Japan’s nuclear watchdog will ease quake-related and other regulations on storing spent fuel to push the use of dry casks and reduce the dangers stemming from power failures at nuclear power plants.
The Nuclear Regulation Authority decided on Jan. 25 that utilities should place spent nuclear fuel in the special air cooling containers instead of the common practice of submerging the fuel rods in pools of water.
Fuel stored in pools is cooled by circulating water with pumps, but the system can shut down if earthquakes and other disasters cut off the power supply. The water could then evaporate, leaving the spent fuel and radioactive substances exposed to air.
Electric power companies have shown a positive attitude toward the dry storage system because it would enable them to keep more spent fuel when the pools are filled close to capacity.
However, municipalities that host nuclear power plants have expressed strong concerns that the system will let utilities keep spent nuclear fuel at plant sites for prolonged periods.
NRA Chairman Shunichi Tanaka stressed the need for safety.
“It (dry cask storage) is much safer than storing fuel in pools,” he said.
The Great East Japan Earthquake and tsunami cut off power to Tokyo Electric Power Co.’s Fukushima No. 1 nuclear plant in March 2011. Three reactors melted down, and the cooling system would not work for more than 1,000 spent fuel assemblies in the pool in the No. 4 reactor building.
Fears arose that all water in the pool could evaporate. But emergency measures, including the pumping in of water, were taken to keep the fuel submerged.
Under the dry storage system, the fuel is sufficiently cooled in pools and placed in dedicated airtight cases. The special casks are then stored inside air-permeable facilities.
The NRA plans to promote use of casks that are currently used to transport spent nuclear fuel.
The containers have passed durability tests and can withstand falls from a height of 9 meters and high-temperature fires.
Dry storage containers are widely used in the United States and Europe.
But the use of dry casks has not spread in Japan because of the high hurdles that must be cleared. One requirement is that those containers must be stored in building that can withstand the strongest earthquake predicted in the area.
As a result, dry storage containers are used at only a few nuclear facilities in the country, such as Japan Atomic Power Co.’s Tokai No. 2 nuclear power plant in Ibaraki Prefecture.
According to the Federation of Electric Power Companies of Japan, a total of 15,000 tons of spent fuel is stored at 17 nuclear plants across Japan.
Seventy percent of their fuel pools and other storage facilities have been filled with spent fuel.