Why we will never have nuclear powered cars
January 4th, 2013
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I have been asked on a number of occasions whether there will ever be a nuclear powered car. The idea of powering a car by nuclear fission certainly seems to have some obvious appeal. The energy density of the fuel for a nuclear reactor is so great that it would be possible to build a car that never needed to be refueled, having a reactor core capable of long outlasting the useful lifespan of the car itself. The average life expectancy of a car is about 11 years and many accumulate 200,000 miles or more. However, a nuclear reactor could, in principle, power a car for decades. Thus, only those who kept their car well past the point of it being a classic would ever need to be concerned about running low on fuel.
Despite the appeal of never needing to buy fuel or worry about mileage, there are a number of reasons why a small nuclear reactor just does not work well as the power plant for a road vehicle. In principle, a nuclear reactor could be made small enough, but doing so push the inherent limitations of fission and result in an exceptionally expensive and problematic vehicle.
Of course, in a sense, all vehicles are really nuclear powered. Fossil fuels contain energy that is derived from ancient plant material, thus being an indirect way of using solar energy, which, of course, was produced by a nuclear reaction. Electric cars also use nuclear energy, whether or not they are connected to a nuclear-powered grid, since all energy on earth had to come from a nuclear reaction at some point.
Powering vehicles with nuclear fission is thus entirely possible if the fission reactors are used to provide grid electricity for charging electric car batteries or if the energy from the reactors produces synthetic fuel or even hydrogen. This is a much more economical and realistic means of having the energy for transportation generated by nuclear power than having everyone drive around with a reactor under their hood.
Of course there are other types of nuclear energy aside from fission. Unfortunately, none would actually be likely to work for an automobile.
Nuclear Fission:
Nuclear reactors are a really great way of producing energy for static applications and for ships and submarines. However, for automobiles, they turn out to be a lot more trouble than they are worth. In 1958, Ford did create an illustration of what a nuclear-powered car would look like, dubbing it the Nucleon, but the Nucleon was more of a publicity piece than a viable transportation concept. No land vehicle propelled by a nuclear reactor has ever been built. The Soviet Union designed several small, transportable nuclear power plants, and the US Army even built a prototype of a road-transportable reactor, but these were not propelled by the nuclear reactors.
For one thing, the regulatory hurdles to getting a nuclear reactor into an automobile are likely to be insurmountable. All nuclear power reactors must conform to strict safety and security guidelines. In the case of an automobile, it is probably not a bad thing that safety regulations would prevent it from taking to the road. The core of an operating nuclear reactor does indeed become very radioactive, and if a road accident lead to a containment breach, the decay of short-lived isotopes could produce lethal levels of radiation exposure to the cars occupants.
Because of the radiation produced by an operating reactors core, all reactors that operate near people must also have substantial shielding. For static applications, this really is not a problem. Just having a large amount of water around the reactor provides ample shielding from both gamma rays and neutrons. Concrete also works well, and in circumstances where a lesser volume is desired, dense metal like lead can be used. This is also no problem for ships and submarines, which need ballast anyway. However, to build a truly portable reactor, as much be in a car, the amount of shielding required presents a real problem. At a minimum, the reactor core would need to be surrounded by a combination of heavy materials to block gamma rays and some kind of neutron shield, which might be composed of large amounts of water or an organic material like polyethylene.
The US ran into the problem of portable shielding when trying to develop nuclear-powered aircraft in the 1950’s. As part of the program to develop a nuclear powered aircraft, a B-36 bomber was modified to carry and operate a nuclear reactor while in flight. Even by modern standards, the B-36 is a massive aircraft. It had the capacity to carry a payload of well over 30 metric tons. Yet even despite this huge capacity, the sheer weight of sheidling needed to maintain minimum crew safety proved a problem. In order to make flights possible at all, designers eventually decided to forgo most of the shielding on the reactor itself and instead shield the crew compartment.
The image to the left shows the crew compartment of the NB-36H. It was surrounded by multiple layers of lead and weighed no less than 11 tonnes. In addition to the shielding around the cabin, large tanks of water and boron were placed in the front and middle bombays to shield against neutrons and gamma radiation. The reactor was placed in the rear bombay, as far back from the crew as possible. Even the massive B-36 struggled to get off the ground with so much additional weight.
All of this was necessary for a relatively small nuclear reactor. The reactor flown on the NB-36H only produced one megawatt of power. This is only a few times larger than the output that would be required to power an automobile.
Providing adequate shielding for an automobile would be no easier. It would not be possible to place the reactor a significant distance away from passengers and shielding the passenger compartment, but not the reactor, would not be an option. Additionally, it would have to be robust enough to survive a highway accident or other mishaps.
Another problem with putting a nuclear reactor in a car is the sheer size of the reactor. There is a limit to how small a reactor can be built, because it must have enough nuclear material to achieve critical mass. Exactly how much is required depends on the type of fuel and how enriched it is. For most reactors, a minimum of several tons of fuel is required to achieve criticality. In large power reactors, a typical core may be hundreds of tons. Reactor size can be reduced, quite dramatically, by using extremely highly enriched fuel, but in addition to such fuel being extremely expensive, it would mean weapons grade material being used in every car.
There are any number of other problems that a nuclear-powered automobile would present. Nuclear reactors require cooling for some time after they are shut down, due to decay heat. Providing adequate cooling could be a major problem if the car is kept in a closed garage. If the reactor were powered up and shut down as often as car engines are, it could become unstable or be susceptible to xenon poisoning. Other concerns range from maintenance to decommissioning and disposal, and if nothing else, it would be extremely expensive.
Radioisotope thermal generators:
In principle, if you wanted to build a nuclear -powered car, this just might be the way to do it. In fact, one does exist, but unfortunately, it does not carry passengers and it’s busy driving around mars. Indeed, radioisotope thermal generators have proven themselves to be highly reliable and rugged power sources for spacecraft and have been used in other applications where remote power is required for long durations.
In an RTG heat is produced not by nuclear fission, but by the decay of a radioisotope. Because of this, only very high energy particle emitters are suitable for RTG’s, as their decay produces a significant amount of heat. Most RTG’s used for space applications use plutonium-238, but a variety of other isotopes, including strontium-90 and polononium-210 have been used successfully.
RTG’s are inherently simple and therefore reliable. Isotopes can be chosen which decay primarily by particle emission and produce only weak gamma emissions. This dramatically reduces the need for shielding. Since the RTG does not need things like control rods or a moderator, it can be simpler and smaller. Also, because it does not need reach critical mass, it can be as small as desired.
However, RTG’s do have a number of drawbacks, which would make them unsuitable for automotive use. One of the biggest is that they cannot be turned off and their power level cannot be decreased or increased at will. This presents a number of problems. For one, it means that the RTG requires constant cooling that is not diminished when the vehicle is turned off. The power output of the RTG must be high enough to power the vehicle during times of high power consumption, meaning that excess power is produced most of the time. This could be reduced by adding a storage battery, allowing for additional power during acceleration or other times it may be needed, but it would not solve the issue entirely. Even with a storage battery, the RTG would need to produce enough power to keep the battery from running down during extended periods of driving.
In order to produce enough power, a very large amount of radioisotope would be required. Exactly how much depends on the energy of the isotope’s particle emissions and its half-life. Isotopes with short half-lives have the advantage of producing more power per gram m than those with long half-lives. For example, polonium-120, which has a half-life of only 138 days produces 140 watts per gram. Plutonium-238 has a half-life of more than 87 years and requires more than a kilogram to produce the same amount of power. However, while the plutonium-238 would easily power a car for years without any noticeable reduction in power output, while the polonium-210 would produce noticeably less power after a month and would need to be replaced at least every few months to a year.
Most RTG’s have used thermoelectric generators to convert the heat from radioactive decay into electricity. However, these have a very low efficiency, typically well under 15%. It’s possible that this could be replaced with a thermal engine, such as a sterling engine, and thus achieve efficiencies of upwards of 30%. However, in either case, a substantial amount of fuel would be required.
The cost alone of these radioisotopes makes the idea impractical. Any automobile powered by an RTG would need an extremely large isotope source costing many millions of dollars or possibly even hundreds of millions of dollars. Even if production of radioisotopes were increased dramatically, the costs are nowhere near practical for a car.
Aside from that, there are other problems. Such a massive amount of radioactive material is inherently dangerous and highly radiotoxic. In an accident or other mishap, if the isotope were ejected, it would be red hot. Since decay cannot be “turned off” there is no way to avoid this. Repairs and servicing would also be complicated by this issue. Inadequate cooling or blocking of radiators could cause overheating, meltdowns or a fire.
Non-thermal nuclear batteries:
There are methods that exist for converting ionizing radiation to electricity without the need to first convert it to heat. As such, much greater efficiencies are at least theoretically possible. Most such systems are currently only experimental or have only been built in relatively small sizes.
Betavoltaic batteries can convert beta emissions directly to electricity, but they tend to be of limited efficiency and have suffered problems with degradation of the semiconductor material used to produce the usable voltage. Because of this, relatively low energy beta emitters such as tritium are preferred. However, these isotopes produce less energy per gram. Thus far, betavoltaics have seen limited applications.
Optoelectric nuclear batteries use a radioactive source to produce light by irradiating a phosphorescent material which then illuminates a photovoltaic cell. This can reduce the problems of materials degradation, but again, it has limitations, due to the efficiency of photovoltaic the limited amount of light that can be produced by a given amount of most phosphorescent material. In most designs, this limits practical applications to low power devices. A very high power version was developed at the Kurchatov Institute in Russia, but it requires a very large amount of highly radioactive gas in a pressurized vessel.
Other types of energy converters have been experimented with over the years. Self-charging capacitors have shown some promise as a way of converting particle radiation into usable voltage. Several years ago, nuclear chemist Paul Brown developed a method for converting particle emissions into electrical current by decelerating the particles within the magnetic field of a resonator. The device showed extremely high efficiency and test versions were able to develop very high current output for a short period of time. Unfortunately, the system suffered from materials degradation and instability that proved insurmountable and prototypes were only able to function for a very short period of time.
Assuming a non-thermal energy converter of sufficient size to power a car could be produced, it might reduce some of the problems associated with an RTG, but it would not eliminate them. Even if the amount of radioactive material could be cut by 75%, it would still constitute an enormous, expensive and potentially dangerous. With current and foreseeable systems, extremely large stacks of converters would be needed. Cooling would likely remain an issue, even if a lesser one.
Fusion:
Aside from the hydrogen bomb, there are currently no methods of producing artificial nuclear fusion that have been able to produce a greater amount of energy than they consume. There are ongoing efforts to develop fusion power, but most of these are nowhere near the point of commercial deployment and have numerous technical hurdles to overcome.
It is possible to build a fusion apparatus that is small enough to be easily accommodated in an automobile. For example, electrostatic-confinement fusion systems like the Farnsworth Fusor can fit on a desktop. However, such devices are inherently limited to relatively small amounts of fusion and cannot produce anywhere near a surplus of energy.
Most current fusion research focuses around fusion reactors like the tokamak or inertial confinement fusion. A cornerstone of these concepts is that they may be able to generate more energy than they consume if they are made large enough. Hence, they would never be able to be scaled down to a size for a car. One novel approach, known as polywell fusion, may work at smaller sizes, but would still have to be much too large for a car in order to produce energy. (and once again, it needs to be stressed that none of these have actually proven a viable energy source)
Even if a fusion reactor could usable energy, there are other problems besides the size of the reactor. Fusion reactors tend to be very complex and expensive, requiring extensive cooling, special materials and numerous subsystems. Fusion also produces intense radiation. Most forms of nuclear fusion produce large amounts of high energy neutrons, which would require substantial shielding. High energy collisions also produce x-ray radiation, also requiring shielding.
Thus, even if some breakthrough made fusion energy possible, it is unlikely to every be suitable to automobiles.
Induced Gamma Emissions:
The concept of induced gamma-ray emissions as a means of energy storage is currently an area of great controversy in the scientific community. If it is possible at all, this represents a branch of nuclear energy that is far different than fission, fusion or decay. It is based on the concept of inducing the release of energy from a nuclear isomer through stimulation by external radiation, such as x-rays.
Nuclear isomers are composed of atoms whose nuclei have entered a highly energized state. In most cases, an atom which enters this state will shed the energy rapidly, within less than a millionth of a second. However, in a few cases, isomers can exist with extended half-lives, a few even being measured in years. Isomers should not be confused for isotopes. They have the same number of protons and neutrons, but are denoted by the letter m to indicate that a given isotope exists in a higher energy state, as a nuclear isomer. A common example is technetium-99m, which decays with a half-life of about six hours into technetium-99. The energy is given off in the form of a gamma ray.
Nuclear isotopes decay at a given rate. The half-life cannot be directly changed. The only way to accelerate the decay of a radioisotope is to transform it into some other isotope by bombarding it with particles. However, in principle, it is possible to stimulate the release of energy from a nuclear isomer, although done so in a manner that produces a significant energy gain has yet to be demonstrated. If this were possible, an isomer containing a huge amount of energy could be stimulated to release that energy rapidly, rather than over a very long period of time.
There are very few isomers that are stable enough to be stored long term and have high enough energy densities to be used as an energy source. One of the most attractive is an isomer of hafnium-178Dallas. In 1998, a team at the University of Dallas reported that they had successfully demonstrated the ability to trigger gamma emissions in Hf-178m2 by means of external x-rays. These experiments have not been independently verified and a great deal of controversy has arisen about whether it is indeed possible.
If this is indeed possible (which it might not be) then a hypothetical power system would work by using a small x-ray machine or radioisotope to expose a sample of Hf-178m2 to radiation. This radiation would trigger the release of much more energetic radiation from the isomer, thus resulting in a very large net gain in energy. In principle, it could store orders of magnitude more than any chemical compound, though less than fission or fusion. However, it has been suggested that making this work would require impractically high energy x-rays or that the losses associated with generating the necessary photons may make end up making an unworkable energy source.
Even if this could be made to work, it would be highly unsuitable for an automobile. For one thing, the energy is released in the form of high energy gamma rays, thus necessitating a great deal of shielding. The amount of gamma radiation that could be produced by such a reaction is high enough to present great concern over its use by anyone with a drivers license.
An isomer like Hf-178m2 is also necessarily very expensive. Such isomers are created by some nuclear reactions, but not in the quantities necessary for use as a power source. In order to create that much of the isomer, Hf-178 would first have to be extracted from natural hafnium and then converted to Hf-178m by energizing it with a particle accelerator. Since the energy would all have to be added to the material, it would not actually be an energy source, but rather an energy storage medium, albeit a very dense one.
Because particle accelerators are very inefficient, only a small amount of the energy used would actually end up being stored in the Hf-178m2 and even less of it would be usable after accounting for the thermal engine it would need to power and the additional expense of running an x-ray source. Thus, the usable energy from the isomer ends up coming at enormous expense, making it much more expensive than conventional fuels, even if only a tiny amount would be needed for the entire lifespan of the car.
In 2008, the Lawrence Livermore National Laboratory Published a Report Stating:
Our conclusion is that the utilization of nuclear isomers for energy storage is impractical from the points of view of nuclear structure, nuclear reactions, and of prospects for controlled energy release. We note that the cost of producing the nuclear isomer is likely to be extraordinarily high, and that the technologies that would be required to perform the task are beyond anything done before and are difficult to cost at this time
Conclusion:
Sorry, but all known methods of producing energy by nuclear means turn out to be wholly unsuitable for use in a car. Baring a breakthrough in direct energy conversion or small-scale aneutronic fusion, it will remain impossible. Even if such a breakthrough were to occur, it is highly unlikely that it would be economically or technically appealing to power the vehicle directly by nuclear means.
This entry was posted on Friday, January 4th, 2013 at 7:52 pm and is filed under Good Science, History, Misc, Nuclear. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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January 4th, 2013 at 9:35 pm
Now a train… that seems like it might almost be possible. Locomotives are hundreds of tons.
One issue might be the side shielding. A railway car has length, but it doesn’t have much width.
Another is heat rejection. It would have to be air-cooled.
But if you could develop that, or probably even if you couldn’t, you could certainly develop stand-by nuclear generators for nuclear plants.
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January 4th, 2013 at 9:59 pm
Joffan said:
A nuclear locomotive? Sounds like something the Soviets would have developed…. and they did, actually.
I do not think any were built, but the concept was researched.
Sure, it’s possible. It could be done. I think it would likely be more trouble than it is worth. Nuclear trains are best realized by railway electrification. Much cheaper to build fewer reactors in stationary locations. Much simpler. Avoids putting all that weight on the train.
but it could be done
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January 4th, 2013 at 10:30 pm
If I were trying to make a nuclear powered car I’d probably use ⁹⁰Sr running a Stirling generator sized to handle cruising load and with a battery or ultracap bank for acceleration.
⁹⁰Sr isn’t as good as ²³⁸Pu from the point of view of energy density, lifetime and shielding requirements but you can mine large amounts of it from nuclear waste.
Also aneutronic fusion would still have about the same neutron flux as a fission reactor due to side reactions so even if we could get it to work it probably wouldn’t be that big a gain for power and non-space propulsion purposes.
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January 4th, 2013 at 11:59 pm
Sr-90 would work. It would need some shielding, because beta particles produce secondary x-rays, but it could work. You’d end up with a very heavy car, of course, with all that shielding and the batteries and the Sr-90 etc.
Sr-90 produces about 500 watts of heat per kg. A good sterling engine might do 33% thermal efficiency. So that gives you about 160 watts per kilogram. I’d expect to keep the batteries well charged in a car that big and heavy would require a good few kilowatts. So maybe 5 kilograms of Sr-90 would do the trick?
That’s quite a lot, actually.
It could be done, I suppose. It would be a difficult engineering challenge to get that in a manageable size and weight and provide adequate cooling.
Also, there would be some stipulations to operation – like never leave it for a week in a small well-insulated garage.
It would be extremely expensive, in any case. Yes, there is plenty of Sr-90 in nuclear fuel (although we would run out fast if we tried to mass produce cars to run on it), but that’s not the expensive part. It would need to be extracted and refined etc. Actually, it is not normally used in its raw form. It’s made into an alloy to improve stability.
All of this would have to be done in hot cells. It’s complicated by the fact that Sr-90 gets to hot on its own. Working with stuff that generates so much heat is very difficult. It requires special precautions and the hotcells need to be refrigerated just to keep temperatures manageable.
Not to mention the regulatory hurdles.
I think a lifetime of gasoline would still be cheaper.
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January 5th, 2013 at 12:26 am
Very informative feature! Thanks a trillion for this!
This feature springs to mind a notion I don’t hear about, as wild as the topic might be, but the issue of conceivable “alternates” to heavy shielding, since this seems almost two-thirds the monkey on small nuclear application’s back. Is there any idea for ways to “reflect” or “deflect” radiation with minimal mass using fields or exotic techniques or materials? Even as a mind exercise it’d be interesting to speculate!
James Greenidge
Queens NY
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January 5th, 2013 at 1:35 am
In terms of power output for a car you’d probably want about 10 kW baseload (though if the battery runs down slowly over several hours it might not be such a bad thing, you should be taking regular breaks from driving anyway).
James Greenidge said:
Not γ-rays or neutrons, electric and magnetic fields could work for α and β as well as protons and heavy ions but you’d need some pretty strong fields to do it (it’s been proposed for space use as charge particle radiation dominates there).
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January 5th, 2013 at 3:59 am
I figured the “nuclear car” would be a bad idea from the start, but this essay explored ideas I had not considered.
However, if we want to build more efficient and clean fueled cars of the future, I think the more difficult engineering problem would be to try to figure out how nuclear could best mesh with that goal. Battery powered cars charged with electricity produced primarily by nuclear is one answer but that has it’s limitations as well. Serial hybrid cars like the Volt seem to solve most of those limitations, but still could be cleaner. Whether a cleanly fueled car could be made with gas, batteries, natural gas, synthetic fuels, or hydrogen depends on practicality, infrastructure support, total lifetime costs, total lifetime pollution output, and probably many other factors I’ve not considered. It would take quite a spreadsheet and some considerable time to sketch out the possibilities.
Personally, I’d like to see new markets open to nuclear with nuclear process heat to create synthetic fuels. I don’t know how close a reactor would need to be to a facility that processes flammable hydrocarbons would need to be, but I suspect it would be close enough that it would be a regulatory show stopper for the whole idea. If nuclear process heat cannot be used in a practical way because of regulations, it would be a greater loss than just synfuels IMHO.
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January 5th, 2013 at 5:38 am
Boron has also been proposed.
A combination of batteries and synthetic hydrocarbons should be able to do the job with direct use of nuclear for shipping and wires for trains.
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January 5th, 2013 at 10:33 am
IBM is working on developing the Zinc-Air battery with the goal of developing a car with a range of 500 miles. We just use conventional nuclear plants to charge the batteries. http://www.engadget.com/2012/04/20/ibm-battery-500/
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January 5th, 2013 at 11:17 am
Regarding the nuclear locomotive: It turns out that some serious conceptual work was done in the US some time ago. Never got to the prototype stage or anything, but a substantial amount of “paper project” research was done. It was proposed by the University of Utah and Bab**** and Wilcox in the 1950’s.
It is definitely possible, but the difficulties, weight, cost etc seem to make it undesirable.
The design that was developed was a 500 ton locomotive unit, divided into two portions. The reactor, turbines and mechanical systems would be in an elongated locomotive and the second car was radiators and fans.
It included 200 tons of sheilding. 100 tons was considered the necessary amount for minimum safety, but they went with more. The reactor had to be of a special design to fit the constraints. Since the train is narrow and sheilding took up most of the girth, it had to be squeezed into an elongated shape.
One of the interesting things about the proposal is that it would have used a reactor type I had not heard of before and which, to my knowledge, has never been built. It would have been a liquid-phase reactor fueled by uranium dioxide dissolved in sulfuric acid
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January 5th, 2013 at 11:28 am
drbuzz0 said:
But all this has already been done! Haven’t you all ever watched “Supertrain”??
James Greenidge
Queens NY
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January 5th, 2013 at 11:42 am
On the other hand I think nuclear powered moon cars are a real possibility. http://news.discovery.com/space/mars-colonies-powered-by-mini-nuclear-reactors-110830.html
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January 5th, 2013 at 12:02 pm
drbuzz0 said:
These types of reactors are called Aqueous Homogeneous Reactors and a fair amount of work was done with these in the late Forties and early Fifties but issues with corrosion and a shift in emphasis to solid fuel technologies halted development in the West. The Kurchatov Institute in Russia has been working on this type for several decades as a source for medical isotopes and their ARGUS reactor has been running since 1981. However despite great promise, commercial deployment still has not happened.
The use of an aqueous homogeneous nuclear fission reactor for the simultaneous hydrogen production by water radiolysis and process heat production was examined at the University of Michigan, in Ann Arbor in 1975. Several small research projects continue this line of inquiry in Europe.
Atomics International designed several examples of this type for sale. One reactor model, the L-54, was purchased and installed by a number of U.S universities and foreign research institutions, including Germany and Japan. (http://www.osti.gov/energycitations/servlets/purl/4315502-KiRPtd/4315502.pdf)
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January 5th, 2013 at 3:07 pm
I’m aware of the Aqueous Homogeneous Reactor, but all the examples I have seen used either uranium sulfate or some uranyl salt that is disolved in water. I’ve never heard of uranium dioxide disolved in sulfuric acid as a reactor fuel
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January 5th, 2013 at 9:39 pm
drbuzz0 said:
Probably a slurry reactor.
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January 5th, 2013 at 10:33 pm
drbuzz0 said:
This I think is a bit of a misreading as not much will dissolve in pure sulfuric acid without the presence of water and the water would be needed to act as a moderator as well. I still think this was a type of Aqueous Homogeneous Reactor and that is born out by this description:
http://brainmindinstrev.blogspot.ca/2012/03/project-x-12-borsts-imaginary-nuclear.html
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January 6th, 2013 at 6:28 pm
drbuzz0 said:
By combining Sr90, a Stirling, and a large hunk of salt, you may have a viable, if heavy system. Use a smaller amount of Sr90 to melt the salt while the car is not being used and then use the molten salt to power the car. As a backup, have a burner to keep up with the heat need during long distance trips. If the car is to be unused for long periods, you may want to have an auxiliary heat engine with generator and feed the grid with its output and the residential thermal needs with its waste heat.
This combination of components yields a plethora of possible system configurations for transportation and CHP.
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January 7th, 2013 at 6:04 am
I just got the idea into my head that using a RTG coupled to a battery electric car could offset some of the trouble of charging cars – it’s easy to plug a car in when it’s parked in a garage at home, not so easy at the workplace.
But the numbers still don’t add up.
Taking some generic and somewhat pessimistic assumptions, you can’t leave your car charging from flat while you’re at work and expect it to get you home. The power isn’t there, unless RTGs take a huge leap forward in efficiency. I admit to being amazed that the Curiosity RTG is so inefficient, though I know nothing of the technology.
For the nerds, I worked with the following :
Equivalent petrol car performance : 8 L / 100 km (30 MPG-US)
Commuting distance : 25 km (15 miles)
Energy density : 36 MJ/L
Approx petrol engine efficiency : 33%
Calculated energy requirement : 24 MJ
Parked time : 6 hours (21600 seconds)
Charge power required : ~1.1 kW = 10x the Curiosity RTG.
You can be more or less generous on a load of the figures (you can double your fuel mileage these days, but that means a lighter, smaller car, which sells only as a cheaper car) and some people won’t be commuting that sort of distance (in Europe in particular) and the charge time might be longer (8, 9 hours?) but the bottom line is that you’re still going to be looking at a few times Curiosity’s RTG and there’s no way you can get that into any sort of viable price range.
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January 7th, 2013 at 8:35 pm
I’mnotreallyhere said:
RTGs are hideously inefficient, and passing that inefficient power into and out of a battery just looses more of the energy. Store the heat, not the electricity, and use a more efficient heat converter (Stirling).
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January 11th, 2013 at 12:33 pm
And… here’s the sensible way to do nuclear trains, just as expected:
http://www.world-nuclear-news.org/C_Nuclear_for_the_long_haul_1101131.html
A nuclear reactor locomotive would still be fascinating, if only as a mobile power source.
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January 13th, 2013 at 8:35 pm
The suggestion of electric (or plug in hybrids) cars powered by nuclear baseload seems the most reasonable “nuclear” solution. If money isn’t really an issue in this thought exercise, which it doesn’t seem to be considering how much it would cost to build some of these ideas, then why not electric cars with induction coils under our major roadways. This would mean your battery range would only be required for residential streets and country roads. It would certainly be material and resource expensive but so would millions of vehicles with RTGs or some of the other methods proposed. Truly, I think if we want to conserve our valuable fossil resources for more important uses, like making medical grade hypoallergenic plastics, etc. rather than just burning them, we need to rethink our entire transportation model. That means change and possible sacrifice which most people seem to have lost all tolerance for.
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January 15th, 2013 at 10:09 pm
drbuzz0 said:
But a uranyl salt is just what it would be, after being so dissolved. Uranyl sulphate, UO2SO4.
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January 15th, 2013 at 10:13 pm
Anon said:
Including by me.
James Greenidge said:
If there were such a gadget, it would be fallible, and so you’d want the brute-force solution that has very seldom failed — thick dense matter — as a backup.
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January 15th, 2013 at 11:52 pm
G.R.L. Cowan said:
Very true.
G.R.L. Cowan said:
Though I can imagine some cases where just having multiple redundancy would be the only option (though this would mainly be for spacecraft that have to be really light but also take a lot of charged particle radiation (where the idea at least doesn’t break the laws of physics)).
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January 16th, 2013 at 3:54 am
Anon said:
You guys are boron me…
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January 16th, 2013 at 5:15 am
I’mnotreallyhere said:
Very true.
You guys are boron me…
And we’ll keep doing it.
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January 16th, 2013 at 10:41 am
It took me a while to remember the name “Woolley”, but now that I have done so, I can link you to the definitive study of the direct nukemobile. Unfortunately I’m not sure any version is currently on offer except the candy-apple-red four-by-four version with very large open wheels, so large that it can run inverted, a 46149-kg reactor shield, and 10000 hp. Who’d want that?
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January 19th, 2013 at 11:48 am
I can’t believe that nobody bothered to mention the nuclear-powered bus.
Best way possible to get from New York to Denver.
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January 27th, 2013 at 4:27 pm
A nuclear powered car wouldn’t need a very powerful nuclear reactor, the genset in a Chevy Volt can only deliver 55 kWe and you can probably get away with much less than that with some compromise with regard to sustained high speed driving.
What kind of reactor could be used to power a car? I suspect that a heat pipe system using a metal cooled fast reactor similar to NASA’s SAFE-400 would be possible to use. SAFE-400 produce 400 kW/100 kWe using the Brayton cycle, and the weight of the reactor is 512 kg. Build one for 50 kWe and we should be down at a reasonable weight for a car. Neutron sheilding is mainly by lithium hydride in stainless steel cans in this reactor design.
I suspect a Stirling engine would be more efficient than the Brayton cycle engine used by the SAFE-400, but with a possible disadvantage in terms of weight. With similar temperatures, 880 degC, Stirling engines designed for automobiles have shown efficiencies close to 40%.
With a compact core (to reduce the amount of shielding required) and a high efficiency it would certainly be possible to build a nuclear powered car, but that car would most likely be very expensive. There is also the safety issues, which also include the use of weapons grade materials in the compact reactor core of these kinds of reactors.
There are far cheaper ways to power cars with nuclear power. Electricity and hydrogen are two options, the latter can be used in current cars with minor modifications (fuel tanks and fuel system). Nuclear energy can also be used with a source of carbon to produce hydrocarbons.
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February 3rd, 2013 at 1:00 am
Since berylium reflects neutrons, could a reactor be shielded by encasing it in a Berylium Sphere?
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February 3rd, 2013 at 7:58 am
Burya Rubenstein said:
Yeah, Be would probably be a part of a lowest mass shield using optimised materials (most radiation shielding doesn’t try to optimise for low mass) but even then it would still be too heavy.
It would also really complicate manufacturing.
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February 3rd, 2013 at 9:37 am
Neutrons are not really the biggest problem. The way neutrons are shielded is by using any kind of a moderator material to slow them down. So any light element will work. Hydrogen works very well. The most typical way of shielding neutrons is with water. Water has plenty of hydrogen atoms and is dense enough to provide gamma shielding too. But you still need quite a bit of water to shield a nuclear reactor.
Organic materials like plastic or fuels work well too.
Adding a neutron absorber like boron can increase the ability of a material to shield neutrons.
There are purpose-made materials for applications where a lot of neutron shielding is needed in a relatively small area. One is borated polyethylene. It contains more hydrogen than an equal volume of water and the boron aids in neutron absorption.
The real issue will be gamma rays. There is no way of stopping gamma radiation other than putting a great deal of mass between you and the source. Any material can be used to shield gamma radiation, as long as you have enough of it. The heavier it is the less you need and the lighter it is the more you need. Water, concrete and lead are common shielding materials.
Lead is familiar as a gamma sheilding material and is often used because it’s dense and thus provides reasonably good sheilding. Tungsten and depleted uranium are even denser than lead and thus can be used at even lower thicknesses to provide an equivalent amount of shielding.
Even if you used tungsten and depleted uranium you’d need many tons of it.
That’s the problem. Gamma sheilding simply requires a large amount of dense material. Having very heavy material is inescapable for gamma rays.
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February 3rd, 2013 at 10:24 am
drbuzz0 said:
Nuclear reactors generate gamma radiation that cannot be effectively shielded in a car. Gamma radiation caused Dr. Banner to transform (when under stress) into The Incredible Hulk.
Kinda takes road rage to a whole new level, doesn’t it?
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April 21st, 2013 at 3:50 am
Hello! I know this is kinda off topic but I was wondering if you knew where I could locate a captcha plugin for my comment form?
I’m using the same blog platform as yours and I’m having trouble finding one?
Thanks a lot!
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