INTERDIFFUSION OF HELIUM AND ARGON IN SPEER MODERATOR NO. 1 GRAPHITE (A TERMINAL REPORT ON LARGE-PORE GRAPHITES--EXPERIMENTAL PHASE)

An experimental investigation of the interdiffusion and forced-flow behavior of helium and argon in Speer Moderator No. 1 graphite was performed. The data were employed to determine a mutual diffusion coefficient and to verify certain superposed-flow equations. In addition, two series of experiments at high values of the forced-flow component were conducted to investigate contributions of the backdiffusion mechanism of those pores whose diameters are equal to or smaller than the mean free path of the gas molecules, approaching Rhudsen or free-molecule difiusion. At small forced-flow rates, normal diffusion was the controlling diffusion mechanism, while Knudsen effects were negligible. Flow equations employed previously are applicable to these data. Experiments conducted at high forced-flow rates show the contribution of small channels, which appears to follow the Knudsen diffusion mechanism. A critical value of sweep rate was determined. If the sweep rate is lower than the critical, the contamination will increase, whereas sweep rates greater than this would require large reprocessing capacities without additional decrease in contamination. (auth