TEPCO forced to drain water overflow from typhoon at Fukushima plant

Heavy rain from Typhoon No. 26 forced Tokyo Electric Power Co. to discharge rainwater Oct. 16 that was threatening to swamp the barriers that surround the radioactive water storage tanks at the devastated Fukushima No. 1 nuclear power plant.

TEPCO said all the water released was well within safety standards approved the previous day by the Nuclear Regulation Authority.

According to the utility, workers drained about 40 tons of water from within barriers in areas called C-West and C-East at around 5:40 a.m. The water was transferred to a temporary storage tank to check its radiation levels before it was released, TEPCO officials said.

But water levels continued to rise inside the barriers, threatening to spill over. Plant workers were eventually forced to open drainage valves on a total of nine storage areas starting around 7 a.m. to allow the water to escape, according to officials.

Earlier, TEPCO had said it would discharge water that accumulated behind the barriers only after transferring it to a temporary storage tank where it would confirm it complied with safety standards. TEPCO officials said circumstances forced it to take "emergency measures" because the water rose at a faster rate than it could transfer to the holding tank.

TEPCO presented a draft of its safety measures to the NRA on Oct. 15. The utility reviewed and modified the draft after NRA officials pointed out flaws in the measures.

The provisional measures, which the NRA approved late on Oct. 15, stipulated cesium-134, cesium-137 and strontium-90 levels should be lower than 15, 25 and 10 becquerels per liter, respectively, before water could be discharged. It also said the combined levels of those and other radioactive substances must, as a whole, be lower than the legal limit before being released into the environment.

Water exceeding the limit levels must be stored in empty tanks. TEPCO said it has secured 4,000 tons of tank capacity to store rainwater.