Before I go ranting off about #NPT2015 and why Zarif and Iran postponed their speech indefinitely (my money is on Iran forgetting the script at home) I actually wanted to briefly cover something about nuclear power. Two weeks ago I was calmly doing my work in the VERTIC office, doing VERTIC intern things with my VERTIC friends, when a coworker poked his head over my screen and said “Yo Cervando, you know nuclear stuff right?” Well I wouldn’t be the NuclearFarmboy if I didn’t now would I? So I went over to his desk to help a brotha out, and he started asking me about the European Pressurized Reactor (EPR) and why in the bloody hell (thanks for that, London) did it not have cooling towers while other reactors do (it is NOT because it is too cool for school). To add more to the conversation, the Institute for Science and International Security recently released a brief outlining their belief that North Korea was once again operating their Yongbyon gas-cooled reactor and I immediately thought “there’s a reactor who had a cooling tower and now no longer has one!“. So for all you nuclear afficionados out there, let’s dive into what a cooling tower actually does for a nuclear reactor and how you can get away with not building one.
First things first. Have you ever Googled “nuclear power plant?” If you haven’t, then you should do it. I dare you. Or if you’d much rather I do it for you (you lazy bums) this is what comes up:
Notice how none of them have the atomic symbol from The Simpsons…except The Simpsons one.
Cooling towers are nowadays synonymous with nuclear power plants, yet a large number of them do not use towers. Why is that?
If you ask a nuclear engineer how a nuclear reactor works and what role cooling towers play, they’ll say some confusing mumbo-jumbo like:
“Well the answer is simple: let’s stop and think of the cooling process needed to cool a pressurized water reactor (PWR). You have your core, and in it cold water comes in, super hot water comes out, super hot water goes into a steam generator where it transfers its heat, that heat boils cold water, the steam turns turbine, steam goes to condenser where cold water pipes absorb the heat and make the steam condense back into water, and the water from the condenser goes to the cooling tower where it cools off and returns back to the condenser.”
(Pretend I said that all in a single breath, because I did. I saw spots.)
Thankfully you don’t have to try to understand that abomination of a run-on sentence, and instead (with the help of your own NuclearFarmboy) we can break it all down piece by piece. Let’s start with a nuclear reactor and a pretty picture courtesy of the U.S. Nuclear Regulatory Commission! (who for some reason chose Comic Sans as their font. It’s almost as if they hate happiness.)
It’s what I picture Wile E. Coyote’s blueprints for an ACME Nuclear Power Plant would look like
That visual pretty much summarizes what I said and clearly shows that your typical PWR has three loops of water: the core loop, the steam loop, and the condenser loop. Let’s focus on the third loop for a minute.
This cheeky bastard (Seriously, you’re killing me London)
As you see, the condenser loop brings cold water in and uses it to absorb the heat from the steam and condense it back into water (yeah water cycle! yeah science!) but what happens to that water that goes into the picture through the condenser and then back out?
Well that’s where the question about cooling towers lies. Obviously in order to condensate super hot water vapor (I’m talking like seriously hot, several hundred degrees Fahrenheit) the water in the condenser loop has to absorb a lot of heat. Where does this heat go? Well, imagine your nuclear power plant draws water in from the river right next door for its condenser loop. This cold water comes in and comes out with all this heat and what do you do? Dump it back into the river?
Do that and you get a rather nasty fish stew.
And a lot of angry hippies.
Worst dinner party EVER.
If you dump a lot of hot water into the river, it can kill a lot of the organisms in it, and that’s generally frowned upon by the Environmental Protection Agency. So what can you do to avoid the angry hippies and the damage to the environment? It’s simple, you cool off the water before you dump it back in!…which is easier said than done.
Thankfully we can get around that by building cooling towers!
A cooling tower is a surprisingly simple structure on the inside. At the base there are nozzles that spray the super hot water from the condenser down into a basin. What this spray does is increase the surface area of the water so that it exchanges the heat more readily with air! In non-sciency terms: the spray makes the water into small drops that give away the heat more easily.
All of that, in combination with the shape of the cooling tower also causes a draft of air to come in from the base and cool the water drops from the nozzle! This draft is due to convection that says “hot air rises and cold air sinks” (thank you high school science) so as the cold air absorbs the heat from the water it rises out of the cooling tower! How neat is that?
For the more visual learners (like yours truly) the Hamon Group that provides environmental solutions also has this fancy drawing of a cooling tower:
Photo Credit to Hamon Group at: http://www.hamon.com/medias/upload/images/NaturalDraft(5).jpg
As you can see here, the hot water enters the cooling tower and is sprayed by the water distribution nozzles. These cause the water to cool down, and the air to heat up. As the air heats up it rises due to convection, and more cold air enters the base to continue cooling the water. This hot air escapes to the cold air in the top where it condenses some steam and creates white, completely clean, poofy clouds that are just water vapor. In the meantime the now cool water from the spray reaches the bottom of the tower, it collects in a basin which then returns to the condenser loop to keep cooling the secondary loop of the reactor like we saw above! #science #AwwYeee
So when someone tells you how cooling towers are releasing “clouds of radioactive steam so that Obama can use it to mind control the American public” you can rest assured that it is not true. #ThanksObama
Now let’s kick it up a notch and look at real life (or is this just fantasy?) and look at ways you can avoid building a cooling tower!
For example the South Texas Project Nuclear Power Plant (STP for short) doesn’t have a cooling tower. Instead to meet all of its cooling needs it has a giant man-made reservoir of water. How big is giant? Check it out for yourself:
What would I do without you Google Maps?
So why is this ok?
Well if you have a reservoir with several MILLION gallons AND it is man made, you know for a fact that there is no major ecosystem that will be hurt by releasing the hot water directly.
Yay happy hippies!
But what about other reactors that have neither a reservoir nor a cooling tower?
Thankfully there are ways to still avoid environmental damage. You can be like the EPR and release the water into a man-made channel so that it cools down as it travels towards the river. You can keep the water in pipes that exchange the heat with the river (or lake, or ocean) and slowly release the hot water into the river to reduce the shock of the hot water entering the natural ecosystem, or you can even set up heat exchangers to release the heat into the air and then dump the water back into a lake. The possibilities are limitless.
Let’s examine a real life scenario: Yongbyon in the DPRK. Back in 2008 (back when dinosaurs still roamed the Earth) Dear Leader decided to tear down this cooling tower:
You can see the gap in the bottom of the tower for the air to come in! #TheMoreYouKnow
We were all excited! This was our face:
Let’s be honest, we all wish we looked like Robert Downey Jr.
North Korea couldn’t produce more plutonium right?
Right?
Who wouldn’t trust this face?
Well, it turns out that they can in fact produce more plutonium for weapons.
Not now Bibi, not now. (Drawing Courtesy of Looney Tunes)
Now that you know cooling towers aren’t that necessary to cool a nuclear reactor, you’ve probably figured out that all the North Koreans did was intake the cold water from the nearby river, cool the reactor, and then dump the hot water right back into the river. #BestKorea
So, let’s recap: cooling towers are a great way to protect bodies of water from possible damage due to the temperatures of regular nuclear reactor operation. You need cold water to cool your reactor no matter what, so some reactors have reservoirs that use large amounts of water from man made bodies, others use rivers, lakes, or even the ocean itself. The systems used to cool off this water depends on the reactor needs, the environment, the availability and accessibility of water for the reactor. As we see with the Yongbyon case, just because you tear down a cooling tower it doesn’t automatically mean that the reactor is shut down and unable to be cooled, because as Jeff Goldblum taught us in the masterpiece that is Jurassic Park: Life finds a way.
Special thanks for editing to: Cassandra Peterson @cassiandrali
-Cervando Banuelos is currently is currently a master’s of science student in computer science at the Naval Postgraduate School, he’s finishing a master’s of arts in nonproliferation and terrorism studies at the Middlebury Institute of International Studies at Monterey, and holds a bachelor’s of science degree in nuclear engineering, with a minor in radiological health engineering, from Texas A&M University. His interests include passive cooling systems in boiling water reactors, nuclear forensics, arms control treaties, treaty verification, cybersecurity issues, and gummy bears. He hopes to some day work for the IAEA, a national laboratory, or the CTBTO.
Follow: @nuclearfarmboy
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