# The Impact of Tritium in the Environment
## 2 Artificial Sources
### Nuclear Power Engineering
During the reactor campaign, tritium release into the environment does not exceed 3% for the most common PWRs (Table 1). Tritium emissions during a reactor's campaign depend significantly on the technological process (Figure 4). As of 1 January 2024, almost 90% of annual tritium emissions were due to the operation of heavy-water reactors. Canada leads the world, generating almost 50% of global tritium emissions. A total of 97-99% of \({}^{3}\)H is contained in spent fuel assemblies subjected to continuous water cooling inside the reactor or independent ponds for 5-30 years. During this period, the diffusion of tritium from the fuel rods into the coolant water environment can reach up to 45%, and the permanent tritium concentration in the pool may exceed 3 GBq\(\cdot\)dm\({}^{-3}\)[25]. After the wet storage period, the spent fuel is transported to concrete dry storage facilities and is subsequently sent to a reprocessing facility. Most of the tritium produced in the power reactors is released during reprocessing: about 20% of the tritium appears in the solvent off-gases and is emitted through the chimney in the gaseous phase. Most of the remaining tritium is transferred to the aqueous phase and released into the environment in low-level waste streams [26]. The utilization of water and nitric acid for reprocessing results in the generation of large volumes of tritiated wastewater, about 100 m\({}^{3}\cdot\)t\({}^{-1}\). At plants close to the coast, these effluents are discharged directly into the sea. In India, tritium water is evaporated in the sun, while in the Russian Federation it is stored for a long time in open water reservoirs [5]. Thus, during the nuclear energy cycle, tritium generated in nuclear reactors is completely released into the environment (Figure 5). Figure 4: Modern annual tritium emissions from nuclear power engineering. Modern trends in the development of nuclear power demonstrate the depletion of heavy-element nuclear fission technology (Figure 6). This is determined by several objective reasons, such as the depletion of the raw material base, reaching the limits of increases in reactor capacity, safety issues, socio-economic problems, etc. During 1954-1973, the unit capacity was increased 200 times: from 5 to 1000 MWe. Over the next 50 years, it was possible to increase the unit capacity by 40-60% (~1.5 times). Currently, there are no technological developments that would allow for a significant (by an order of magnitude) increase in the unit capacity without compromising nuclear and radiation safety. If the current trend (Figure 7) continues, the share of nuclear energy (NEG, %) in global energy production will more than halve to 4% of global energy production by  
Figure 5: Release of tritium into the environment during the nuclear power cycle. Figure 6: Integrated Energy Generation (IEG) by different types of nuclear reactors. The shown trends were calculated based on the WNA and IAEA databases [13]. 2050, which is in line with the IAEA forecast (2.8-5.4%) [27], and to 1% by the end of this century [24]. The 28 th United Nations Climate Change Conference (COP-28) in December 2023 was a historic event that identified nuclear energy as a possible way to address climate change by helping countries meet their net zero emission targets by 2050, achieving the goals of the Paris Agreement [28]. The main achievement was the signing of an agreement to triple nuclear power capacity by 2050 by 22 world leaders [29]. Contrary to the trend of decreasing the share of nuclear power in global energy production, this decision will make a significant contribution to maintaining energy security while reducing carbon dioxide emissions. In anticipation of new fusion reactors in the coming decades, small modular reactors characterized by high construction rates, a higher level of safety, and acceptable technical and economic indicators can serve as a bridge between fission and fusion. The development of a hydrogen energy complex based on nuclear reactors also seems promising.