Water levels in the basement of the No. 1 reactor building at the stricken Fukushima No. 1 nuclear power plant increased dramatically on May 29 and 30, raising fears of radioactive water leaking from the site.
The plant's operator, Tokyo Electric Power Co. (TEPCO), said the water level rose 19.8 centimeters over the 24 hours to 7 a.m. on May 30, 18 times the increase over the previous 24 hours.
The rising water level, apparently caused by rain flowing into the basement, is the latest headache for workers trying to contain the crisis at the plant.
With the typhoon and rainy seasons already drenching Japan, TEPCO had already expressed concern that a deluge could result in leaks.
TEPCO spokesman Junichi Matsumoto said before the latest data was announced: "The roofs of the No. 1, No. 3 and No. 4 reactor buildings have collapsed, so it is unavoidable that rain will get into those facilities."
With huge quantities of radioactive water being stored in various locations at the plant, and workers continuing to pump water to cool down the reactors, the worry is that additional heavy rainfall will inevitably increase the volume of contaminated water.
In the basements of the No. 2 and No. 3 reactors' turbine buildings, in particular, there is evidence that the pools of contaminated water are not isolated from the surrounding groundwater. Water levels in those buildings do not drop when water is removed.
As long as water is flowing from the surrounding groundwater into the contaminated water, because the level of the groundwater is higher than that in the basements, the threat of substantial leaks is not considered acute.
But if the level of the contaminated water rises above that of the groundwater, water would begin flowing in the other direction and is likely to spread contamination.
It has not been confirmed that contaminated water has leaked into the groundwater from the basements in large quantities, but the levels of contaminated water in the basements are currently only a few meters lower than that of the groundwater.
TEPCO has not yet decided how to deal with the issue. However, it has secured hoses to transfer contaminated water from the basements of the No. 2 and No. 3 turbine buildings. A large floating container, dubbed a "mega-float," is in place offshore to hold the contaminated water.
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