The operator of Japan's crippled Fukushima Daiichi nuclear power plant says a system to decontaminate the radioactive water in the plant's reactor buildings is not working as expected.

Tokyo Electric Power Company says a newly installed U.S.-built device has reduced radioactive cesium in the water to one percent of the previous level. But that is still 10 times higher than it was supposed to have been.

The system is critical to efforts to bring the plant under control as operators are running out of places to store the highly radioactive water after it is used to keep the plant's nuclear fuel from overheating. The recycling system will allow them to use the same water over and over, removing the risk of the overflow spilling into the sea.

TEPCO says other parts of the system are working as expected and that testing is continuing Thursday.