It likely took highly radioactive water two months to travel just over 10 meters to reach a monitoring well that is at the forefront of the crippled Fukushima No. 1 nuclear power plant’s latest leak scare, according to Tokyo Electric Power Co.
The plant operator said Oct. 18 that 400,000 becquerels of strontium and other beta-ray sources per liter of water were detected a day earlier in the well located near the storage tank from where 300 tons of highly radioactive water leaked during the summer. The spike is about 6,500 times more than the 61 becquerels recorded in the well on Oct. 16. In addition, a record 790,000 becquerels of tritium per liter of water were also detected, more than three times the previous reading.
"Radioactive water that escaped the tank probably seeped into the soil around pumping equipment adjacent to the well and migrated into the well itself," Masayuki Ono, acting general director of the Nuclear Power and Plant Siting Division at TEPCO, said Oct. 18.
The utility is considering collecting the radioactive soil near the well and pumping out the contaminated groundwater, Ono added.
Strontium is believed to accumulate in bones and can cause bone cancer and leukemia. Tritium is a radioactive isotope of hydrogen.
The legal limit for release into the environment is 30 becquerels per liter for strontium and 60,000 becquerels per liter for tritium. They both emit beta rays, which are more easily shielded than the gamma rays emitted by cesium and other radioactive substances.
TEPCO began sampling groundwater from the well in question on Sept. 8 to gauge the spread of radioactive contamination. The levels of tritium, which easily spreads with groundwater, reached 320,000 becquerels per liter on Oct. 10. Strontium, on the other hand, sticks to soil and spreads more slowly. While 3,200 becquerels of strontium were found per liter of water when the monitoring began, its levels hovered between 60 and 90 becquerels per liter just days earlier.
As a precautionary measure, TEPCO dug an array of "bypass" wells where groundwater is intercepted before reaching the contaminated areas around the reactor and turbine buildings. If necessary, the groundwater will be rerouted to the ocean directly. There would be no risk of the water becoming contaminated. Those wells are located about 130 meters on the sea side of the well in question.
TEPCO officials said they will now take additional measures to prevent water in the bypass wells from becoming contaminated, adding that detection wells that are located between the storage tank where the leak occurred and the bypass wells so far have shown no increased radiation levels.
The utility also said Oct. 18 that it had collected 2,400 tons of rainwater that had accumulated behind barrier walls that surround storage tanks that hold radioactive water as a result of Typhoon No. 26.
It did so after determining radiation levels exceeded provisional safety standards. The utility said it will store the contaminated water in the basement of the turbine building for the No. 2 reactor.
TEPCO added it had discharged another 2,400 tons of rainwater from behind the barriers after confirming radiation levels met safety standards. Workers did so by opening up drainage valves on the barriers to let the water run into surrounding soil and along a drainage ditch to eventually reach the ocean.
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