Tokyo Electric Power Co. says there is somewhat less radioactive water in the tunnel linked to one of the reactors, amounting to 210 metric tons of water, according to broadcaster NHK.
The report says the water level in a tunnel that holds piping and wiring for the reactor building is seven centimeters lower, indicating that removing it is showing some success.
TEPCO outlined plans Monday to take about 10,000 cubic meters of contaminated water from the turbine building of reactor unit 2, and move it to a treatment plant that will be built on site. The plan is to use the treated water to cool the reactors, so that new water need not be brought in and TEPCO can stop dumping radioactive water into the ocean.
The water treatment equipment will be supplied by AREVA, the French nuclear power plant company. The system will first remove oil from the water, said Jean Christophe Piroux, deputy director of research and development at AREVA. After that, chemicals will be added to react with the cesium and strontium, which will precipitate out as solids that can be removed.
At that point the water will be desalinated, as it is a mixture of fresh water and seawater that was used to cool the reactor after a tsunami knocked out the generators that powered the pumps.
Robots sent in to two other damaged reactors buildings, No. 1 and No. 3, found levels of 49 and 57 millisieverts per hour, respectively. The levels in reactor No. 1 are enough to kill a person after about eight days of exposure. The levels in reactor No. 2, Piroux said, are even higher.
The high levels of radioactivity in the water means that it will have to be shielded as it is moved from the reactor building to the treatment facility, Piroux said. Radiation dosages are cumulative, so the amount of time a workers spends in the area has to be limited, even with protective clothing.
Piroux also noted TEPCO asked that the water be treated again after AREVA's process is complete, with zeolite, a mineral absorbent.
Contamination of the water, according to TEPCO, is mostly iodine-131 and cesium-137. There are also traces of strontium-90.
Iodine-131 has a half-life of about eight days and the cesium's is about 30 years. Iodine and cesium are particularly dangerous because even though iodine decays quickly, it concentrates in the thyroid. Cesium dissolves easily in water and is thus absorbed by several different tissues. Strontium is a bone seeker and concentrates there.
Contamination levels are at 3 billion becquerels of cesium per liter of water and 13 billion becquerels of iodine per liter. The legal limits for radioactive cesium in Japan are 200 becquerels per liter, while for iodine it is 100 becquerels per liter.
Radiation exposure inside the plant for workers is expected to be high as they try to extract the water. TEPCO said radiation exposure will likely be about 0.011 millisieverts per hour surrounding the building where the water is stored. Nuclear plant workers at Fukushima are limited to doses of about 250 millisieverts per year. It would take two years to reach that limit at the exposure level TEPCO is planning for -- if one is outside the building. The radiation dosage from working around the water itself is expected to be much higher.