On 10 August Ukraine’s Zaporizhzhya Nuclear Power Plant (ZNPP) was reconnected to its only remaining main 750 kV supply, Dniprovska power line, at approximately 19:00 local time after it had been disconnected at 16:13. It was the second outage of this power line on that day.

The disconnections meant that ZNPP had to rely on its only remaining off-site power line, the 330 kV backup line, to supply the electricity that is required, for pumping reactor cooling water and other essential nuclear safety and security functions. There was no total loss of off-site power to the site and there was no need to use the emergency diesel generators. The International Atomic Energy Agency team on site were informed that the disconnection occurred 5.5 km from the open switchyard on the southern bank of the river owing to the activation of an overcurrent protection system.

“The repeated power line cuts underline the continuing precarious nuclear safety and security situation at the plant” said IAEA director general Rafael Grossi on 10 August. The plant’s external power situation remains highly vulnerable, underlining the precarious nuclear safety and security situation at the site.

Cold shutdown

ZNPP has started transferring reactor unit 4 to cold shutdown following the detection of a water leak at one of its four steam generators located in the containment of unit 4. This is to determine the precise cause of the water leak and to conduct maintenance to repair the affected steam generator. There was no radiological release to the environment.

Unit 6 is now being heated to hot shutdown state to continue steam generation. As the unit is not yet in hot shutdown state, there is currently no steam being generated at ZNPP.

The other units at ZNPP remain in cold shutdown. The Ukraine national regulator – SNRIU – some time ago issued regulatory orders to limit the operation of all six units to a cold shutdown state. The IAEA continues to strongly encourage the installation of an external source of process steam, which, from a nuclear safety perspective, would provide the safest longer-term solution for the steam needs at the site.

The availability of cooling water remains relatively stable at ZNPP. While the height of the ZNPP cooling pond continues to drop by about 1cm per day, the height of the discharge channel from the neighbouring Zaporizhzhya Thermal Power Plant (ZTPP) is regularly being topped up by pumping water from the ZTPP inlet channel.

Mining of the perimeter

On 4 and 8 August, the IAEA team visited the dry spent fuel storage facility, and the unit 2 main control room, emergency control room and other safety-related rooms. They did not observe any mines or explosives in these areas or in any new locations, they did confirm the presence of the mines located at the perimeter of the site, and previously observed on 23 July 2023.

Following the IAEA experts’ visit to the unit 3 and unit 4 rooftops previously, the team continues to request access to conduct walkdowns on the rooftops of the other four units.