Fukushima Daiichi nuclear power plant. File photo: Toru Hanai

Tokyo - A Japanese nuclear plant may have to clean 15,000 tons of radiation-contaminated water again because of malfunctions in a water treatment system, news reports said Thursday.

Plant operator Tokyo Electric Power suspended the Advanced Liquid Processing System on Tuesday because one of its three lines did not remove radioactive material sufficiently. It said water that was not properly treated may have flowed into a total of 21 connected tanks, each with room to store 1,000 tons, at the Fukushima Daiichi Nuclear Power Station, the Kyodo News agency reported. The 21 tanks contain a total of some 15,000 tons of water, which workers may have to put through the system again to reduce its radiation level, the operator said.

Tokyo Electric has been struggling with the massive amounts of radioactive water at the plant as it continues to inject water into three of its six reactors to keep them cool.

The plant suffered meltdowns at the three reactors after a tsunami swept through the complex in March 2011.

Tokyo Electric started operating the water treatment system on a trial basis in February, but it has encountered a series of problems. If it was working at full capacity, about 750 tons of toxic water could be treated every day, the operator said.