September 10, 2026 marks the 40th anniversary of the start of operation of the “wet” type spent nuclear fuel (SNF) storage facility — ISF-1.

The storage facility was built in 1986 and provided temporary storage of spent nuclear fuel using the technology adopted at that time: fuel assemblies are immersed in water, which is constantly circulated and cooled.

However, this storage method has its drawbacks. In addition, ISF-1 was designed as a temporary storage facility and is not designed for long-term safe storage, and its operation requires constant energy supply. The systems for circulating and cooling water in the fuel aging pools, ventilation, special water treatment, radiation control and automation operate around the clock. All this requires uninterrupted power supply.

In the conditions of a full-scale war and russian attacks on the energy infrastructure, dependence on electricity supply has become an obvious risk factor. In the event of a complete power outage at the Chornobyl NPP site, the critically important equipment of the SNF-1 is switched to power from stationary emergency diesel generators.

A modern solution is to store spent fuel in “dry” type storage facilities, where an active cooling system is not required to remove harmful heat from the fuel — the heat is removed due to natural air circulation.

This is the principle by which the ISF-2 of the Chornobyl NPP operates, the construction of which was completed by the American company Holtec. In 2020, the storage facility received a license for operation. At that time, the Ukrainian division of Holtec was headed by the current Director General of the Chornobyl NPP, Serhiy Tarakanov.

During the operation of the Chornobyl NPP in 1977–2000, more than21 thousand fuel assemblies were accumulated at the three power units of the plant. After the end of the operation of the power units, the spent nuclear fuel was placed in the ISF-1. The final unloading of fuel from the power units of the Chornobyl NPP was completed in June 2016.

On June 8, 2021, the long process of moving spent nuclear fuel from ISF-1 to ISF-2 began, designed for 10 years. The work was suspended during the occupation of the Chornobyl NPP in 2022, but after their resumption, the process continues according to plan.

As of September 10, 2026, 7,107 fuel assemblies have already been moved to ISF-2 — about 33% of the total. ISF-1, according to the license issued by the State Nuclear Regulatory Inspectorate of Ukraine, can be safely operated until December 31, 2034 (subject to the implementation of safety improvement measures).

All operations for the transfer of spent fuel are ensured in compliance with the requirements of nuclear and radiation safety, in particular in conditions of full-scale war.

“If we can work at this pace, we will have time to transfer all the spent nuclear fuel remaining in ISF-1 to ISF-2 within the validity period of the license for the operation of ISF-1.

After transferring the spent nuclear fuel from the old storage facility to ISF-2, we will be able to safely store the spent fuel for 100 years. It is very important that the dry storage facility does not require power supply to ensure long-term storage of spent nuclear fuel,” notes Serhiy Tarakanov, General Director of the State Enterprise “Chornobyl NPP”.