The Zaporizhia NPP (ZNPP) lost the connection to its last remaining main power line for almost five hours again amid reports of widespread military action, once more highlighting ever-present dangers to nuclear safety and security during the conflict, International Atomic Energy Agency (IAEA) Director General Rafael Mariano Grossi said in his latest update. It was not immediately clear what had caused the disconnection, but the plant was informed that a short circuit of the power line occurred around 95 km from the site, on the other side of the Dnipro River (in Ukrainian-controlled territory).
ZNPP has repeatedly lost power over the past two years due to military-related events at varying distances from the site. While the 750 kV line was unavailable, ZNPP continued to receive the external electricity it needs for reactor cooling and other essential functions from its only remaining back-up 330 kV power line, which itself was only restored in mid-March after an outage of more than three weeks. All 20 emergency diesel generators remain available in standby mode, in case of a total loss of off-site power. Before the conflict, the plant had access to ten off-site power lines, four 750 kV and six 330 kV lines.
IAEA experts at the South Ukraine NPP (SUNPP) reported that it too temporarily lost connection to one 750 kV and one 330 kV power line. It continued to have access to other power lines and remained in operation, albeit it at a reduced power output until the 750 kV line was reconnected.
“We are reminded once again about the very real dangers the ZNPP – as well as Ukraine’s other NPPs – are continuing to face every day as long as this devastating war continues. Once again, the off-site power situation at the ZNPP has been hanging by a thread,” Grossi said.
The power cut and reports of military action in Ukraine came after ZNPP earlier postponed planned maintenance of some of its reactor safety systems due to the “general situation in the plant’s surroundings”, without elaborating. Also this week, IAEA experts at ZNPP reported hearing an increased number of daily explosions occurring at different distances from the site, including what appeared to be outgoing artillery and machine gun fire from areas outside the ZNPP perimeter. It was the second time in recent weeks that the ZNPP postponed some maintenance at the site, adding to concerns about nuclear safety and security there, Grossi said.
Routine maintenance work on the safety systems of reactor unit 1 was first delayed when the ZNPP last month lost the connection to its only remaining back-up power line. After the 330 kV line was restored last week, the plant had intended to resume this work and conducted the necessary preparatory tests, before it decided to postpone it again.
After this decision, one of the unit’s safety trains that had been taken off-line and tested ahead of the planned maintenance work was put back into service again. ZNPP reactors each have three separate and independent redundant systems – known as safety trains – comprising their safety systems. However, maintenance on the same unit’s power transformer had already begun and it remains electrically isolated, though the unit can still receive off-site power.
“The world’s attention is rightly focused on the continued danger of Europe’s largest nuclear power plant being hit or losing its off-site power. But there are several other challenging areas that we must continue to monitor closely to help prevent the risk of a nuclear accident, including maintenance, as well as staffing and the availability of spare parts. They all form part of our deep concern regarding nuclear safety and security at the plant,” Grossi said. Before the postponement decision, IAEA experts had been informed that extended maintenance periods were being planned for units 1, 2 and 6 of the ZNPP during 2024.
The further postponement of maintenance activities has the potential to adversely affect the implementation of the ZNPP’s preventive maintenance plan for this year. Director General Grossi said in a report to the IAEA Board of Governors last month that the “situation in respect of maintenance activities, should it continue, is expected to have implications for nuclear safety over time, due to degradation of the safety systems and components”.
The IAEA team conducted walkdowns of the six main control rooms of the unit 6 reactor hall and safety systems rooms, as well as the emergency feedwater pumps and tanks of the same unit and unit 1, and observed the scheduled testing of several emergency diesel generators. The team also visited the turbine hall of unit 5, where the experts were able to visit all levels of the hall but were restricted from viewing the western part of the hall. The IAEA experts did not observe any nuclear safety issues during these walkdowns. The experts were informed that the four diesel steam generators had been shut down following the processing of around 1200 cubic metres of liquid waste and borated water.
Image: Zaporizhia nuclear power plant
