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.