Ukraine’s Zaporizhia ZNPP (ZNPP) has been re-connected to its only remaining back-up power line after it was suddenly lost two weeks ago, International Atomic Energy Agency (IAEA) Director General Rafael Mariano Grossi said in his latest update. However, he stressed that the site’s overall supply of off-site electricity remains fragile and vulnerable to further disruptions.

During the military conflict, frequent power cuts have remained a source of serious concern for safety and security at ZNPP, which needs electricity to cool its reactors and for other essential functions, even when all units have been shut down.

Earlier this month, the ZNPP suffered its eighth complete loss of external electricity in less than 18 months, caused by grid events outside the plant itself. Since 2 December, it has depended on a single 750 kilovolt (kV) line, until the back-up 330 kV line could be repaired and restored this week. Before the conflict, the ZNPP had four 750 kV lines available as well as several back-up options.

ZNPP once again has two alternative sources of external electricity, said Grossi. “But we know only too well just how risky the power situation continues to be. Unfortunately, we can’t rule out more external power blackouts as long as this war continues.” Further underlining the potential dangers facing the plant, the IAEA experts at the site have continued to hear explosions relatively close to the plant, indicating ongoing military activities in the region where it is located.

Over the past week, the IAEA team has continued to conduct regular walkdowns, including to the plant’s temporary emergency response centre, used fuel dry storage area, and the reactor building of unit 5 as well as to the main control rooms of all six reactors, one after the other.

Recently ZNPP conducted an emergency communication drill, involving on-site and off-site representatives from different Russian organisations. The IAEA experts observed part of the drill. The IAEA team at the ZNPP again this week requested access to the 330 kV switchyard at the nearby thermal power plant to assess the situation regarding external back-up electrical connections there. As with previous requests, they were not granted such access this time.

However, the IAEA team was informed that they will be able to access the reactor rooftops in the coming days. The IAEA has previously been given access to three of the reactor roofs – of units 2, 3 and 4 – but not the others. Last week, the experts were granted partial access to the turbine halls of all six reactor units.

The IAEA team is continuing to pay close attention to maintenance activities at the site, including actions taken by ZNPP following last month’s detection of boron in the secondary circuit of a steam generator of unit 5. The IAEA experts were recently informed that the boron concentration levels in the secondary circuits of all the plant’s 24 steam generators were within the established limits, and that no further action would be taken at this time.

Of the site’s six reactors, five remain in cold shutdown, while unit 4 is in hot shutdown to produce steam and heat, including for the nearby town of Enerhodar, where most plant staff live. ZNPP has informed the IAEA that there are currently no plans to return unit 5 to hot shut down. Additional heating is provided by mobile diesel boilers installed at ZNPP together with boilers located in the nearby industrial zone and in the operators town of Energodar.

The IAEA teams of experts present at Ukraine’s Rivne, Khmelnitsky, South Ukraine NPPs and the Chornobyl site continue to report that nuclear safety and security is being maintained despite the challenging circumstances.

However, the IAEA teams at the Rivne and Khmelnitsky NPPs reported earlier this week that the mobile phone network had occasionally been disrupted in recent days. The teams were informed that the cause was a cyber attack on Ukraine’s communications network that affected most of the country. The IAEA experts were still able to carry out their work and communicate with headquarters in Vienna. Communications were also maintained between the NPPs, the national nuclear operator Energoatom and the state nuclear regulatory body.