Water releasing as much as 10 trillion becquerels of radioactive strontium and 20 trillion becquerels of cesium-137 from the Fukushima No. 1 power plant has flowed into the Pacific Ocean since May 2011, Tokyo Electric Power Co. estimates.

The combined figure of 30 trillion becquerels, announced late Wednesday, implies that highly radioactive water is entering the trenches under the damaged reactors’ turbine buildings.

The three reactors that had core meltdowns are being flooded by emergency cooling water needed to keep the leaky units stable, but the water is leaking from the reactors into the basements, where it is mixing with groundwater penetrating the walls of the 40-year-old plant.

Since the 30 trillion becquerels can’t be accounted for just by groundwater alone, it is likely the toxic water from the trenches is entering the mix as well, the beleaguered utility said after conducting various simulations.

The Fukushima complex was built on a maze of trenches that guide cables and pipes needed to transport electricity and water. The pipes lead to the sea because the power plant, like all the others in Japan, needs seawater for cooling purposes.

The 30 trillion figure is about 100 times more than what Tepco had been allowing to enter the sea each year before the crisis.

Containment fences set up in the plant’s man-made harbor are failing to keep the flow from reaching the greater Pacific.

Tepco belatedly acknowledged last month that about 300 tons of groundwater from the mountains behind the crippled plant flows daily to the sea after mixing with radioactive water leaking from the reactor buildings’ cracked foundations.

This week, however, it discovered that about 300 tons of filtered water from one of its hundreds of temporary storage tanks had escaped. The water had been cleansed of most of the cesium but still contains other harmful materials, including tritium. The incident has been rated level 3 on the International Nuclear Event Scale. The meltdowns were rated level 7, a status that remains unchanged.

Tepco first claimed the tank water had not reached the sea, only to reverse itself Wednesday after detecting a relatively high reading of 6 millisieverts per hour in a drainage channel running from the tanks to the sea. The channel, made to prevent rainwater from flooding the tank premises, is not covered.

Tepco said Thursday that two more tanks are leaking.

On Monday, when Tepco announced the first tank leak, it confirmed seeing traces of water running from the tank to the drainage channel, and detected 96 millisieverts per hour of radiation in the air near it.

Tepco has been unable to locate the leak but said it finished transferring the water to other tanks nearby Wednesday night. It plans to check for more tank leaks.

While some of the water might have gone into the sea, it is hard to determine where it all went. Tepco projects that it’s been losing about 10 tons a day for the past 30 days from the tank, which is considered a temporary model as it is made of steel sheets bolted together with their seams sealed, instead of the more reliable welded tanks.

The leak was discovered after workers noticed water puddles near the tank Monday. Nuclear Regulation Authority officials and outside experts said Wednesday that if 10 tons of tainted water flowed out over 30 days, it is hard to imagine no one would notice it before Monday.

At an NRA meeting Wednesday evening on the tainted water issue, the panelists pointed out a long-held suspicion: that the water may be going into the ground through cracks in the concrete base.

“It is more natural to think the water went underground,” said Masaya Yasuhara, a researcher at the National Institute of Advanced Industrial Science and Technology. Tepco rejects that scenario because concrete isn’t that permeable.

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