Tokyo Electric Power Co. has presented a two-stage scenario to stabilize the crippled Fukushima No. 1 nuclear power plant, but it is unclear whether its goals can be achieved as scheduled.
Tokyo Electric Power Co. has presented a two-stage scenario to stabilize the crippled Fukushima No. 1 nuclear power plant, but it is unclear whether its goals can be achieved as scheduled.
At least six months will be needed to achieve a cold shutdown of the reactors, which means bringing core temperatures under 100 degrees, according to the company's road map announced April 17.
In the first step, which will take about three months, TEPCO plans to cool the reactors in a stable manner and cap the amount of radioactive materials released.
In the second step, expected to be completed in six to nine months, the company aims to achieve cold shutdown and substantially reduce the amount of radioactive materials.
Industry minister Banri Kaieda said April 17 that the government plans to decide whether evacuees who were living in areas from around the Fukushima plant can return home after TEPCO's second step ends in six to nine months.
The government plans to review evacuation zones at that time after consulting with the Nuclear Safety Commission of Japan.
But TEPCO Chairman Tsunehisa Katsumata suggested the road map is only a list of all conceivable measures to deal with the crisis.
"There is no guarantee that we will be able to carry out the plan 100 percent," he said April 17. "We want to start with whatever we can do and cool the reactors successfully."
The key goal is to stabilize the reactors and storage pools for spent fuel rods, which have been releasing radioactive materials.
According to TEPCO, the risk of hydrogen explosions continues at reactors No. 1, 2 and 3, which have been cooled just enough to keep temperatures from rising to dangerous levels.
Nitrogen has been injected into the No. 1 reactor's containment vessel. In the first step of the road map, it will also be injected into the No. 2 and 3 reactors.
Water will also be poured into the containment vessels to cool the pressurized vessels that contain the fuel rods in a stable manner.
In the second step, TEPCO aims to restart circulating cooling systems to achieve a cold shutdown of the reactors.
Radioactive steam is still leaking from the containment vessels at the No. 1 and 3 reactors. TEPCO must locate and plug the leaks before the containment vessels are filled with water.
According to TEPCO, the No. 2 reactor will require additional work because its containment vessel was damaged and highly radioactive water is still flowing out.
While the company plans to close the damaged parts with cement, identifying those parts will be difficult.
In addition, the suppression pool connected to the containment vessel was likely damaged in a hydrogen explosion. Large amounts of highly radioactive water will flow into the ocean if water is poured into the containment vessel.
TEPCO therefore plans to seal the areas around the suppression pool with cement to prevent water leakage.
TEPCO aims to restore regular circulating cooling systems for the fuel storage pools at reactors No. 1, 3 and 4, where pumping trucks have been pouring in water from the outside.
A normal cooling system is already in operation at the No. 2 reactor.
According to TEPCO, the No. 4 reactor's fuel storage pool is vulnerable to earthquakes because of damage to the lower sections of the walls of the reactor building that support the pool.
In the first step, concrete supports will be installed at the bottom of the storage pool to bolster its anti-quake strength. The cracks in the lower parts of the walls will also be sealed.
TEPCO said it cannot yet tell when work can begin on anti-quake reinforcements.
In the road map's second step, a circulating cooling system will be restored while water trucks are deployed to pour water into the pool.
Over the midterm, TEPCO hopes to remove fuel rods from the pool, but specific methods to safely remove and store the damaged fuel rods have yet to be worked out.
The road map also aims to contain the release of radioactive materials into the atmosphere and the ocean.
In the first step, tanks and other facilities will be installed to store highly radioactive water found in the basements of the turbine buildings and outdoor trenches.
In the second step, the reactor buildings will be covered with special sheets.
An estimated 60,000 tons of highly radioactive water is in the basements of the turbine buildings alone.
TEPCO plans to move the contaminated water to a 30,000-ton central waste processing facility at the plant and install temporary tanks to store 12,000 tons by late April.
The water will also be moved to an offshore floating structure provided by the Shizuoka city government that can hold 10,000 tons.
The company also plans to set up a water treatment facility to remove radioactive materials using filters and flocculation agents.