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Thursday, October 8, 2015

Nuclear desalination of sea water is THE answer


Nuclear desalination is the answer for the world-wide short supply of potable water. One-fifth of the world’s population does not have access to safe drinking water! Without water, one cannot imagine any sustainable development taking place. Brackish or sea water and treatment of urban waste water can be converted to fresh water by nuclear desalination.  

Use of nuclear energy is a much cost competitive method as compared to fossil fuels for desalination, and it has a great potential. Desalination of sea water is used in Middle East and North African countries. Many countries already are into this technology for producing potable water.  China is building 1 million cubic meter per day RO plant to supply water to Beijing. The International Atomic Energy Agency (IAEA) is fostering research and collaboration in the technology in its Member States.

One of the impotent cost-effective technologies used for desalination is Reverse Osmosis (RO). Using electric pumps, sea water is pressurized and forced through semi-permeable membrane against its osmotic pressure. The salt content of the water gets removed. The process is driven by electricity driven pumps. However, the feed water needs to be filtered in this technique. High operating pressure of the order of 55 to 82 bars are required for desalination of sea water. As proved by Australia, renewable energy (CO2 free) sources can be used for desalination.

Multi-stage flash (MSF) distillation process uses steam. It works by flashing a portion of the water into steam in multiple stages in counter-current heat exchangers and this method for desalination accounted for 23% of the world capacity in 2012. It is more energy intensive process, but can cope with suspended solids and any degree of salinity. There are many other processes such as Multiple-effect distillation (MED) that can be used for desalination

Nuclear desalination studies using small and medium sized nuclear reactors are carried out in US and France. IAEA reports, based on the IAEA Coordinated Research Programs in Kazakhstan, India and Japan, are available which give details on nuclear desalination of sea water. Indicative costs are US$ 70 – 90 cents/cubic metre.

In India, Bhabha Atomic Research Centre (BARC) has undertaken extensive research in the field of nuclear desalination since the 1970s, and thermal desalination process, Multi Stage Flash (MSF) and Reverse Osmosis (RO) process were successfully demonstrated. A demonstration scale hybrid MSF-RO desalination plant coupled to a nuclear power plant at MAPS, Kalpakkam (Tamilnadu) is designed to provide around 6300 cubic metre of desalted water per day. Low pressure steam is gainfully used here. A mechanical vapour compression plant is reported to be set up at Kudankulam (Tamilnadu) to supply fresh water for the plant’s requirement of cooling water.

A low temperature nuclear desalination plant uses decay heat from radioactive waste for desalination. Heat from the high-level waste packages seems to have great potential to meet the requirement of nuclear desalination. Instead of disposal in geological repositories, the decay heat from the high level waste should be utilised to meet heating and steam requirements of a desalination plant. The potable water thus produced can be used at all the nuclear sites and residential areas in coastal areas of India.