Seawater desalination

Due to water scarcity, total contracted desalination capacity (from both seawater and brackish water) has almost tripled in the past decade, reaching a global online capacity of about 50 million m3/d. Desalination has proven during the last 50 years its reliability to deliver large quantities of fresh water from the sea. Technological advances of the last decade have helped desalination to spread faster and to become a reliable way to supply water and consequently to promote sustainable development. Among the drivers for the growing interest in seawater desalination using nuclear energy are cheaper energy, less uncertainty on energy costs, higher load factor of the desalination plant, better load factor of the nuclear unit, utilization of the nuclear plant’s unused land, and reduction of the desalination carbon foot­print. The future requires effective integration of energy resources to produce power and desalinated water economically with proper consider­ation for the environment.

The principal desalination processes are based either on distillation or on membrane separation. The first group includes the widely applied com­mercial methods of Multi-Stage Flash Distillation (MSF) and Multiple Effect Distillation (MED). Still under development is Thermal Vapor Compression distillation (TVC) which is a promising process with a higher conversion ratio. The main characteristics of distillation processes are high energy cost, independence from feed water quality and simple technology with wide experience worldwide. The processes using membranes are char­acterized by having lower energy costs, dependent on the feed water quality, and simplicity. Major thermal energy in the range of 100-130°C is required to heat the feed water.

All existing designs of nuclear reactors could be used to provide electric­ity, low-temperature heat and/or combinations of both as required for desalination. Relevant experience with nuclear desalination is already available. The use of nuclear heat requires a close location of the nuclear plant to the desalination plant, while the use of electricity generated by nuclear energy for reverse osmosis (RO) does not differ from any other use of electricity in that the energy source may be located far from the cus­tomer, with electricity being provided through the electricity grid. It should be noted, however, that electricity taken directly from the plant is cheaper than the electricity from the grid and that a distant location would not allow the use of warm water from a condenser for the RO feed.

Limited experience exists with nuclear desalination since the 1960s from nine nuclear units in Japan and one in Kazakhstan. The latter was a BN-350 fast reactor which produced 135 MWe and 80,000 m3/d of fresh water by MED over 27 years before it was removed from operation in 1999. In Japan, nuclear desalination is experienced in the form of having the desalination plants constructed on-site of the nuclear power plant with aim at supplying the required make-up cooling water to these nuclear power plants. Such desalination plants have in general small capacities of 1000-3000 m3/d. In India, a combined MSF and RO hybrid system connected to twin 170 MWe pressurized heavy water reactors has been constructed and is, presently, in the commissioning phase. With capacities of 1800 m3/d by RO and 4500 m3/d by MSF, it will become the largest nuclear-based desalination plant in the world. Optimization of water desalination using nuclear reactors has been analysed, and studies are still under investigation in several countries.

New developments in nuclear desalination are numerous as many coun­tries have consistently progressed almost simultaneously in three technical fields: the development of improved or new generation nuclear reactors, the improvements in desalination technologies and the adoption of many cost reduction strategies. An interesting feature of this development is that many countries, normally not considered as exporting countries, have begun to develop their own nuclear reactors. For example, Argentina is developing the CAREM reactor. China is pursuing the development of the dedicated heat only reactor NHR-200 providing relatively low-temperature heat for an MED process, with some electricity production to meet the local electric­ity needs. India is going along with a consistent evolutionary approach to develop its advanced PHWRs. The Republic of Korea continues with its program to develop the System-integrated Modular Advanced Reactor (SMART). South Africa is developing the PBMR which can be used for electricity generation, hydrogen production and desalination (although the project is currently frozen).