Using Nuclear Power Plants to Desalinate Seawater

I wrote this message to my brother, who knows a lot about nuclear reactors.

I was just poking around Wikipedia and stumbled across the article about desalination. One thing that's mentioned here is the possibility that nuclear desalination may become economic in the future.

Now since you know all about nuclear stuff* I thought I'd ask you about this. I assume that they're talking about using seawater as the coolant for their reactor, but I could be wrong. I mean, seawater is a hellish environment for steel and other materials at the best of times, so pumping it directly into a nuclear reactor seems like a Bad Idea. But if they were to put the seawater into a tray or tank over the reactor and let the heat from the reactor boil off the water and then condense it into a freshwater storage tank, they'd be right. The evaporation would probably cool the reactor.

There's a big argument about desalination, because the salts left behind are superconcentrated into the remaining water. This is a Bad Thing because it makes the environment toxic for Cute Fishies. So my thought is that we take the desalination to the next level: Drive the water off completely leaving only the salts behind. The salt would then be collected and sold to whoever wants it. Maybe ODOT would like to have a cheap source of road clearing salt. Or we could package it and sell it to the public. ("Atomic Salt Makes Everything Taste Better!")

Another alternative is to have the plant operator could build a nuclear waste storage facility on site and surround the waste with a salt mixture. Then pump the superconcentrated salts into the chamber so the salts in the water reinforce the surrounding materials, like a grain of sand becomes a pearl.** (Wasn't that one of Yucca Mountain's purported benefits?)

* "know all about some subject" means "you know more than me"

** Yeah, I wouldn't want to put it in any jewelery anyone would wear, but you get the idea.

My brother's initial thoughts

He's only speaking for himself, and these are his inital thoughts, meaning they may sound disorganized. He's actually very smart, and gave me a lot to think about.

Some plants do use seawater as coolant, however I believe they are all PWR's so seawater does not enter the actual reactor. The water in the reactor must meet some very specific conditions and seawater wouldn't cut the mustard for use inside the reactor. It is used in the secondary loop (the water that transfers heat away from the reactor to turn the turbine but isn't in the reactor). [I think this is called the "working fluid." --Matt]

To the best of my knowledge the plants that use seawater don't desalinate it. Water is drawn in and then either exits as steam or hot water depending on how it is directed. To use nuclear power for desalination I'm not sure if they would try and combine it with power generation or not as this would combine two very complex processes. [According to Wikipedia, desalination would be done via cogeneration. --Matt] In theory you could evaporate the water using heat from a nuclear reactor, but as I understand it the plant needs to draw in water as it releases steam so you would never be rid of all the water to collect the salts as solids. You would end up with the high salinity muck that you mentioned in your message. You would have to derive a way to get this concentrated water out of the collection vessel.

I guess a standard garden hose fitting would be out of the question...but you never know. Putting the "high salinity muck" through a series of multiple effect distillers or evaporators could do the trick, but a conventional multi-stage flash distiller would do the job just fine. I wonder if we could use one of those big tower separator things they use in power plants. Wikipedia says they're used in a "continuous distillation process" and the towers have these big plates and trays of stuff in them to gather up the stuff you're distilling. If we can swap the trays in and out of the collector vessel gathering the salt would be no problem.