Could Ukraine nuclear plant REALLY trigger a blast '10 times larger than Chernobyl'? Experts say 'contained' reactors at Zaporizhzhia won't explode like 1986 disaster - but damage to cooling system may mirror 2011 Fukushima accident
Nuclear experts have quelled fears that Europe's largest nuclear power plant is at risk of becoming 'another Chernobyl', after Russia's 'reckless' overnight shelling attack sparked a fire at the site.
Ukrainian President Volodymyr Zelensky branded the offensive 'nuclear terrorism', while Foreign Affairs minister Dmytro Kuleba tweeted: 'If it [the plant] blows up, it will be 10 times larger than Chernobyl!'The latest chapter in the ongoing conflict has raised fears of a nuclear blast that could affect all of central Europe for decades, similar to Chernobyl near Pripyat in Ukraine in April 1986 – the worst nuclear disaster in history.
But experts say this is very unlikely, in part because of the differences in design between Zaporizhzhia and Chernobyl.
The six nuclear power reactors at Zaporizhzhia are not Chernobyl-type reactors, but pressurised water reactors, brought online between 1985 and 1995.
Unlike Chernobyl, the reactors are also housed in thick steel reinforced concrete containment units which are built to withstand extreme explosions, such as an aircraft crash.
One nuclear expert said the 'worst-case scenario' for Zaporizhzhia would be similar to what happened at Fukushima in Japan in 2011, a disaster which unlike Chernobyl did not result in any direct fatalities.
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Zaporizhzhia’s nuclear reactors are contained – they have a shell of metal and cement around them. Chernobyl had NO containment around the nuclear reactors. Also, Zaporizhzhia’s nuclear reactors are water-moderated; Chernobyl’s were graphite-moderated. (Nuclear reactor moderators reduce the speed of neutrons and allow a nuclear reaction to be sustained)
Nuclear experts have quelled fears that Europe's largest nuclear power plant is at risk of becoming 'another Chernobyl', after Russia's 'reckless' overnight shelling attack sparked a fire at the site (pictured)
Six power units generate 40-42 billion kWh of electricity making the Zaporizhzhia Nuclear Power Plant the largest nuclear power plant not only in Ukraine, but also in Europe
Russian armoured vehicles and troops attacked the nuclear power plant in the early hours of Friday, shooting and shelling guards holed up in administrative buildings near the nuclear reactors - setting one of them on fireAt Fukushima, water from a 33ft (10m)-high tsunami that killed nearly 19,000 people overwhelmed the defensive sea wall and flooded the power plant.
It also knocked out emergency generators which provide power to the cooling system.
Professor David Fletcher, who previously worked at UK Atomic Energy and is now at the University of Sydney, said: 'At present it seems as though it is only ancillary buildings that have been damaged by Russian missiles.
'The real concern is not a catastrophic explosion as happened at Chernobyl but damage to the cooling system which is required even when the reactor is shut down.
'It was this type of damage that led to the Fukushima accident.'
While Chernobyl had graphite moderated reactors, Zaporizhzhia uses water moderated reactors which are generally considered safer.
In nuclear reactors, a moderator is used to reduce the speed of fast neutrons. (At Zaporizhzhia, the moderator used is the same material as the coolant – water.)
'At Chernobyl, the graphite moderator (an essential part of maintaining the nuclear chain reaction) caught on fire and burned for 10 days,' Professor Claire Corkhill, nuclear materials expert at the University of Sheffield, told MailOnline.
'The radioactive smoke from the reactors was taken high up into the atmosphere, which is the reason why the spread of radiation was so vast, all over Europe.'
'The same could not happen at Zaporizhzhia because there is no graphite. Any release in radiation would be much more localised.'
Another advantage in the design of Zaporizhzhia, when compared to older style nuclear plants, is that the core of the reactor contains less uranium.
This lowers the risk of additional fission events happening and therefore makes the reactor safer and more controllable.
It stops the reaction from 'running away with itself' and exploding like it did at Chernobyl, when a sudden power surge caused by human error resulted in a massive reactor explosion.
This exposed the core and blanketed the western Soviet Union and Europe with radiation.
According to Dr Mark Wenman, Reader in Nuclear Materials at Nuclear Energy Futures, Imperial College London, Zaporizhzia's six pressurised water reactor units produce a fifth of Ukraine’s electricity.
Unlike Chernobyl, they are well-protected in the event of a direct strike — although whether doing this would be in Russia's interests is questionable.
'The plant is a relatively modern reactor design and as such the essential reactor components are housed inside a heavily steel reinforced concrete containment building that can withstand extreme external events, both natural and man-made, such as an aircraft crash or explosions,' Dr Mark Wenman said.
'The reactor core is itself further housed in a sealed steel pressure vessel with 20cm [8 inch] thick walls.
'The design is a lot different to the Chernobyl reactor, which did not have a containment building, and hence there is no real risk, in my opinion, at the plant now the reactors have been safely shut down.'
But despite the reassurance, some experts have warned that the containment structure may not hold up against
WHAT WAS JAPAN'S 2011 FUKUSHIMA NUCLEAR DISASTER?
In 2011, a 33ft (10m)-high tsunami that killed nearly 19,000 people crashed into Japan's Fukushima nuclear power plant.
This led to several meltdowns, allowing harmful radioactive fuel rods and debris to escape from contained areas.
Approaching a decade after the disaster, researchers are still struggling to clean up fuel in the waters of the wasting reactors.
Pictured is an aerial view of the reactors of the tsunami-stricken Fukushima Dai-ichi nuclear power plant stand in Okuma, Fukushima
It's estimated that plant officials have only located 10 per cent of the waste fuel left behind after the nuclear meltdowns.
And the damaged plant is believed to be leaking small amounts of the radioactive waste into the Pacific Ocean, which could be travelling as far as the west coast of the United States.
Researchers are now pinning their hopes on remote-controlled swimming robots to locate the lost fuel in order to work out the safest way to remove it.
The government has lifted evacuation orders for much of the region affected by the meltdown, except for some no-go zones with high radiation levels.
Authorities are encouraging evacuees to return, but the population in the Fukushima prefecture has more than halved from some two million in the pre-disaster period.
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