EXPLAINER: Ukraine’s Threatened Nuclear Power Plant Shuts Down

The last operating reactor at Ukraine’s Zaporizhzhia nuclear power plant, which is the largest in Europe, was shut down on Sunday to reduce the threat of a radioactive disaster amid continued fighting.

The move became possible after the plant was reconnected to the Ukrainian power grid.

Here is an overview of the situation at the factory after 200 days of war with Russia:

RADIATION THREAT

Fighting near the plant has fueled fears of a disaster like Chernobyl in 1986, where a reactor exploded and spewed deadly radiation, contaminating a large area in the world’s worst nuclear disaster.

The plant, one of the 10 largest nuclear power plants in the world, has been occupied by Russian forces since the early days of the war. Ukraine and Russia have swapped responsibility for the bombardment around the plant, which did not damage its six reactors or the storage of spent nuclear fuel, but repeatedly struck power lines and some auxiliary equipment.

While Zaporizhzhia’s reactors are protected by a reinforced shelter that could withstand an errant shell or rocket, an interruption in the power supply could knock out cooling systems critical to the reactors’ safety. Emergency diesel generators may be unreliable.

After the facility was cut off from transmission lines on September 5 following a fire caused by bombing, a single reactor remained operational to power cooling systems and other crucial equipment in so-called “island” mode. “.

RISKY “ISLAND MODE”

Operation in “island mode” feeds the removal of waste heat from reactor cores and spent fuel pools.

Experts say it is very unreliable. They point out that if the diesel generators fail, a core meltdown could occur within hours.

If the reactor is already shut down, the risk depends on the time elapsed since the shutdown. The less time has elapsed, the more cooling is needed.

Although the pool containing spent fuel from Zaphorizhzha is located inside the plant’s containment area, a severe reactor accident would likely affect the pool as well.

WHAT HAPPENS NOW?

Ukrainian nuclear operator Energoatom said restoring one of the power lines connecting the plant to the country’s power grid enabled engineers to shut down its last working reactor.

Energoatom said the move was necessary to avoid a situation where the plant would have to rely exclusively on emergency diesel generators to keep the reactors cool and prevent a nuclear meltdown. The company chief told The Associated Press on Thursday that the plant will only have diesel fuel for 10 days.

The International Atomic Energy Agency, the UN nuclear watchdog that has two experts at the plant, confirmed to the AP on Sunday that its last reactor was shut down after power was restored. external.

IAEA Director General Rafael Grossi called for a safe zone around the plant to avert disaster, but fighting continued.

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