Safe operation guarantees

Protective barriers for radioactivity isolation:

1. I barrier – fuel cladding
2. II barrier – multi sealed basket – internal steel container filled by helium
3. Ventilated concrete cask (mechanical and biological protection, vertical stability of MSB during transportation and storage)
4. Concrete storage site (structural and seismic stability)

Safety of storage in ventilated concrete casks is based on the following physical processes and is ensured by the structural decisions accepted in the design:

• ‌ In the process of spent fuel storage in the spent fuel ponds during 5 years, most part of short-lived radionuclides is decayed. Due to this, residual heat production of each fuel assembly is decreased to 1 kWt or even lower allowing for residual heat removal by means of natural convection.
• ‌ The storage system is designed for tight fuel not having any radioactivity release beyond the fuel cladding higher than the specified limits both during their operation in the core and storage in the spent fuel pond. This means that the primary protection barrier retains its efficiency during powerful energy impact and it is unlikely that it will lose this efficiency during long-time and slow cooling down in helium-air medium.
• ‌ 24 fuel assemblies to be stored are placed in hexagonal tube band located n the multi sealed basket. Thus, the multi sealed basket represents the second protective barrier preventing radioactivity release into the environment during unlikely situations of loss of integrity of the primary protective barrier. The multi sealed basket serves as radiator removing residual heat from the spent fuel to the ventilated concrete cask volume. Helium atmosphere is created and preserved in the cask during the entire storage period.
• ‌ Transportation of the basket within the reactor compartment volume is done in the specialized reloading container performing the following functions:
  • ‌ Biological protection of the personnel performing the transportation;
  • ‌ Protection of the multi sealed basket from mechanical impact during transportation;
  • ‌ Protection of the external MSB surface from contamination contained in the spent fuel pond.
• ‌ The multi sealed basked is placed into the VCC performing the following protection functions:
  • ‌ Removal of residual heat from the basket;
  • ‌ Protection of the basket from external climatic, mechanic and heat impact;
  • ‌ Biological protection of the personnel servicing SFDS;
  • ‌ Assurance of stable vertical location of the multi sealed basket with spent fuel during transportation and storage.
• ‌ Loaded ventilated concrete cask is installed on a specialized storage site. The site is located on the secured NPP site. It has its own security border and ensures the following conditions:
  • ‌ Seismic stability;
  • ‌ Prevention of free access of non-authorized persons to the SFDS area of radiation impact;
  • ‌ Stability of transport and lifting devices used during transporting and technological operations with the casks;
  • ‌ Removal of rain water from SFDS.

Thus, SFDS protective functions listed above ensure safety of spent fuel storage in ventilated concrete casks not worse – and in part of some parameters even better – than the level of spent fuel storage in the spent fuel ponds at the power units. Besides, risk of emergencies during transportation of VCC to SFDS on the plant size is not commensurable with risk of similar emergencies during transportation of TK-13 containers via railway. For 50 years of intermediate storage at the plant the potential risk will even be reduced and accordingly the risks during spent fuel transportation to the locations of their constant disposal or processing will be significantly reduced.