Tokyo Electric Power Co. says it has found that an unspecified amount of water contaminated with a highly concentrated radioactive substance escaped from another storage tank at the Fukushima No. 1 nuclear plant and some may have reached the Pacific Ocean.

Tepco said Wednesday it detected 200,000 becquerels per liter of beta ray-emitting radioactive substances, including strontium-90, far above the legal limit of 30 becquerels per liter, as well as cesium-134 and -137, both within their legal limits.

A ditch adjacent to the tank is linked to a drainage channel reaching the ocean. “Contaminated water may well have flowed into the sea,” Tepco said.

At a news conference held early Thursday at the Fukushima Prefectural Government office, a Tepco official apologized for “causing anxiety.”

The latest leak was found at one of the tanks in the B South cluster, separate from the H4 cluster where in August around 300 tons of water tainted with 80 million becquerels per liter of strontium and other beta-ray substances was discovered to have leaked. Some of that water is also believed to have reached the sea

The August leak was assessed as a “serious incident” on the international scale of nuclear accidents.

For the latest leak, a worker found water overflowing from the top panel of the tank in the B South area at around 8:05 p.m.

The tank was tilted, but it was “within a permissible range,” Tepco said.

The company said it gave a statutory notice to the central government about the leak and is checking the volume of water leaked.

The Nuclear Regulatory Authority has ordered Tepco to take steps to stem the flow of tainted water into the sea and remove contaminated soil.

The tank in question is a flange type made of steel sheets joined by bolts for storing contaminated water moved from cesium removal and desalination facilities. Tepco has said it is planning to replace these tanks with more watertight welded tanks.

Concerns have grown over Tepco’s handling of water in its fields of storage tanks at Fukushima No. 1.