All eyes on Zaporizhzhia plant as nuclear disaster fears grow

London — The Zaporizhzhia nuclear power plant in southern Ukraine has been shelled in recent days, raising the possibility of a grave new accident just 500km from the site of the world’s worst nuclear calamity, the 1986 Chernobyl disaster.

UN secretary-general Antonio Guterres has called for the area around the plant, Europe’s largest, to be demilitarised. A UN nuclear agency team hopes to visit the site in the near future.

The Zaporizhzhia plant has six Soviet-designed VVER-1000 V-320 water-cooled and water-moderated reactors containing Uranium-235 (U235), which has a half-life of more than 700-million years. Construction began in 1980 and its sixth reactor was connected to the grid in 1995. Up to July 22 2022, just two of its reactors were operating, according to the Nuclear Energy Agency (NEA).

The biggest risk is from a drop in water supply. Pressurised water is used to transfer heat from the reactor and to slow down neutrons to enable the U235 to continue its chain reaction.

If the water were cut, and auxiliary systems such as diesel generators failed to keep the reactor cool due to an attack, the nuclear reaction would slow and the reactor would heat up swiftly. At such high temperatures, hydrogen could be released from the zirconium cladding and the reactor could start to melt down.

However, experts say the building housing the reactors is designed to contain radiation and withstand major impacts, meaning the risk of a major leak there is still limited.

“I do not believe there would be a high probability of a breach of the containment building even if it was accidentally struck by an explosive shell and even less likely the reactor itself could be damaged by such. This means the radioactive material is well protected,” said Mark Wenman, reader in nuclear materials at Nuclear Energy Futures, Imperial College London.

Spent fuel

Besides the reactors, there is a dry spent fuel storage facility at the site for used nuclear fuel assemblies, and spent fuel pools at each reactor site, which are used to cool down the used nuclear fuel.

“The basins of spent fuel are just big pools with uranium fuel rods in them, they are really hot depending on how long they have been there,” said Kate Brown, an environmental historian at the Massachusetts Institute of Technology whose book Manual for Survival documents the full scale of the Chernobyl disaster.

“If fresh water is not put in then the water will evaporate. Once the water evaporates then the zirconium cladding will heat up and it can catch fire and then we have a bad situation — a fire of irradiated uranium which is very like the Chernobyl situation releasing a whole complex of radioactive isotopes.”

An emission of hydrogen from a spent fuel pool caused an explosion at reactor 4 in Japan’s Fukushima nuclear disaster in 2011.

According to a 2017 Ukrainian submission to the International Atomic Energy Agency (IAEA) at Zaporizhzhia there were 3,354 spent fuel assemblies at the dry spent fuel facility and about 1,984 spent fuel assemblies in the pools. That is a total of more than 2,200 tonnes of nuclear material excluding the reactors, according to the document.

After invading Ukraine on February 24, Russian forces took control of the plant in early March. Ukrainian staff continue to operate it, but special Russian military units guard the facility and Russian nuclear specialists give advice. The IAEA has warned that the staff are operating under extremely stressful conditions.

If there were a nuclear accident, it is unclear who would deal with it during a war, said Brown.

“We don’t know what happens in a wartime situation when we have a nuclear emergency,” Brown said. “In 1986 everything was running as well as it ran in the Soviet Union so they could mobilise tens of thousands of people and equipment and emergency vehicles to the site. Who would be taking charge of that operation right now?”

The plant was struck in March but there was no radiation leak and the reactors were intact. Russia and Ukraine blamed each other for that strike. In July, Russia said Ukraine had repeatedly struck the territory of the plant with drones and missiles. Pro-Ukrainian social media said “kamikaze drones” had struck Russian forces near the plant.

Reuters was unable to immediately verify battlefield accounts of either side.

August 5: The plant was shelled twice. Power lines were damaged. An area near the reactors was hit.

Russia said Ukraine’s 45th Artillery Brigade also struck the territory of the plant with 152mm shells from the opposite side of the Dnipro River. Ukraine’s state nuclear power company, Energoatom, said Russia fired at the plant with rocket-propelled grenades.

August 6: The plant was shelled again, possibly twice. An area next to the dry spent nuclear fuel storage facility was hit.

Energoatom said Russia fired rockets at the plant. The Russian forces said Ukraine struck it with a 220mm Uragan rocket launcher.

August 7: The plant was shelled again. Russia said Ukraine’s 44th Artillery Brigade struck the plant, damaging a high-voltage line. The defence ministry said power at reactors 5 and 6 was reduced to 500MW.

August 11: The plant was shelled again. Energoatom said it was struck five times; Russian-appointed officials said it was struck twice during a shift changeover.

August 24: Russia’s National Guard said it had detained two employees of the plant for passing information to Ukrainian authorities.

August 25: The IAEA is “very, very close” to being able to visit the plant, its chief Rafael Grossi said.

Reuters