Tokyo Electric Power Co. said Oct. 24 it has started transferring pools of rainwater at the Fukushima No. 1 nuclear plant to underground storage tanks that it had previously stopped using over fears of leaks.
The three underground storage tanks that TEPCO plans to fill have not leaked, according to the utility. But radioactive water escaped the No. 2 underground tank in April, and the company decided to no longer use the seven underground water storage tanks available at the site.
However, recent typhoons and heavy rains in the area have flooded enclosures around storage tanks holding radioactive water. Contaminated rainwater has spilled over the barriers and is believed to have reached the ocean.
The Nuclear Regulation Authority said TEPCO can use the underground storage tanks at its own discretion. But local government officials have called for the water to be transferred from the underground tanks to other storage tanks as soon as possible, TEPCO said.
Rainwater will be transferred from six storage tank areas where waterborne radioactivity levels exceed provisional safety standards. The readings of radioactive strontium and other beta-ray sources range between 29 and 970 becquerels per liter of water in the six areas, according to TEPCO officials.
The operations are intended to lower water levels in the enclosures to 10 cm or less ahead of possible downpours from Typhoon No. 27, which is threatening to hit the Kanto region this weekend. The barriers of the enclosures are 30 centimeters tall.
The utility said workers began transferring the water early on Oct. 24 into the No. 4 underground storage tank, which has a capacity of 4,000 tons.
On Oct. 16, TEPCO used the No. 7 underground storage tank in an emergency operation to deal with the heavy rains from Typhoon No. 26. It also transferred water from the barriers to the No. 7 tank during another downpour on Oct. 20.
In addition, TEPCO said it will temporarily simplify the protocol for testing radioactivity levels in rainwater within the barriers to help prevent the escape of contaminated water.
Currently, TEPCO is supposed to move the rainwater from within the barriers to temporary storage tanks for testing to eliminate errors caused by different readings from sampling point to sampling point.
TEPCO said that during heavy rainfalls, workers will now sample water directly from within the barriers for pre-drainage tests in areas that have shown low levels of radioactive contamination.
“It is not in our intention to change the protocol, but we are talking (to the NRA) about what to do during heavy rains,” said Noriyuki Imaizumi, acting general director of TEPCO's Nuclear Power and Plant Siting Division.
NRA Chairman Shunichi Tanaka said Oct. 23 that the protocol should be heeded in principle.
“Highly radioactive water in a tank may have dripped into the water pool behind a barrier,” Tanaka said. “Basically, it should be stored somewhere else before being released, if it can be released.”
TEPCO also presented a summary of the downpour on Oct. 20.
It said 2,400 tons of radioactive rainwater was collected in storage tanks, while an additional 3,000 tons of water that met the safety standards was discharged from the barriers.
The amount of water that overflowed is still not known, TEPCO added.
HIGH LEVEL OF RADIATION IN POOLING WATER
TEPCO also said Oct. 23 that 510,000 becquerels of radioactive strontium and other beta-ray sources were found per liter of water pooling behind a barrier surrounding an area where 300 tons of highly radioactive water escaped from a storage tank during the summer.
The company said the high readings have had no impact on the outside environment because no water has overflowed the barrier.
No new leaks have occurred from other tanks in the area, the utility added.
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