8 Mai 2013
May 8, 2013
The Asahi Shimbun
After a series of blunders, miscalculations and unresolved problems, Tokyo Electric Power Co. adopted a new strategy to avoid a total collapse of its system for handling radioactive water at its crippled nuclear plant.
TEPCO is running out of storage space for water used in the nonstop process of cooling the melted and spent fuel at the Fukushima No. 1 nuclear plant. Exacerbating the storage problem is the groundwater that keeps flowing into the plant’s buildings.
The company has dug 12 wells to the west of the reactor buildings, where it plans to pump up groundwater before it can enter the facilities and become contaminated.
“We would like to release that water into the ocean if we can gain the understanding of the relevant officials,”Toshihiko Fukuda, who heads TEPCO's Nuclear Quality and Safety Management Department, said at a May 7 news conference.
TEPCO officials will explain the plan at a meeting scheduled for May 13 of representatives of fisheries cooperatives in Fukushima Prefecture. If approval is obtained, the utility plans to start dumping the pumped-up water into the ocean the following day.
“We would like to cooperate in settling the situation by giving our approval once safety has been confirmed,” Tetsu Nozaki, chairman of the federation of prefectural fisheries cooperatives, said.
It would be the second time for water at the plant site to be released into the ocean.
Fisheries cooperatives in Fukushima Prefecture were forced to refrain from sending out their boats after highly radioactive water was dumped into the ocean in the immediate aftermath of the March 2011 nuclear accident.
Dealing with the radioactive water has long been an uphill battle for TEPCO in its overall plan to decommission the crippled reactors, a process expected to take decades to complete.
The situation deteriorated on April 5, when radioactive water was found leaking from underground storage tanks at the plant.
Water used to cool the fuel in the No. 1 to No. 4 reactors that were damaged during the accident has accumulated in the basements of the reactor buildings. Under TEPCO’s recycling system at the plant, this water has been pumped out, treated, and used again to cool the fuel.
However, about 400 tons of groundwater flow into the reactor buildings on a daily basis and mixes with the radioactive water.
According to calculations, 300 tons of groundwater would still flow into the reactor buildings every day even after TEPCO starts pumping up the water through the wells.
A general contractor on April 26 proposed building a wall to block the inflow of the groundwater. However, a similar proposal was dropped immediately after the nuclear accident over fears the water-shielding wall would cause contaminated water in the buildings to flow into groundwater at lower levels.
Currently, surface tanks at the Fukushima No. 1 plant hold about 280,000 tons of radioactive water. An additional 100,000 tons are believed to be flooding the basements of the No. 1 to No. 4 reactor buildings as well as the turbine buildings.
After the leaks were discovered in the underground storage tanks, TEPCO transferred about 8,000 tons of radioactive water from the faulty tanks to surface tanks by May 6. The remaining 16,000 tons or so will remain in the underground tanks until new surface tanks are completed in late May, according to TEPCO’s plan.
An estimated 120 tons of radioactive water leaked into the ground from the faulty underground tanks. Officials of TEPCO and the Japan Atomic Energy Agency say the contaminated water could mix with groundwater and reach the ocean in 10 years at the earliest.
TEPCO officials have yet to determine the cause of the leaks. One factor may have been the fact that they did not follow Environment Ministry guidelines for industrial waste.
The underground storage tanks were protected by a double layer of polyethylene waterproof sheets and a 6.4-millimeter-thick sheet of bentonite, a clay-like substance.
The ministry’s standards for controlled disposal sites for industrial waste call for at least 50 centimeters of bentonite to surround the waterproof sheets.
TEPCO officials apparently felt that a double layer of polyethylene waterproof sheets would be sufficient.
“It would be theoretically possible to prevent leaks for several decades to about a century if a layer of packed bentonite measuring at least 50 centimeters had been laid out outside of the sheets,” said Hideo Komine, a civil engineering professor at Ibaraki University. “The company should consider rebuilding the underground tanks.”
Handling radioactive water was often an afterthought for TEPCO officials. Soon after the accident, the main priority was cooling the reactors, so water was pumped in from every available source, including the ocean and nearby dams.
When the utility was criticized for dumping highly radioactive water into the ocean from the basements of the reactor buildings, officials decided a new approach was needed.
They stored the water at nearby buildings and started building surface tanks.
In June 2011, the utility began recycling some of the radioactive water to cool the reactors, after installing about 4 kilometers of piping.
TEPCO officials apparently never considered 400 tons of groundwater would flow into the reactor buildings on a daily basis.