13 Mars 2015
A contaminated rainwater leak reported at the crippled Fukushima No. 1 Nuclear Power Plant earlier this week might have been caused by radioactive soil that had been left untreated since 2012, plant operator Tokyo Electric Power Co. (TEPCO) said.
TEPCO reported on March 10 that approximately 747 metric tons of contaminated rainwater has leaked from barriers (30-50 centimeters in height) built around water storage tanks that hold radioactively contaminated water generated at the nuclear plant. Following the rainwater leakage, some 11,000 becquerels of beta emitting radioactive materials, such as strontium-90, were detected per liter of underground water around the water tank area, suggesting the possibility of contamination in underground water.
According to the utility, high doses of radiation -- up to 35 millisieverts of beta rays per hour -- were measured at an area outside the barriers on March 11. The soil in the area had absorbed some 100 tons of highly contaminated water when it leaked in 2012. A TEPCO representative says the utility may have failed to collect all the contaminated soil in the area.
TEPCO is beefing up the monitoring system at the shattered nuclear plant to find out the extent of the rainwater leak. A utility official commented, "There is no leakage from the storage tanks, and the underground water will not flow into the ocean."