Nuclear Power's Climate Protection : Water-Use Tradeoff
by John Laumer, Philadelphia on 02.18.06
Most non-natural gas electrical plants use steam to drive their turbines. After superheated steam makes a pass through the turbines, the discharge is condensed, and then recycled back to the hot end of things for another pass through the turbines. Cooling process choices will be very important in coming decades because of the prospect of many "clean coal" or new nuclear plants added to counter climate change. At the heart of the issue is water consumption in a supply-constrained world. Background for non-engineers: -- there are three ways to cool these plants; two wet, and one dry. The wettest way is to withdraw surface water from ocean bay, lake, pond, or river, and pass it through a secondary cooling loop. The one-pass cooling withdrawls are the least aquatic-life friendly, which we'll detail with an example after the fold.
There's a variation where a man-made pond is discharged to and recycled from. The other common wet method, much more costly than one-pass withdawl, is to build a bank of evaporative cooling towers, an example of which is shown here. The towers evaporate much water, need a water purification system up front, use biocides to inhibit fungal and algal growth on the tower media, create a fog-laden microclimate, and stab at the horizon. The third method is to use dry (air) cooling towers, which are expensive, less "proven" and more suitable for biomass or coal fired plants than nuclear. Guess which method those twenty new nucs per year or "clean coal" plants would most prefer to use?
The Post-2000 generation of nuclear plants will have plenty of design innovations. The first licensed will be 'prototypes', although you'll not hear the word "experimental" at a public hearing. The last thing designers will want to do is add unnecessary complexity and cost to a "new design." So, they'll almost certainly go for 1-pass cooling water withdrawl when there's plenty of water to be had.
Layer upon this added water consumption Western states mired in extended drought, Mexican farmers bankrupted for lack of water, seriously overtapped aquifers in the grain belt, coastal and Great Lakes fisheries stressed by habitat destruction, a growing population, competition with hydroelectric power plants and you get the picture. By avoiding the cooling water issue, the "clean coal" and new nuclear options can look pretty good. Put it on the table for all to see and water will become a powerful issue for local opponents.
To get an idea of what is at stake, we've included, below, a few excerpts from a recent Asbury Park Press story (subscription only) regarding cooling methods at New Jersey's Oyster Creek nuclear plant site.
Feb 15, 2006 - Asbury Park Press, N.J. "Can the Oyster Creek nuclear power plant afford to install costly cooling towers, or would the plant close to avoid the expense? State environmental officials want towers to be built to preserve aquatic life from Barnegat Bay, but the plant's operator, AmerGen Energy Co., said they are costly and unneeded...In a 2004 meeting with DEP officials, managers with Exelon, which owns AmerGen, said cooling towers, if required, "would cost $25 million to install and would result in Oyster Creek no longer being financially viable," according to the DEP.
Oyster Creek, which began operating in 1969, withdraws about 1.3 billion gallons of water a day from an intake canal linked to the South Branch for cooling, according to a DEP fact sheet. The water intake and discharge system kills millions of small fish, shrimp and other aquatic species each year, according to estimates cited by the DEP".
NOTE: to avoid a visit from Homeland Security (money wasting bureaucrats) we have refrained from posting here any aerial photos or identifiable building pictures (gutless TreeHuggers). That's a shame because only by looking at such images can you get an idea of how important water consumption is to large scale power production (out of sight, out of mind). Ideally, we'd have included a false-color infrared satellite picture showing thermal pollution from hot water discharge plume. We'll just have to close our eyes and imagine (cryptome).
there are various methods of electrically generating water from the air. There is also a treatment which can be applied to a metal similar to anodyzing which is fundamentally hostile to microbes. Applied appropriately, there would be no real problem with the water. Also the promising pebblebed reactor method is supposed to use helium as the heat exchange gas, neatly eliminating the water issue.
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Air extraction takes energy and would not work with low relative humidity. Unreliable coolant supply would not be acceptable.
Cooling tower designers go with whatever is cheapest to install and operate. If anodyzing with copper were so cheaply and benignly done I have a hunch that trans-oceanic ships would have hulls treated so and they do not. Further, all metals corrode to varying degrees, even stainless, and the resulting blowdown water discharges are likely to present aquatic toxicity issues if solid metal is the functional aspect.
I invite you to look into the sustainability of commercial helium sources, both with and without the pebble bed option, and excluding the "we'll get it off the moon" nonsense.
I know that atleast new york is heated by steam.. maybe they could use similar heating methods in other cities?
Agree that combined heat and power is a great way to up total fuel effiiency and is done already with coal fired plants (Duluth MN a well known example). But one can not intentionally locate a nuclear generator in a major metropolitan area (evacuation impossible).
Interesting article. I have a couple of comments:
1. Your concerns about water use are certainly valid for many nuclear and coal plants; when the plant is fed by an aquifer, there is definitely an engineering problem to be solved.
There are several plants, however, that have access to an unlimited supply of sea water. In those cases, the once through cooling is less of a problem. There is plenty of salt water in the world and none of it is "consumed" by the once through process.
There are a number of ways to minimize the effects on aquatic life through the use of large volume flows, properly located suction and discharge pipes, and effective filters. Based on the number of fishermen that hang out near the Calvert Cliffs plant a few miles south of my home, it seems that the added thermal energy is actually beneficial to at least some parts of the ecology.
2. I roger your concerns about helium supply eventually being a limiting factor for helium gas cooled reactors. That is one of the reasons that Adams Engines are designed to use nitrogen. Since 80% of the atmosphere is inert N2 gas, there is no concern for supply of that material.
3. Air cooled heat exchangers are well understood and proven. Steam plants avoid them because the optimal discharge temperature from the turbines is quite low, leading to a small temperature difference, poor heat transfer and a requirement for very large heat transfer surface area - ie a very big cooler.
Our engines have much higher turbine outlet temperatures so they can use air cooled heat exchangers quite effectively.
Just thought you would like some information from a horse's mouth.
Rod Adams
President and founder, Adams Atomic Engines, Inc.
www.atomicengines.com
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Wonderful insights: thank you.
In a long ago job I performed nuclear plant stiting studies and had the job of picking dead fish off the intake grates. This turned out to be a trivial impact compared to the extra fish being caught by sports fishermen situated in the discharge plume at certain seasons. What can be critical is a situation where the thermal shock hits early life stages of esturarine breeding fish and aquatic life. There's really no way for engineers of overcome a 20 degree hit on them, regardless of dilution. Anyone who has bought a tropical fish and dropped it directly into an aquarium that was 5 or ten degrees warmer than the bag of water they are in can relate to how an organism of small mass can be stressed. This concern seems to have been the driving force behind the Oyster Creek plant dispute with state permiting authorities.
All that aside, TreeHugger out to have a look at the Atomic Engine. THanks
TreeHugger:
I am not sure I understand your comment "What can be critical is a situation where the thermal shock hits early life stages of esturarine breeding fish and aquatic life. There's really no way for engineers of overcome a 20 degree hit on them, regardless of dilution."
Engineers certainly cannot change the biological response to a 20 degree thermal shock, but they can design the system so that such temperature difference does not occur when the systems are properly operated.
The rise in temperature can be controlled by the quantity of water flowing through the condenser and the rise in temperature at the outlet of the pipe can be affected by the length of the pipe.
As I understand the Oyster Creek issue that occurred a few years ago, someone erred in ordering maintenance to be conducted on dilution pumps while the plant was in operation. With a much lower water flow, the temperature increase was much larger than expected and did kill some fish.
BTW - based on the number of fish killed and the fine that the owners of the plant paid, each fish was determined to be worth about $170. I think I would not be able to afford to eat fish in New Jersey.
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Sensible comments. I should not have cited a specific temp. Too hard to know what delta T affects which life stage of which species per a given site. The faster the intake flow (which could lead to greater volume taken in) the greater the entrainment of juvinile and adult fish that hit the bar screens. If spawning adults are attracted to the intake area due to elevated temp, it's made even a more difficult tradeoff.
Two other concerns:
Thermal optima for endemic species might be more frequently exceeded with climate warming runoff waters. Plant plume adds to the stress locally.
Mean ocean levels might be increasing within the operating life of the plant(s): also climate change related. This would change lfish behavior in unpredictable ways.
Increased probability of storm surge effects in coastal zone due to climate increased hurricane intensities, laid over increased sea surface height.
I find the latter to be the most interesting risk managment concept. Others will disagree surely.
Thanks for the ideas!
The true answer is to use the the system to purify sea water.
you get your reactor cool, and fresh water at the same time.
unfortunally, getting people to drink water that has come from a nuke will be quite the task.
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Very large nuks are under construction in desert-like climates, where the electricity is used to power banks of reverse osmosis membrane filters. The brakish water produced is piped to homes and appartments for toilets,showers, etc. A finer cut can be bottled for drinking an cooking. The major problem is disposing of the hypersaline waste brine left behind as a waste product of desal. Dumping it at sea eventually produces a biological stress when done at large scale.
Distillation only on that scale is impractical because of corrosion and solids disposal issues.
Would be better to find a way to convert the waste heat to electricity, warm buildings, etc.
I am not an engineer, but a company in Texas, WOW Energies, seems to have a solution. They claim they can significantly lower the tempterature of the exhaust and generate electricity by boiling propane with the waste heat in a closed loop.
A number of years ago when I worked at San Onofre Nuclear Power Station there was a proposal floating around to divert a small percentage of the Hudson bay runoff back toward the US and sell it to the US. It would have been a massive project, but they estimated we would have ended fresh water problems throughout the midwest for a century (which would give us time to find a permanent answer). Unfortunately, politics shot it down. So, the largest single source of fresh water in North America continues to drain into the ocean.
This statement is incorrect: "So they'll almost certainly go for 1-pass cooling water withdrawel when there's plenty of water to be had." That is because 1-pass cooling is no longer a legal option for new power plants of any kind constructed in the US.
One cooling option was not discussed. Palo Verde uses recycled sewage water for cooling. It is tough to get people to drink that type of water as well.
=== author's response follows ====
Thanks for the fact check.