Friday, April 8, 2016


Thirty years ago this month, on 26 April 1986, Reactor 4 at the Soviet-run Chernobyl Nuclear Power Plant exploded when operators undertook a safety experiment. The nuclear accident remains the worst to date, although debate and controversy surround the extent and types of damage incurred—from cancers to ecological impact to the effects of mass evacuations on communities and individuals.

Today the site, some 100 km north of Ukraine's capital of Kiev and near the border with Belarus, is buzzing with activity. Two major construction projects are under way: a "new safe confinement" structure for the destroyed reactor, which remains highly radioactive, and a concrete spent-fuel storage facility. In addition, Ukrainian authorities are overseeing the decommissioning of the plant's other three reactors, the last of which stopped operating in 2000; the process will take decades and cost billions of dollars. Much of the exclusion zone, the area within a roughly 30 km radius around the power plant, is abandoned and overgrown.

Enough time has passed that about half of the released cesium-137 and strontium-90 has decayed, but half remains; plutonium and other long-lived nuclides will continue to contaminate the area for millennia. Radiation levels in the exclusion zone soil vary, with highs mostly around 8–10 MBq/m2 but at some spots reaching 200 MBq/m2, according to Sergiy Dubchak, an associate professor at the State Ecological Academy of Postgraduate Education and Management in Kiev. Staying in areas with 8–10 MBq/m2 for a year corresponds to an annual exposure of about 175 mSv, he says. That's roughly equivalent to a dozen CT scans. The exposure in the worst spots would be equivalent to nearly one scan a day.
The city of Pripyat, just 3 km from the disaster site, remains abandoned. And the town of Chernobyl, about 15 km from the power plant, provides temporary housing for workers on the building projects. 

A pilot project to grow canola for biofuel started a few years ago; the crops would both produce fuel and, by accumulating radioactive nuclides, help detoxify the soil. There is talk about turning part of the exclusion zone into a wildlife preserve. A couple hundred people returned to live in their homes within the exclusion zone. And the zone has become a popular destination for disaster tourism.

Over the past decade or so, and especially since the 2011 nuclear accident in Fukushima, Japan (see Physics Today, November 2011, page 20), research has intensified in matters related to nuclear accidents, and in preparedness for and response to them. "The lessons of Chernobyl were not internalized in the West until Fukushima," says Jan Beyea, chief scientist at the Lambertville, New Jersey–based Consulting in the Public Interest. Beyea served on a National Academy of Sciences committee that in 2014 reported on lessons learned from the Fukushima nuclear accident. "You have more attention now to what can be learned," he says.
A new sarcophagus 
The concrete and steel structure currently enclosing the destroyed reactor at Chernobyl was completed quickly—206 days after the accident. It had a design lifetime of 25 years. Today the protective structure is crumbling; its roof partly collapsed in 2013. The new confinement sarcophagus, a 29 000-ton steel arch that is roughly 110 m tall, 160 m long, and 260 m wide at the base, is scheduled to be installed next year. It is designed to stop incursions of water and snow, prevent release of radioactivity, and provide a shelter for decommissioning the destroyed reactor; it will house two cranes that can each lift up to 50 tons. 
 A new safe confinement sarcophagus (left) is being built about 300 meters from the destroyed reactor (right); the sarcophagus is scheduled to be slid over the reactor next year. The memorial was erected a few years after the disaster.

According to the European Bank for Reconstruction and Development (EBRD), the shelter cost comes to €1.5 billion ($1.6 billion), plus €600 million in associated costs, such as preparing the site, installing monitoring and surveillance systems, and constructing a changing facility for workers. The European Commission is contributing €450 million; of the 45 countries that are pitching in, the US is covering €295 million, and Ukraine, Germany, France, the UK, and Japan are putting in amounts ranging from €185 million to €85 million.

The other major project at the site is a storage facility for the plant's spent fuel. The estimated cost is €400 million, according to the EBRD. Some 20 000 spent-fuel assemblies need to be moved to dry storage from their current pools, where they are starting to corrode. After years of delays, design problems, and a change in contractors, the facility is supposed to be completed late this year.

For a long time, the prevailing view in the West was that a Chernobyl-scale event couldn't happen there. The thinking was that the accident was due to a faulty Russian reactor design, poor training, and a corrupt Soviet system, says Sonja Schmid, a faculty member in science and technology studies at Virginia Tech. But, she says, the Soviets "were competitive and at the same level [as the West] in skills and expertise, so why would they choose a reactor design that was manifestly bad?"
"We will have more accidents"
After the Fukushima disaster, the dismissive logic no longer held up. "We will have more accidents. What do we do?" she says. "Fukushima has changed a lot to the better, in terms of learning from both accidents."
As examples, Schmid notes that after the Fukushima disaster, many countries conducted risk and safety assessments of their nuclear reactors. And policymakers and power-plant regulators in different regions intensified talks about coordinating responses to any future accident. Last year France instituted a program whereby reactor operators are trained to respond to a nuclear emergency.

One lesson learned from both the Chernobyl and Fukushima disasters is to weigh the risks of evacuation against those of radiation, says Clemens Walther, director of the Institute for Radioecology and Radiation Protection (IRS) at Leibniz University in Hanover, Germany. "The evacuation should have been faster at Chernobyl. It was done better by the Japanese." Still, better preparation, including for evacuating the elderly, sick, children, and their caretakers, would reduce fatalities. "A lot of elderly people died after the evacuation; for them there was no radiation-induced cancer risk due to old age."
Uncertain consequences

Among the first responders to the Chernobyl explosion, the official immediate death toll was 28, with another 134 suffering acute radiation syndrome. The total number of people who have or will become sick in the ensuing years from radiation exposure is impossible to pin down; estimates range from a few thousand to hundreds of thousands.

The best-documented sickness caused by Chernobyl is cancer of the thyroid gland, which takes up iodine to make metabolism-regulating hormones. Even though it was known that nonradioactive iodine could saturate the thyroid and minimize uptake of radioactive iodine, iodine was not efficiently distributed after either Chernobyl or Fukushima. In the 20 years after Chernobyl, more than 6000 cases of thyroid cancer in children and adolescents were attributed to radiation exposure, according to the United Nations Scientific Committee on the Effects of Atomic Radiation. Numbers are hard to come by for other health problems. Indeed, says Beyea, "the changes in occurrence are expected to be small compared to background, but you can project that there will be some excess cancers."
Kate Brown, a science historian at the University of Maryland, Baltimore County, is among those who have reported increased medical problems of many sorts due to radiation exposure from Chernobyl. Because medicine was socialized in the Soviet Union, state clinics treated everyone, and they sent quarterly reports to headquarters, she says. "They had always done that, and they continued." In sifting through doctors' notes in the Ukrainian archives, she found patterns that started with chronic tonsillitis, gastritis, ulcers, and bronchitis. Solid cancers appeared later—of the thyroid, throat, lip, oral cavities, and stomach—followed by reproductive issues, including a big jump in birth defects, premature births, and babies who died within six months.

Such findings remain controversial. Walther, for example, says there is little evidence of "statistically meaningful hereditary effects among Chernobyl victims" and warns against confusing the effects of radiation with effects uncovered by increased screening and malnutrition.
Mental health matters
The psychological impact of radiation exposure is increasingly viewed as one of the greatest health consequences of Chernobyl and Fukushima. "People feel sick, and believe their ills are caused by radiation exposure, even when their actual exposure was very low," says Johan Havenaar, a Dutch psychiatrist who in the decade or so after Chernobyl focused his research on Ukraine and Belarus. Psychiatrists call it the "nocebo" effect: If you believe your health is in danger, you feel worse. Such feelings were compounded by the stress, disruption, and economic losses caused by moving, and by losing jobs, livelihood, and community.

After the collapse of the Soviet Union in 1991, responsibility for the affected areas ceased being centralized. Havenaar recalls how the different radiation levels for later evacuations set by the different countries added to the contradictions, confusion, and concern.

Even if the radiation exposure does not cause physical health problems, mental health matters. "It affects people's daily lives. It's linked to physical health, mortality, and the ability to work," says Havenaar's colleague Evelyn Bromet of Stony Brook University. "And if you don't deal with things, they fester." Awareness about mental health is growing, she says—in part, because of post-traumatic stress disorder and suicides among soldiers from recent wars and emergency personnel who responded to the 2001 World Trade Center attacks. "A lot of things have contributed. There is now a broader understanding of common disorders like depression," she says.
Ecological studies

Timothy Mousseau, a population biologist at the University of South Carolina, says that when he and his colleague Anders Møller of the Université Paris–Sud first began fieldwork in the Chernobyl exclusion zone more than a decade ago, they had heard that everything was fine and the animals were thriving. They started looking for signs of adaptation. "We thought maybe female birds would change how they allocated antioxidants to eggs," says Mousseau. But they found no evidence of adaptation. In fact, he says, "we realized they live half as long as they normally would."
In the ensuing years, Mousseau and Møller have studied birds, insects, rodents, and larger mammals around both Chernobyl and Fukushima. Living in a radioactive area, says Mousseau, "causes tumors, cataracts, reproductive problems, smaller brains." In their studies, he says, he and Møller found no threshold below which there was no health effect. Moreover, he adds, animals living in the wild are more sensitive to effects of ionizing radiation than lab animals. He also points to the finding that cesium-137 is not migrating as deep into the soil as expected. The isotope gets stuck in the top 5–10 cm of soil, which prolongs its ecological impact.
It's rare for wild birds to have tumors, but population biologists observe them in 2–3% of birds near Chernobyl.
Since Fukushima, Mousseau says, "there has been a tremendous investment in Japan in radionuclide movement through the biosphere." A spillover effect, with increased funding for research at Chernobyl, mostly focused on engineering and geochemistry, has also occurred, he adds.
Public trust

So what should be done differently in the event of a future nuclear accident? In preparation, says Havenaar, "doctors in disaster areas should receive training packages, to remind them how radiation works, what it can cause, what it can't, and about the psychological effects."

Bromet wants to see risk conveyed more effectively. She points to radiation scientists, saying they need to communicate better with the public. Contradictory statements by scientists and government authorities breed fear and lack of trust, she says.

The public's trust of government and nuclear industry representatives is low when it comes to information related to a disaster. "The authorities know radioactivity scares people, so they are cautious about what they say. And that can be perceived as them keeping the truth from the people," says Beyea. One lesson learned from Chernobyl, he says, is that public trust matters. "The chance of a major nuclear accident is small. To efficiently allocate emergency-planning resources, you need an all-hazards approach, to be better prepared for everything—chemical releases, terrorists, …"

Bringing in experts and tools that are perceived as impartial is one approach to winning public trust. In the wake of Chernobyl, Germany installed a network of 1800 radiation monitors around the country; their readings are now accessible online. Following the Fukushima nuclear accident, members of the public were provided with Geiger counters to map radioactive hotspots. And researchers in Japan developed and distributed a photodiode radiation detector that plugs into the microphone port of a smartphone for data logging and display.

To reassure and protect the public, Japan is monitoring crops from the Fukushima region. And the Fukushima Ambassadors program brings international students for visits to learn about the area and the accident. The program reminds locals that they have not been forgotten and is intended to serve as an antidote to fears of being in the area. 
International students visit Fukushima for two-week stints as part of a program to learn about the area and show locals they are not fearful of the radiation, and that their nuclear disaster has not been forgotten. 
Unsurprisingly, nuclear accidents elicit a backlash of antinuclear sentiment. That worries people who hold that nuclear power is a necessary part of the energy mix needed to combat climate change. Says Georg Steinhauser of Leibniz University's IRS, "It's important not to let accidents like Chernobyl and Fukushima prevent the development and implementation of safer reactors."
© 2016 American Institute of Physics


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