17 Février 2016
February 15, 2016
By HIROMI KUMAI/ Staff Writer
The nation’s nuclear watchdog decided that Tokyo Electric Power Co. can start freezing soil in a limited area around crippled reactor buildings at the Fukushima No. 1 nuclear power plant to prevent radioactive water accumulating in the buildings from leaking into the ground.
The conditional permission by the Nuclear Regulation Authority on Feb. 15 means TEPCO will get the go-ahead for a section of frozen soil wall in the area of the complex facing the sea.
Initial plans called for TEPCO to surround the four reactor buildings with a 1,500-meter-long circular frozen soil wall by inserting 1,568 pipes to a depth of 30 meters at 1-meter intervals. Each pipe would then freeze the soil around it once liquid of minus 30 degrees circulated inside the cylinder.
Building the wall was intended to prevent the flow of groundwater into the reactor buildings, where melted nuclear fuel has accumulated in the basements, thereby reducing the volume of water contaminated with radioactive substances.
TEPCO completed the installation of the pipes on Feb. 9.
However, the NRA was worried that the level of groundwater inside the frozen soil wall could drop drastically once the frozen soil wall surrounds the reactor buildings, causing levels of highly contaminated water in the reactor buildings to become higher than the groundwater level. That, NRA officials feared, would cause the highly contaminated water to leak into the ground.
With caution the buzzword of the day, the NRA had called on TEPCO to change plans and operate only a part of the frozen soil wall.
In a meeting held Feb. 15, the utility said it would freeze only the soil on the side of the stricken facility facing the sea.
Once the NRA grants official approval, TEPCO will move quickly to freeze the soil.
TEPCO also said that it wants to freeze the remaining portions in a step-by-step manner. The NRA supported the proposal, saying it would make it possible to "collect data on water levels.”
However, the two sides did not reach any agreement on this other than to continue their discussions.
The Nuclear Regulation Authority (NRA) approved a plan on Feb. 15 to gradually freeze a wall of soil around the crippled Fukushima No. 1 nuclear plant, starting with shields on the ocean side.
The NRA had expressed concern that if all the soil walls were frozen and if the groundwater level were mismanaged, highly contaminated water could leak out from the reactor buildings. With the NRA's approval of the plan, measures to deal with contaminated water will move a step forward. But it remains to be seen how effective the plan will be, as groundwater will continue to seep into the reactor buildings from the mountains.
Tokyo Electric Power Co., the operator of the damaged plant, presented an outlook for the project which stated that if the soil walls were frozen in stages, it would take about eight months to complete work to freeze all of the walls. The NRA is likely to allow TEPCO to start freezing the walls in or after March, making it impossible for the utility to meet its target of finishing work to freeze the walls by the end of March this year.
The shields set to make use of frozen soil have been built around the No. 1 to 4 reactors at the Fukushima nuclear plant. The NRA had pointed out that if the groundwater level inside the walls were to become too low, the level of highly contaminated water in the reactor buildings would exceed that of the groundwater, threatening to flow out of the reactor buildings. At a review session held on Feb. 15, TEPCO explained that the risk of contaminated water leaking from the reactor buildings would be smaller if the soil walls on the ocean side were frozen first, rather than following its original plan to freeze the walls on the mountain side first.
TEPCO explained that it would monitor future groundwater through a total of 69 water-level gauges, injecting water into the ground during an emergency and urgently transporting contaminated water from the reactor buildings in the event of operations of the frozen walls coming to a halt, among other measures.
NRA Commissioner Toyoshi Fuketa expressed his understanding of TEPCO's plan, saying concerns of the leakage of contaminated water had basically been defused. At the same time, he deferred a decision on whether to allow TEPCO to freeze all of the walls including those on the mountain side of the reactor buildings, saying that the NRA would make a decision on whether to approve the utility's subsequent plans after having the utility submit a detailed step-by-step process.
The project to install equipment to freeze walls of soil began in June 2014 and was completed on Feb. 9, 2016. The government has put more than 32 billion yen into the project. Altogether, 1,568 pipes are being used to create frozen soil walls stretching a total of about 1.5 kilometers around the reactor buildings, and walls reaching a depth of about 30 meters have been built underground to drastically reduce the flow of groundwater into the reactor buildings. Upon completion of construction, TEPCO has said it will be able to reduce the inflow of groundwater to several dozen metric tons per day from about 150 to 200 tons.