The effort is aimed at replacing the water with cement. The water is believed to be leaking into the nearby sea after mixing with groundwater.
Workers on Tuesday poured into the tunnels 80 cubic meters of cement that can solidify in water. The plant's operator, Tokyo Electric Power Company, said the water did not overflow during the work.
The operator says it plans to check the effectiveness of the measure in about a month after suspending the work temporarily. It says if there are no problems, it will resume the work to finish it by March.
The firm initially planned to freeze water at the ends of the tunnels to stop inflow from reactor buildings, and remove the contaminated water. But the plan did not work. By last week, the utility had decided to adopt the new method.
Workers using the method are likely exposed to more radiation than under the original plan.