Freezing water contaminated with radioactive cesium reduces the element to just 1/25th of its pre-freezing concentration, according to researchers at the University of Toyama.
The research team — including professor Masao Matsuyama of the university’s Hydrogen Isotope Research Center and professor emeritus Katsutoshi Tsushima, Japan’s leading glaciology researcher — added that the method could help reduce the amount of radioactively contaminated water at the Fukushima No. 1 nuclear plant.
The researchers contaminated water with 1,500 becquerels per liter of radioactive cesium to simulate the levels seen at the Fukushima plant. They put 10 liters of the water in a special freezing container, which they froze to minus 4 degrees Celsius, forming a 5.4 kilogram icicle with cesium concentration reduced to 61 becquerels per liter. The drop was particularly pronounced in the outer parts of the icicle, down to a maximum 1/270th the original concentration.
The method takes advantage of the fact that freezing the water slowly into a “single crystal” — a crystal where the direction of the crystallization is uniform — produces ice without impurities. Should this method be applied at the Fukushima plant, it could cut down the amount of contaminated water.
“I recalled icicles in nature, (and how pure they are even in mud), and though I was skeptical, our experiment produced results. This method should be able to assist the ALPS system,” said Matsuyama, referring to the decontamination system at the Fukushima plant.
March numbers put the amount of contaminated water at the Fukushima plant at around 530,000 metric tons. With full-scale operation of ALPS not expected for the foreseeable future, plant workers are coping by adding more storage tanks to hold the contaminated water.
Filed under: 8.Eathquake & Nuclear accident