Bad weather has damaged a silt fence erected to contain radioactive material escaping from the crippled reactors at the Fukushima No. 1 nuclear plant, Tokyo Electric Power Co. said Thursday, raising fears that more tainted water might flow into the Pacific Ocean.

The breach was found at 10:40 a.m. Thursday near intact reactors 5 and 6, which take in core-cooling seawater that is later pumped back into the ocean.

Unfavorable weather has prevented a thorough examination of the fence, a Tepco spokesman in Tokyo said Thursday afternoon. Repair work will start as soon as the sea calms.

The fence is meant to keep earth and sand out of seawater intakes for units 5 and 6. It is also designed to block radioactive material coming from damaged units 1, 2, 3 and 4, where another silt fence is set up.

The fences are suspended from floats and anchored with weights on the seafloor. But it is thought that large amounts of radioactive materials have already drifted into the Pacific anyway.

However, the density of radioactive substances outside the artificial bay remains well within legal limits, probably because it is being diluted by seawater.

The Nuclear Regulation Authority has ordered Tepco to take seawater samples and monitor the density of radioactive materials. In April, the same fence near units 5 and 6 was damaged by rough waves and bad weather.