# The Impact of Tritium in the Environment
## 3 Waste Management
### Clay-Tritium Interactions  
The storage of solid tritium waste is accompanied by a \"fast\" diffusion of tritium gas desorbed from the metal and a \"slow\" formation owing to oxidation, as well as the diffusion of aqueous forms of tritium, requiring an improvement to the design of the engineering barriers [44].  
Experimental studies have shown that phyllosilicates (montmorillonite, sepiolite, palyorskite) can be such materials. The potential properties of layered silicates for the  
Figure 10: Tritium decay during storage: the points on the graph correspond to successive half-decays; the scale of the ordinate axis is logarithmic.  
accumulation and retention of tritium are determined by the structural and chemical features of minerals [45].  
The intensity and rate of isotopic exchange in the mineral-water system are determined by the accessibility of the reaction surfaces of the mineral particles for HTO molecules, the rate of exchange at the interface of these phases, and the rate of tritium diffusion in different parts of the system, including the pores, adsorbed layer, interlayer or zeolite water, and crystal structure. The main sorption positions for tritium in the order of exchangeability decrease are the surface, interlayer, and isotopic exchange of structural OH groups. The potential adsorption capacity of layered silicates (kaolinite, montmorillonite, palygorskite) for tritium is (1.06-1.81) \(\times\) 10\({}^{22}\) hydrogen atoms per gram of mineral [46; 47].  
Experimentally, we found that the most effective silicates were mixtures of bentonite and zeolite, with a potential tritium capacity of 10\({}^{13}\) Bq\(\cdot\)g\({}^{-1}\). It was found that 63 \(\pm\) 11% of the total tritium inventory in the mineral was accumulated in the surface-adsorbed state. In the interlayer space or channel structures, this amount was, on average, 24 \(\pm\) 10%, and in structural OH groups, it was up to 13 \(\pm\) 9%.  
Since clays lose their filtration properties after swelling, a clay-sand-zeolite mixture can be used. Changes in the volumetric ratio of minerals allow for regulating the filtration and adsorption properties of composites for various technological tasks (creation of filtration reaction barriers, arrangement of beds of NPP cooling ponds and technological reservoirs of spent nuclear fuel reprocessing plants, storage of radioactive waste, etc.) The retention rate of tritium (including decay) in these mixtures reaches 90% [48; 49].  
Based on the filtration and sorption properties of silicates of various structures and their mixtures, several technological improvements for the arrangement of NPP technological reservoirs, radioactive waste storage facilities, and liquid waste purification from tritium have been developed at the SI \"Institute of Environmental Geochemistry of NAS of Ukraine\" jointly with the DICI, University of Pisa.  
The current strategy in France to manage tritiated waste at 10\({}^{3}\)-10\({}^{4}\) Bq\(\cdot\)g\({}^{-1}\)\({}^{3}\)H involves interim storage for up to 50 years without any treatment. Nevertheless, several options are under study that are aimed at reducing the temporary storage duration and minimizing out-gassing rates and tritium discharges into the environment. It is also worth mentioning that no strict out-gassing limit has been set due to the very low level of tritium [50; 51]. An air emission assessment is required on a case-by-case basis before cementing large amounts of waste into disposal chambers. As for the disposal concept, it consists of two main biological barriers: an active one with a watertight geomembrane and a passive one that involves the use clay for its watertight properties [44].