Removal of tritiated water molecules by isotope exchange reaction between HO vapor and tritium water.

Developing a cost-effective method for separating and concentrating tritium water (HTO) from light water (HO) without consuming additional energy is crucial for achieving reliable and safe nuclear fission and fusion energy technologies. However, this presents a significant challenge because of the difficulties in obtaining basic information, such as the chemical and physical properties of HTO molecules. Here, we investigate the isotope exchange reaction (IER) between HTO molecules in HO solution and HO vapor in the atmosphere. The reduction and purification rates of HTO-containing water were measured by varying the system conditions, such as temperature (20-50 °C) and humidity (50 %-90 %), under an equilibrium state between the liquid phase (water) and vapor phase (air). Our findings indicate that the concentration of HTO in the solution can be significantly reduced by increasing HO vapor in the atmosphere. This result can be quantitatively explained by considering the entropy of mixing between the solution and vapor phases. The results obtained here provide both basic understanding on the exchange process between liquid- and vapor-water molecules and a passive technology for treating HTO-containing water.