Nuclear Desalination

International Atomic Energy Agency Website ^ | International Atomic Energy Agency

[Willie Green]

Website excerpts:

For education and discussion only. Not for commercial use.

Water Supply & Demand

Seventy percent of the planet is covered with water, but only 2.5% of that is fresh water. Nearly 70% of this fresh water is frozen in the icecaps of Antarctica and Greenland. Most of the rest is in the form of soil moisture or in deep inaccessible aquifers or falls at the wrong time and place – in monsoons and floods. Less than 0.08% of the world´s water is thus readily accessible for direct human use, and even that is very unevenly distributed. Currently an estimated 1.1 billion people lack safe water. The resulting human toll is roughly 3.3 billion cases of illness and 2 million deaths per year. Moreover, even as the world´s population grows, the limited easily accessible freshwater resources in rivers, lakes and shallow groundwater aquifers are dwindling as a result of over-exploitation and water quality degradation. According to “business-as-usual” forecasts, about two thirds of the world´s population will face shortages of clean freshwater by 2025.

Better water conservation, water management, pollution control and water reclamation are all part of the solution to projected water stress. So too are new sources of fresh water, including the desalination of seawater. Desalination technologies have been well established since the mid-20th century and widely deployed in the Middle East and North Africa. The contracted capacity of desalination plants was 20 Million m³/d worldwide as of 1995 (IDA statistics) and has since been increasing by an annual average of 1 Million m³/d.

Desalination Processes

Large-scale commercially available desalination processes can generally be classified into two categories:

• Distillation processes that require mainly heat plus some electricity for ancillary equipment. The two major processes in use are :

  • Multi-Stage Flash (MSF) Distillation:

    This process produces vapor by heating the seawater close to its boiling temperature and passing it to a series of stages under successively decreasing pressures to induce flashing. The vapor produced is then condensed and cooled as distillate.

  • Multi-Effect Distillation (MED)

    In this process, vapor produced by an external heating steam source is multiplied by placing several evaporators (effects) in series under successively lower pressures, and using the vapor produced in each effect as a heat source for the next.

• Reverse Osmosis (RO) processes

  In this process, pure water is forced to pass under pressure through special semi-permeable membranes, while salt is rejected. The pressure differential must be high enough to overcome the natural tendency of water to move from the low salt concentration side of a membrane to the high concentration side, as defined by osmotic pressure.

Nuclear Desalination

Nuclear desalination is defined to be the production of potable water from seawater in a facility in which a nuclear reactor is used as the source of energy (electrical and/or thermal) for the desalination process. The facility may be dedicated solely to the production of potable water, or may be used for the generation of electricity and the production of potable water, in which case only a portion of the total energy output of the reactor is used for water production. In either case, the notion of nuclear desalination is taken to mean an integrated facility in which both the reactor and the desalination system are located on a common site and energy is produced on-site for use in the desalination system. It also involves at least some degree of common or shared facilities, services, staff, operating strategies, outage planning, and possibly control facilities and seawater intake and outfall structures.

Role of Small & Medium Reactors (SMRs):

Small and medium reactors are important for desalination because the countries most in need of freshwater often have limited industrial infrastructures and electricity grids. The size of the grid limits the possibilities for integrating a co-generating nuclear power plant into the grid to supply the electricity market, in addition to meeting the energy requirements of a desalination plant. The largest power unit that can be integrated into an electricity grid is about 10-20 % of the grid capacity. Thus existing large reactor designs developed principally for North America, Western Europe, the former Soviet Union, or Japan are less compatible with electricity grids in many developing countries. Smaller reactors are also more appropriate for remote areas that are not suitable for connections to the grid. For both cases – i.e., remote areas and limited grids – progress on new smaller reactor designs should make nuclear power an increasingly attractive potential energy source for desalination.

Experience with nuclear desalination:

• Japan: Over 100 reactor-years of nuclear powered desalination

• Kazakhstan: About 30 reactor-years with the Aktau fast reactor (Shutdown in 1999 at end of reactor life)

• India: A 6,300 m³/d MSF-RO unit at the Kalpakkam nuclear power plant

Experience in nuclear desalination has been obtained in Kazakhstan and Japan. The fast breeder reactor BN-350 in Kazakhstan had for many years been used partly for desalination. Several nuclear power units in Japan are equipped with seawater desalination facilities to get fresh water for make-up of the plant water system and in-plant household use. The experience has proven technical feasibility of nuclear seawater desalination over the 100 reactor-years of successful operation. Relevant technical experience has been also accumulated in Russia, Eastern European countries and Canada in utilizing nuclear heat for district heating and other process heat use. Successful operating experience exceeds 1000 reactor-years.

[techcor]

Yes, as a matter of fact. There was an article in Sci. Am. called "Pyramid power" in which a couple of engineers noticed that their roads (in Libya I think) were showing signs of water damage. After some investigation they determined it came from dew in the morning. Then they discovere some pyramids that looked as if they were set-up to condense water out of the air so that it could be used. They estimated the pyramid may have produced 1200 gallons a day. Finally, the walls of Babylon were reported to do this and they were just outside of Baghdad. Even dry air has some moisture in it.

[RightWhale]

We'll probably have to do this on Mars, and if we are lucky, on the moon, too.

[techcor]

See my post #21 and it is interesting to hear about the
Saudi towers. I hadn't heard about them.

[dgallo51]

Absolutely! I also envision coupling either a nuclear or conventionally fired power generating system to massive solar collector arrays, thereby dramatically multiplying the heat transfer effect during daylight hours.