Ukraine's Zaporizhzhia power plant is not at risk for now

Experts say Ukraine's biggest nuclear power plant is stable after the Nova Kakhova dam explosion and under no risk in the short term.

The explosion of the Nova Kakhovka dam along the Dnipro river in southern Ukraine has caused catastrophic flooding throughout the area, forcing people to evacuate their homes en masse.

With the Zaporizhzhia power plant situated some 200 kilometers (124 miles) up the Dnipro River from the dam, many are wondering what effect, if any, the explosion has had or will have on the plant's security. Zaporizhzhia is cooled with water from the Kakhovka reservoir, which has been draining water since the explosion on Tuesday.

For now, according to all experts consulted by DW — independent and from the IAEA — the explosion's impact on Zaporizhzhia is small and poses zero risk in the short-term.

Because the plant is up river from the explosion, it is not being flooded, and there is no concern that it will in the coming days, experts say.

If the plant were in operation, the loss of water would mean it would need to be shut down, but it already is and has been for the past eight months.

According to Philip Thomas, a civil engineering professor with expertise in nuclear fuel at the University of Bristol, UK, when a plant is active, it needs a significant amount of water for cooling.

This water plays a role during the generation of the nuclear energy itself and cools the spent fuel (nuclear waste) leftover.

The day a plant is shut down, he said, it only needs around 7% of the water it typically needs to run. And in the days following, that amount drops even lower, to around 1%.

"After eight months, the decay heat will have gone down even more, and it will now be less than a 10th of 1%," said Thomas. "So you still need to provide some cooling water. But the amount of cooling water you require will be rather small."

Along with its own cooling pond, the plant also has 18 further backup pools and 18 mobile pumping units, according to University of Bristol physics professor Tom Scott, who has conducted experiments at Chernobyl.

This supply gives engineers working at the plant enough time to redirect the source of water if needed, said Thomas.

International Atomic Energy Agency (IAEA) chief Rafael Grossi has confirmed in statements made since the dam broke Tuesday that the risk to the plant is low as long as the cooling pond remains intact.

"Nothing must be done to potentially undermine its integrity," he told reporters. "I call on all sides to ensure nothing is done to undermine that."

For the next months, the plant will be able to get water from the backup pools, which can be topped off by a large retention basin located on-site.

At some point this basin will need to be topped off itself. In order to do this, engineers will need to redirect the source of water: It used to come from the Kakhovka reservoir, now it will need to come from the Dnipro. In the short term, this can be done using pump trucks.

In the long term, "They'd need to put in new, very extensive pipe work…they'd have to extend what they've got at the moment, which assumed there was a reservoir that was going to stay there," Thomas said.

According to a statement released by the French government's Institute for Radiation Protection and Nuclear Safety, a drop in the level of the Dnipro river could cause problems for the plant's retention basin, leading to leakage "or even to the collapse of the surrounding dike, due to the pressure exerted by the water contained in the basin."

The institute wrote that the dike separating the reservoir from the Dnipro can withstand a river level of 10m near the power plant.

"This water level and the watertightness of the retention basin will be closely monitored over the coming days. In the event of damage to the dike of the retention basin, pump trucks could be used to top up the spray ponds with the remaining water," in the Dnipro, the institute wrote.

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Edited by: Carla Bleiker