10 Février 2016
February 10, 2016
By HIROMI KUMAI/ Staff Writer
The nation's nuclear watchdog has put the kibosh on plans by Tokyo Electric Power Co. to start freezing underground soil at the crippled Fukushima No. 1 nuclear power plant--a stunningly expensive project intended to solve the crisis of accumulating radioactive groundwater at the site.
TEPCO has maintained that once the soil is frozen, it will form a circular barrier and reduce the flow of groundwater into the reactor buildings; and that, in turn, will prevent water contaminated with radioactive substances from accumulating.
But the Nuclear Regulation Authority contends that contaminated water accumulated in the reactor buildings could leak into the groundwater if the level inside the frozen soil wall drops too much.
TEPCO planned to construct a 1,500-meter-long frozen soil wall around the four reactor buildings by inserting 1,568 pipes to a depth of 30 meters at 1-meter intervals. Each pipe will freeze the soil around it once liquid of minus 30 degrees circulates inside the cylinder.
On Feb. 9, TEPCO completed the last part of the project to install temperature indicators, allowing it to start freezing the soil at a moment's notice.
Groundwater is continuing to flow into basements of reactor buildings with melted nuclear fuel, adding to the amount of highly contaminated water being produced.
In May 2013, a committee of the Ministry of Economy, Trade and Industry drew up a report on the merits of constructing a frozen soil wall to reduce the volume of contaminated water.
Based on the report, TEPCO started the construction work in June 2014. The government has already spent about 34.5 billion yen ($300 million) on the project.
TEPCO maintained that once the frozen soil wall is completed, it should reduce the flow of groundwater into the reactor buildings from about 400 tons a day to 100 tons in tandem with other measures, including work to pump out groundwater from wells dug around the reactor buildings.
From the outset, the NRA cast doubt on the effectiveness of the frozen soil wall, saying that highly contaminated water accumulated in reactor buildings could leak into the ground if the groundwater level inside the wall drops too much.
The NRA repeatedly asked TEPCO whether the frozen soil wall would prove truly effective in reducing the amount of contaminated water.
“TEPCO is scattering a strange illusion that the problem of contaminated water can be solved completely if a frozen soil wall is constructed,” NRA chairman Shunichi Tanaka said in spring 2015.
In a test operation which started that spring, the reduction of groundwater levels was larger than expected in some places. The speed and direction of the groundwater flow could not be clarified in some locations.
Because it takes two months or so for the soil to thaw out, countermeasures cannot be taken immediately if problems crop up.
TEPCO acknowledges that there are limits to its crystal ball-gazing with regard to the problem of groundwater. However, it contends that it can prevent contaminated water from leaking into the groundwater by pouring water into the ground through wells if the level drops too much.
In December, the NRA took the rare move of proposing to TEPCO in a written document that the utility operate the frozen soil wall only in places where contaminated water is unlikely to leak into the ground.
However, TEPCO dug in its heels and said it intended to operate the frozen soil wall as a whole. But it also plans to consider the NRA’s proposal.
On Feb. 9, TEPCO President Naomi Hirose visited the NRA office and told Tanaka, “We will consider your proposal and get back to you in a most sincere manner.”