The giant confinement building encapsulating the Chernobyl nuclear reactor that exploded nearly 40 years ago is smooth and curved—built with scientific precision. Installed in 2016, the structure was designed to prevent the escape of radiation from the stricken reactor, which is also encased in a smaller concrete sarcophagus. The confinement enshrouds both reactor and sarcophagus and is so massive that if you placed the Statue of Liberty inside it at its center, her torch wouldn’t come close to prodding the ceiling. But like a slightly cracked egg, this gargantuan covering has been violated. It is one of many victims in Russia’s war with Ukraine.
In February, a drone armed with explosives smashed into the confinement, leaving a 15 m2 hole. While some of the damage has been repaired, the building’s radiation-blocking abilities have been compromised, the International Atomic Energy Agency (IAEA) confirmed earlier this month. Importantly, the IAEA also said that radiation levels in the area have not yet changed. But unless more significant repairs are carried out, the specter of a potential leak remains.
Radiation occurs naturally everywhere. It is produced by food you eat, and even by tissues in your own body. Think of it like a grand carnival of subatomic particles—including neutrons, electrons, and photons—that whizz around, always in motion, always present. An invisible world that shadows the world we can see. But the carnival is always changing and, today, we are better positioned than ever to notice fluctuations in radiation that deviate from normal, background levels.
When disaster struck Chernobyl in 1986, a huge cloud of radioactive material spread across much of Europe. It was how the world found out about the accident—when radiation monitors in eastern Sweden detected unusual activity two days after the explosion. In the wake of Chernobyl, many countries including Austria and the UK, installed radiation detectors that constantly monitor for any uptick in radioactivity. Today, some radiation-monitoring networks are run by governments, and yet more are the work of volunteers and researchers. If another major radiation incident were ever to happen, the world would discover it very, very quickly.
“The pandemic I found very terrifying, because there’s not an easy way of detecting the Covid virus,” says Kim Kearfott, professor of nuclear engineering and radiological sciences at the University of Michigan. “I can grab a detector and immediately detect radiation.” On the roof of her university building, Kearfott has an array of radiation sensors. She also has some in her lab. And in her lab’s basement. And in another building nearby. You get the idea.
The project is largely an informal one, sparked by curiosity and an absence of easily accessible public data on environmental radiation levels. “We put [this] into place after the Fukushima nuclear accident,” she says, referring to the 2011 disaster in which a huge tsunami struck the Fukushima Daiichi nuclear power plant in Japan, which ultimately resulted in the release of significant amounts of radiation into the atmosphere.
After Fukushima, Kearfott realized that she and her colleagues had no mechanism for monitoring radiation levels. There are monitoring systems all over the US, she says, but it’s hard to get access to the measurements they gather. “The nuclear plants,” she says, “they don’t like releasing their monitoring data.”
Kearfott’s detectors have picked up occasional, minor fluctuations in background levels in recent years. Hospitals with radiation-emitting equipment, such as positron emission tomography scanners, sometimes release radioactive gases into the atmosphere. “We think we were actually detecting those gases,” says Kearfott.
Kearfott was far from the only one left yearning for environmental measurements of radiation in the wake of Fukushima. At the time, there was a run on detector devices. “There was no real-time monitoring. Most of the systems that were in place…were government, so they were behind closed doors,” says Sean Bonner, cofounder of environmental monitoring non-profit Safecast.
He and collaborators initially helped to design DIY radiation detectors that people could make at home, as well as an online platform that would publish data from these devices worldwide. Today, 14 years on, there are more than 5,000 detectors on the network, which supply information to Safecast’s digital map of radiation levels.
In the early days, as volunteers trudged around the streets of Tokyo, say, taking readings, the Safecast team soon realized that radiation levels varied noticeably even within the same street. “We would see much higher levels in rains off gutters and things,” says Bonner.
Kearfott’s measurements are also affected when the wind blows in certain directions. And rain and snowfall move radiation readings, too. In 2023, ambient gamma radiation levels in Hong Kong rose after heavy rainfall washed radioactive decay products of radon—a radioactive gas that naturally occurs in the Earth’s crust—out of the air and brought those decay products down to ground level. Background radiation levels are typically measured in microsieverts per hour. In Hong Kong, they might usually sit around 0.1 microsieverts per hour, for instance. But the weather and other factors can push measurements around within a range of roughly 0.06 to 0.3.
And a paper published last year explained that, in northern Spain in 2009, powerful storms known locally as Galernas—which feature intense winds and sometimes heavy rainfall—had induced a spike in radon-related radiation big enough to trigger false alarms in the Basque Country gamma ray monitoring network.
Bonner says Safecast has also found instances of tides in coastal areas affecting background levels slightly, as waves alter the distribution of radioactive rocks on beaches.
Today, some countries, such as Poland, publish data from their national radiation-monitoring systems in near-real-time on the open web, and such data is also available for many nations via the European Commission. And at the offices of the IAEA in Austria, staff have access to their own monitoring data. “We have a big map of the world and the data appears on that map,” says Marion Damien, response data officer at the IAEA’s Incident and Emergency Centre, explaining that staff at the organization and also authorities within dozens of member countries have access to this map on their computers. Data from member nations appears in near real time, arriving within minutes or after up to an hour or so, says Damien.
I ask what the map looks like on the day we speak, in early December. Everywhere is green, except Fukushima and Chernobyl, she says. Higher levels can be visualized in yellow, orange, or red—the latter indicating 1,000 microsieverts per hour, or more. This was the kind of radiation level measured at the Fukushima power plant during the height of the crisis in 2011.
“The wonderful thing about this map [is] it doesn’t discriminate,” says Damien. “We will see [any radiation] that is more than a certain threshold.” She adds that fluctuations in background radiation, for instance those caused by weather events, are not generally significant enough to have an impact on the environment or people. Though it’s worth noting that exposure to radon gas, which can enter buildings in some areas depending on local geology, is associated with lung cancer. Your exposure over time may be affected if you live in an area where radon is present and where permafrost is also currently melting due to climate change, for instance, since this can allow more radon gas to escape from the ground.
Most people are not aware of how much radiation monitoring goes on around them all the time, including in public places. Airports have sophisticated radiation detectors, for example. In 2022, devices at Heathrow flagged a package that turned out to contain a small amount of uranium. There was no risk to the public, authorities said at the time.
Mirion is one of several companies that make radiation detectors. Their products are used for defense and security applications, as well as in nuclear power plants, laboratories, and research contexts. “If there’s an incident in a nuclear plant like a fuel leak…these systems are connected to the safety system of the nuclear plant, so the nuclear plant will shut down,” explains James Cocks, chief technology officer. Area monitors suck particulate emitted by power plants onto filter paper, which can be analyzed to see whether or not there has been an uncontrolled release of radiation.
The company even makes a radiation detector designed to fit to the underside of a drone. Cocks says that, in the immediate aftermath of Fukushima, such was the need to collect data on radiation that someone drove around on a motorbike with a radiation detector. Drones would, today, offer a safer way of gathering such information, he suggests.
But Mirion also makes handheld detectors that can be carried by personnel keeping an eye on major sports events, for example. And these can distinguish between different types of radiation. You want to be able to tell, for example, whether your higher-than-normal readings are coming from a dirty bomb—or just someone who recently had medical treatment involving a radioisotope. “We can identify whether it’s background, naturally occurring radiation…whether it’s a medical radioisotope or whether it’s…a fission product,” says Cocks.
And so one legacy of the Chernobyl and Fukushima disasters is that we now have hugely upgraded radiation-monitoring systems dotted around the world. There has been a marked increase in efforts to track radiation in the wake of those accidents, says Kearfott.
Bonner acknowledges that some people experience anxiety regarding radiation—now and again, a volunteer would build a Safecast detector, switch it on and “freak out” when it began detecting activity, he says. However, it is important to show how pervasive, and variable, background radiation really is, he says: “We absolutely believe that it’s reassuring to let people know what’s going on.”
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