The latest contaminated water leak at the Fukushima No. 1 nuclear power plant occurred at a flange-type storage tank, whose seams are connected by bolts.

Up to 32 liters of radioactive water leaked from a storage tank at the crippled Fukushima No. 1 nuclear plant, but the contaminated liquid has been contained, Tokyo Electric Power Co. said Oct. 6.

The leaked water is currently within barriers surrounding the tank that are designed to block the flow of fluids, TEPCO, the plant’s operator, said.

The liquid contained water that had been treated to remove radioactive strontium and other substances, as well as highly contaminated water from the bottom of the tank that was stored shortly after the nuclear accident started in 2011.

A radioactivity level of 590,000 becquerels of beta ray-emitting materials was detected per liter of the leaked water.

The water seeped out of a tank with bolted seams on its sides, which are more prone to leaks than those with welded walls.

TEPCO continues to use the bolted containers despite the risk because production of welded tanks cannot keep pace with the buildup of contaminated water, mainly from groundwater entering the damaged reactor buildings, at the nuclear plant.