with this meltdown scenario. Its fatal RBMK reactor had no containment structure, allowing radioactive material to spill into the atmosphere. Fukushima’s reactors did have steel-and-concrete containment structures, although it’s likely that at least one of these was 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 toward the fatal explosion. The opposite is true of Fukushima, where the reactivity reduced as temperatures rose, effectively operating as a self-shutdown measure.
The second factor was government response. In the case of Fukushima, the Japanese government responded quickly to the crisis with evacuation efforts extending rapidly from a 3-kilometer (km), to a 10-km, to a 20-km radius whilst the incident at the site continued to unfold. In contrast, the response in the former Soviet Union was one of denial and secrecy.
It’s reported that in the days which followed the Chernobyl disaster, 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 by dispersing radionuclides. As we saw above, it’s estimated that approximately 4,808 thyroid cancer cases in children and adolescents could be linked to radiation exposure from contaminated milk and foods. This could have been prevented by an earlier response.
Finally, while an early response from the Japanese government may have prevented a significant number of deaths, many have questioned whether the scale of the evacuation effort – where more than 160,000 people were displaced – was necessary.18 As we see from the figures above, evacuation stress and disruption are estimated to have contributed to several thousand early deaths. Only one death has been linked to the impact of radiation. We don’t know what the possible death toll would have been without any evacuation. That’s why a no-evacuation strategy, if a future accident was to occur, seems unlikely. However, many have called for governments to develop early assessments and protocols of radiation risks, the scale of evacuation needed, and infrastructure to make sure that the disruption to those that are displaced is kept to a minimum.19
Nuclear is one of the safest energy sources
No energy source comes with zero negative impact. We often think of nuclear energy as being more dangerous than other sources because these low-frequency but highly-visible events come to mind.
However, when we compare the death rates from nuclear energy to other sources, we see that it’s one of the safest. The numbers that have died from nuclear accidents are very small in comparison to the millions that die from air pollution from fossil fuels every year. As the linked post shows, the death rate from nuclear is roughly comparable with most renewable energy technologies.
Since nuclear is also a key source of low-carbon energy, it can play a key role in a sustainable energy mix alongside renewables.
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Update: This article was first published in 2017. It was updated in June 2022 based on more recent data published by UNSCEAR in 2018, and updated figures from the Japanese government in 2020.