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Директор Інституту проблем безпеки атомних електростанцій НАН України академік Анатолій Носовський дав інтерв’ю журналу Science

     У статті в журналі Science директор Інституту проблем безпеки атомних електростанцій НАН України | Інститут проблем безпеки атомних електростанцій НАН України| академік Анатолій Носовський прокоментував ситуацію на Чорнобильській атомній електростанції.

      Він розповів про можливість радіаційної аварії на ЧАЕС під час знеструмлення, а також про зникнення з лабораторії радіаційного моніторингу радіоактивних ізотопів, які можна змішати зі звичайними вибуховими речовинами, щоб утворити «брудну бомбу», що поширить забруднення на велику територію.

     Insecure radioactive materials are the latest worry as Russia continues occupation of infamous nuclear reservation

     When the lights went out at Chornobyl Nuclear Power Plant on 9 March, the Russian soldiers holding Ukrainian workers at gunpoint became the least of Anatolii Nosovskyi’s worries. More urgent was the possibility of a radiation accident at the decommissioned plant. If the plant’s emergency generators ran out of fuel, the ventilators that keep explosive hydrogen gas from building up inside a spent nuclear fuel repository would quit working, says Nosovskyi, director of the Institute for Safety Problems of Nuclear Power Plants (ISPNPP) in Kyiv. So would sensors and automated systems to suppress radioactive dust inside a concrete “sarcophagus” that holds the unsettled remains of Chornobyl’s Unit Four reactor, which melted down in the infamous 1986 accident.

     Although power was restored to Chornobyl on 14 March, Nosovskyi’s worries have multiplied. In the chaos of the Russian advance, he told Science, looters raided a radiation monitoring lab in Chornobyl village—apparently making off with radioactive isotopes used to calibrate instruments and pieces of radioactive waste that could be mixed with conventional explosives to form a “dirty bomb” that would spread contamination over a wide area. ISPNPP has a separate lab in Chornobyl with even more dangerous materials: “powerful sources of gamma and neutron radiation” used to test devices, Nosovskyi says, as well as intensely radioactive samples of material leftover from the Unit Four meltdown. Nosovskyi has lost contact with the lab, he says, so “the fate of these sources is unknown to us.”

     The drama at Chornobyl began on 24 February, the very first day of the invasion. At 5 a.m., as Russian troops poured across Ukraine’s border with Belarus—just 15 kilometers from Chornobyl—ISPNPP managers were ordered to evacuate most staff, who monitor the safety of the plant, provide technical support for decommissioning, and develop protocols for managing radioactive waste in the off-limits “exclusion zone” surrounding Chornobyl. Within 2 hours, 67 had cleared out; two who live in Chornobyl village stayed behind to keep an eye on the institute’s lab. “We’ve lost contact with these brave people,” says ISPNPP senior scientist Maxim Saveliev.

     By 5 p.m., Russian troops had taken control of all Chornobyl facilities. A shift supervisor, Valentin Geiko, negotiated a deal under which the plant’s Ukrainian guards would disarm and the Russian soldiers would not interfere with civilian workers, Nosovskyi says. But for nearly a month, the soldiers forbade a shift change—essentially holding the workers hostage—and confiscated their cellphones. In a gesture of defiance, the workers played the Ukrainian national anthem every morning, cranking up the volume, Nosovskyi says. Finally, earlier this week, the occupiers allowed fresh staff to rotate in. But some captive workers chose to remain, he adds, “so as not to put at risk people who should come in their place.”

     Chornobyl is not the only Ukrainian nuclear installation at risk in the war. On 4 March, Russian forces shelled the Zaporizhzhya nuclear power plant—fortunately missing its reactor halls. Two days later, a rocket attack damaged a research reactor used to generate neutrons for experiments at the Kharkiv Institute of Physics and Technology. Nosovskyi labels the assaults as nothing short of state-sponsored “nuclear terrorism.”

     But Chornobyl has a unique set of radioactive hazards. On 11 March, wildfires ignited in the nearby radioactive forests, which harbor radioisotopes that were disgorged in the accident and taken up by plants and fungi. Russian military activities have prevented firefighters from entering the exclusion zone, Nosovskyi says. The fires continue to burn and could grow more intense as the weather warms, he says, releasing radiation that could lead to “significant deterioration of the radiation situation in Ukraine and throughout Europe.” So far, remote measurements suggest radioactive particle concentrations in the smoke do not pose a health hazard, he adds, but an automated radiation monitoring system that went down in the power outage has not yet been brought back online. That means “there is no information on the real situation in the exclusion zone,” says Viktor Dolin, research director of the Institute for Environmental Geochemistry in Kyiv.

     The restoration of electricity averted the nightmare of a hydrogen explosion in the spent fuel repository, where 8500 tons of uranium fuel rods continue to cool off in pools of water. The repository poses a major radioactive threat: Through radioactive decay, the assemblies have accumulated about 240 times more cesium-137 and 1500 times more strontium-90 than the destroyed reactor spewed in 1986, Dolin says. Staff intend to punch holes in the repository’s walls to allow hydrogen gas to escape in the event of a future power outage, Nosovskyi says.

     The other big menace at Chornobyl are the fuel-containing masses (FCMs)—fuel rods, zirconium cladding, and other materials that melted into radioactive conglomerations during the accident and continue to smolder under Unit Four’s sarcophagus, hastily erected in the wake of the disaster. For years Ukrainian scientists, with Russian colleagues from the Kurchatov institute, have kept a tense vigil. (The institute severed ties with its Ukrainian partners in a statement earlier this month supporting the war and the “denazification” of Ukraine.) Occasional spikes in the number of neutrons streaming from certain FCMs—a sign of fission—prompt sprinkler systems to spray gadolinium nitrate solution, which absorbs neutrons.

     The odds of self-sustaining fission, or criticality, in an FCM are minuscule, and even if criticality triggered a small explosion, the burst would probably be contained within an arching steel structure, called the New Safe Confinement (NSC), that was erected over the sarcophagus in 2016 to shield it from the elements and create a safe space for cleanup work. But the NSC was not designed to withstand shelling, and a breach could disturb the FCMs. It could also release some of the hundreds of tons of highly radioactive dust that have accumulated in the sarcophagus over the years as the FCMs gradually disintegrate.

     Thousands of other sites in Ukraine have radiological materials. Most are under the watchful eye of Ukraine’s nuclear regulator. “There’s a lot of ongoing effort to secure material,” says Peter Martin, a nuclear physicist at the University of Bristol who collaborates with scientists at Chornobyl. That means, where possible, moving sources into vaults and repositories. But Vitaly Fedchenko, a nuclear security expert at the Stockholm International Peace Research Institute, notes that Ukraine, like other parts of the former Soviet Union, has not kept track of all the Soviet nuclear legacy. “There are a lot of radioactive sources that are not on anyone’s radar,” he says. “Even Ukraine’s radar.”

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