Hard Light Productions Forums
Off-Topic Discussion => General Discussion => Topic started by: Kosh on November 05, 2008, 04:30:24 am
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http://www.timesonline.co.uk/tol/news/environment/article5024190.ece
“If we want to continue to enjoy the benefits of air travel without hindrance from environmental concerns, we need to explore nuclear power. If aviation remains wedded to fossil fuels, it will run into serious trouble,” he said.
“Unfortunately, nuclear power has been demonised but it has the potential to be very beneficial to mankind.”
Professor Poll said an alternative to carrying nuclear reactors on aircraft would be to develop aircraft fuelled by hydrogen extracted from sea water by nuclear power stations.
However, he said that while hydrogen could be suitable for ground-based transport, its energy density was much lower than kerosene and it would be
And he is absolutely correct in his assessment. Thoughts?
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What's with the sudden interest in nuclear power?
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It's probably somehow related to certain other sources of energy running out rather rapidly.
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What's with the sudden interest in nuclear power?
What Spicious said + fossil fuels are bad for a number of reasons (heavily polluting, bad for the locals, magnet for corruption, magnet for war, dependency on Saudi Arabia, and probably a few other things too).
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Heh.. also ruskies got their nuclear powered aircraft flying with reactor - though they seemed to believe that operational flight time of the aircraft was limited by radiation sickness.. Also one another bright idea born from the nuclear powered flight was the - possibly warheadless, as it didn't really need any - cruise missile which apparently luckily never left the drawing boards...
http://en.wikipedia.org/wiki/Tupolev_Tu-119
http://en.wikipedia.org/wiki/Project_Pluto
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I am pretty sure that in this day and age we would put enough shielding around the reactor to deal with the radiation.
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Seems like something that'd be great until the day one of the planes crashes and nuclear material lands in some residential neighborhood. I don't have a problem with a submarine or carrier hauling a reactor across the ocean, or even with a couple sitting in my backyard. I do kind of have a problem with one flying over my head at 35,000 feet and 500mph, though :blah:.
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All the more reason not to live under flight paths. ;)
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http://www.timesonline.co.uk/tol/news/environment/article5024190.ece
“If we want to continue to enjoy the benefits of air travel without hindrance from environmental concerns, we need to explore nuclear power. If aviation remains wedded to fossil fuels, it will run into serious trouble,” he said.
“Unfortunately, nuclear power has been demonised but it has the potential to be very beneficial to mankind.”
Professor Poll said an alternative to carrying nuclear reactors on aircraft would be to develop aircraft fuelled by hydrogen extracted from sea water by nuclear power stations.
However, he said that while hydrogen could be suitable for ground-based transport, its energy density was much lower than kerosene and it would be
And he is absolutely correct in his assessment. Thoughts?
We still can't store hydrogen gas efficiently enough to get a jet airplane running on it. There is an experiment going on in Switzerland about a fuel-cell powered GA jet (SmartFish), but don't ask me how it works. They don't seem to have gotten far with it yet.
I am pretty sure that in this day and age we would put enough shielding around the reactor to deal with the radiation.
No. The one thing that counts in radiation shielding, is mass. AFAIK. The one thing that counts in airplane design, is also mass. The Soviets did it, yes, but they had so little shielding that after a couple of years, most of the crews that flew it were dead.
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And nuclear radiation accelerates metal fatigue like crazy.
I, for one, eagerly await our new thermonuclear jet engine-powered overlords.
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Hey, don't knock it. Uranium-232 has a half-life of 69 years. If we can find a way to channel its power into sustainable thrust, then the savings on fuel costs alone would be more than worth it.
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True. Unfortunately, as long as we're talking about airplanes, there is none. Yet.
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Is it possible for Hydrogen to be stored much more densely? I believe the problem is not that it doesn't have enough energy / mass, it's that it doesn't have enough energy / volume.
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Me thinks that compressing large amounts of hydrogen into a relatively small place would be unwise.
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True...it would be like the Hindenburg. Only this time at about 40 000 feet and moving at better than 300 miles per hours. And the boom would probably be quite a bit bigger.
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True...it would be like the Hindenburg. Only this time at about 40 000 feet and moving at better than 300 miles per hours. And the boom would probably be quite a bit bigger.
This bothers me the most.
The Hindenburg didn't go boom. It had an accident and all it's hydrogen slowly burnt out. Instead of rapidly crashing, it slowly drifted down.
Also, quite interestingly, the only two persons surviving the accident were in the cabin, the others died because they tried to jump out/other stupid stuff.
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Me thinks that compressing large amounts of hydrogen into a relatively small place would be unwise.
Why would it be any more unwise than a nuclear powered airplane?
True...it would be like the Hindenburg. Only this time at about 40 000 feet and moving at better than 300 miles per hours. And the boom would probably be quite a bit bigger.
:wtf: Um... no. Jet fuel is quite as flammable as hydrogen. If a fuel tank is leaking at 40,000 feet, you're going to have problems, whether you're using hydrogen, ethanol or JP-5. Hindenburg burned because it used hydrogen as a means of making the blimp less dense than air. Copious amounts of fairly loosely contained hydrogen, combined with a readily flammable skin, it was a populated fire bomb. A plane would not have that problem, because the hydrogen would not be in a large open area contained by only a thin, flammable skin.
Planes engines do burn on occasion, sometimes with lethal consequences. Hydrogen would not change that, either way.
A nuclear powered plane would be a problem because in the event of a crash (and crashes will happen) the nuclear fuel has the potential to escape its containment, and a radiological disaster shouldn't be the result of every plane crash.
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Let's not forget these ideas have been floating around since 1964 (Gerry Anderson gave us this: http://davidszondy.com/future/Thunderbirds/fireflash.htm).
Personally, as an Aviation graduate, I'm all for finding alternate fuels for airlines, so that we can continue to enjoy the opportunity to fly for next to nothing. However Nuclear powered aircraft concerns me. Not only for those who live around the airport in case of fuel disposal or even worse material leakage. But in this current climate, albeit, I fully recognise that these plans will take decades to go into motion if they get the goahead, we cannot rule out the attractiveness of flying nuclear reators to terrorists. Just think of the global desvestion of an airbourne nuclear explosion would have.
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I'm afraid nuclear powered aircrafts are far away in the future.
There are two reasons for this: the energy density is pretty good in kerosene and fossilized fuels (compared to current batteries for example). This fact rules out battery based systems, unless somebody figures out dramatic improvements on the energy density.
The second reason is that no matter what, there is a need of dense materia around the reactor, otherwise radiation will make a short work of pilots (and the passengers too). This increases the weight of the aircraft quite radically. And, unfortunately the materials (aluminum, ceramics, titanium) used elsewhere in the airframe aren't getting stronger at the same time, unless somebody adds more of them (which increases weight -> which increases power demands of the reactor -> which increases the weight of the reactor and thus the weight of the plane...)
Before someone says to install it in the tail of the aircraft, the answer is most likely not possible with current technology (says my common sense). The reason being that airliners are according to my understanding, designed to be stabile, so their COGs should be located in the fore parts of the aircrafts. Adding a reactor behind will shift the weight heavily towards aft part, making aircraft unstable by nature, meaning that it doesn't want to fly straight and it doesn't want to recover - though this can be overcome with electronics, but I haven't heard about this being done in airliners (modern fighter aircraft are another case).
Besides, who of the passengers would then like to sit in the aft part? Discussions like these make me always think that in engineering point of view, oil has been pretty good compromise in the energy density, storage, safety and weight sides in the end. The only bad things are CO2 outputs and that it is running out. Let's say it is well understandable why it has been chosen as the main energy source in many applications.
Mika
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What if the airliner were a flying wing instead of the conventional design? Not everything has to be so conventional :)
What if the reactor were a Fusion instead of Fission reactor? The various Fusion projects are starting to bear some fruit...maybe that'd be the solution?
Actually I wonder if the solution would be to still have the reactor on the ground and that we'll have some sort of super battery or super capacitor (apparently such a thing exists) that could be charged enough for hours of flight.
Also...propulsion. If we're using a electrical source like a reactor...would we be "back to" using propellers for nuclear powered airliners? Even with super efficient propellers we run into the classic issues with drag that aircraft designers at the end of WWII experienced. Essentially...the drag caused by the propeller increases exponentially the faster you try to go. Even if our energy source was powerful...I wonder how good this could be made.
Interesting...sort of a thought experiment for the moment.
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The point of this is that we can't continue to rely on fossil fuels for our transportation. For airplanes, other than kerosene, what else is there? Answer: At the moment nothing, because nothing has enough energy density, except nuclear which isn't used for other reasons.
So does anyone have other ideas for what can be used instead of fossil fuels?
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The benefits are great, but the only problem I have would be when a group of people decides to pull a 9/11. It may be safe for the passengers, but how much damage would it do to the ground? Several square miles seems a lot on the ground.
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The classic answer to sustained thrust with a nuclear powersource has been something like a ramjet, only substitute "air piped through a nuclear reactor" for "bleeding ignited fuel into the jet." It's a fairly elegant solution, if you can make it work, as the limit on the system is how long until it builds up a dangerous amount of heat instead of any real need for an external fuel source. The problem is that reactors are safe because they are more or less closed systems. This system would be emitting god-knows-what into the environment.
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It's like I said, Hydrogen is the only way to go, really, if you're looking for something remotely sustainable and safe. IIRC it has twice the energy density / mass of most fuels (assuming wiki isn't lying), but 1/16 the energy per volume. The obvious solution is a larger airframe, but then mass goes up. It seems like a problem that can be solved, and eventually, will need to be.
Nuclear powered plane = more stupid than nuclear powered truck.
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The point of this is that we can't continue to rely on fossil fuels for our transportation. For airplanes, other than kerosene, what else is there? Answer: At the moment nothing, because nothing has enough energy density, except nuclear which isn't used for other reasons.
So does anyone have other ideas for what can be used instead of fossil fuels?
Helium airships with charged batteries plus the latest in solar panels along the top to charge the batteries. Its slow but the environmental impact is very small from what I know.
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Nuclear powered plane = more stupid than nuclear powered truck.
Perhaps. But the unlimited range and possibly operating time sound pretty good, yes? If a way can be found to render it radiation-safe, then this is an incredibly appealing system. Unfortunately, that's probably going to mean waiting until viable small-scale fusion.
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Fusion tends to release dangerous particles too.
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I say they need to bring prop planes back into circulation. They are many times more efficient than jet fuel injection.
Either that, or have the turbine system should be driven by electric motors... Though the kind of electric motor of that size is suspect to issues regarding power, stability, and reliability. However, in conjunction with solar plates and a supplemental natural gas based generator, it would make for a MUCH cleaner and cheaper solution.
But then again, I don't know how well (or even if) heavy electronic components would hold up to the stresses of an airliner.
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The point of this is that we can't continue to rely on fossil fuels for our transportation. For airplanes, other than kerosene, what else is there? Answer: At the moment nothing, because nothing has enough energy density, except nuclear which isn't used for other reasons.
So does anyone have other ideas for what can be used instead of fossil fuels?
Helium airships with charged batteries plus the latest in solar panels along the top to charge the batteries. Its slow but the environmental impact is very small from what I know.
We don't want it to take a week to go from one side of the pacific to the other.
I say they need to bring prop planes back into circulation. They are many times more efficient than jet fuel injection.
But also have their own problems such as needing highly refined (read: expensive) fuel, and they are nowhere near as fast as a jet.
Either that, or have the turbine system should be driven by electric motors... Though the kind of electric motor of that size is suspect to issues regarding power, stability, and reliability
The motor wouldn't be the problem, it would be the batteries. Their energy density just isn't enough and, to make matters worse, they wear out relatively quickly.
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Regarding travelling times, what is your hurry? You would see a lot more on that single trip than nowadays!
Batteries then, take a look at the proposed hybrid cars and the weight of their batteries. Normal gasoline tank contains about 60 litres of fuel, it probably weighs something like 40 kgs (Stealth?), so that the fuel storage of average car weighs about 100 kgs. With this, it is possible to travel ~ 700 kms at the speed of 100 km/h. The electric or hybrid cars are quite a far away from that. Why is this relevant? Because the power demand in aircraft is actually higher, and more than ever, every kg counts!
Again, anything that has "nuclear" in it means radiation in many forms. And when photon energies get high, you need something dense to stop and absorb them (+ their residuals!). Unfortunately, anything dense is also heavy. Traditionally, that something dense has been lead, graphite and reinforced concrete. And since you cannot use open air reactors due to the pollution effects, reactor has to be a closed system, from which the power is then collected via heated water and turbines and is transformed to electricity. This will also require a lot of space, but also weight. Maybe the only alternative would be a nuclear battery if they happen to work. Even then you would have to fight hard with the weight and radiation protection.
The reason why I'm thinking more traditional engineered airliners is that even though USAF has proven the flying wing concept, nobody else uses it. The reason? I don't know, but I suspect it is a pretty good one.
Mika
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Could the prop plane design be modified using existing technologies, making it slightly faster / more efficent?
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The reason why I'm thinking more traditional engineered airliners is that even though USAF has proven the flying wing concept, nobody else uses it. The reason? I don't know, but I suspect it is a pretty good one.
Some of the bigger airliner firms are working on a Blended Wing Body. (I haven't got time now to find a link, sorry). So it's likely that there will be 'flying wing' airliners in the (distant) future.
Could the prop plane design be modified using existing technologies, making it slightly faster / more efficent?
Yes, it can. It's called a propfan, but it's fairly new and unproven yet.
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Certainly with complex computer calculations you can make the propeller based engine better than anything they had during WWII ...but really there are limits to what a propeller can do. During WWII propeller design went incredible steps to the point of making some very efficient designs that from what I understand haven't changed too much since then. We can do things with more precision now...but even back then they were really far along on this stuff.
Propeller based aircraft are still going to be nosier, with more vibration, and they simply won't be able to go as fast.
And yes an airship might take a long time but if it comes down to it and were desperate...we may have to "take several steps back". The airships might be a very good way to do long distance cargo hauls. I've read a bit saying that might be a possibility. Travel time wouldn't be too much different than a ship.
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I can see that used only for a NASA shuttle.
anywhere else - no.
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Regarding travelling times, what is your hurry? You would see a lot more on that single trip than nowadays!
On a modern 747 it takes 13 hours to go from San Francisco to Shanghai (or more if you have a head wind). What is there to see except endless amounts of ocean?
The airships might be a very good way to do long distance cargo hauls. I've read a bit saying that might be a possibility. Travel time wouldn't be too much different than a ship
In which case it would be more cost effective to simply send it on a ship. The reason people would send freight via an airplane is because even though it is much faster, and often time = $$$$$$$. So if the speeds are similar, why bother?
And since you cannot use open air reactors due to the pollution effects, reactor has to be a closed system, from which the power is then collected via heated water and turbines and is transformed to electricity.
Part of this is finding better radiation shields and part of it is smaller reactor designs. Right now the worlds smallest closed loop reactor system that I know of (made by Toshiba) is 20 feet by 6 feet.
EDIT: Whoa, just recently discovered this gem (http://www.aviation-history.com/articles/nuke-american.htm) describing the Air Force's attempt to build a nuclear power bomber. Evidently they had some success and it looks pretty promising. Check it out.
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On a modern 747 it takes 13 hours to go from San Francisco to Shanghai (or more if you have a head wind). What is there to see except endless amounts of ocean?
[Sales pitch]
Tired of growing risk of heart attack due to bad lower body blood circulation? Annoyed about the jetlag in the destination country? Cannot get sleep in the aircraft? Why risk your health in a long non-stop flight? Spend a couple of days in the beautiful tropical islands of the Pacific Ocean! Bask in the glory of the sunshine, experience interesting people and local delicacies! Order your tickets today!
[/Sales pitch]
{Man, I'm getting good at this. I almost don't feel dirty anymore. Anyone note the obvious deficiency of this approach, by the way?}
Part of this is finding better radiation shields and part of it is smaller reactor designs. Right now the worlds smallest closed loop reactor system that I know of (made by Toshiba) is 20 feet by 6 feet.
Isn't this similar to the nuclear battery by Los Alamos research groups? What is the weight of that system?
Regarding the nuclear powered bomber, there are a couple of things to note: the aircraft where the reactor was fitted is large even by today's standard. But, it took away a lot of payload of the aircraft, and required quite a bit of shielding around the crew compartment. According to my understanding, the crew was restricted pretty much in the cockpit of the aircraft. This means that in order to use the reactor in current airliners, one would need to add a lot more of the shielding since the passengers must be protected also = more weight.
I'm not that hopeful on finding new materials to block radiation. Asking for a dense but light weight material sounds like a physical impossibility. Even if that could be done, the next question is price. These aircrafts should be commercially viable, after all.
After browsing through some introductory articles of the blending wing, I'm starting to see why it is taking long. First is flight control, indeed the blended wing design functions more like a fighter aircraft, being unstabile and all. Judging by some of the reports, turbulence has proved to be pretty difficult in these cases, and sometimes the test models have experienced great accelerations (in non-intended directions) in these conditions. Though I'm curious to see a large aircraft in a deep stall.
Second thing is the pressurization of the compartments. Current airliners use cylindrical hull to equalize the pressure differences around the passenger cabin, but in blended wing the cabin is not cylindrical, which will stress the airframe differently in different places. Some researchers are placing hope for computer aided design to find the difficult places in the cabin, some are working with new materials. Though I'm a little sceptical about the new materials. Of course it is possible to find them, but at commercially viable price?
Mika
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No. The one thing that counts in radiation shielding, is mass. AFAIK. The one thing that counts in airplane design, is also mass. The Soviets did it, yes, but they had so little shielding that after a couple of years, most of the crews that flew it were dead.
The Americans converted a B-36 to carry a nuclear reactor, and it had all the shielding required. Of course, that meant that it needed a crapload of engines (It had a combination of jets and props, IIRC). (My bad, all B-36 had jets and props.)
(http://upload.wikimedia.org/wikipedia/commons/5/58/NB36H-2.jpg)
In May 1946, the Air Force began the Nuclear Energy for the Propulsion of Aircraft (NEPA) project which was followed in May 1951 by the Aircraft Nuclear Propulsion (ANP) program. The ANP program required that Convair modify two B-36s under the MX-1589 project. One of the modified B-36s studied shielding requirements for an airborne reactor to determine whether a nuclear aircraft was feasible. The Nuclear Test Aircraft (NTA) was a B-36H-20-CF (Serial Number 51-5712) that had been damaged in a tornado at Carswell AFB on 1 September 1952. This plane, designated the NB-36H, was modified to carry a 1 MW, air-cooled nuclear reactor in the aft bomb bay, with a four ton lead shield between the reactor and the cockpit. The cockpit was encased in lead and rubber, with a 6-inch (15 cm)–thick acrylic glass windshield. The reactor was operational but did not power the plane; its sole purpose was to investigate the effect of radiation on aircraft systems. Between 1955 and 1957, the NB-36H completed 47 test flights and 215 hours of flight time, during 89 of which the reactor was critical.
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Regarding the nuclear powered bomber, there are a couple of things to note: the aircraft where the reactor was fitted is large even by today's standard.
True, but then again the reactor was also designed and built with late 1950's technology, surely we have progressed at least a little in that regard.
I'm not that hopeful on finding new materials to block radiation. Asking for a dense but light weight material sounds like a physical impossibility. Even if that could be done, the next question is price. These aircrafts should be commercially viable, after all.
Radiation can also be reflected, right? So maybe it's not a question of piling on more lead but rather using some kind of crazy nanoscale engineering on what we've already got to reflect it.
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And yes an airship might take a long time but if it comes down to it and were desperate...we may have to "take several steps back". The airships might be a very good way to do long distance cargo hauls. I've read a bit saying that might be a possibility. Travel time wouldn't be too much different than a ship.
Issues like the one raised above make me uneasy about the complications fossil fuel scarcity presents. If things do get that desperate, I fear air travel may be more dispensable than we thought. Intercontinental trade is heavily dependent on ships, more so than airplanes in terms of both monetary value and tonnage, and they too thrive on the readily available hydrocarbons found in petroleum. At the end of the day, goods such as grain, shipped in bulk via freighters, demonstrate how keeping these ships running is essential to feeding countries that rely on imports for their food. Even if the worldwide merchant fleet is able to replicate the U.S. Navy's record on nuclear safety, we still have the issue of distributing product once it reaches land. Trains can go electric, and that electricity can be provided by nuclear reactors too, or renewable power sources where applicable. But trucks are another problem. As mentioned before, current battery technology is not yet up to the task of hauling around 40 tons of trailer. Having observed what ethanol production entails, we should hope that a more environmentally and economically sound solution is developed.
It will be interesting to see how we answer the question of air travel in the coming decades. Personally I wonder if synthetic fuels are the answer, or if we can reduce the chances of miniature Chernobyls happening such that nuclear powered planes are viable. I like the blimp idea. :)
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or if we can reduce the chances of miniature Chernobyls happening such that nuclear powered planes are viable.
If we could make a black box survive almost any wreck, surely we could with a reactor, add to that an automatic shutdown routine when the plane gets to a certain distance from the ground.
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If nuclear reactors failed as often as black box's, then we'd have had several minuture Chernobyl s.
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No. The one thing that counts in radiation shielding, is mass. AFAIK. The one thing that counts in airplane design, is also mass. The Soviets did it, yes, but they had so little shielding that after a couple of years, most of the crews that flew it were dead.
The Americans converted a B-36 to carry a nuclear reactor, and it had all the shielding required. Of course, that meant that it needed a crapload of engines (It had a combination of jets and props, IIRC). (My bad, all B-36 had jets and props.)
(http://upload.wikimedia.org/wikipedia/commons/5/58/NB36H-2.jpg)
In May 1946, the Air Force began the Nuclear Energy for the Propulsion of Aircraft (NEPA) project which was followed in May 1951 by the Aircraft Nuclear Propulsion (ANP) program. The ANP program required that Convair modify two B-36s under the MX-1589 project. One of the modified B-36s studied shielding requirements for an airborne reactor to determine whether a nuclear aircraft was feasible. The Nuclear Test Aircraft (NTA) was a B-36H-20-CF (Serial Number 51-5712) that had been damaged in a tornado at Carswell AFB on 1 September 1952. This plane, designated the NB-36H, was modified to carry a 1 MW, air-cooled nuclear reactor in the aft bomb bay, with a four ton lead shield between the reactor and the cockpit. The cockpit was encased in lead and rubber, with a 6-inch (15 cm)–thick acrylic glass windshield. The reactor was operational but did not power the plane; its sole purpose was to investigate the effect of radiation on aircraft systems. Between 1955 and 1957, the NB-36H completed 47 test flights and 215 hours of flight time, during 89 of which the reactor was critical.
I know that. But there were about 5 people in the whole of the huge aircraft, and the power still came from normal fuel. Commercial airliners with a nuclear reactor will not work until 2367 :p As for fusion reactors: the bigger they are, the better they work. The JET in Oxford, including all its heating-up equipment, is too big to fit inside a plane, but too small to produce more energy than it needs to stay functioning.
If we could make a black box survive almost any wreck, surely we could with a reactor, add to that an automatic shutdown routine when the plane gets to a certain distance from the ground.
The bigger something is, the more vulnerable it is. A fission reactor is a bit bigger than a black box. And an automatic shutdown routine doesn't remove the radioactivity. As for reflecting the radiation: when, on a crash, the reflector would break, all of the accumulated radiation would be released, no?
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True, but then again the reactor was also designed and built with late 1950's technology, surely we have progressed at least a little in that regard.
I don't think that the development has progressed in those areas. They have improved the reliability and security of the reactors, but not sizes or weights.
Radiation can also be reflected, right? So maybe it's not a question of piling on more lead but rather using some kind of crazy nanoscale engineering on what we've already got to reflect it.
In practise there is no such thing as mirror surface for x-ray photons, much less for gamma photons. While the x-rays can be operated with diffractive elements, gamma photons are much more difficult, them affecting the nucleus themselves and pretty much ignoring all the electrons on the atomic shell. If one would add reflectors around nuclear reactor and by some miracle got it working, the reflectors would heat up quickly due to x-rays, be structurally weakened by gamma rays, and would also turn radioactive also by themselves not to mention mess up the chain reaction itself by launching stuff back there. This time, radiation would not come from the reactor directly, but from the shielding itself. This is the reason there is need for huge thicknesses to really absorb those nasty thingies and to keep them protecting stuff for extended period of time.
[Off topic]
Some interesting non-related links:
http://www.youtube.com/watch?v=O_TuqaK3B0U
http://www.ejectionsite.com/stapp.htm (holy cow, human testing of the early ejection seats!)
http://www.youtube.com/watch?v=unz8Tf3ZMbA (nuclear rifle - yes, nuclear rifle)
[/Off topic]
Mika
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Carbon nanotubes/buckyballs seem to be good at everything else, would they be any good at sheilding? What about ceramics? Ah screw it, just have someone invent energy sheilds already. :p
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Carbon nanotubes/buckyballs seem to be good at everything else, would they be any good at sheilding? What about ceramics? Ah screw it, just have someone invent energy sheilds already.
Unfortunately no, nanotubes and buckyballs don't work, neither do ceramics. This is caused by the fact that the higher the energy of a photon, the more deeper it will travel in the target atom. At gamma ray's case, translations happen in the very core of the atom, not in the electron shell. This effectively means that the area the photon has to struck in an atom in order to become absorbed is a lot smaller. So, you have to improve the odds that the photons will hit an atom in a blocking material. That is done by adding more material around the shield, another factor improving the odds is the density of the atoms in the material.
Carbon nanotubes are strong, but not dense (hence the weight saving). Same applies to ceramics.
This is then of course, what I think would happen, not a general answer from the community called Scientists.
Mika
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Scientists
Where is Herra Tohtori?
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The bigger something is, the more vulnerable it is. A fission reactor is a bit bigger than a black box. And an automatic shutdown routine doesn't remove the radioactivity. As for reflecting the radiation: when, on a crash, the reflector would break, all of the accumulated radiation would be released, no?
Nuclear reactors are inherently sturdy objects. More than a few nuclear-powered submarines have been lost without a dangerous reactor failure ("crush depth" does not exist on this planet for reactor containment vessels manufactured in the US, and presumably in most other places). Studies of the problem indicate that even in the event of combat damage nuclear-powered ships would not pose a danger 99.9% of the time. This is an impressive feat when you consider that they were testing against a ton of Torpex or three thousand pounds of high explosive from a surface-to-surface missile. It can be done.
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Studies of the problem indicate that even in the event of combat damage nuclear-powered ships would not pose a danger 99.9% of the time.
This begs for further questions: what is meant by not "a danger" in this case? How does this apply to airplanes?
Mika
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A nuclear submarine is not dangerous, unless it flies over NYC :p
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This begs for further questions: what is meant by not "a danger" in this case? How does this apply to airplanes?
Even in the case of a direct torpedo hit against the enigneering spaces, the reactor will automatically scram and the containment vessel will not be breached. The point is, it's possible to make them safe against extremes of impact and pressure.
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Regarding the nuclear powered bomber, there are a couple of things to note: the aircraft where the reactor was fitted is large even by today's standard. But, it took away a lot of payload of the aircraft, and required quite a bit of shielding around the crew compartment.
It's also worth mentioning that they refitted an airplane designed for a completely different kind of propulsion system instead of building a new one from scratch, which is why its payload was taken away. Something along the lines of a flying wing designed from the beginning to use this instead of traditional jet engines and fuel tanks might work better.
Here is something that came out recently that might be somewhat better suited for this task:
http://www.physorg.com/news145561984.html
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Regarding the nuclear powered bomber, there are a couple of things to note: the aircraft where the reactor was fitted is large even by today's standard. But, it took away a lot of payload of the aircraft, and required quite a bit of shielding around the crew compartment.
It's also worth mentioning that they refitted an airplane designed for a completely different kind of propulsion system instead of building a new one from scratch, which is why its payload was taken away. Something along the lines of a flying wing designed from the beginning to use this instead of traditional jet engines and fuel tanks might work better.
Here is something that came out recently that might be somewhat better suited for this task:
http://www.physorg.com/news145561984.html
I remember reading about that. Sounds pretty good if it works as advertised. Sounds like they have the problems anticipated at least.
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Even in the case of a direct torpedo hit against the enigneering spaces, the reactor will automatically scram and the containment vessel will not be breached. The point is, it's possible to make them safe against extremes of impact and pressure.
Depends on the actual location. I recall reading they tested a ferro-concrete wall with a fighter plane to determine if combat aircraft can breach the outer wall of nuclear power plant. Turned out that it can't (penetrated only a couple of centimeters). Testing with high explosives, depends on the actual test. Doing things with penetrating shaped charges could yield results with low amount of explosives. Results of those tests can just as easily not be generalized to aircrafts. The accelerations and stresses are different on aircraft, say a momentarily acceleration of 300 gs is pretty high for anything constructed by man.
It's also worth mentioning that they refitted an airplane designed for a completely different kind of propulsion system instead of building a new one from scratch, which is why its payload was taken away. Something along the lines of a flying wing designed from the beginning to use this instead of traditional jet engines and fuel tanks might work better.
I stand by my reasoning that using nuclear reactor there would only add the weight of the aircraft as the whole passenger cabin should be protected from radiation, leading to usage of heavy materials.
Mika
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Apart from that, the reactor in submarines is probably heavily shielded, something you can't afford in airplanes.
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I stand by my reasoning that using nuclear reactor there would only add the weight of the aircraft as the whole passenger cabin should be protected from radiation, leading to usage of heavy materials.
Ok, so how much extra weight is there?
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I stand by my reasoning that using nuclear reactor there would only add the weight of the aircraft as the whole passenger cabin should be protected from radiation, leading to usage of heavy materials.
The radition protection would be built into the reactor containment vessel itself, not the passenger cabin. This is a much more rational and lighter-weight design. Similarly applying the same design principles originally developed for quieting measures on a submarine would increase its safety by not making it part of the structure or truly connected to it at all. The weight is a significant factor, the typical pressurized water reactor weighs a good twenty tons, but there are aircraft flying a lot heavier than that.
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I also did some checking on how many pounds of fuel several kinds of airplanes are carrying around for comparison (keep in mind 2000 pounds per ton, so a 20 ton reactor weighs 40,000 pounds):
Based on wiki answers, 1 gallon of kerosene weighs 6.82 pounds
b-52: 47,975 U.S. gal * 6.82 = 327,190 pounds
747-400: 57,285 U.S. gal * 6.82 = 390,684 pounds
737-700: 6,875 US gal * 6.82 = 46,887.5 pounds
So something like that is actually practical for something the size of a 737 or bigger.
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What's the power output of your 20-ton reactor? And can it survive a plane crash without containment failure?
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What's the power output of your 20-ton reactor? And can it survive a plane crash without containment failure?
Nghtm1r already stated it could survive a crash intact. The power output depends on the size, I'm not sure what a 20 tonner could do (nghtm1r?), but the one they were originally thinking about using back during the Air Forces nuclear bomber program had a 1 MW output, but I don't know how heavy it was.
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Nghtm1r already stated it could survive a crash intact. The power output depends on the size, I'm not sure what a 20 tonner could do (nghtm1r?), but the one they were originally thinking about using back during the Air Forces nuclear bomber program had a 1 MW output, but I don't know how heavy it was.
I'm pretty sure it cannot withstand a crash intact. Black box flight data recorders are required to withstand momentarily accelerations of 3200 gs. The data recorder inside the box weighs about 30 grams, so the force experienced by the support structure is 0,04 kg * 3200 * 9,81 m/s^2 ~ 1256 Newtons, so 30 gram chip weighs about 120 kgs (numbers are from Wikipedia). And sometimes the flight data recorder has not survived the crash intact!
So you'll have a hard time to convince me that it would be possible to build an reactor to withstand such accelerations and keep an airplane airworthy.
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So you'll have a hard time to convince me that it would be possible to build an reactor to withstand such accelerations and keep an airplane airworthy.
I think you've got your terminology a bit mixed up there.
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So you'll have a hard time to convince me that it would be possible to build an reactor to withstand such accelerations and keep an airplane airworthy.
That should have been along the lines:
You'll have a hard time to convince me that it would be possible to both build a reactor to withstand such accelerations and to allow the airplane to be airworthy.
Meaning that if such reactor is constructed, the weight of the encasing is so high that the aircraft will never take off, or, that the encasing will not withstand the acceleration without compromising structural failure of reactor containment.
Mika
EDIT: Damn typos.
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I would say that if the airliner would be built to withstand the pressure, it could easily hold whatever encasing. However, it would have a much denser mass over volume compared to liquid fuel. This could be very detrimental to stability control, as the center of gravity would be far more concentrated.
But then again, I'm no pilot, so I don't know :p.
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In the Convair B-36 related article it is actually mentioned that the crew protection is divided along the larger section of the fuselage because of the controlling reasons and flight dynamics. Aircrafts tend to create larger forces than submarines and marine vessels.
I'm not sure about the pressure withstandability; you can have a fighter colliding with the reactor wall, but what about when the reactor containment vessel itself is moving and the stress is applied only on a small surface area (its own weight basically)? This would be expected of a crash.
Mika
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The official output is classified. It's enough to drive more than a thousand/two thousand tons of metal at better than 30 knots through water, though, plus various electronics including an active sonar capable of killing fish too close to it when it's on, so you have to figure it's perhaps half as powerful as a civilian plant. This means at least 20 megawatts, possibly more.
The thing is, yes, we've not had something crash an airplane, but you have to remember, submarines have been sunk with active reactors aboard. The Scorpion and the Thresher, and the Russians have lost a few too. As far as is possible to determine, none of them breached their containment vessels. The Scorpion and Thresher were both lost in deep water in the mid-Atlantic, and neither of them was capable of diving deeper than about 900 feet. (Furthermore, they wouldn't be that deep willingly, because that deep you can't tell what's going on on the surface because the thermocline layer over your head is in the way.) The water where they were lost was at least five times that. What is often forgotten about ships sinking is that they more or less fall the rest of the way to the ocean floor. It's not like dropping them from equivalent altitude, maybe a quarter of that. A ship hitting a rock bottom can look every bit as crumpled as if it had fallen onto a concrete surface from the air.
Scorpion's reactor containment vessel was confirmed to be undamaged when it was found...because the sub had hit the bottom hard enough it more or less pancaked and the reactor was forced out the top of the hull. Scorpion was, of course, brand new, and it is known that after ten years or so reactor containment vessels become very brittle because of constant radiation exposure. Nonetheless, it effectively fell the surface equivalent of 1000+ feet onto a rock surface without sustaining damage sufficent to breach the containment vessel.
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half as powerful as a civilian plant. This means at least 20 megawatts, possibly more.
I hoppe you realise that the majority of civilian nuclear plants are over 1,000 megawatts, and the largest civilian turbines are rated at 1,700 megawatts (and there are two of them off that reactor).
Compared with vehicle engines (even large ship ones) they aren't even the same order of magnitude.
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NGTM-1R, I really had to read your message several times during several days and I still have problems with understanding the information content in there. Could you clarify a couple of points:
It's not like dropping them from equivalent altitude, maybe a quarter of that. A ship hitting a rock bottom can look every bit as crumpled as if it had fallen onto a concrete surface from the air.
Should I understand this as a statement that the energy released in dropping to the ground from 2 km height is about four times higher than when the same object drops 2 kms in water?
Again, I'm not sure if I understood correctly, but is it really stated that form defects of the ship have occured only when the hull hits the bottom?
Scorpion's reactor containment vessel was confirmed to be undamaged when it was found...because the sub had hit the bottom hard enough it more or less pancaked and the reactor was forced out the top of the hull. Scorpion was, of course, brand new, and it is known that after ten years or so reactor containment vessels become very brittle because of constant radiation exposure. Nonetheless, it effectively fell the surface equivalent of 1000+ feet onto a rock surface without sustaining damage sufficent to breach the containment vessel.
Again, is it stated that the reactor was within the hull when the hull hit the ocean floor? Also, how it is deduced that the hull was pancaked after it struck the ocean bottom?
How is this related to nuclear powered aircraft? I believe the stress factors are radically different in submarine reactor shielding and in airplane, and the results of marine reactors cannot be compared to hypothetical airborne reactors - but I need to make sure I understood your post correctly before that.
Mika
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Okay, I'll leave my opinion at this:
If it can be shown that a nuclear powered plane can be cheaper to run than other alternative fuels (such as hydrogen and bio fuel), will never loose containment as a result of a crash (even in say, a hijacking), and still be light enough to allow for a safe plane... then I'll agree it's a good idea.
BTW... good luck selling that to (silly) Americans, who won't even allow nuclear waste to be shipped in (indestructible) containers on freeways.
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even in say, a hijacking
Actually in a hijacking it might be even better because you can just scram it by remote control.
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Hey,
I've read the first two pages and skimed over the second two, so forgive me if I go over stuff that's already been said, but I thought I would add my $0.02 to this conversation.
A few things have come up here.
As already mentioned, with current technology the biggest problem with placing a reactor in an aircraft is weight. You can't just consider the weight of the reactor and its containment vessel, either. You also have to consider the weight of its support equipment. Nuclear reactors work by converting fission reactions into heat. That heat is then converted into power by means of a steam turbine. So you would need a turbine large enough to generate enough power to support 4+ engines. In order to do that safely, you need at least two separate enclosed systems (one for the heated reactor coolant and another for the turbine). You also need some way to cool the turbine water. Simply running it around the airframe probably wouldn't provide enough area to bleed the heat, especially at lower altitudes and slower airspeeds. You also would need a type of regulator equipment to handle the power conversion/transfer/etc.
The second issue with weight is the power-to-weight ratio of the motors. Piston and jet engines are very powerful for their weight. Electric engines generally cannot output the same amount of power for their size -and the ones that can require massive amounts of power. It would be more efficient putting a large diesel generator in a plane and run it like a diesel-electric locomotive. It hasn't been done because it's less efficient than current piston and jet engines, and weighs a godawful amount.
Also, in line of safety. If the reactor shuts down, that airliner now has NO engine power. If one engine shuts down... the airplane still has power to the remaining engines. Most jetlines are able to fly with only half their engines operational. Not well, but they'll stay airborn.
Someone else brought up the fact that props are not as fast as jet engines. This isn't exactly true. The Tupolev Tu-114 was turboprop powered and could fly as fast as all of the jet liners of the day (around 550 mph in the mid 1950's). Granted, today it's probably unlikely that even modern props will be able to reach high subsonic speeds, but they're not as slow as a lot of people seem to think.
Lastly, you'll see a lot of other kinds of transportation convert to nuclear or some other power before aircraft. There are so many more ways to make aircraft more efficient through engine and airframe refinements (anyone who's interested should look at what was done for the A380) that it's not financially feasible in any way to convert them to another fuel source. Automobiles burn far more fuel far less efficiently than aircraft.