Effusion of radioactive cesium from incinerator fly ash by moisture absorption of hygroscopic chlorides

Abstract

The moisture absorption of calcium chloride in incinerator fly ashes was studied for estimating the effusion time of radioactive cesium from the fly ashes. Incinerator fly ashes generated around Fukushima Daiich Nuclear Reactors contain water-soluble cesium, so that they are planned to be stored for a long time in watertight structures. However, since the fly ashes contain a significant amount of hygroscopic calcium chloride, the radioactive secium is possible to be  eluted from the ashes by moisture absorption from the atmosphere no matter how the structures are watertight. Th results are summarised as follows: 1) The rate of moisture absorption is linearly propotional to the root square of time. 2) The effusion takes place when the pores of the ashes are filled with solutions generated by the moisture absorption. 3) The effusion time is proportional to the square of the height of the stored fly ash.