1 Mai 2015
May 1, 2015
By HIROMI KUMAI/ Staff Writer
Tokyo Electric Power Co. started freezing soil at the Fukushima No. 1 nuclear plant in trial operations for an underground wall aimed at preventing groundwater from flowing into the damaged reactors and becoming radioactive.
The work was conducted at 18 points around the No. 1 through No. 4 reactor buildings on April 30 for the first time since the project started last June.
TEPCO plans to eventually create a 1,500 meter-long frozen soil wall around the reactors by circulating liquid of minus 30 degrees inside pipes 30 meters deep at 1-meter intervals. Under the project, the wall will divert the clean groundwater away from the plant and into the ocean, thereby stemming the daily accumulation of radioactive water at the plant.
The company says it will start creating the complete frozen soil wall after the tests are completed at the 18 points, where surrounding piping and other factors will likely make it difficult to freeze the soil.
But it is unclear when TEPCO will be able to begin the full operations.
In the trial run, TEPCO will use 58 underground pipes to freeze soil over a 60-meter distance on the mountain side of the nuclear facility. The company will monitor changes in temperature and groundwater levels near the test sites.
The trial operations, which are expected to take weeks to complete, are intended to determine if the method can create frozen walls even in locations with nearby structures and large volumes of groundwater.
TEPCO originally planned to start the freezing process of the entire 1,500-meter frozen wall by the end of March. But delays in preparatory work near the ocean, as well as a suspension of operations associated with safety checks following a worker’s death in January, pushed back the scheduled date.
In addition, the Nuclear Regulation Authority has required the utility to carefully examine the effectiveness of the project, so TEPCO decided to conduct the test operations before fully introducing the underground wall.
Tokyo Electric Power Co. (TEPCO), the operator of the stricken Fukushima nuclear station, began a test operation on the frozen soil wall installed around reactor buildings on April 30 to restrict groundwater flowing into the buildings.
The utility plans to ultimately surround No. 1 to No. 4 reactor buildings at Fukushima No. 1 Nuclear Power Plant with a 1.5-kilometer-long ice wall. Along with other countermeasures such as pumping groundwater out of the area, TEPCO expects to cut the daily amount of groundwater flowing into the reactor buildings from approximately 400 metric tons to less than 100 tons.
In the test operation, the utility poured cooling liquid into 58 pipes installed in 18 locations on the mountainside where the freezing time is believed to take longer due to buried objects in the area, and evaluated temperatures in surrounding areas and changes in the level of groundwater. There are 1,551 pipes surrounding the reactor buildings, including the 58.
In this diagram of the layout of Fukushima No. 1 Nuclear Power Plant, the blue arrows show how groundwater flows, the red dots show the 18 locations where test operations are being carried out and the ice wall is shown by a blue line surrounding the four reactor buildings.
TEPCO plans to release the test results sometime after mid-May.
It has emerged that when the frozen soil wall holds back water from flowing into reactor buildings, the groundwater level in areas inside the wall drops below the level of radioactively contaminated water in the reactor buildings, leading to concerns over the contaminated water leaking through damaged parts of the reactor buildings.
In the meantime, questions over water-level management are still under debate between the government, TEPCO and the Nuclear Regulation Authority, and the timing to start the full-scale freezing operation is still up in the air.