Earlier in May this year, the power company began construction of a similar dry storage facility at the Genkai Nuclear Power Plants (PWRs, 1180 MWe x 2 units), which is expected to start operation in FY2027.
In a dry storage system, spent fuel that has been sufficiently cooled in the spent fuel pool is placed into a metal cask and cooled within a building through natural air convection. The system is characterized by not requiring water or an external power supply.
Both storage facilities are designed on the assumption that the stored spent fuel will eventually be transported to the Rokkasho Reprocessing Plant in Aomori Prefecture, which is scheduled to begin operation in FY2026.
At the Sendai NPPs, the storage capacity of the spent fuel pools had reached about 75% for Unit 1 and about 80% for Unit 2 as of September this year, and both were expected to reach their limits around 2034 and 2028, respectively. The lack of capacity had therefore become an urgent issue.
According to the company’s plan, the new storage facility will have the capacity to store up to 560 fuel assemblies. The structure will measure approximately 15 meters in height, 40 meters in width, and 40 meters in depth. The dry storage casks will be housed inside a reinforced concrete building equipped with radiation shielding. Even with the addition of the new facility, radiation levels at the site boundary, including existing buildings, are designed to remain well below the target of 50 μSv per year.
Each dry storage cask features a heat removal system that cools the fuel using outside air, a double-lid structure providing containment to prevent any release of radioactive materials, shielding functions using a metal body and neutron-absorbing materials, and a criticality prevention design achieved through the optimized arrangement of the fuel assemblies.
