Fukushima Daiichi Nuclear Power Station

Fukushima Daiichi Nuclear Power Station. Juan Carlos Lentijo, team leader for an IAEA mission to review Japan's plans and work to decontaminate the Fukushima Daiichi Nuclear Power Station. Credit: Flickr/CC BY-NC-ND 2.0

On the eve of 25th of April 1986, workers at the Chernobyl Nuclear Power Plant in Ukraine were preparing reactor number 4 for maintenance shut-down. It was to be a night they – and the rest of the world – would never forget, as poorly designed equipment and a series of errors led to the most disastrous nuclear accident in history.

”We all gathered in the control room,” plant worker Sergei Gazin recalled later. “The officer in charge of safety for the shift came in and stood in the middle of the room. He told us that all his instruments for reading radiation levels had already reached the limits of what they could measure”.

According to official figures, 30 nuclear and rescue workers died as a direct result of the accident – the majority from acute radiation sickness.

Almost 25 years later, on 11th of March 2011, the Fukushima Daiichi Nuclear Power Plant was hit by a tsunami, triggered by a magnitude 9.0 earthquake off the east coast of Japan. The flooding shut down its emergency cooling systems, triggering the most serious nuclear accident since Chernobyl.

Partly as a result, the safety of nuclear power – and the effects of such accidents on our lives and health – has long been an area of concern for many.

Today, 30 years after Chernobyl and five years after Fukushima, we’re taking a look back at the impact of these two nuclear accidents. How many people were exposed to radiation as a result? What have they taught us about radiation-linked cancers? And have they helped make nuclear power safer?

Chernobyl and Fukushima – not the same

Fukushima and Chernobyl are the only Level 7 nuclear events to date – the highest category on the International Nuclear Event Scale. Both received worldwide media attention, but they were very different indeed.


Chernobyl. Credit: Flickr/CC BY 2.0

Chernobyl was down to a combination of human error and poor reactor design, causing a sudden, explosive release of large amounts of radioactive material into the atmosphere over a short period of time.

Fukushima, on the other hand, was brought about by a natural disaster, and the resulting damaged cooling systems led to a comparatively slow release of radioactive material over several days (even though there were later explosions) – considerably less radioactive material than Chernobyl.

And the differences don’t end there. The emergency responses that followed these events were also hugely different.

In Chernobyl, residents who lived near the plant were only evacuated a day after the event. By this time, they’d already been exposed to radioactivity released during the explosion.

By contrast, residents near the stricken Fukushima power plant were ordered to evacuate within hours of the cooling systems failing, well before the subsequent explosions on 12th, 14th and 15th of March that released radioactive material into the atmosphere. And Chernobyl remains the only nuclear accident with any immediate radiation-related fatalities in the days following the event.

But what actually happens in a nuclear accident?

No two nuclear accidents are exactly the same, but Fukushima and Chernobyl both had one key feature – a massive build-up of steam inside the power stations’ cooling systems triggering explosions which then released water-vapour into the air, carrying two very different types of radioactive compounds: iodine-131 and caesium-137.

Radioactive iodine decays quickly – it has a half-life of 8 days, meaning that, every 8 days, the level of radiation halves. Caesium on the other hand hangs around for a very long time – it has a much longer half-life – 30 years.

Since both radioactive elements can be carried many miles by the wind, they both have the potential to cause harm – in one of two ways.

The first seems fairly obvious – by being near radioactive compounds in the environment, humans and other animals can be exposed from the outside-in, as radiation penetrates their skin.

The second is potentially more serious – by breathing contaminated air or dust particles, or by consuming contaminated water or food, we can be exposed internally. This allows the radiation to damage internal organs and systems.

So how did these different factors – the two types of radiation, and two types of exposure – affect human health after Chernobyl and Fukushima?

Putting radiation into context

One of the things that can seem scariest about radioactivity is that it’s invisible – you can’t see it, smell it or hear it (unless you happen to have your very own Geiger counter lying around). And one of the biggest concerns people have after a nuclear accident is cancer.

Ionising radiation – the type of radiation emitted by iodine and caesium – is a known cause of cancer, since it has sufficient energy to damage the genetic material (DNA) inside our cells – it’s this damage that can lead to cancer.

But it’s important to remember that all of us are constantly exposed to low levels of ionising radiation from natural sources in our environment. Most of this comes from a gas called radon, which leaks out of the earth’s crust at a steady rate – but some of it also comes from trace levels of radioactive elements in the food we eat, the water we drink, and from cosmic rays from space.

Thankfully, we’ve evolved sophisticated repair machinery to be able to tolerate this natural, unavoidable exposure – most of the time, it doesn’t cause us any significant harm.

But artificially-created higher levels of radiation – for example from X-rays or nuclear power plants – can be harmful, so they’re very tightly regulated. People who work in nuclear industries, or in medical centres, have to follow strict safety procedures and some even have to wear personal exposure monitors.

Radiation after nuclear accidents

Obviously, the radiation released after a nuclear accident means it can be difficult to know who in the surrounding area has been exposed to it. So researchers have to rely on estimates drawn from information about a person’s whereabouts and the levels of contamination in those areas, and they usually use a worst case scenario approach to ensure they over- rather than under-estimate any risk.


Fukushima Daichi Nuclear Power Station. Credit: Flickr/CC BY-SA 2.0

Reassuringly, such research has estimated that, following the Chernobyl and Fukushima accidents, radiation levels to the public weren’t actually as high as many initially feared.

While rescue and clean-up workers in Chernobyl did receive relatively high doses of radiation, members of the public who had been in the most contaminated areas when the plant meltdown took place were only exposed to about as much extra ionising radiation over the first 20 years following the accident as they’d get from three whole body CT scans. And in the case of Fukushima, estimates suggest most evacuees will be exposed to less ionising radiation in the 10 years following the accident than they would get from a single whole body CT scan.

So although these two nuclear accidents were very serious events, they only exposed members of the public to relatively low levels of radiation on top of what they’d get going about their normal lives – particularly in Fukushima, where the emergency response was appropriate and timely.

This exposure can be further reduced by washing down buildings and scraping away topsoil and plants. This has been done in some areas around Fukushima, where radiation levels since the accident have been reduced and some people have even been allowed to return to their homes.

So what about cancer risk?

In 2008, the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) looked at all the evidence and data on newly diagnosed cancers from areas affected by Chernobyl and concluded that, apart from thyroid cancer in those exposed as children and leukaemia in rescue and clean-up workers, there hadn’t been a detectable increase in other types of cancer (you can read their full report here).

“Although those exposed as children and the emergency and recovery workers are at increased risk of radiation-induced effects”, UNSCEAR concluded, “the vast majority of the population need not live in fear of serious health consequences due to the radiation from the Chernobyl accident”.

The best estimates we have predict that Chernobyl could eventually result in up to around 4000 cancer deaths in the 600,000 people exposed to the highest levels of radiation, mostly the people involved in the recovery and clean-up work, who received very high doses.

But for the general public, the evidence suggests it’s not actually cancer that’s been the most serious public health consequence of the accident – it’s the mental health impact and worry due to a lack of accurate information.

A huge tragedy and a chance to learn

As is so often the case with accidents, they’re not just tragic events – they’re also opportunities to discover what went wrong, and learn how to avoid the same thing from happening again.

For example, research linked the increase in thyroid cancer observed after Chernobyl to radioactive iodine from contaminated milk children had drunk. This built up in their thyroid glands, increasing the chances of thyroid cancer.

Understanding how children were exposed after Chernobyl led to better emergency protocols for nuclear accidents like Fukushima. There, residents were quickly provided with stable iodine supplements to reduce the amount of radioactive iodine their bodies could absorb, and people were advised not to consume milk, water or food from the region – so exposure was kept to a minimum.

Thanks to what was learnt following Chernobyl, experts don’t expect to see a big increase in any type of cancer at Fukushima. “The doses to a vast majority of the population in Fukushima were not high enough to expect to see any increase in incidence of cancer and health effects in the future.” explains Japanese researcher Professor Shinichi Suzuki, director of thyroid examination in Fukushima.

But there’s always more to learn, and when people’s health is involved it’s vital to sit up and pay attention, so the Japanese government launched the Fukushima Health Survey, to assess behaviour after the accident, and health checks. This is helping researchers to estimate how much ionising radiation a person was exposed to – and over time it will allow them to see what, if any, effects this has on people’s health.

But it’s important to keep in mind that this kind of increased surveillance can also mean that more cancers are found – simply because we’re looking for them – including cancers that would never have caused harm in someone’s lifetime – this is called overdiagnosis. And thyroid cancer seems particularly prone to overdiagnosis. “The thyroid cancers identified so far [in the Fukushima Health Survey] are unlikely to be due to radiation exposure, and are more likely to be the result of screening using highly sophisticated ultrasound techniques”, says Professor Suzuki.

So while there appears to be a rise in the number of thyroid cancers found in Fukushima, it’s difficult to tell how many of these are really due to radiation and how many are just found as a result of the increased screening. It’s something researchers are still trying to disentangle.

So what does it all mean?

30 years after Chernobyl and five years after Fukushima, we now know a whole lot more about nuclear safety.

Equipment, procedures and emergency protocols have all improved, as has data collection – and so far it seems that for the general population at least, with the exception of thyroid cancer, cancer risks following nuclear accidents don’t actually rise by as much as one might expect.

Jana Witt is a health information officer at Cancer Research UK