20 Août 2014
August 20, 2014
By SHUNSUKE KIMURA/ Staff Writer
Tokyo Electric Power Co. said it will test cement and other materials as a sealant to completely stem the radioactive water pouring from turbine buildings into trenches at the crippled Fukushima No. 1 nuclear power plant, as ice walls are proving insufficient.
TEPCO's latest plan comes after ice walls at connecting points between the turbine buildings and the trenches failed to halt about 10 percent of the flow.
The plan was reported at a meeting of the Nuclear Regulation Authority on Aug. 19, which will consider the utility's proposal in September. If it gets the green light, TEPCO will immediately begin implementation, which is expected to be complete by the end of the month.
Currently, 11,000 tons of highly radioactive water have accumulated in the trenches, which extend from the turbine buildings toward the ocean. The water flowed into the trenches after the March 11, 2011, Great East Japan Earthquake.
The government and TEPCO have been constructing “frozen soil walls” to encircle reactor buildings and turbine buildings to prevent groundwater from entering those buildings and increasing the amount of contaminated water.
The process calls for first pumping out the radioactive water in the trenches. That also requires the construction of walls at connecting points between the turbine buildings and the trenches to prevent more contaminated water from flowing into the trenches. The construction of ice walls in trenches started in late April.
In the construction, bags filled with clay and cement are amassed before being frozen with chilled pipes to create the ice barriers.
But the ice walls have failed to completely block the flow of radioactive water. From late July, TEPCO added more than 400 tons of ice and dry ice around the connecting points in an attempt to freeze the radioactive water.
Ninety percent of the radioactive water at the connecting points was successfully frozen, but the remaining 10 percent continued to flow into the trenches. TEPCO concluded that the ice walls are insufficient.
The utility said it will test the effectiveness of concrete, adhesive sodium silicate glass, iron sand and various absorption agents as an additional barrier to halt the remaining flow.
TEPCO will decide by mid-September on which materials are most effective.
During the Aug. 19 NRA meeting, Shigeaki Tsunoyama, former president of the University of Aizu in Fukushima Prefecture, asked TEPCO to consider measures other than the ice walls.
“You took the current measures without making sufficient preparations and are now facing difficulties," said Tsunoyama, who is an adviser to the Fukushima prefectural government on nuclear issues. "You should change your way of thinking.”
However, TEPCO director Takafumi Anegawa said the ice walls have been effective, despite allowing the remaining flow.
“The ice walls can block 90 percent (of the flow of radioactive water)," he said. "We want to continue efforts with this method for the time being.”
Tokyo Electric Power Co. (TEPCO) has revealed a plan to review its ambitious scheme to create an ice wall in the entire section between a turbine building and an underground trench at the crippled Fukushima No. 1 Nuclear Power Plant to block radioactive water from flowing from the reactor building into the underground tunnel.
TEPCO, the operator of the Fukushima nuclear power station, had planned to remove contaminated water from the trench near the No. 2 reactor building after creating an ice wall to stop the inflow of contaminated water. But because the utility failed to completely freeze the water in the section between the turbine building and the trench, it will take an additional step of filling chinks in the ice with filler material.
A total of 11,000 metric tons of contaminated water has accumulated in the trenches built near the No. 2 and No. 3 reactors facing the Pacific Ocean, and the utility is to first start work to remove contaminated water from the trench for the No. 2 reactor. If the utility fails to remove contaminated water from the underground tunnels, it will not be able to proceed with a project to freeze soil and create a wall of ice around the four reactor buildings. Therefore, whether the additional measure is effective or not is likely to vastly affect measures to reduce radiation levels of water at the wrecked nuclear complex.
TEPCO has been trying to create the frozen wall since April by installing underground pipes to circulate coolant, but the work has not been done as originally planned. The company started to add a total of about 415 tons of ice and dry ice at the end of July, but it could freeze only 92 percent of the water in the section between the turbine building and the trench. Therefore, TEPCO judged that there were chinks at four locations in the frozen section at least. TEPCO officials say the speed of the water flow through the chinks increased, making it difficult to freeze water there.
At a meeting of experts from the Nuclear Regulation Authority (NRA) on Aug. 19, TEPCO showed a plan to seal chinks with filler material such as special cement. NRA officials are concerned about whether TEPCO's plan will have an adverse effect on the entire "ice wall" project. TEPCO will proceed with its original plan to install more refrigeration equipment. The utility will then decide whether to go ahead with the additional step after confirming the status of the operations again as soon as early September or mid-September.
NRA Commissioner Toyoshi Fuketa said, "The situation needs to be firmly confirmed because it could affect subsequent measures."
August 19, 2014
Aug. 19, 2014 - Updated 12:44 UTC+2
The operator of the damaged Fukushima Daiichi nuclear power plant is planning to try another method to freeze radiation-contaminated water in underground tunnels.
In April, Tokyo Electric Power Company began installing pipes to carry coolants in and out of the tunnels at the No.2 reactor. Workers hoped to freeze the wastewater to stop it flowing out to the sea.
But 3 months into the project, the water had yet to freeze. So the utility last month added more than 400 tons of ice and dry ice. It says this helped freeze over 90 percent of the tunnel cross sections, but there are still unfrozen areas where pipes could not be installed.
TEPCO now says it will be difficult to halt the flow of water with an ice blockade alone, so it has decided to seal chinks in the ice with filler material such as cement.
The utility on Tuesday explained the new plan at a meeting of the Nuclear Regulation Authority.
NRA experts agreed to make a decision on whether to approve the plan after they assess the effectiveness of using filler material in tests to be conducted by TEPCO.
A separate and larger project is now underway at the plant to freeze soil and create a wall of ice around the 4 reactor buildings. But concerns about the ice wall plan are rising, as the measure hinges on the success of removing contaminated water from the tunnels.