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| Fig. 1: Shevchenko BN-350 nuclear heated desalination plant (Source: Wikimedia Commons). |
Approximately 4 billion people are currently experiencing severe water stress for at least one month per year, with half a billion people facing severe water scarcity all year round. Furthermore, global freshwater demand has increased by nearly 1% per year since the 1980s, while renewable freshwater availability per capita has declined by 7% over the past decade, reflecting growing pressure on finite water resources. [1,2] This crisis has intensified in recent decades, fueled by rapid population growth, urbanization, agricultural expansion, and the escalating effects of climate change.
To curb this growing crisis, seawater desalination has emerged as a potential technological response, with global contracted capacity being approximately 95 million m3/day across more than 15,000 plants. [3] Seawater desalination is the process by which a plant is used to remove the salt and minerals from seawater to produce freshwater. Seawater desalination processes use reverse osmosis, a process in which seawater is pushed through a high-pressure semipermeable membrane that allows water molecules to pass but blocks salts and other impurities. However, traditional desalination techniques are highly energy-intensive and carbon-intensive, with fossil-fuel-powered desalination producing 76 Mt CO₂ annually and projected to reach 218 Mt CO₂/year by 2040 if current trends continue. [4]
One method that has shown up in response to this is nuclear desalination. Nuclear desalination addresses fossil-fuel dependence by directly coupling nuclear reactor electrical or thermal energy outputs to desalination systems, enabling freshwater production with lower operational carbon emissions. [5] Historically, these systems have been applied, with one example being the Soviet BN-350 fast reactor at Aktau, Kazakhstan, shown in Fig. 1, which co- produced electricity and up to 120,000 m3/day using a Multi-Stage Flash process with fossil boiler supplementation from 1973 to 1999. [6] Ultimately, the reactor was shut down in 1999 upon reaching the end of its 20-year design life, as post-Soviet funding constraints precluded the safety upgrades required for continued operation. [7] Currently, countries like India and Japan operate their own nuclear desalination plants, and several others, including China, Egypt, and Saudi Arabia, have shown interest in developing them. With water stress intensifying globally and climate change increasing precipitation variability, nuclear desalination offers a low-carbon pathway to secure freshwater supplies.
Nuclear reactors can be coupled to desalination systems through three pathways: thermal, electrical, and hybrid. In thermal coupling, low-pressure steam is extracted partway through the turbine cycle and routed to thermal desalination processes like Multi-Stage Flash (MSF) or Multi-Effect Distillation (MED), which use heat to evaporate seawater and condense the vapor into freshwater. In electrical coupling, the reactor operates conventionally to generate electricity, which then powers the high-pressure pumps needed for Reverse Osmosis (RO), a membrane-based process that forces seawater through filters to separate salt from water. Hybrid coupling combines both approaches, using extracted steam for thermal desalination while the remaining steam generates electricity to power RO systems. One of the primary challenges when designing these systems is balancing the outputs and the split between power and water production, which entails choosing whether to extract more steam for desalination; however, that reduces electricity generation. [8]
Beyond mechanical coupling, these two methods offer different operational benefits. Thermal processes like MSF and MED are robust, relying on evaporation rather than filtration, allowing them to process saltier water that could clog or damage a filter. Furthermore, thermal desalination produces high-purity water, which is often required for sensitive industrial applications. On the other hand, RO is a more energy-efficient and compact choice. Because RO doesn't require the energy needed to boil water, RO systems have a much smaller physical footprint and lower overall energy consumption for the water they produce. Additionally, RO systems have recently undergone major developments in membrane durability and energy recovery devices, making them one of the most common choices for large-scale desalination projects. [8,9]
The primary radiological concern for the outputs of nuclear desalination systems is tritium, which has a viable transport pathway from reactor to product water during normal operations because of its incorporation into the water molecule and ability to permeate metal barriers. One key regulatory factor for these systems is that tritium production varies by reactor type. Pressurized heavy water reactors produce multiples more tritium than pressurized water reactors do due to neutron capture in heavy water. Despite this concern, since the operation of these systems, no instances of radioactive contamination entering the freshwater supply have been recorded. Due to the design of the nuclear desalination systems, for radioactive products to enter freshwater would require a steam generator tube rupture, which could create a pathway for fission products; however, contamination would reach product water only if both the steam generator tube and intermediate isolation loop fail simultaneously, an extremely low probability event. For purely electrical coupling, the IAEA concludes that no direct path for the transfer of radioactive material exists. This combination of engineered barriers and operational experience demonstrates that nuclear desalination can maintain product water quality well within international safety standards. [8,10,11]
One key question in the application of nuclear desalination systems is the energy economics, especially in the context of solving the global water crisis. Current seawater reverse osmosis plants consume approximately 3-4 kWh/m3 of product water at the system level, with large-scale plants going below 3.0 kWh/m3. [12] The global water gap currently stands at approximately 458 km3/year and is projected to grow by 6-15% under 1.5-3°C warming scenarios. [13] Closing even half of this gap would require RO systems to generate 800 TWh of dedicated electricity annually, roughly 3% of current global generation, making the choice of electricity source a decision with both economic and climatic consequences.
For electrically coupled nuclear-RO systems, the relevant low-carbon competitor is not fossil-fuel generation; instead, it is solar photovoltaic power. Yoo et al. compared small modular reactor (SMR)-powered Seawater Reverse Osmosis (SWRO) against renewable-powered SWRO, finding that a single SMR unit yields a levelized cost of water of $0.398/m3 and a levelized cost of electricity of $54.5/MWh. [14] However, this comparison is sensitive to assumptions about energy storage. Because seawater desalination plants require continuous 24/7 operation, solar photovoltaic (PV) systems must be paired with large-scale battery storage, which drives the solar PV levelized cost of energy to $158/MWh and the LCOW to $0.739/m3, an 85.6% cost premium over the SMR configuration. Without storage, standalone solar PV LCOE drops to $44.9/MWh, which is competitive with nuclear. Therefore, the cost disadvantage arises specifically from the continuous-operation requirement of desalination rather than from solar generation costs alone. [14]
From a carbon perspective, both nuclear and solar PV offer dramatically lower lifecycle carbon emissions than fossil fuels. Nuclear power produces approximately 12 gCO₂eq/kWh and solar PV approximately 18-48 gCO₂eq/kWh, compared with 490 gCO₂eq/kWh for natural gas. [15,16] Applied to RO at 3.5 kWh/m, either low-carbon source reduces emissions by over 97% relative to gas-RO, against a fossil-fuel desalination baseline already emitting 76 Mt CO₂/year and projected to reach 218 Mt CO₂/year by 2040. [4]
Finally, it is important to note a constraint on what desalinated water can address. While RO product water is suitable for drinking, it lacks the calcium, magnesium, and sulfate ions essential for plant growth. Field studies have shown that irrigating with desalinated water without mineral supplementation causes crop deficiency symptoms and yield losses, meaning nuclear desalination addresses municipal and industrial demand but not the agricultural water crisis, which accounts for roughly 70% of global freshwater withdrawals. [2,17]
As global freshwater availability continues to decline, seawater desalination has become a strategic necessity for the future. By integrating nuclear energy with desalination systems, we can decouple water supply from fossil fuels and dramatically reduce the carbon footprint of freshwater production, achieving emissions lower than those of traditional gas-powered methods. Furthermore, the operational history of facilities like Kalpakkam and Haiyang shows that this technology is technically feasible and maintains water quality within international standards. As climate change continues to destabilize traditional water cycles, the transition toward nuclear- powered desalination provides an opportunity for global climate adaptation, ensuring a resilient, carbon-free future for the billions of people currently facing water stress.
© Anirudh Mazumder. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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