A large forest fire is spreading through the Chernobyl exclusion zone after a drone struck the area yesterday. Though the fire is serious, those on the ground say the risk of radioactive contamination outside the area is minimal.

The Chornobyl Radiation and Ecological Biosphere Reserve (CREBR) wrote in a that around 12 square kilometres of land, located to the south-east of the Ukrainian town of Chernobyl and the nuclear plant’s former cooling ponds, are burning due to a drone crash – but didn’t give details on the type or origin of the device. As of Friday afternoon, some 331 people and 75 pieces of equipment are involved in the emergency response.

“It’s really big. Guys who are working on [the] fire line are breathing air with high concentration of radionuclides,” says Denys Vyshnevskiy at the CREBR. “After the shift, they check concentration radionuclides in the body.”

Vyshnevskiy says that 5 to 10 kilometres from the fire, the radiation levels are normal, and there is little risk of contamination outside the exclusion zone.

Other estimates using satellite images seen by 91av suggest that the area of the fire has actually grown to 24.4 square kilometres.

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at the Institute for Nuclear Research in Kyiv, Ukraine, was near the site when the fire started, but saw only smoke because the affected area was closed to scientists at the time by the military. She also thinks there is very little risk of radioactive contamination outside the zone.

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The State Emergency Service of Ukraine (SES) said in a Telegram post that tackling the fire is . “The fire is rapidly spreading across the territory,” it wrote. Vyshnevskiy says the hope on the ground is that rain expected this evening will aid firefighters.

The SES said that some areas are too dangerous for firefighters to access because of land mines, so are being left temporarily while efforts are concentrated elsewhere.

The man who crawls into the perilous heart of the Chernobyl reactor

Ever since the Chernobyl nuclear reactor exploded in 1986, scientists have needed to monitor radioactive conditions inside. That job currently falls to Anatoly Doroshenko, who explains the dangers and importance of his work to 91av

The Chernobyl exclusion zone is frequently overflown by Russian drones en route to Kyiv and other targets within Ukraine. Last year, a Russian drone struck the New Safe Confinement shelter, which protects the highly radioactive remains of the 1986 disaster, blasting a hole all the way through its multi-layer construction.

Footage from that night shows fire and smoke billowing from a gaping hole – luckily, it was far enough towards the edge of the building that debris didn’t fall onto the fragile reactor or sarcophagus below, which could have caused collapse and stirred up dangerously radioactive material.

Nuclear experts from the International Atomic Energy Agency (IAEA) have formally backed Japan’s controversial plan to release radioactive wastewater from the Fukushima Daiichi nuclear power plant into the Pacific Ocean – but is it the right thing to do?

In 2011, Japan was hit by a serious earthquake and tsunami, which caused the meltdown of three reactors at Fukushima. The contaminated water, which is currently sitting in roughly 1000 giant tanks on site, was used to keep Fukushima’s reactors and debris cool following the disaster.

Japan wants to gradually release 1.3 million cubic metres of this water into the sea over the next three to four decades, so it can continue decommissioning of the Fukushima site.

In a report issued on 4 June, the IAEA concluded that the approach will have “a negligible radiological impact on people and the environment”. IAEA director general Rafael Mariano Grossi said in the report that Japan’s plans were “consistent with relevant international safety standards”.

The water has already been treated to remove 62 radioactive contaminants, but it remains tainted by tritium, a radioactive isotope of hydrogen. Because tritium is bonded to the water molecule itself, it is challenging to remove, says at the University of Cambridge. “It’s not possible, really, to separate [tritium from water],” he says.

Tritium, which has a radioactive half-life of just over 12 years, emits low-energy beta particles and does little damage to cells, says Farnan. Because of its bond with water, it will pass through most marine organisms without causing harm, he says. Many nuclear plants around the world already discharge tritium into the ocean.

Japan says it must start discharging the water soon because the tanks will hit capacity in 2024. It insists the wastewater will be diluted to ensure levels of tritium never exceed World Health Organization guidelines.

But , South Korea and Pacific Island nations have expressed doubts over Japan’s discharge plan, amid fears the wastewater release could contaminate the marine food chain. In January, Henry Puna of the Pacific Islands Forum .

suggested that if the contaminated wastewater were released gradually, spikes in tritium concentrations would be confined to the east coast of Japan – and would represent only a tiny fraction of the background concentration of tritium already present in the ocean.

at the University of Plymouth, UK, warns that more research is needed to investigate the risks tritium poses to the marine food chain. Jha’s laboratory experiments suggest tritium can accumulate in the tissues of shellfish such as mussels and oysters, . “It needs an international [research] effort,” he says.

Meanwhile, Tokyo Electric Power Company, the firm that runs the site, that water in the tanks will need additional, “secondary” treatment to filter out more dangerous isotopes, such as ruthenium-106, cobalt-60 and strontium-90, in order to meet regulatory standards.

at the Woods Hole Oceanographic Institution in Massachusetts is concerned these other isotopes could pose a threat to marine life.  “Unlike tritium, cobalt-60 is 300,000 times more likely to accumulate on the seafloor at the outlet of the pipes,” he says. “It will build up over time, it will accumulate. So whatever amount you put in, it doesn’t just dilute away.” As a result, cobalt-60 could be ingested by bottom dwelling fish, he warns, entering the marine food chain.

Ultimately, Jha says the Japanese authorities have no choice but to discharge the contaminated water into the ocean, particularly given the earthquake risk of storing it on land. “They don’t have any other options,” he says.

Buesseler disagrees. He has the contaminated water is treated to remove dangerous isotopes, and then used to make concrete for use on the Fukushima site or to construct coastal tsunami barriers.

The potential for radiation exposure to the public would be essentially eliminated with this approach, Buesseler argues. “Once the tritium is in something as stable as concrete, the radiation can’t escape,” he says.

Fighting at the largest nuclear power plant in Europe continues to present a real risk of a radiation leak, a nuclear scientist working in Ukraine has warned.

The Zaporizhzhia Nuclear Power Plant (ZNPP) near the Ukrainian city of Enerhodar has six nuclear reactors, all fuelled by uranium-235. The site has been controlled by Russian soldiers since March and reports from Ukrainian officials suggest that Russian troops are shelling parts of the site. These reports haven’t been independently corroborated, but satellite images have revealed

On 14 August, Ukraine’s president Volodymyr Zelenskiy warned Russian forces that for “our intelligence agents, for our special services, for our army”. He also claimed that Russian troops were to fire on the cities of Nikopol and Marhanets.

In a joint statement issued on 12 August, 42 countries, including the US and the UK, and allow normal operations at the plant to resume to ensure safety. The director general of the International Atomic Energy Agency, Rafael Mariano Grossi, has also and stressed that there is an urgent need for an expert team to travel to the site to carry out safety checks.

One nuclear scientist working in Ukraine, who asked to remain anonymous, told 91av that the reactors at the ZNPP are built to a more modern design – known as VVER-1000 – than those at the Chernobyl nuclear power plant, with a better containment structure, but that there are still risks from nearby fighting.

“Normally, the design of containment should resist an external impact like the crash of an airplane. The concrete shell of VVER-1000 containment is about 1.2 metres thick,” he says. “However, the safety of a nuclear power plant is not only down to the containment of the reactor itself; it’s also the work of auxiliary equipment that ensures the cooling of the reactor and spent fuel. We have to keep in mind that [a] loss of power caused the accident in Fukushima [in Japan in 2011].”

Aside from the reactor, there is also liquid and solid radioactive waste stored on site. If damaged during shelling, this could cause a radiation leak to the environment, the nuclear scientist says. “The plant is designed to be protected from terrorist threats, but not [from] military fighting. All should be done to avoid any chance of fighting, not only at the plant site, but in all the areas around,” he says.

An , Ukraine’s state-controlled energy company, said that as of 8am local time on 15 August, the ZNPP is operating safely, but that fighting is continuing. “Periodic shelling of the ZNPP by Russian troops with anti-aircraft missiles since last week has caused a serious risk to the safe operation of the plant,” it said. “There are still risks of hydrogen leakage and sputtering of radioactive substances, and the risk of fire is high.”

The agency said that auxiliary buildings at the site had been damaged and three radiation monitoring sensors around the site had been hit. It also claimed that a fire station outside the plant had been shelled, increasing the potential danger of fires. Reports last week suggested that one member of plant staff had received shrapnel wounds.