Unlikely that Zaporizhzhya accident could trigger another Chernobyl say experts

The worsening security situation around Ukraine’s Zaporizhzhia Nuclear Power Plant has understandably prompted fears that Europe could be on the brink of a nuclear accident on the scale of the 1986 Chernobyl disaster, or perhaps even worse.

Since the start of Russia’s invasion of Ukraine, both Moscow and Kyiv have accused each other of shelling the Russian-held nuclear plant - Europe’s largest such facility - raising fears of a large-scale nuclear disaster that spreads radiation across Europe.

Just last week - echoing similar comments from UN secretary general Antonio Guterres - the director general of the International Atomic Energy Agency (IAEA) Mariano Grossi warned that further escalation at the six-rector plant could lead to a severe nuclear accident with global consequences.

And whilst observers cautiously welcomed last week’s announcement (20^th August, 2022) that Russian officials are to grant UN inspectors access to the complex, Vladimir Putin’s refusal to demilitarise the plant means that tensions continue to grow.

However, commenting on the potential outcome of an accidental or deliberate strike on the facility some UK nuclear experts have suggested that comparisons with the Chernobyl disaster are unhelpful and inaccurate.

“This is not Chernobyl,” said Prof Malcolm Sperrin, director of the Department of Medical Physics and Clinical Engineering, at Oxford University Hospitals NHS Trust, “The type of reactor is different and the potential failure modes are also different.  It also needs to be pointed out that there is a fundamental difference between the causes of the Chernobyl and Fukushima reactor releases and any potential breaching of containment using munitions.  The various levels of containment are very strong and not easily penetrated.”

Paul Norman, Professor of Nuclear Physics & Nuclear Energy, University of Birmingham, agreed that whist the reactor is designed to withstand aircraft impact, earthquakes, explosions, it’s not immune from attack.  “Nothing is indestructible,” he said, “and sufficiently powerful and sustained targeted attacks would eventually break through”.  

However, Norman added that even in this scenario a direct missile strike would not trigger a nuclear explosion. “It's important to note that this would not trigger a nuclear explosion from the nuclear material itself (so it doesn't further detonate, like a chemical explosive might do - nuclear fission works in a different way to that),” he said.  

The main danger, he said, would be the release of radioactive inventory from either the reactor or - more likely - the areas of the plant outside of the reactor confinement that also hold radioactive materials, such as the cooling systems, storage pool and laboratories. “Hitting the fuel cooling ponds (whilst fuel is in them) could cause a radioactive dispersion,” said Norman. “Similarly with any radioactive waste stores on site. Damaging certain cooling systems could also prevent the reactor from properly cooling itself and lead to overheating - a "meltdown".

The outcome of such an attack would, said Norman, depend on the amount and nature of the radioactive release - the so-called “source term” and prevailing weather conditions but it would be surrounding areas that would be most at risk.

Indeed, Professor Gerry Thomas, former Professor of Molecular Pathology at Imperial College London, played down the risks posed further afield.  “The only health concern, in the unlikely event of a release from Zaporizhzhia … would be to those within the power plant itself, and to a lesser extent those still living in the towns and villages in the immediate area,” he said.

The major concern for those not in the immediate vicinity of the plant would, he added, be exposure to volatile isotopes ejected into the atmosphere – primarily and 137-Cs.   However, the relatively short half-life of these isotopes - around 8 days for  131-I would, he said, limit its chances of affecting neighbouring countries.

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