# The Impact of Tritium in the Environment
## 5 Isotopic Effects of Hydrogen in Living and Inanimate Matter
### The Phenomenon of Isotope Osmosis
The fastest isotopic exchange occurred in the external water environment, with the rate constant of 2-3 orders of magnitude higher than the \"biogenic assimilation\" of tritium and isotopic exchange in the organic matter of plants. So, after a \"fast\" decontamination of the external water environment (feeding  
Figure 12: Fractionation of tritium during the growth of white willow. solution), one can observe a \"pseudo-accumulation\" of tritium in plants due to \"slow\" decontamination in the organic matter of living organisms after an accidental release of tritiated water into the environment. This was caused by the considerable difference between the rates of 3H/1H isotopic exchange in the water, the OH- and CH\(\equiv\) groups of living organic matter, and the diffusion of tritiated water through pores, cell membranes, and the root system [101]. Thus, currently, the most effective technique for phytoremediation from tritium contamination is phytovaporization by plant species that are able to fractionate hydrogen isotopes, such as white willow (see Figure 12). The electrochemical mobility of hydrated protons is almost twice that of hydroxyl anions. At the same time, the strength of the bond between the oxygen and hydrogen of the hydroxyl anion increases significantly in the triad of protium, deuterium, and tritium. When an external electric field is applied in the capillaries of clay membranes, ionic movement occurs uniformly in both directions at speeds corresponding to their mobility and the gradient of the applied electric field voltage. Therefore, the electro-osmotic method has a higher efficiency of hydrogen isotope fractionation compared to hydraulic filtration methods due to the electrocapillary effect. The results of a study on the electro-osmotic processes of hydrogen isotope separation in electrolyte solutions using clay membranes showed the high efficiency of this method for the purification of liquid radioactive waste from tritium contamination: up to 30% of the superheavy hydrogen isotope was removed from the solution in one purification cycle. The accumulation of the superheavy isotope in a solution of protium water (HTO) occurred in the anolyte and the neutral chamber (Figure 13a); the degree of fractionation (\(\alpha\)) reached 1.19. In a solution of deuterium water (DTO), tritium accumulated in the neutral chamber of the dialyzer (Figure 13b), and the degree of fractionation reached 1.25 [101]. The application of isotope osmosis phenomena is especially important for HWRs. The accumulation of tritium in the moderator of heavy water reactors above 10\({}^{11}\) Bq\(\cdot\)kg\({}^{-1}\) requires either the replacement of D\({}_{2}\)O (about USD 50 million/year for CANDU) or the isotopic purification of heavy water from tritium. Current facilities are very energy intensive and use a combined method of isotope exchange in a water-hydrogen vapor system and cryoscopic hydrogen isotope rectification. Through a catalytic isotope exchange reaction between water vapor and deuterium (Equations (11) and (12)) at a temperature of 200 \({}^{\circ}\)C, tritium and protium are extracted from heavy water and transferred to the gas phase:  
\[\text{DTO}+\text{D}_{2}=\text{DT}+\text{D}_{2}\text{O} \tag{11}\]  
Figure 13: Separation of hydrogen isotopes from water solution in 3-chamber dialyzer divided with bentonite membranes: (**a**) tritium–protium, (**b**) tritium–deuterium. \[\mathrm{HDO}+\mathrm{D_{2}}=\mathrm{HD}+\mathrm{D_{2}O} \tag{12}\]  
The degree of extraction of tritium from heavy water is limited by the equilibrium constant of the above reaction, and at the third stage, the purification is about 30%. The heavy water purified from tritium and protium is returned to the reactor. The mixture of hydrogen isotopes, i.e., \(\mathrm{D_{2}}\), DT, and HD, after purification from impurities and cooling to a temperature of 25 K is fed to the low-temperature column.