Tokyo Electric Power Co. is sticking to its goal of stabilizing the crippled Fukushima No. 1 nuclear power plant by July despite radical revisions to its initial strategy after larger-than-expected damage was confirmed.
Tokyo Electric Power Co. is sticking to its goal of stabilizing the crippled Fukushima No. 1 nuclear power plant by July despite radical revisions to its initial strategy after larger-than-expected damage was confirmed.
New data has painted a clearer picture of what happened at the plant immediately after the March 11 Great East Japan Earthquake and tsunami, including the start of a meltdown at the No. 1 reactor hours after the disaster.
Under TEPCO's new plan, the goal remains to achieve a cold shutdown of the reactors within five to eight months.
"There have been no changes that would have made us change" the goal," Sakae Muto, a TEPCO executive vice president, said.
But there have been major alterations in what TEPCO now plans to do. And because workers have still been unable to enter many locations within the plant, further revisions could be required if new problems arise.
The most progress has been made so far at the No. 1 reactor building, which workers entered in May. Based on their findings, they started a study of preparations on constructing a cooling system.
Under the company's strategy announced April 17, one of the first tasks was filling the containment vessels with water to cool the fuel rods within the inner pressure container.
The volume of water pumped into the No. 1 reactor building was increased in preparation for submerging the containment vessel at the No. 1 reactor.
However, workers realized that work within the reactor building would be difficult because of the high radiation levels found. And when the water gauge was adjusted, it showed that water was not accumulating in the reactor core as expected.
After a huge amount of water was found in the basement of the reactor building, TEPCO officials acknowledged that a meltdown had occurred in the No. 1 reactor and damaged the pressure vessel.
With the water leaking as soon as it was pumped into the core, workers faced the problem of finding and plugging the leaks in preparation for filling the containment vessel with water.
Realizing the extreme difficulty of that task, TEPCO officials abandoned the plan to submerge the vessel and downgraded that measure to a step requiring further study if water could not be pumped into the reactor.
High radiation levels prevented workers to take specific measures over the past month at the No. 2 and No. 3 reactors, including injecting nitrogen gas to prevent hydrogen explosions
Robots have been used to study the situation within the reactor buildings, but TEPCO could not determine specific levels of radiation in the No. 2 and No. 3 reactor buildings and whether workers could safely enter.
The suppression pool in the No. 2 reactor building that is connected to the containment vessel is believed to have cracks. The TEPCO plan calls for closing those cracks with concrete, but work has not started on that task.
One addition to the revised work schedule is consideration of ways to stop the flow of contaminated water underground or into the ocean.
Until now, TEPCO officials were considering moving radioactive water and storing it before decontaminating it.
Under the new plan, contaminated water will be recycled back into the reactor building to cool the core, meaning that radioactive water will accumulate in the building for long periods. TEPCO needs to come up with measures to prevent that water from leaking outside plant facilities.
Contaminated water that has already accumulated within the plant has posed persistent problems for the workers.
As delays emerge in moving the contaminated water to a storage pool, water must still be pumped into the reactor buildings to cool the fuel rods.
The water pumping is now a one-way process. That water is believed to be leaking through damaged parts to the basements of the reactor and turbine buildings as well as trenches outside the buildings.
The danger exists that this contaminated water could spill into groundwater or the ocean.
If TEPCO is unable to come up with a way to purify the contaminated water before recycling it for cooling purposes, radioactive water will continue to increase in volume.
About 87,500 tons of contaminated water is believed to have accumulated within the plant. That figure could increase to 200,000 tons by December.
Contaminated water in the turbine building of the No. 2 reactor and outside trench had particularly high levels of radiation and caused further problems because some of it flowed into the ocean. Work began from April 19 to move that water to the central waste processing facility within the plant.
However, checking the No. 2 reactor building for leaks has been a time-consuming task. Under the new plan, TEPCO officials decided to reduce the amount of water moved to minimize the risk of leakage.
Even when water was moved, the levels in the trench and building basement did not decrease very much. Instead of trying to move all the water as originally planned, TEPCO officials have decided to move only enough water so that it does not overflow from the trench.
Other measures are needed to prevent contaminated water from flowing into the ocean from the trench.
On May 11, highly contaminated water was found leaking into the ocean from near the water intake of the No. 3 reactor. The possibility exists that radioactive water can leak from anywhere at anytime into the groundwater or ocean.
TEPCO officials said work to install a temporary tank for the contaminated water by mid-July is continuing.