Tokyo Electric Power Company suspended one of 3 lines of the Advanced Liquid Processing System on Tuesday after workers found it was not reducing the concentration of calcium through the decontamination process.
The utility says the process relies on the chemical agent carbonate of soda to remove the calcium.
But it says a valve used to inject the agent was found to be shut, and that this was the cause of the problem.
The utility says it opened the valve and resumed the operation of the line on Wednesday.
The trouble arose not long after workers fixed another problem with the line that caused the water to be unusually cloudy in late March.
The company says it is possible the latest incident occurred because workers forgot to open the valve.
The treatment system is capable of removing almost all nuclear materials from radioactive water at the plant. TEPCO has been putting it through a test run since last year, and wants to launch full-fledged operation from April.
Filed under: 8.Eathquake & Nuclear accident