A crucial difference between the accident at the Fukushima No. 1 nuclear power plant and the 1986 Chernobyl nuclear accident is the huge volume of highly radioactive water that is accumulating at the Fukushima plant.
A crucial difference between the accident at the Fukushima No. 1 nuclear power plant and the 1986 Chernobyl nuclear accident is the huge volume of highly radioactive water that is accumulating at the Fukushima plant.
There is a constant danger that the water could leak outside the plant.
Both the Fukushima and Chernobyl accidents are assessed at the most serious level of 7 on an international scale.
Tokyo Electric Power Co., the plant's operator, estimates that about 119,000 tons of contaminated water had accumulated in the basements of the No. 1 to No. 4 reactors of the Fukushima plant, as well as in the central waste processing facility, as of July 5.
The water is believed to have leaked from core vessels and leaky pipes after radioactive materials dissolved into the water pumped in from outside to cool the fuel rods.
According to one estimate, the contaminated water contains about 800,000 terabecquerels of radiation (1 tera is 1 trillion).
Radiation levels equivalent to what has already spewed into the atmosphere have accumulated in the contaminated water, and experts fear it could leak outside the plant.
While releases of radiation into the atmosphere peaked in March and are now moving toward being placed under control, the volume of contaminated water continued to increase by between 400 and 500 tons a day until the end of June.
Even now, four months after the accident, the danger of leaking contaminated water still exists, making it extremely difficult to bring the Fukushima accident under control.
The contaminated water has also accumulated in the trenches and shafts that connect the reactor and turbine buildings to the outside. Water containing high levels of radiation has leaked into the ocean.
On April 2, highly contaminated water flowed into a work pit near the water intake of the No. 2 reactor at the Fukushima No. 1 nuclear plant. That water later leaked into the ocean from cracks in walls near the reactor.
Over a four-day period before the leak was plugged, 520 tons of contaminated water flowed out, carrying an estimated total radiation of approximately 4,700 terabecquerels. That is about 20,000 times the annual emission standard established by the central government.
While TEPCO stopped the leak by plugging the cracks and shafts, as long as contaminated water remains there is always the danger of water leaking into the ocean through cracks in the wall that could allow it to flow into underground water.
The prospect of processing the contaminated water became more likely from July when a system of purifying the water to recycle it for cooling purposes started operating.
In its road map for bringing the Fukushima accident under control, TEPCO states that its first-step objective is the "stable cooling of fuel rods."
A main pillar for reaching that objective will be recycling purified water to cool the reactors.
TEPCO is seeking to purify 200,000 tons of contaminated water by the end of the year to eliminate all the highly contaminated water.
The recycling system comprises about 4 kilometers of piping that connects the reactor buildings and storage tanks. At the core of the system is the purification equipment.
Besides equipment to separate oil from the contaminated water and to desalinate water, equipment manufactured by Kurion Inc. of the United States uses a mineral to absorb radioactive cesium in the water.
Another machine manufactured by Areva SA of France uses a special solution to reduce the concentration of radioactive materials in the water.
The recycling system is an unprecedented one that mixes technology developed all around the world.
Plans call for purifying 1,200 tons of water a day and to reduce the concentration of radiation to one-10,000th to one-millionth of its original levels.
Unless the concentration is reduced to at least one-10,000th of its original levels, contaminated seawater cannot be passed through a desalination mechanism.
However, various problems arose in the early stages of the purification process.
On June 17, immediately after beginning normal operations, the radiation level in the cesium-absorbing equipment reached a level requiring replacement of parts very quickly, causing the equipment to stop operating.
After the recycling of purified water began June 27, operations had to be suspended after leaks were found in piping and the Areva equipment.
The problems are blamed on the rush to begin operations, which shortened the period for trial runs of the equipment to a minimum.
While additional steps to install more storage tanks have been taken, there is no change in the process: The recycling system must be operated while keeping a close eye on problems that arise.
The system is operating at 76 percent of capacity, below TEPCO's initial goal of 80 percent. If it becomes difficult to continuously operate the system 24 hours a day, TEPCO will have to extend its time frame for the volume of water to be purified.
Any delay in purifying the water will also affect the date at which the objectives in the road map can be declared achieved.