The Effects of Particle Size and Moisture Content on the Emanation of Rn From Coal Ash

Abstract

Measurements of the emanation coefficients of ²²²Rn from coal ash were performed. Samples of coal ash from a stoker-fired furnace were mechanically sized into four categories. The mean ²²⁶Ra concentration ofthese categories ranged from 11.82–16.77 dpm g⁻¹ and increased as a function of decreasing particle size. The mean bulk density and mean specific gravity of these categories ranged from 0.488–0.944 g cm⁻³ and 2.017–2.390 g cm⁻³, respectively, and both increased as a function of decreasing particle size. Samples of coal ash from four pulverized coal-fired furnaces were obtained, and demonstrated mean ²²⁶Ra concentrations ranging from 6.44–7.59 dpm g⁻¹. The mean bulk density and mean specific gravity of these samples ranged from 1.254–1.520 g cm⁻³ and 2.357–2.588 g cm⁻³, respectively. Construction of chambers and methods for measuring 222Rn emanation coefficients are described. The measured emanation coefficient is shown to be insensitive to ingrowth time at times greater than three days. Measurements of emanation coefficients from ash samples were conducted at moisture contents of 0, 1.0, 10, 20 and 40% moisture by weight, and showed an increase in the emanation coefficient as a function of moisture content up to about 20% moisture by weight. Above 20% moisture content, most samples showed a trend toward decreasing emanation coefficients. The fractionated ash samples showed an increase in the emanation coefficient as a function of decreasing particle size. An experiment was also conducted which confirmed that sample depth was insignificant in explaining the observed emanation coefficient over the range of depths used in the other experiments.