Ukraine's Zaporizhzhya Nuclear Power Plant (ZNPP) lost its immediate back-up power supply to the reactor units for several hours this week, in the latest incident underlining persistent nuclear safety and security risks at the site, Director General Rafael Mariano Grossi of the International Atomic Energy Agency (IAEA) said today.
Thursday's failure of two of the ZNPP's back-up power electrical transformers showed the continuing vulnerability in the availability of external power, which the plant needs to cool its six reactors and for other essential nuclear safety and security functions.
Even though the back-up 330 kilovolt (kV) line remained available and could have provided power to the ZNPP if the 750 kV line was lost, the failure reduced the redundancy of the already fragile power supply. These two power lines are the only ones that remain available for Europe's largest nuclear power plant (NPP), compared to four 750 kV lines and six 330 kV lines before the conflict.
The back-up power supply was restored eight hours later when two other back-up power electrical transformers were put into operation. The ZNPP is investigating the cause of the failure, informing the IAEA experts at the site that there was no sign of external transformer damage.
The incident came just a few weeks after the ZNPP - following discussions with the IAEA - carried out work on the back-up power electrical transformers so that the 330 kV line could immediately deliver electricity if the 750 kV line were to fail, as has happened repeatedly during the armed conflict.
"The plant's vulnerable power status remains one of the main dangers for nuclear safety and security at the site. The situation remains extremely worrying in this respect. The site has already lost all off-site power eight times since August 2022, forcing it to rely on emergency diesel generators," Director General Grossi said.
During the past week, the IAEA experts discussed the plant's maintenance activities with the ZNPP and were shown its high-level 2024 maintenance plan for such work, which is vital for nuclear safety and security. The ZNPP informed the IAEA team that the priority is to perform maintenance on the site's safety systems as well as important activities not conducted last year. The annual maintenance plan includes the safety systems, diesel generators, unit transformers and the 750 kV electrical switchyard.
The IAEA team did not receive a copy of the maintenance plan for a detailed review. However, based on discussions and information provided to the team, the IAEA concludes that the ZNPP will not be implementing a comprehensive maintenance plan during 2024.
"A well-established maintenance plan and its timely implementation are essential to ensure plant safety and security," Director General Grossi said. "This maintenance needs to be performed to ensure nuclear safety, especially in the current situation where the six reactors have been shut down for an extended period. It is important that the IAEA has a thorough understanding of the maintenance plans to be able to fully assess nuclear safety at the ZNPP. We will continue to monitor the maintenance situation closely."
The IAEA team has continued to conduct walkdowns at the site, including to all six main control rooms yesterday, where the experts were able to observe staffing levels but could not ask questions about their qualifications and experience.
After being granted access to the reactor hall of unit 6 earlier this week, the IAEA experts are still seeking access to the other reactor halls, as well as to parts of all six turbine halls that they have not yet been able to visit, as well as to some of the reactor rooftops. Such access is needed to monitor nuclear safety and security as well as adherence to the five concrete principles for the protection of the ZNPP, Director General Grossi said.
The IAEA team has continued to monitor the situation and gather information regarding boric acid deposits in some of the safety system rooms of unit 6, which were first observed on 22 December. During yesterday's visit to its main control room, the team confirmed that the level of boric acid in the storage tank was above the minimum level in the technical specifications, despite the previously observed leak of boric acid.
Mines along the perimeter of the ZNPP, in a buffer zone between the facility's internal and external fences, which were previously identified by the IAEA team and were removed in November 2023, are now back in place. This is a restricted area inaccessible to operational plant personnel. Director General Grossi reiterated that the presence of mines is inconsistent with the IAEA safety standards.
Elsewhere in Ukraine, the IAEA teams at the Rivne, Khmelnitsky, and South Ukraine NPPs as well as the Chornobyl site continue to report that nuclear safety and security is maintained despite multiple air raid alarms heard over the past week. The IAEA experts at the Khmelnitsky, Rivne and South Ukraine NPPs have reported air-raids on a near-daily basis with the teams at the Khmelnitsky and Rivne NPPs required to take shelter on several occasions.
