Between 1996 and 1999 a reconstruction project of the interim spent nuclear fuel storage facility was realized, including seismic reinforcement and expansion of the storage capacity.

The main objectives of the reconstruction were:

• the seismic reinforcement of structures and technological systems to withstand 8° on the MSK 64 scale,
• the expansion of the storage capacity from 5,040 to 14,112 pcs of SNF,
• the lifetime extension of the ISFS for another 50 years minimum, counting from the end of reconstruction work,
• the installation of a structural and technological monitoring system, including the monitoring of the condition of the spent nuclear fuel,
• the reconstruction of important technological, controlling, electrical and safety systems and of radiation control systems,
• the addition of a system for monitoring the tightness of the fuel cladding,
• the addition of an autonomous pool water cooling circuit,
• the addition of an own-supply diesel generator.

The expansion of the interim storage facility was not achieved by horizontally expanding the preexisting facility, but by using storage magazines more compact than the original ones. Spent nuclear fuel cartridges are currently being put into compact magazines, each with a capacity of 48 (originally 30). One pool can contain up to 98 of the compact magazines (originally 56). The storage capacity of the interim storage facility is now 14,112 fuel cartridges (originally 5,040). The temperature of the cooling water in the pool is maintained at 31–40 °C, 50 °C being the limit, which is secured, in response to the expansion of the interim storage facility capacity, primarily by the increase of the power of the pool water cooling station. The planned SNF storage period in the interim storage facility has been extended to 50 years.