31 Mai 2013
May 31, 2013
TOKYO (Kyodo) -- The government told Tokyo Electric Power Co. on Thursday to take action to prevent radioactive water from further increasing at its Fukushima Daiichi complex by building shielding walls in the ground by freezing the soil around the crippled reactor buildings.
The frozen soil, to be created by circulating coolant underground, is intended to block massive amounts of groundwater from seeping into the reactor buildings, where it gets contaminated by radioactive substances. The government expects the system to be in use from the first half of fiscal 2015.
According to a report compiled by a government panel on Thursday, there are no previous examples of walls to intercept water, created from frozen soil, being used for longer than a few years, making the project at the Fukushima plant "an unprecedented challenge in the world."
Economy, Trade and Industry Minister Toshimitsu Motegi told TEPCO President Naomi Hirose that the project is "very challenging" but drastic measures should be taken to address "one of most serious problems" in the process of decommissioning the plant's four units, which is expected to continue up to 40 years or so.
About 400 tons of groundwater seep into the reactor buildings every day, flowing into the lengthy and complicated water circulation loop that keeps the plant's damaged reactors cool. This means that the total volume of toxic water is increasing by the same amount daily.
TEPCO once considered building walls to intercept water after the plant was crippled by a huge earthquake and tsunami in March 2011, but it abandoned the idea due to fears that change in water pressure could lead contaminated water accumulating inside the reactor buildings to flow onto the soil outside.
The risks will remain even after the creation of walls with frozen soil, a method originally proposed by a contractor Kajima Corp., so TEPCO would have to control the level of water inside the reactor buildings such as by installing pumps.
To create frozen soil, pipes to run coolant will be inserted around the reactor buildings. The wall is expected to be 1.4 kilometers long and could be 30 meters deep in some areas, the industry ministry officials said.
According to one of the officials, the costs for creating the system will not become clear until details are worked out, but tens of billions of yen may be needed.
Motegi said the government will financially support the project's feasibility study by allocating part of the funds earmarked for research and development related to reactor decommissioning in the fiscal 2013 budget.
The problem of keeping massive amounts of radioactive water at the plant has drawn renewed attention after TEPCO recently found some underground water storage pools had leaked contaminated water and had to find a secure storage space.
The government also requested TEPCO to build tanks to secure a total of 800,000 tons of water storage capacity by the end of fiscal 2016, compared from the current 330,000 tons.
The Asahi Shimbun
May 31, 2013
Tokyo Electric Power Co. will implement a "difficult" proposal to use walls of frozen soil to reduce the amount of groundwater flowing into reactor buildings at its crippled Fukushima No. 1 nuclear power plant.
A government committee working on measures to deal with water contaminated with radioactive materials submitted the proposal to industry minister Toshimitsu Motegi on May 30. Motegi then instructed TEPCO President Naomi Hirose to carry it out.
"From a technical viewpoint, it will be difficult to do so," a TEPCO official said, "but we will implement the proposal along with other measures."
According to the industry ministry's Agency for Natural Resources and Energy, the proposal to create frozen soil walls to block the flow of groundwater into the reactor buildings was made by Kajima Corp., a leading construction company.
The proposal will also be incorporated into the government's "middle- and long-term road map" to decommission reactors at the plant.
According to the proposal, ducts will be inserted into the ground around reactor buildings at intervals of 1 meter to a depth of up to about 30 meters. Then, coolants of about minus 50 degrees will be circulated in those ducts to freeze the soil. The frozen soil will then serve as a wall against groundwater.
The wall will be able to block more groundwater than other walls that are made of clays or crushed stones and can be constructed more quickly.
However, the cost of creating the system is expected to reach several tens of billions of yen, and maintenance of the system will also entail considerable outlays. There are no instances of the system being used for extended periods.
The government, TEPCO and construction companies will set up a joint working group in June at the earliest to design the system, with the goal of putting it into practical use in the first half of fiscal 2015.
Contaminated water at the plant is being produced and accumulated in reactor buildings when water is used to cool melted nuclear fuel. Now, groundwater flowing into those buildings through cracks made by earthquakes and other impacts is increasing the amount of contaminated water by 400 tons every day.
The government estimates that the frozen soil walls will reduce the amount of groundwater flowing into the reactor buildings to 100 tons a day.
TEPCO is also considering a "groundwater bypass" plan in which it digs wells around reactor buildings, pumps up groundwater before it flows into the buildings, confirms its safety and then dumps it in the sea.
However, local fishermen are opposed to the plan on grounds it may fan groundless rumors that fish caught in local waters are contaminated with radioactive materials. TEPCO and the government are now trying to dispel that fear by offering detailed explanations to the fishermen.
(This article was written by Shunsuke Kimura and Keisuke Katori.)