Zaporizhzhia Nuclear Power Plant to Raise Spent Fuel Pool Water Levels to Mitigate Power Outage Risks

The International Atomic Energy Agency (IAEA) stated that the operator of the Zaporizhzhia Nuclear Power Plant has decided to raise the water levels in the spent fuel pools on site to enhance safety buffer capacity in the event of a prolonged loss of external power.

The primary purpose of raising the water levels is to extend the time before water in the spent fuel pools begins to boil and evaporate under extreme conditions where external power to the plant is interrupted for an extended period, diesel reserves are depleted, and emergency diesel generators can no longer supply power to the cooling systems. Spent fuel pools are used to store used nuclear fuel underwater, typically for at least five years, allowing its radioactivity and residual heat to gradually decay, making continuous cooling a critical element of nuclear safety.

All six units at the Zaporizhzhia Nuclear Power Plant have been shut down, with the last unit transitioning to cold shutdown in April 2024. Although the reactors no longer generate electricity, spent fuel cooling, monitoring, and other critical safety functions still depend on a stable power supply. The IAEA reported that the plant has experienced 24 instances of loss of external power to date, half of which occurred in the past four months, with two occurring in just the past week.

Currently, the plant relies primarily on a 330 kV backup power line for its electricity supply, while the main 750 kV Dniprovska line has been unavailable since March this year. Although repairs were carried out with IAEA coordination, the line has not yet been restored due to damage to the associated substation. IAEA Director General Grossi noted that the plant requires reliable external power and that substations are an indispensable part of the nuclear safety system.