Heavy Water Displacement in Molecular Sieve Drying Beds at Various Humidities

TL;DR

This study investigates how heavy water vapor displaces lighter water in molecular sieve dryers at various humidities, revealing that higher humidity accelerates mass transfer and can be modeled with sigmoid curves, aiding tritium control in nuclear systems.

Contribution

It demonstrates the displacement phenomenon of heavy water in dryers and quantifies the effect of humidity on mass transfer dynamics, informing passive tritium control strategies.

Findings

Significant displacement observed with humid heavy water streams.

Higher humidity results in faster, steeper mass transfer profiles.

Displacement profiles can be empirically modeled with sigmoid curves.

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.