Tepco, the operator of the crippled Japanese nuclear power station Fukushima Daiichi said Tuesday that it had completed installation of the facilities required for creating a wall of frozen soil to the depth of 35 meters (about 115 feet) below the damaged plant, which is needed to stem the flow of water moving into radioactive areas.
About 400 metric tons of water flow underground through the plant each day, becoming contaminated as it does so. Tepco has been storing and treating the water, but not nearly at a fast enough pace to keep from having to buy and install huge water storage tanks on an ongoing basis.
The new system was expected to be installed and operational by March 2015, but delays hampered the project, which involved installing 1,550 pipes underground through which coolant will flow. The system will work, Tepco explains, in a manner similar to an ice skating rink, except that the pipes are vertical, and underground, rather than horizontal.
Tepco also explains that this is tried and true technology that has been used in construction of tunnels. The wall surrounding such construction projects is not frozen water, but frozen soil, the company said.
The company said the installation was funded by the Japanese government and cost $280 million. The containment area includes a tight rectangle that encompasses the containment buildings for Units 1 through Unit 4. The wall, once it is operating, will freeze the soil forming a barrier down to the bedrock, including the eastern side of the compound, which faces the sea. The wall, in this manner, is expected to halt or slow water flowing both in and out of the contaminated area.
The power plant, nestled next to the sea, is closer to sea level than the surrounding hills that rise behind it. Tepco says other water control measures, such as diversion ditches and tiling, are being taken in areas on the inland (western) side of the plant.
Tepco says the concept of the ice wall was developed to overcome the challenge posed by the many pipes and other subsurface structures associated with the reactor buildings – the underground infrastructure that comes along with an enormous nuclear power plant. If a conventional wall were built around these obstacles, creating watertight seals would have been extremely difficult, the company said.
By freezing the soil in a complete perimeter around those underground structures, the goal is to eliminate the need for other kinds of barriers by turning the soil itself into a watertight barrier.
The project was contracted to Kajima Corporation. Construction began in June 2014 and a test that has circulated the chilling liquid to specific parts of the wall has been underway since April 2015.
The north, south and west sides of the facility were completed last September and the remaining east side facing the sea were placed in the ground last November.
Even under ideal conditions, farmers, construction workers and civil engineers will tell you that water containment is extremely difficult. Water and gravity have frustrated humanity through the ages.
The current goal is to reduce water inflow from 400 metric tons a day down to 150 metric tons per day, but Tepco says the tonnage will change “based on weather and other fluctuating factors.” The aim is to reduce the water to a rate that is slower than the water treatment systems now in place. Contaminated water has been a major focus of the disaster containment and cleanup effort that began with the devastating Great East Japan Earthquake of March 11, 2011.
Here's a clip of Tepco's explanation of the ice wall technology:
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