Nuclear and Freshwater - Part 2

Despite the comparably high freshwater use in the cooling process of nuclear energy production it must be noted that power plants, according to the US Geological Survey return 98% of the water that they initially withdraw (NEI 2013). Only 1-2% is actually consumed which is relatively efficient when put in comparison to irrigation, which withdrawals more water than the energy sector and only returns around 20% of this to the hydrological cycle (NEI 2013). Further contextualisation shows nuclear “once-through” cooling to consume 13 gallons/day/household, if a power plant is taken to provide for the average 740,000 homes. This contrasts to the average 94 gallons/day/household consumed by an average 3 person household in the US (NEI 2013). Therefore in the face of a water security issue, it is arguably household consumption that needs to be prioritised over the energy sector!

Irrigation is by far the largest freshwater-consuming sector (NEI 2013). Image Source (National Geographic 2015).

The cooling water requirements are currently higher in nuclear than fossil fuels, as mentioned in the previous post, due to the variable operating temperatures of the procedures (Brook 2014). However, this disparity may not be a long-term issue with new nuclear power plants, using the “liquid-metal-cooled-fast reactor, operating at a similar temperature to fossil fuel energy generation and therefore the difference is going to be gradually diminished (Brook 2014). The power plants only consume negligible amounts of water; much of it is heated and then returned to the origin as clean water. Within cooling towers the water is evaporated and returned to the natural cycle as clean water vapour (Brook 2014). Therefore in terms of the process as a whole, nuclear can be viewed as a relatively efficient water sector. This only contains the consumption within the actual generator, therefore perhaps underestimating the full use within the nuclear sector – for example water requirements will be required during mining and transportation also. Therefore it is important to broaden the view, to ensure that the full process chain is accounted for in regards to nuclear energy efficiency.

Nuclear does not necessarily remove freshwater; there is the potential for freshwater improvements. For example in some power plants the cooling towers use urban waste water that is first cleaned, then evaporated back into the environment (Brook 2014). Therefore the energy generation is not using any water that could have been put to any other use, increasing freshwater availability.

Furthermore, nuclear has a large role in desalination with recent nuclear generators constricted in Argentina, China and South Korea that have dual benefits of electricity production and freshwater generation (NEI 2015). Many of the desalination technologies currently use fossil fuels which therefore can increase global warming and place freshwater security at a greater threat. Many countries are already highly dependent on desalination, for example around 40% of Israel’s freshwater comes via desalination processes (WNA 2015). In many areas the need for water resources for consumption and agricultural is high, yet supply is low. Oman for example opened a nuclear desalination plant in 2011, with the eventual capacity desired to be 220,000m³/day freshwater production (WNA 2015). The quality produced will therefore enable agricultural and domestic use, whilst also allowing aquifers to be recharged with potable water to facilitate the regeneration of long-term freshwater stores.

The Al Ansab submerged membrane bioreactor desalination plant, Oman (ACWA 2012).

Types of desalination process (OECD N/A):

• Multi-stage Flash distillation Plant – water vapour is generated by heating the seawater close to boiling point. Then it is passed through gradually reducing pressures to provide flash evaporation. The vapour is then condensed as a freshwater.
• Multi-effect distillation Plant – Vapour generated by external heat appliance. Again lower pressures promote further evaporation. The vapour produced from one heating is used to provide the heat for the next evaporation process. Forming a chain reaction.
• Reverse Osmosis – seawater is passed through a high pressure system with semi-permeable surfaces. This rejects brine and produces pure water.

The latter requires less energy, costs and water input, suggesting it may be the more efficient process to use.

Costs per m3 production of desalinated freshwater. Lowest costs seen within nuclear reverse osmosis (OECD N/A).

The UK Environmental Agency suggests that all future nuclear plants should be built on the coast to enable the greatest supply for reactor cooling as well as enabling large scale desalination projects (NEI 2013). This is perfect in the UK, however as seen in Fukushima coastal positioning generates large risk within active seismic areas – meaning the UK policy is unlikely to be replicated on a global scale.

Nuclear energy therefore is not a sector that should be targeted in regards to freshwater security issues. Withdrawal and consumption are comparably low to other sectors. However it must be examined as a potential source of improvement. Desalination through fossil fuels is simply adding to the problem, nuclear desalination can provide additional freshwater in the short-term and reduce global warming and the consequent freshwater reduction in the long-term also!