Study on the measurement method of diffusion coefficient for radon in the soil (IV)

Iida, Takao*

The aim of this study is to clarify the radon behavior in the soil at the waste rock yards of uranium mine. We have developed an apparatus for measuring radon diffusion coefficient in soil under the control of soil temparature. The radon diffusion coefficients changed suddenly around the soil temperature of 0 degrees centigrade. The radon diffusion coefficients in dry soil have little temparature dependency, and were comparable coefficients obtained by empirical formula of Rogers & Nielson. To study the restraint effect of radon exhalation by covering with bentonite on soil, we carried out the measurements and the calculations by using one-dimensional transport model of atmosphere and soil. The decrease of radon exhalation rate was 2.9 Bq m-2 s-1 when soil covered with the bentonite of 5 cm thick. The radon consentrations in snow cover and the radon flux from the snow surface were measured at the waste rock yard in Ningyo-toge Environmental Engineering Center. The simulation of the radon transport in snow also carried out using measured snow parameters. The radon concentrations in snow cover ranged from 500 to 3,000 Bq m-3, and the radon flux from the snow surface was about 9 mBq m-2 s-1. The small radon flux results mainly from the wet condition of soil surface caused by melting of the snow.