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[GalenEvil]

Concerning a power source, we could use Nuclear power plants since they have high output with relatively little effect on the environment outside of fuel cell disposal or during catastrophic meltdown situations (Chernobyl style issues: though this stemmed from flawed design and a series of unfortunate events coming together in the right order). The likelihood of a catastrophic meltdown situation is relatively low compared to the potential output over time.

Other than the issue of disposing of fissile materials in a non-harmful and secure manner, as well as the inherent risk of meltdown, nuclear reactors could be a viable source of power for these waterborne cities.

I am not sure how we might go about doing a large scale atmosphere scrubbing, but it is definitely something to think about in more depth.

Also, hydroelectric plants could serve as a good method for supplementing nuclear power while in motion. The salt water of the ocean could also be broken down into its oxygen and hydrogen components [1] to provide high-oxygen environments for domestic use [2] and also for agricultural yield increases [3].

As for maintenance issues: I was going to write up a small wall-o-text but I think that it can wait for another time. This is already a kinda long post so I will go ahead and end it.

[1] - (done in practice on nuclear submarines. Cannot go into details because my dad won't explain what they actually used everything for; also, my time is short so can't do the actual research necessary to get a better source)
[2] - (high oxygen environments keeps productivity and happiness levels high; used to some effect in casinos)
[3] - citation needed. Not sure if this is viable or I am talking out of my rump here.

[Putnam]

Nuclear power would be great as an intermediate power source until actual fully renewable sources come about in full force.

[GalenEvil]

Okay, THEORY!!!

Nuclear power + Hydroelectric + Steam / Wind... Here is how it would work!

Nuclear power initially keeps the city in motion. The hydroelectric systems allow sea water into a reservoir, creating electrical energy as well as using the water as coolant for the reactor. This water turns into steam. The steam since it is hot, rises and can be pressurized which could be used to slowly generate wind. The steam then can be used in other ways to produce electricity, heat things (hydro-thermal domicile heating anyone?), and on condensation produces drinkable water (I think, might not be potable due to use as coolant).

This would be a huge multi-system reactor, and could be highly inefficient in some respects. It could produce products of: drinkable water (*), salt, heat, and electricity. The total electrical output of the system might be reduced due to the mechanical inefficiencies introduced from system interactivity. However, I think that having a reliable salt resource as well as the potential for large amounts of potable water (even if it isn't exactly cold) in addition to electricity could offset the inefficiencies with benefits.

I hope that the above made sense >.>

(*) I have no idea of the potability of water after it is used as reactor coolant. I will have to think more about that part.

[Pnx]

You realize nuclear power, is steam power, right? You seem to actually have a very poor understanding of how these things actually work.

[Reelya]

From what i understand about estimated uranium deposits, if the world went 100% nuclear the estimated uranium deposits wouldn't last long enough to pay back that single generation of reactors.

http://www.scientificamerican.com/article.cfm?id=how-long-will-global-uranium-deposits-last

If the Nuclear Energy Agency (NEA) has accurately estimated the planet's economically accessible uranium resources, reactors could run more than 200 years at current rates of consumption.

And nuclear makes up 14% of current usage, so a 100% nuclear world would last 28-30 years before we run out of deposits. That's assuming demand doesn't increase. Let's assume both incremental increases in demand and efficiency, so ~30 years max, and your stuck with contaminated sites for ~30,000 years afterwards.

And i'm inclined to think the Nuclear Energy Agency has been generous in it's 200 years estimate. 1/3rd of that is estimated known deposits, and 2/3rds of that is estimated deposits that aren't known.

Note, that unknown deposits could very likely have higher extraction costs that known deposits (being in harder to access deeper locations etc), something not taken into account by the blanket estimates.

They're trying t hype up the possibility of getting uranium from sea-water in the future, which would be viable if the price of uranium skyrockets, but they neglect to mention that if that happened, wind and solar would become better options, without the waste issues.

[Luke_Prowler]

From what i understand about estimated uranium deposits, if the world went 100% nuclear the estimated uranium deposits wouldn't last long enough to pay back that single generation of reactors.

http://www.scientificamerican.com/article.cfm?id=how-long-will-global-uranium-deposits-last

If the Nuclear Energy Agency (NEA) has accurately estimated the planet's economically accessible uranium resources, reactors could run more than 200 years at current rates of consumption.

And nuclear makes up 14% of current usage, so a 100% nuclear world would last 28-30 years before we run out of deposits. That's assuming demand doesn't increase. Let's assume both incremental increases in demand and efficiency, so ~30 years max, and your stuck with contaminated sites for ~30,000 years afterwards.

And i'm inclined to think the Nuclear Energy Agency has been generous in it's 200 years estimate. 1/3rd of that is estimated known deposits, and 2/3rds of that is estimated deposits that aren't known.

They're trying t hype up the possibility of getting uranium from sea-water in the future, which would be viable if the price of uranium skyrockets, but they neglect to mention that if that happened, wind and solar would become better options, without the waste issues.

Oh course, there are other radioactive materials that can be used to run a reactor.

[Reelya]

Probably not the SAME reactors though. Total re-design i'd say to e.g. make a thorium reactor. But at least it doesn't sound like thorium can be used for bombs.

So, thorium is no excuse to build more uranium reactors.

I'm going to predict though that the "no bomb material" kills of thorium reactors, when the full life-cycle costs of production is compared to alternatives.

[sneakey pete]

The hydroelectric systems allow sea water into a reservoir, creating electrical energy

Um, do you realize that the energy lost from collecting the sea water under speed to generate hydro power would have had to be produced by the nuclear power anyway?

Personally, i'd love to see how a solar thermal plant on the deck of a large ship could work, if it would have enough area to supply the electricity demands. I mean, its never going to be enough to produce the power required to make a large ship go anywhere in a hurry, but if you were just aimlessly floating around it might do.

[GalenEvil]

@ Pnx:
Lack of thinking about the random thought while I was writing, as well as trying to incorporate all of my thoughts into one system quickly, likely brought on my looking stupid. It was just an idea that I didn't think through fully before posting. Yes, nuclear power is steam power. I did not explain the thought well at all >.< This would be more of an open system where sea water is input, used to produce steam via coolant uses, and then used for other purposes upon condensation if at all possible.

I never said that I actually knew what I was talking about It was a theory that I was hoping was plausible. The way my thought process goes for outlandish theories (see my last post) is figure out if it "sounds" plausible enough to actually research. Usually figure out through the research that things just don't work that way. Revise my theory with things that make sense and still work within the bounds of my theory (if possible).

I was also hoping that the closing sentence "I hope that the above made sense >.>" would act as a disclaimer against anyone taking the preceding as anything other than un-researched theory. That didn't work it seems, so I will have to preface things that I write with disclaimers now.

@sneakey pete:
Yeah... it was sorta a crap shoot to try to get a theory out on how to power a city sized floating mass in the middle of the ocean. It was mentioned in my post:

The total electrical output of the system might be reduced due to the mechanical inefficiencies introduced from system interactivity

I took into account the probability of inefficiencies in the system. And I will make sure that I have disclaimers surrounding further theories of mine on these forums when they are related to real world things.

[Heron TSG]

1. Seawater makes a terrible coolant and it is extremely corrosive. They only allowed it to be used at Fukushima as a last resort to stop a total meltdown - and it made things worse. (Though not as bad as a total meltdown)

2. Might I present the breeder reactor, a machine that outputs more fissile material than you put in? Hell, some kinds even give back about 70% of the input uranium (with the other 30% turning partially into energy and mostly to other fissile materials) Beyond that, you can put in very dense but non-fissile materials such as lead with the fissile materials, and they become fissile.

3. Hell yeah fusion reactors! We just have to make our current ones more efficient. The National Ignition Facility had one working at about 99% efficiency, but soon they hope to significantly optimize the systems maintaining the containment field, which would allow the reactor to actually generate power. (Instead of just using a lot of power in order to fuse some elements to make almost as much power.)

[Reelya]

Fusion may be viable one day, though the cost per unit of KWH is exorbitant right now, right now they're just a research toy.

breeder reactors aren't expected to become economically viable compared to light water reactors until demand for uranium jacks up the price. But that doesn't take into account what other non-uranium energy sources will be doing in the meantime.

I'm older than most on this forum and they've been promising breeder reactors since before I was born.

[GalenEvil]

Concerning the saltwater coolant. Since it is not viable as a coolant would it be possible to make contained evaporation pools to sort out the salt and make it viable as coolant? Would the process be: too slow for quantities of water needed, too inefficient for "land" use, too heavy and thus energy inefficient?

[Heron TSG]

Fusion may be viable one day, though the cost per unit of KWH is exorbitant right now, right now they're just a research toy.

The cost is expected to fall dramatically after ignition. 'Ignition' being the point at which the reaction is self-sustaining. Also note that the National Ignition Facility has suddenly started running 30-50 tests per month, and says that they hope to ignite hydrogen by October. So... one day soon, I hope. Unless something catastrophic happens.

Concerning the saltwater coolant. Since it is not viable as a coolant would it be possible to make contained evaporation pools to sort out the salt and make it viable as coolant? Would the process be: too slow for quantities of water needed, too inefficient for "land" use, too heavy and thus energy inefficient?

Evaporation pools would make the remaining water saltier, which is the main problem. Salt builds up on walls and pipes and makes everything generally worse. Most reactors are built near rivers because freshwater doesn't have this problem. They just pass the water over the condensers and right back out. (Note that because it is only being used as coolant, there's not much radioactivity spread to the river. The coolant that does become radioactive is in a different system and is usually stored as waste. The few you see at sea (Fukushima Daichi being a prime example) are more prone to mineral build-up and require careful maintenance. (And repairs of concrete sea barriers, as was found out there!) If there isn't a large suply of water nearby, plants often use hyberbolic towers to allow for evaporation based cooling, though most of the water is simply recirculated, with the warmest evaporating. If there's no water around, smaller plants just use dry cooling, blowing air over the heavy water pipes or constructing massive heatsinks.

(Fukushima was a hyberbolic tower plant because they didn't want to use constant water flow and thereby increase maintenance costs. The problem came when they tried to cool the -tower- with seawater, which actually caused a gigantic hydrogen explosion. The zirconium rod casings holding the fuel like to explode on contact with water or steam when extraordinarily hot as in the case of a non-cooling plant. Fukushima's cooling systems were down, so the thousands of rods were hot, so they tried to cool them with saltwater... BOOM. Larger than expected due to zirconium drawing oxygen out of water before it reaches the temperature threshold for an explosion, as the water molecules became free hydrogen. Seeings how zircaloy explodes harder than nitroglycerin, the problems were manifold. Freshwater wouldn't have been so bad, but with seawater, the salt corrodes the uranium itself, creating long-lasting and highly radioactive Uranium VI. Fun stuff, eh?)

[GalenEvil]

Concerning the saltwater coolant. Since it is not viable as a coolant would it be possible to make contained evaporation pools to sort out the salt and make it viable as coolant? Would the process be: too slow for quantities of water needed, too inefficient for "land" use, too heavy and thus energy inefficient?

Evaporation pools would make the remaining water saltier, which is the main problem. Salt builds up on walls and pipes and makes everything generally worse.

When I said "contained evaporation pools" what I meant was something along the lines of an evap pool inside of a greenhouse like structure so that the evaporated water can be collected from it. Similar to how you can use a plastic sheet over collected sea water, have it evap and condense onto the underside of the sheet, and then collect it in another container to get fresh water. I guess this is a situation where I should have elaborated a bit more than I did. If sufficient quantities of water were able to be filtered in this way then it could be used as both coolant and for drinking.We would not want to keep the salt / salt solution in any quantity aside from dietary requirements.

[Nadaka]

From what i understand about estimated uranium deposits, if the world went 100% nuclear the estimated uranium deposits wouldn't last long enough to pay back that single generation of reactors.

http://www.scientificamerican.com/article.cfm?id=how-long-will-global-uranium-deposits-last

If the Nuclear Energy Agency (NEA) has accurately estimated the planet's economically accessible uranium resources, reactors could run more than 200 years at current rates of consumption.

And nuclear makes up 14% of current usage, so a 100% nuclear world would last 28-30 years before we run out of deposits. That's assuming demand doesn't increase. Let's assume both incremental increases in demand and efficiency, so ~30 years max, and your stuck with contaminated sites for ~30,000 years afterwards.

And i'm inclined to think the Nuclear Energy Agency has been generous in it's 200 years estimate. 1/3rd of that is estimated known deposits, and 2/3rds of that is estimated deposits that aren't known.

Note, that unknown deposits could very likely have higher extraction costs that known deposits (being in harder to access deeper locations etc), something not taken into account by the blanket estimates.

They're trying t hype up the possibility of getting uranium from sea-water in the future, which would be viable if the price of uranium skyrockets, but they neglect to mention that if that happened, wind and solar would become better options, without the waste issues.

That is also assuming we keep throwing away 98% of the nuclear fuel in "spent" fuel rods. Breeder reactors can extend the lifespan of nuclear fuel by several dozen times. You just have to say screw you to the non-proliferation crowd and accept that plutonium will exist, even if only as a transitional stage in a fully sealed process.