Tokyo Electric Power Co. had to halt the transfer of radioactive seawater from one leaking sunken reservoir to another at its stricken Fukushima No. 1 nuclear plant after it found a new cistern leak, the Nuclear Regulation Authority said Tuesday.
Tepco had been moving the tainted water from reservoir No. 2 when water samples taken Tuesday morning from between waterproofing sheets of reservoir No. 1 showed salt concentrations had risen sharply from a day earlier. Tepco was also testing the water for radioactive substances.
The current water level of the No. 1 reservoir was unclear because Tepco had been in the process of transferring water.
There are seven sunken reservoirs at the Fukushima plant, whose surfaces are capped above ground, and three of them so far have been found to be leaky.
On Saturday, Tepco announced that 120 tons of seawater containing about 710 billion becquerels of radioactivity had escaped from reservoir No. 2 and leaked into the ground.
Because of that leak, Tepco had planned to transfer about 9,200 tons of its water to reservoir No. 1. But because of the leak in that cistern, the utility will move 6,200 tons of water that had already been transferred, as well as the remaining water in reservoir No. 1, to above-ground storage tanks.
Tepco said Tuesday it will continue using the remaining four reservoirs that haven’t leaked.
The utility has introduced a system to purify contaminated seawater leaking from containment vessels — first by removing radioactive substances and then removing salt — and recycling it as coolant for the crippled reactors.
The reservoirs were used to store water removed in this process that has high salt concentrations. Although cesium is removed, strontium still remains. Tepco has been testing a new purifying system called ALPS, which can remove 62 kinds of radioactive substances — including strontium, since the end of March.
Tepco built the cisterns as temporary storage for the tainted water by digging ditches and lining them with three waterproof sheets made of polyethylene and bentonite to prevent water from leaking into the ground.