2 Septembre 2016
September 2, 2016
By KOHEI TOMITA/ Staff Writer
Rainfall from recent typhoons caused partial melting of the “ice wall” at the Fukushima No. 1 nuclear plant, allowing highly radioactive water to leak from around the damaged reactor buildings, the plant’s operator said Sept. 1.
Tokyo Electric Power Co. said melting occurred at two sections of the ice wall, which is designed to divert groundwater away from the reactor buildings.
TEPCO officials believe that during the latest typhoon, contaminated water from around the reactor buildings flowed through openings of the ice wall created by the deluge and reached downstream toward the sea.
The groundwater level near a seaside impermeable wall temporarily rose to 28 centimeters below the ground surface when Typhoon No. 10 passed the area on Aug. 30.
Before the typhoon hit, the water level was 35 cm below the surface.
Around 5.5 cm of rainfall a day fell in the area when the typhoon hit.
The groundwater level, however, actually rose by 7 cm, although 740 tons of groundwater was pumped out of the section.
“If there had been an additional 15 cm of rain, (the contaminated water) could have poured out over the ground surface” and spilled into the sea, a TEPCO official said Sept. 1.
The Meteorological Agency’s initial forecast said Typhoon No. 10 would bring a maximum 20 cm of rain a day at some locations in the Tohoku region.
The 34.5-billion-yen ($335 million) frozen wall was completed in spring to prevent groundwater from entering the reactor buildings and mixing with highly radioactive water.
TEPCO admitted the underground wall of frozen dirt is not working.
The company said the temperatures at the two sections of the frozen wall have climbed above zero since Typhoon No. 7 approached Fukushima Prefecture on Aug. 17.
The company believes that the partial melting was caused by the influx of water brought by the typhoons and heavy rain in between.
TEPCO plans to freeze the wall again by pouring chemicals into pipes that extend underground.
The operator of the crippled Fukushima Daiichi nuclear power plant says due to recent heavy rain temperatures rose above zero degrees Celsius in some parts of an underground ice wall.
Tokyo Electric Power Company has been trying to freeze soil around damaged reactors since March. The aim is to cut the volume of contaminated water by reducing the flow of groundwater into damaged reactor buildings.
But the company says a series of storms have been dumping heavy rain in and around the plant since mid-August, pushing up temperatures in some sections of the ice wall.
The utility says wall temperatures to the south of the No.4 reactor rose from minus 5 degrees to plus 1.8 degrees at the highest through Thursday. It adds wall temperatures to the east of the No.3 reactor also went up from minus 1.5 degrees to plus 1.4 degrees.
Temperatures in these sections had been higher than others parts of the wall even before the storms. It's feared that some ice in the sections may have melted as the rain increased groundwater flows.
In response, the firm decided to inject a chemical agent in these 2 places to solidify soil, reduce water flow, and speed up freezing.
Experts point out that the ice wall is not as effective as estimated in decreasing groundwater flows. Discussion on the effectiveness is underway at the Nuclear Regulation Authority.