Last reactor at Zaporizhzhia nuclear plant shuts down. What happens now?

The lack of external power to the Ukraine plant had removed what are effectively lines of defence guarding against a meltdown there, which has been subject to fierce fighting.

The last operating reactor at the Russian-held Zaporizhzhia nuclear power plant in Ukraine has been put into what is known as a cold shutdown after an external power line was restored, making it possible to shut it down more safely.

The lack of external power to Europe’s biggest nuclear plant had removed what are effectively lines of defence guarding against a nuclear meltdown at the site, which has been subject to fierce fighting in recent weeks.

What is the current situation at Zaporizhzhia and what are the safety implications?

Zaporizhzhia has been occupied by Russian forces since March. Ukrainian staff have, however, continued to operate the plant, albeit in stressful conditions that the International Atomic Energy Agency has repeatedly described as unsafe.

Despite the Russian occupation, Ukraine continues to decide what happens at the plant in terms of which reactors operate and how, IAEA chief Rafael Grossi told a news conference on Monday.

Russia and Ukraine have accused each other of shelling at the site that has damaged buildings and brought down power lines essential to cooling fuel in its six reactors, even when the reactors are in cold shutdown as they are now.

Controlled fission, the splitting of nuclear fuel atoms inside a reactor core, generates heat that turns water into steam to spin turbines and produce electricity. A runaway chain reaction can, however, cause a major accident like those at Fukushima or Chernobyl.

Grossi has called for an immediate stop to the shelling as well as for a more formal protection zone to be set up around the plant to reduce the risk of catastrophe.