Ukraine: cooling pond at Zaporizhzhia plant at risk after dam collapse

Nuclear safety organisation says loss of pool would not necessarily be catastrophic, but would dramatically increase safety concerns

The cooling pond at the Zaporizhzhia nuclear power plant is in danger of collapse as a result of the destruction of the Kakhovka dam and the draining of its reservoir, according to a French nuclear safety organisation.

Without the reservoir on the other side to counteract it, the internal pressure of the water in the cooling pool could breach the dyke around it, a report by the Paris-based Institute for Radiation Protection and Nuclear Safety (IRSN) said.

The loss of the pool would not necessarily be catastrophic as other sources of water could be brought in, such as pumping trucks, to prevent a meltdown of the plant's nuclear fuel, but a loss of the cooling pool would dramatically increase safety concerns at the plant.

Officials at the Ukrainian nuclear energy corporation, Energoatom, said that any collapse of the dyke around the cooling pond would be partial even in a worst-case scenario and that there would still be sufficient water to keep reactor cores and spent fuel cool, but they warned of the dangers of sabotage by Russian forces who are occupying the plant.

Since the collapse of the Kakhovka dam on Tuesday, its reservoir has been draining into the Dnipro River and the Black Sea beyond, and will soon drop below the water intakes used to pump water into an array of spray ponds that are used to cool the reactor cores and spent fuel at the site and the much bigger cooling pool used as a water reserve.

"We are reaching this dead zone, which is 12.70 [metres], after which there will not be any water intake either for the cooling ponds at the Zaporizhzhia station," Ihor Syrota, the head of Ukrhydroenergo, Ukraine's hydro power corporation, said on Thursday.

In the wake of the dam disaster, for which Ukraine, the UN, EU and other world leaders are holding Russia responsible, the head of the International Atomic Energy Agency (IAEA), Rafael Mariano Grossi, warned that "it is vital that this cooling pond remains intact". "Nothing must be done to potentially undermine its integrity," he said.

He later added that water from the Kakhovka reservoir was still being pumped to the power plant to cool reactors and other areas, though levels are at values earlier thought to make it impossible.

The plant can also rely on a large cooling pond above the reservoir with several months’ worth of water, Grossi said.

The IRSN report suggests that the integrity of the dyke around the pond could be in danger of collapse even without Russian sabotage.

"A drop in the Dnipro's water level could lead to basin leakage, or even to the collapse of the surrounding dyke, due to the pressure exerted by the water contained in the basin," it said. It added that Energoatom had conducted stress tests after the Fukushima nuclear disaster following a tsunami in 2011. Those tests, it said, estimated that the dike can "withstand a Dnipro level of 10 metres in the vicinity of the power plant".

"This water level and the watertightness of the retention basin will be closely monitored over the coming days," the report said.

Karine Herviou, the IRSN's deputy director general for nuclear safety, said that because all six reactors at the Zaporizhzhia plant had been shut down some months ago as a result of fighting in the area, the plant's cooling needs are limited and could be met by other means.

"If the dyke is destroyed as a result of the water pressure, there are other means to replenish the spray ponds, like pump trucks bringing water from the Dnipro or other water basin located nearby," Herviou told the Guardian.

Asked about the IRSN report, an Energoatom official said: "If the water level in the Kakhovka reservoir drops to less than 10 metres, the dam on the cooling pond may collapse, but not completely. Only the upper part may collapse.

"But even then, the amount of water that will remain will be enough to keep the plant in a cold mode."

The president of Energoatom, Petro Kotin, said on Thursday that the current water supply at Zaporizhzhia is enough "to keep the nuclear power plant in a safe mode of operation", but warned of the threat of Russian sabotage.

"The very fact that the Russians blew up the Kakhovka hydroelectric power station demonstrates that the Russians have no qualms about creating man-made disasters on earth," Kotin said in an interview on Ukrainian television. "They can do the same on the territory of Zaporizhzhya NPP [nuclear power plant]. The consequences will be very bad."

"The Zaporizhzhia nuclear power plant is heavily mined – both the interior and the access roads to it," he said. "We currently have no information about whether the Russians have mined the plant's equipment. This will become known after the plant is liberated."

Edwin Lyman, a physicist and director of nuclear power safety at the Union of Concerned Scientists, said: "Anything that challenges the integrity of the cooling pond would cause complications and require alternate means of getting water to the spray ponds, as the paper points out.

"My main concern at the moment is the increasing fragility of the site and the uncertainty regarding the ability of the reduced and stressed personnel to cope with a long-term emergency situation."