Following the explosion at the Kakhovka dam and hydro plant in southern Ukraine – which flooded a huge area and displaced thousands of people amid the beginning of the anticipated military counter-offensive by the Ukrainian army – the International Atomic Energy Agency issued a statement on 11 June about the threat to the nearby Zaporizhzhya nuclear power plant. IAEA director general Rafael Grossi emphasised the need for experts of the IAEA to gain access to a location near the NPP to clarify the situation.

The level of the Kakhovka reservoir has been dropping rapidly since the downstream dam was breached on 6 June, but the ZNPP reported shortly afterwards that it had been stable for about a day as measured at the inlet of the Zaporizhzhya thermal power plant (ZTPP) where water is pumped into a channel for use at the nearby nuclear power plant.

By 9am local time on 11 June, the water level by the ZTPP was estimated at 11.27 metres, down from nearly 17 metres before the dam was breached, according to data received by IAEA personnel at the ZNPP site.

However, the height is reportedly continuing to fall elsewhere in the huge reservoir, causing a possible difference of about two metres compared with the level reported by the ZTPP. The water level is a key parameter for the continued operability of the water pumps.

IAEA visits the site

“With military activities and tension intensifying in the area near Zaporizhzhya … and with this month’s dam catastrophe further complicating the facility’s extremely challenging nuclear safety and security status, it was very important for me to travel to the site again to review developments on the ground, including the plant’s ongoing and planned measures to manage the new water-related difficulties,” said Rafael Grossi.

Subsequently during the week of 12 June Mr Grossi assessed at first hand the impact of the Kakhovka dam disaster on the safety of Zaporizhzhya NPP during his third visit to the site in less than a year. The DG and his team crossed the frontline just over a week after the water level in the reservoir that supplies cooling water to the ZNPP started to drop significantly. He also met with president Volodymyr Zelensky in Kyiv, presenting a new IAEA technical assistance package to help Ukraine cope with the subsequent flooding devastation through the application of nuclear science and technology in areas ranging from potable water, human health, soil and water management to integrity assessment of critical infrastructure.

It is clear that the level of the Kakhovka reservoir has declined markedly – even exposing previously submerged sand banks – but also that the plant’s large cooling pond and different channels at or near the site hold sufficient reserves to be able to provide cooling water in the short to medium term in case the reservoir can no longer be used.

At the moment, water from the discharge channel of the nearby Zaporizhzhya Thermal Power Plant (ZTPP) supplies the ZNPP’s spray ponds, which cool the six shut down reactors and spent fuel, and also keeps the separate cooling pond full, mainly compensating for evaporation.

Together, the discharge channel and the large cooling pond can provide cooling water for some months provided they stay intact, although it is difficult to say exactly how long the existing water reserves can last in view of various external factors, such as evaporation and any future leaks.

There are also indications that some water resources from the reservoir itself currently remain available in areas near the ZNPP but it is unclear if the level is high enough to pump it up for use at the plant. The pumps have not been in operation for over a week.

The IAEA team has evaluated all the main components of the site’s water supply systems, including the gates separating the large pond and the ZTPP discharge channel from the reservoir, and how the plant is seeking to ensure that these bodies of water are kept secure and preserved.

For example, the plant has completed activities to seal and reinforce the isolation gates to prevent leakage. Director General Grossi witnessed how they had been reinforced with counterweights and sand.

“The integrity of these gates must be maintained to ensure that the plant has enough water for cooling the reactors. At the same time, it is essential that the plant implements a longer-term solution. The IAEA team can assist and advise in this work,” he said. The measures the plant is taking are buying it some extra time to prepare additional back-up water supply options, the DG added.