The operator of the Fukushima Daiichi nuclear power complex said Saturday that highly radioactive water was leaking from a pit near a reactor into the ocean, which may partially explain the high levels of radioactivity that have been found in seawater off the coast.

Tokyo Electric Power Co. said it had detected an 8-inch crack in the concrete pit holding power cables near reactor No. 2 and was working to seal the fracture. Tepco said the water was coming directly from the reactor and the radiation level was 1,000 millisieverts an hour. The annual limit of radiation exposure allowed for Fukushima workers is 250 millisieverts.

Workers pumped concrete into the shaft Saturday, but by the end of the day the flow of water into the ocean had not diminished. Engineers speculated that the water was preventing the concrete from setting, allowing it to be washed away.

Tepco officials said that on Sunday morning they would explore using a polymer — a type of quick-setting plastic — to plug the leak.

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