Tokyo Electric Power Co. on Friday formally revised its groundwater flow simulation and now believes up to 400 tons of contaminated water is seeping into the Pacific every day from the damaged Fukushima No. 1 nuclear plant.

The previous estimate was about 300 tons per day.

According to Tepco President Naomi Hirose, who was invited to appear as an unsworn witness at a special Diet committee session, the utility now believes 800 tons of groundwater are flowing each day into the compound and damaged reactors 1, 2, 3 and 4.

Of that, 400 tons is getting into the underground floors of the four reactor buildings while the other 400 tons is reaching the Pacific, according to a Tepco analysis based on the new simulation.

Hirose stressed that Tepco does not believe all 400 tons of the water entering the sea is contaminated with radioactive materials.

Even so, he said, the company has adopted a conservative scenario assuming that up to 400 tons is contaminated.

In its previous simulation, Tepco estimated that 1,000 tons of groundwater was entering the compound and 300 tons was eventually reaching the sea.

Hirose was speaking at a special session of the Lower House Economy And Industry Committee called to address the water problems at Fukushima No. 1. The committee is planning to meet again Monday.

Hirose repeated his apologies for the recent leaks of toxic water and a number of other troubles at the wrecked power station.

Meanwhile, Sumio Mabuchi, once an advisor to former Prime Minister Naoto Kan of the Democratic Party of Japan, claimed that the DPJ-led administration was considering back in 2011 to build a wall around the damaged reactors to keep groundwater from seeping in.

According to Mabuchi, Tepco persuaded the Kan administration to cancel the announcement of the ¥100 billion plan because the utility was worried about its financial situation.