At Ukraine’s Zaporizhzhia nuclear power plant, accident risk has increased: NPR

The Zaporizhzhia nuclear power plant has been cut off from the electricity grid since September 5. Nuclear power plants need electricity to cool their reactors.

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The Zaporizhzhia nuclear power plant has been cut off from the electricity grid since September 5. Nuclear power plants need electricity to cool their reactors.

ED JONES/AFP via Getty Images

The head of the International Atomic Energy Agency warns that the risk of a nuclear accident at the Zaporizhzhia nuclear power plant has “significantly increased”, following ongoing fighting around the site.

“Let’s be clear, the shelling around the Zaporizhzhia nuclear power plant must stop,” said IAEA Director General Rafael Mariano Grossi. a recorded brief statement released on Friday.

Grossi also warned that the ongoing crisis could force the plant to shut down its last operating reactor. This would trigger a chain of events that could intensify the current nuclear crisis. Here’s how.

Nuclear power plants need electricity

The Zaporizhzhia nuclear power plant is the largest in Europe, capable of producing thousands of megawatts of electricity. But the plant also needs power from the same electricity grid it feeds.

The head of the International Atomic Energy Agency, Rafael Mariano Grossi, said recent developments have “significantly increased the risk of a nuclear accident”.

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The head of the International Atomic Energy Agency, Rafael Mariano Grossi, said recent developments have “significantly increased the risk of a nuclear accident”.

GENIA SAVILOV/AFP via Getty Images

Electricity is used to run the various parts of the plant, including its security and cooling systems. Specifically, nuclear power plants need water to be constantly pumped through their cores to operate safely, and pumps need electricity.

In Zaporizhzhia, electricity is normally supplied by four high-voltage lines, which connect the nuclear complex to the Ukrainian electricity grid, but the conflict has seen these lines systematically cut. The last 750kV line was cut on September 3 according to the IAEA.

A backup line has been disconnected two days later due to a fire at the site. At a press conference shortly after his return from Zaporizhzhia, Grossi told reporters he believed the power lines were deliberately targeted:

“It is clear that those who have these military objectives know very well (…) to hit where it hurts so that the plant becomes very, very problematic,” he told reporters shortly after returning from factory.

Zaporizhzhia makes its own power, but it’s a limited solution

Since it lost its last connection to the grid on September 5, the nuclear power plant has been powered in a so-called “islanding” operating mode. In this configuration, the Unit 6 reactor produces low levels of electricity which powers the rest of the facility.

Zaporizhzhia’s reactors are designed to operate in this mode during start-up, according to a nuclear engineer who worked directly with Zaporizhzhia’s reactors when the plant began operations in the 1980s, but was not authorized to speak publicly by his current employer.

“It’s not good, it can’t be done for a long time,” he said. The problem is less with the reactor itself than with the turbine, generators and other systems, all of which are designed to operate at power levels significantly higher than those provided by the island mode of operation.

Adding to the problem, Grossi said in his statement, is the growing pressure on the plant’s Ukrainian operators. Much of the plant’s current workforce, which numbers just under 1,000 people, lives in the nearby town of Enerhodar. Its water, sewage and electricity supplies have all been disrupted in recent days by the same fighting that damaged lines around the plant.

“The shelling endangers operators and their families, making it difficult to adequately staff the plant,” Grossi said.

Shutting down the last reactor will trigger emergency generators

With conditions deteriorating, it seems more likely that the Ukrainian authorities will decide to shut down the last reactor. But in the short term, it could worsen the crisis.

The Russian army has controlled the site since March. Ukrainian workers continue to operate its reactors.

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The Russian army has controlled the site since March. Ukrainian workers continue to operate its reactors.

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This is because nuclear reactors are more like charcoal grills than gas stoves. Even when turned off, they stay hot for a long time. Water must still flow through the nuclei to prevent melting.

With its reactors shut down, Zaporizhzhia will switch to emergency diesel generators to keep the reactors cool. Standby generators themselves are a proven method of cooling a nuclear reactor. In fact, the Nuclear Regulatory Commission requires US power plants to immediately switch to emergency diesel generators, bypassing the “island mode of operation” used at Zaporizhzhia.

“We don’t want to use the diesel generators, but it’s a situation you can put up with for a while,” says Steven Nesbit, a nuclear engineer and member of the American Nuclear Society’s Rapid Response Task Force, which is following the current crisis. For example, after losing power during Hurricane Andrew in 1992, Turkey Point Nuclear Power Plant in Florida operated for days on emergency diesel power.

If the generators run out of fuel, a meltdown could occur

According to the IAEA, the Zaporizhzhia plant has more than a dozen emergency generators on standby. Normally, the plant holds a 10-day reserve of diesel fuel, according to the agency, and currently has about 2,250 tonnes of fuel available.

If this fuel runs out or the generators are damaged in further fights, it could trigger a meltdown.

But Nesbit says that doesn’t necessarily mean there would be a Chernobyl-like disaster. The Chernobyl collapse was due to a unique mix of design flaws and operator error that would be virtually impossible to replicate in Zaporizhzhia.

And unlike the Fukushima nuclear disaster in 2011, some of Zaporizhzhia’s reactors have already been shut down for a while, allowing the nuclear fuel to cool somewhat, Nesbit says.

Even in the worst-case scenario, the Zaporizhzhia reactors are of a modern design surrounded by a heavy “containment” building, Nesbit explains. “It’s reinforced concrete, usually about three to four feet from that; it’s designed to withstand very high internal pressures.”

This could allow him to retain any radioactive material.

But the world nuclear agency does not want to test any of this. And for this reason, Grossi calls on all parties to immediately set up a safe zone.

“There is no time to waste,” he said.

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