It was the world's worst nuclear disaster, but have we learned enough from Chernobyl? Becky Allen reports
The first official announcement of the Chernobyl nuclear disaster was an understatement of epic proportions. “An accident has occurred at the nuclear power plant at Chernobyl, north of Kiev in the Ukraine,” said the Soviet council of ministers. “The accident has damaged the atomic reactor; there were some casualties.”
The statement confirmed what some already knew: that somewhere in the northern hemisphere a massive radiation leak had occurred. In the afternoon of Sunday 27 April 1986, more than 24 hours before the Soviet announcement, the Swedish National Defence Research Institute recorded a marked rise in radiation over Stockholm.
Registering similar readings next morning, Forsmark nuclear power station, 100km north of the Swedish capital Stockholm, declared a yellow alert, shut down the reactor and evacuated the plant. Within hours, high levels of atmospheric radiation were reported across Denmark, Finland and Norway.
The causes of the Chernobyl disaster can be traced to the night of 25 April. Engineers at the plant’s number four reactor were conducting an experiment to find out how well the cooling pump system would work if the auxiliary electricity supply failed. Despite struggling to stabilise the reactor under the low power conditions they had created for the experiment the engineers continued with the tests. At 1.23am on the morning of 26 April – with the reactor’s automatic shutdown systems intentionally disabled – power levels surged and the reactor overheated.
At 1.24am, after attempts to control the reactor failed, two explosions blew off the reactor’s roof and released its contents. As air was sucked in, it ignited and began to burn. The blast killed one worker, pump operator Valeri Khodemchuk; a second, Vladimir Shashenok, died later in hospital having been doused in boiling water and radioactive steam from burst pipes.
As firefighters tried to control the blaze, which burned for nine days, helicopters piloted by veterans of the Afghan war negotiated pylons and the reactor chimney to dump thousands of tonnes of sand, clay, boron carbide and lead on to the reactor. Three kilometres away, the town of Pripyat was evacuated of its 40,000 residents.
Some estimates put the amount of radiation released from Chernobyl at 100 times more than the atomic bombs dropped on Hiroshima and Nagasaki at the end of the second world war. Among the radioactive gases and particles released by the blast were caesium-131, caesium-137, strontium-90, plutonium-238 and americium-241. Caesium-137, which has a half-life of 30 years, is still measurable in the soil and food in many parts of Europe.
In 2006, a report by UN agencies said that 518,000km2 of Europe had been blanketed with radioactive fallout and that five million people were exposed – and 100,000 remained exposed – to radiation from their food and the environment.
Thousands of emergency and recovery workers or “liquidators” involved in the cleanup in 1986 and 1987 received radiation doses of more than 100 millisieverts (mSv) – 50 times the radiation the average human is exposed to over a year (2mSv) and the level at which long-term cancer risks increase. A further 270,000 people in the severely contaminated zone received doses upwards of 50mSv. According to estimates from the World Health Organisation (WHO), five million residents in low-contamination zones around Chernobyl received radiation doses of 10–20mSv in the 20 years from 1986.
More controversial – and contested – have been figures on the health effects of Chernobyl. The impact on those most heavily exposed is most certain. According to UNSCEAR, the UN scientific committee on the effects of atomic radiation, of the 600 people working at the plant on the day of the disaster 134 suffered radiation sickness; 28 died within three months and a further 19 between 1987 and 2004.
Outside the plant, the clearest evidence of Chernobyl’s health impacts is damage to the thyroid gland, which absorbs radioactive iodine. By 2006, more than 6,000 cases of thyroid cancer had been diagnosed in those who were children at the time of the disaster. Although only nine have died, experts agree thyroid cancer rates will continue to increase. While levels of leukaemia do not appear to have risen in the general population, the WHO says: “Recent investigations suggest a doubling of the incidence of leukaemia among the most highly exposed Chernobyl liquidators.”
A major report issued jointly in 2006 by the WHO, the UN development programme and the International Atomic Energy Agency (IAEA) predicted that Chernobyl would eventually claim 9,000 lives – 4,000 among the three most exposed groups and 5,000 among the five million people who live Belarus, parts of the Russian Federation and Ukraine. About 45% of the caesium released by the explosion was deposited in states of the former USSR. Belarus was most affected with more than 23% of its land contaminated. Greenpeace and other anti-nuclear groups claim the final death toll will be significantly higher than 9,000.
Chernobyl’s environmental and associated economic effects are less controversial. Agriculture and forestry in the region were hard hit: some 784,320 ha of farmland were taken out of cultivation and timber production was halted in 694,200 ha of forest.
Restrictions were imposed on hunting and farming in many parts of Europe. High levels of caesium-contamination were found in reindeer in the Arctic and sub-Arctic areas of Finland, Norway, Russia and Sweden, and in fish from German and Scandinavian lakes. The second Chernobyl forum report concluded that the water and fish in lakes with no outflowing streams, such as the Kozhanovskoe in Russia, would remain contaminated with caesium-137 for decades.
The German government paid $550,000 in 2009 to hunters whose wild boar meat was too contaminated to sell; in some areas radiation in the meat was more than 11 times the safe limit. And in the UK, more than four million sheep on 9,800 farms were placed under restrictions, the last of which were lifted only in 2012.
The disaster also had consequences for wildlife. Some claim that flora and fauna are thriving in the exclusion zone around the reactor; that there are more wolves, lynx, przewalski’s horses, elk, wild boar, deer, eagles and bats than before the disaster. Others disagree, aying that wildlife numbers are increasing simply because there is so little pressure from human activity in the area, and that radiation is having a significant effect on the local environment.
Dr Anders Moller, of the University Paris-Sud, and Professor Tim Mousseau, of the University of South Carolina, have spent the past 15 years studying the long-term ecological effects of the Chernobyl disaster, and found evidence of genetic damage in more than 20 species. One of those studied, the barn swallow, seems particularly sensitive to radiation. “We know that they consume much of their antioxidant reserve during the period of migration, so when they arrive back in Chernobyl they seem to be particularly sensitive to contaminants,” explains Mousseau.
Like the debate over the human health impacts of the disaster, discussion over its ecological effects reflect the fact that too little research has been done at Chernobyl since 1986. “Despite the accident happening 25 years ago, there is a dearth of scientific information available, and what is available often isn’t considered if it doesn’t fit into a preconceived view of the effects of radiation. We strongly urge scientists to help break this mold,” Mousseau told Geographical magazine in 2011.
Social and economic disaster
As well as the disaster’s health and environmental impact, its social, economic and mental health effects have been “devastating”, according to former IAEA director Mohamed ElBaradei. Speaking in 2005, he explained: “More than 100,000 people were immediately evacuated, and the total number of evacuees from contaminated areas eventually reached 350,000. While some of these resettlements were essential to reduce the dose of radiation, the experience was of course deeply traumatic for those involved.”
The economic costs are almost impossible to calculate. However, the UN estimates at hundreds of billions of dollars the cost of direct damage, recovery and mitigation, resettlement of evacuees, social and health care, research, monitoring and loss of agriculture and forestry, as well as the cancellation of Belarus’s nuclear power programme.
A major ongoing cost is the construction of a shelter to replace the hastily-built concrete sarcophagus covering reactor four, which is now crumbling. The gigantic new concrete shield – 110m high and weighing 29,000 tonnes – will cost $2 billion and is being funded by 24 nations and the EU. Designed to last 100 years and scheduled for completion in 2015, the structure is being built onsite and will be placed over the existing sarcophagus. The long-term plan is to clean up the site by 2065, almost 80 years after the disaster.
Lessons from Chernobyl
As the world’s worst nuclear disaster, Chernobyl had a major impact on international radiation standards, nuclear safety, emergency response and mitigation procedures. It also affected public and government attitudes towards the industry. According to ElBaradei: “The accident at Three Mile Island had already cast doubt on the ability of nuclear power plant operators to prevent severe accidents. Chernobyl had far greater impact; the accident imprinted itself on public consciousness as proof that nuclear safety was an oxymoron.
“Some countries decided to reduce or terminate further construction of nuclear facilities, and the expansion of nuclear capacity came to a near standstill. It took nearly two decades of strong safety performance to repair the industry’s reputation.”
The Fukushima disaster in 2011 put the industry under the microscope again, with Germany deciding to phase out nuclear power altogether.
ElBaradei believes Chernobyl’s greatest legacy lies in the multilateral approach now taken to such disasters. He describes the 1986 disaster as “a defining moment” in the history of nuclear energy, adding: “The lessons are interwoven with a recurrent theme: namely the importance of international cooperation.” Chernobyl revealed a sharp disparity in nuclear design and operational safety standards, and reminded everyone that nuclear risks transcend national borders.
“Since , international cooperation has become a hallmark of nuclear safety, [resulting in] a body of globally recognised IAEA safety standards,” ElBaradei says. “One of the few positive aspects of Chernobyl’s legacy is today’s nuclear safety regime.”
But at the time of the disaster, the international community failed. “It was the lack of coordination of international efforts in the months and years that followed the Chernobyl accident that helped exacerbate the social effects of the disaster,” ElBaradei argues.
Others warn that vital lessons have not been learned because too little research has been done into Chernobyl’s long-term health and ecological effects. Dr Keith Baverstock, a former health and radiation adviser to the WHO, argues that research has been frustrated by pro- and anti-nuclear campaigners, who have turned debate over Chernobyl’s impact into a battleground. As a result, he says, governments and organisations, such as the IAEA, have missed lessons about responding to nuclear emergencies and communicating with the public.
“[Lobby groups] seek to interpret the effects or absence of effects to their own advantage and are apparently unwilling to find the truth,” he told the British Medical Journal. “Apart from exacerbating the psychosocial effects on those directly affected, this situation has prevented a comprehensive evaluation of the importance of the event to public health.”
On 11 March 2011, a major earthquake off the north-eastern coast of Japan triggered a 15m high tsunami, which disabled the power supply and cooling facilities of three reactors at the Fukushima Daiichi nuclear power plant. All three cores largely melted in days immediately after the tsunami hit, while a fourth unit, which had not been operating at the time of the flooding, later became a problem. Two further units were unaffected.
The earthquake caused no significant damage to the Daiichi plant, with units 1–3 shutting down automatically, as designed. Emergency, diesel-powered generators in the basement turbine buildings started because the earthquake had damaged external power supplies. The first tsunami wave hit the plant 41 minutes after the earthquake – a second hit eight minutes later – and submerged and damaged the seawater pumps, drowned the diesel generators and inundated the electrical switchgear and batteries.
At 7.03pm on 11 March a nuclear emergency was declared, and the next day the evacuation order for the region, initially been set for within 2km of the plant, was extended to 20km.
According to the World Nuclear Association (WNA), which represents the global nuclear profession, the design for the Daiichi plant was based on a potential tsunami height of 3.1m – a height derived from a 1960 Chilean tsunami. The power station was therefore built 10m above sea level, while the seawater pumps were 4m above the sea. Despite subsequent research indicating that earthquakes in the region had triggered tsunamis much higher than 3.1m, and the design basis being revised in 2002 to 5.7m above sea level, no countermeasures were introduced.
In December 2011, a mid- to long-term decommissioning plan for units 1–4 was agreed by the Tokyo Electric Power Company, which operates the stricken plant, and Japanese authorities. The three-phase plan involves:
- Beginning the process of fuel removal from the spent fuel pools within two years. This process began on 18 November 2013.
- Starting to remove fuel debris – the solidified fuels and claddings that melted – within 10 years.
- In 30–40 years, completing the fuel debris removal and the processing and disposal of radioactive waste.
Three Mile Island
At 4am on 28 March 1979, a cooling malfunction caused part of the core to melt in the second of two pressurised water reactors at the Three Mile Island power station near Harrisburg, Pennsylvania, in the US. The reactor, which at the time was almost new, was destroyed and the accident led to a release of some radioactive gas, though not enough to cause any dose above background levels to local residents.
The incident was the result of what the World Nuclear Association describes as a “relatively minor malfunction” in the secondary cooling circuit. This breakdown resulted in the temperature of the primary coolant rising, causing the reactor to shut down automatically. At this point a relief valve failed to close, resulting in much of the primary coolant draining away. As a result, the residual heat in the reactor core was not removed, causing severe damage.
The $973 million cleanup of the damaged nuclear reactor started in August 1979 and ended in December 1993. In 1991, measurements of the fuel remaining in inaccessible parts of the reactor vessel revealed that around 1% remained. The other reactor at Three Mile Island was restarted in 1985 and continues to generate electricity.