Heavy Water Displacement in Molecular Sieve Drying Beds at Various Humidities

Abstract

Tritium plays a critical role in nuclear fusion power plant designs and dryer beds are an essential tool for managing tritiated water vapor. A series of tests were performed to investigate the ability of a saturated dryer to preferentially adsorb heavy water vapor. The design of passive tritiated control systems is feasible by utilizing a dryer's ability to preferentially trap heavier isotopologues of water. This work investigates this displacement phenomenon and the effect of the heavy water humidity on the dryers performance. Significant displacement was observed when a humid stream of heavy water was diverted through a dryer pre-saturated with light water, as indicated by changes in the partial pressures of $D_2O$ and $H_2O$. After the capture of heavy water in the bed, the subsequent rise in $D_2O$ partial pressure depended on the humidity of heavy water in the gas stream. Higher humidity values lead to faster and steeper mass transfer profiles in the dryer, which could be empirically fit with sigmoid curves.