EXPLANATOR: What’s behind the latest warning at the Chernobyl power plant?

When fighting from Russia’s invasion of Ukraine led to power cuts to the critical cooling system at the closed Chernobyl nuclear power plant, some feared the spent nuclear fuel would overheat. But nuclear experts say there is no imminent danger because time and physics are on the safe side.

Because the fuel rods have been cooling for more than 20 years already, it’s not a situation like the Fukushima nuclear disaster in 2011 or even the original Chernobyl meltdown nearly 36 years ago, several experts have said. in nuclear energy at the Associated Press.

The International Atomic Energy Agency also said it “sees no critical impact on the safety” of the plant, which was the site of the world’s worst nuclear accident in April 1986.

WHAT HAPPENED IN THE LAST DAYS AT CHERNOBYL?

Ukrainian power grid operator Ukrenerho said electricity had been cut at all Chernobyl facilities and diesel generators had fuel for 48 hours. Without electricity, “nuclear and radiation safety parameters” cannot be controlled, he said.

Ukrainian Foreign Minister Dmytro Kuleba said the plant, which was occupied by Russian forces at the start of the February 24 invasion, “lost all power,” and he called on the international community “ to urgently demand that Russia cease fire and allow repair units to restore power.

French government spokesman Gabriel Attal stressed that Russian leader Vladimir Putin was “committed to ensuring the safety and security of nuclear sites in Ukraine” during his phone call with French President Emmanuel Macron on Sunday.

WHAT WAS THE BIGGEST FEAR IN THE LAST CRISIS?

The Chernobyl power plant, which closed in 2000, has fuel rods containing 230 kilograms (500 pounds) of uranium, and they are submerged in water at least 15 meters (49 feet) deep, with an active cooling system, said Frank von Hippel, a Princeton University physicist who co-founded the science and global security program.

The general concern was that the power outage would cause the cooling system backup generators to shut down, the radioactive fuel rods would heat up and boil the water which also helps to cool them, raising the temperature to 800 degrees Celsius ( 1,470 degrees Fahrenheit), and causing a fire.

But that’s “pretty unlikely in the situation because the fuel is so cold,” said Edwin Lyman, director of nuclear energy safety at the Union of Concerned Scientists.

Even in this unlikely worst-case scenario, it would take “weeks to months” for the 2,000 pieces of fuel assembly in Chernobyl’s deep-sea pool to evaporate, von Hippel added.

Such heating would be “very slow, if it got there”, he said, calculating that it would take “about 40 days for the pool to dry out”.

Under normal circumstances, cooling fuel rods loses a massive amount of energy and radioactivity – by a factor of 10 – every seven days, said Patrick Regan, professor of nuclear physics at the University of Surrey.

He said the current scenario was not like the Chernobyl meltdown in 1986 or the Fukushima power plant disaster with fuel rods so cool and hot “that the water has to keep flowing”.

After the Fukushima disaster, which was caused by an earthquake and a tsunami, the Ukrainian government commissioned a study to examine the melting potential of power loss in busbar cooling. The study found that it wouldn’t be possible for the coolant water to reach boiling temperature and the fuel rods to be uncovered to trigger true meltdown, Lyman said.

THE PHYSICS OF FUEL ROD COOLING

When the fuel rods are exhausted after generating energy, they still have a lot of internal radioactivity and are still hot. Internal radioactive decay gives off heat and stays in the fuel rods for tens of thousands of years, so they can get hotter unless something is done to cool them, Regan said.

The rods are placed in cooling pools or ponds where water and an active electrical system cool them with a heat exchange pump.

“As soon as you turn off the coolant, as soon as you turn off the heat removal mechanism, it (the temperature) is going to rise,” Regan said.

Eventually, in most plants, the radioactivity and heat decrease enough that they can eventually switch from water cooling to air cooling.

NO IMMEDIATE HAZARD CONSIDERED

The Swedish Radiation Protection Authority estimates that a power outage at Chernobyl will result in no radiological emissions for the next two weeks.

“The fuel storage ponds are also very deep and it would probably take weeks for the water to subside, even without active cooling pumps. cooling is restored,” said Mark Wenman, a nuclear energy expert at Imperial College London.

The IAEA, which is the UN’s nuclear watchdog based in Vienna, said it saw no critical safety impact at Chernobyl as there could be “effective heat removal without the need for ‘power supply’ of spent nuclear fuel on site.

Lyman and others said they were more concerned about potential damage to cooling systems and other problems at Ukraine’s other four operating nuclear power plants, rather than the former Chernobyl site. In 2017, Chernobyl secured a new €2 billion containment system to cover the old sarcophagus.

OTHER CONCERNS

The post-Fukushima study raised concerns about the production of hydrogen gas and the pooling of the cooling process, which is eliminated with an electronic system, Lyman said. The problem is that the explosive gas can build up further without the ventilation system and lead to hazards including sparks when the electricity is restored if it ever goes out.

Another problem is that the lack of electricity means the IAEA’s monitoring system, for safety and security, will be blinded, Lyman said.

“It’s not just pool cooling, but all offsite radiation monitoring systems have been lost,” Lyman said. “The IAEA has no more cameras.”

He described the overall situation as not good, but said it was not an immediate emergency. There are layers of security that help, but the lack of power eliminates some of them.

“He limps with kind of less resilience,” Lyman said. “So if something else happens, there’s less headroom.”

Given that experts say a major radioactive release is weeks or months away, if at all, the biggest consequence of shutting down power or targeting nuclear power plants during war is fear, Emma said. Claire Foley, policy researcher on US-Russian nuclear policy. .

“People hear ‘Chernobyl’ and think ‘nuclear disaster,'” Foley said. “It’s scary. And it causes a feeling of uncertainty.

If anything serious were to happen, Belarus’ Ukrainian neighbor, a Russian ally, “should be more concerned than anyone” because of its proximity to the Chernobyl site, said the nuclear engineering professor at the University of Southern California, Najmedin Meshkati. The Belarusian border is less than 10 miles from Chernobyl, while the Ukrainian capital of Kiev is about 130 kilometers (80 miles) south of the plant,

“Belarus suffered the brunt of the impact of Chernobyl” because of the radioactive cloud released in 1986, he said, adding that Belarusian President Alexander Lukashenko should “take the initiative to beg Mr Putin to ‘stop military operations around Chernobyl’.

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