When Russia's fight against Ukraine's invasion of Ukraine resulted in power cuts to the critical cooling system at the closed Chernobyl nuclear power plant, some feared that the spent nuclear fuel would overheat. But nuclear experts say there is no imminent threat as time and physics favor safety.
Because the fuel rods have already been cooling for more than 20 years, this is not a situation like the 2011 Fukushima nuclear disaster or even the original Chernobyl meltdown nearly 36 years ago, several nuclear energy experts told The Associated Press. told.
The International Atomic Energy Agency also stated that it "sees no significant safety impact" at the plant, which was the site of the world's worst nuclear accident in April 1986.
What happened in Chernobyl in recent days?
Ukraine's electrical grid operator Ukranerho said power had been cut at all Chernobyl facilities and that diesel generators had fuel for 48 hours. Without power, "parameters of nuclear and radiation safety" cannot be controlled, it said.
Ukrainian Foreign Minister Dmitro Kuleba said that the plant, which was previously occupied by Russian forces in the February 24 invasion, "lost all power supplies," and he called on the international community to "immediately provide Russia with firefighting and repair units." Demand should be made to allow the power supply to be restored.
French government spokesman Gabriel Attal underlined in his phone call with French President Emmanuel Macron on Sunday that Russian leader Vladimir Putin had "committed to guaranteeing the safety and security of nuclear sites in Ukraine".
What was the biggest fear in the latest crisis?
The Chernobyl plant, which closed in 2000, has fuel rods containing 230 kilograms (500 lb) of uranium, and they are submerged in water at least 15 meters (49 ft) deep with an active cooling system, Frank von Hippel said. Said, a Princeton University physicist who co-founded the Program on Science and Global Security.
The general concern was that the loss of power would shut down the cooling system's backup generators, overheating the radioactive fuel rods and boiling the water that also helped cool them, causing temperatures to reach 800 °C (1,470 °F). rises up to, and is causing fire.
But it's "very unlikely in this situation because the fuel is so good," said Edwin Lyman, director of nuclear energy safety for the Union of Concerned Scientists.
Even boiling 2,000 fuel assembly pieces in a Chernobyl deep-water pool in a worst-case scenario would take "weeks to months," von Hippel said.
Such heating "would be very slow, if it ever got there," he said, calculating that "it would take about 40 days for the pool to dry out."
Patrick Regan, professor of nuclear physics at the University of Surrey, said that under normal conditions, cooling fuel rods loses enormous amounts of energy and radioactivity - a factor of 10 every seven days.
He said the current scenario was not like the 1986 Chernobyl meltdown or the disaster at the Fukushima plant, in which the fuel rods were so fresh and hot "that you need to keep the water flowing constantly."
After the Fukushima disaster, which was caused by an earthquake and tsunami, the Ukrainian government commissioned a study to look at the potential for meltdowns ranging from loss of power to the cooling of the rods. The study found that it would not be possible for the cold water to reach boiling temperature and that the fuel rods would not be open to initiate the actual deceleration, Lyman said.
Physics of cooling fuel rods
When fuel rods are spent after generating electricity, they still contain a lot of internal radioactivity and they are still hot. Regan said that internal radioactive decay releases heat and remains in fuel rods for thousands of years, so unless something is done to cool them, they can overheat.
The rods are placed in cooling pools or ponds where both water and an active electrically-powered system cool them with a heat exchange pump.
"As soon as you stop the coolant, as soon as you stop the mechanism to remove the heat, it (the temperature) will rise," Regan said.
Eventually in most plants, the radioactivity and heat are reduced enough that it can eventually switch from water cooling to air cooling.
No immediate threat seen
The Swedish Radiation Safety Authority estimates that the Chernobyl power outage will cause no radiological emissions in the next few weeks.
“The fuel storage ponds are also very deep and it can take weeks for the water to boil, even without a cooling pump. "This should give hope enough time for the cooling system to restore power," said Mark Weinman, a nuclear energy expert at Imperial College London.
The IAEA, the Vienna-based UN nuclear watchdog, said it had no significant impact on security at Chernobyl because spent nuclear fuel at the site could lead to "effective heat removal without the need for an electrical supply".
Lyman and others said they were more concerned about potential damage to cooling systems and other problems at Ukraine's four other operating nuclear power plants rather than the defunct Chernobyl site. In 2017, Chernobyl received a new containment system worth 2 billion euros to go over the old coffin.
Other concerns
Subsequent studies at Fukushima raised issues of pooling from the generation and cooling process of hydrogen gas, which is then removed from the electronic system, Lyman said. Worryingly, without a venting system, explosive gas can accumulate excessively and pose dangers, including sparks when the power is ever turned off.
Another issue is that the lack of power means the IAEA's monitoring system will be blindsided for safety and security, Lyman said.
"It's not just the cooling for the pool, but all the off-site radiation monitoring systems have been lost," Lyman said. "The IAEA no longer has cameras."
He did not describe the overall situation as good, but said it was not an immediate emergency. There are layers of protection that help, but the lack of power puts some of them away.
"It's lame as well as reduced flexibility," Lyman said. "So if anything else happens, there's a lower margin."
Given that experts say a major radioactive release is weeks to months away, if the biggest consequence of a war involving power outages or targeting nuclear plants is fear, Emma Claire, a policy researcher on US-Russian nuclear policy Foley said. ,
"People hear 'Chernobyl' and think 'nuclear disaster,'" Foley said. "It creates fear. And it creates a sense of uncertainty."
If anything bad happens, Ukraine's neighbor Belarus, a Russian ally, will need to be "more concerned than anyone else" because of its proximity to the Chernobyl site, said Najmedin Meshkaty, a nuclear engineering professor at the University of Southern California. The border with Belarus is less than 10 miles from Chernobyl, while the capital of Ukraine is about 130 kilometers (80 mi) south of the Kyiv plant,
"Belarus bore the brunt of the Chernobyl effect" from the radioactive cloud released in 1986, he said, adding that Belarus President Alexander Lukashenko "should take the lead in begging Mr. Putin to stop military operations around Chernobyl."