Nuclear Power (merged threads)

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Nuclear Power (merged threads)

Postby Haploanddogs » Sat Aug 04, 2007 3:22 am UTC

So I have been reading the XKCD forums for a bit and there seems to be a lot of interest in Nuclear power, but not a lot of specific Knowledge. As I work in the Nuclear power industry, at LaSalle County plant in Illinois, I would be happy to answer any specific questions anyone has about it.

However I wanted to first clear a few things up that people seem to be missing in there admirable attempts to either promote nuclear power, or dismiss it.

1. "The Spent Fuel is not a problem because we it now has less energy than it did when we mined it"
-This is false as the problem with spent fuel is that it now has many decay products of U-238 and U-235 in it that would not normally exist. It is, when pulled from the reactor, many thousands of times more radioactive than when it was mined. It is fatal to the touch, and also emits copious amounts of heat. It must be stored for many years in a pool to allow it to cool off and let the radioactivity approach a more reasonable level.

2. "Three-Mile Island was Human Error"
-This is only partly true. Three mile island was a combination of many failures of equipment, such as a pressure relief value in the vessel, of personnel, and of planning. The first two layers of containment, the fuel itself and the fuel cladding both failed from excessive heat flux. However the next three layers of containment held. The amount of radioactivity released was very small, and I find it unlikely that anyone would die from it.

3. "Nuclear Power is perfectly safe/Won't kill anyone"
-This idea is the most dangerous for nuclear power for every activity we do is dangerous. In the future nuclear power will kill people. However so will every other human activity. Everything we do has risk in it. The question is do we accept the risks that nuclear power has for its benefits? I think the answer is a very enthusiastic yes, as all other base-load power sources kill more people than nuclear does.

I will answer any other questions to the limit of my ability.

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Postby pollywog » Sat Aug 04, 2007 4:06 am UTC

My questions:

Spent fuel: How long must it be left in the pool? How long must it be removed, and can it be put back in the ground?

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Postby Haploanddogs » Sat Aug 04, 2007 4:15 am UTC

If the goal is to put the fuel into dry cask storage then the NRC requires that we hold the fuel for no less than a year. However as all plants have extensive fuel pools with many diffrent ages of fuel, genearlly the fuel that is taken out is much older, around 5 to ten years. This fuel, when taken out, is still not safe to handle, and will not be for hundreds of years. This problem can be fixed by either using Breeders, to reduce the fuel to MOX and reuse it, or with fast reactors. The United States only uses once through fuel. This fuel will never be taken out to just be put into the ground un-sheilded.

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Postby pollywog » Sat Aug 04, 2007 4:40 am UTC

So once you put it in to the ground, how long is it before you can take it out again. Or, how long would it be before a leak in the containment was relatively safe?
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Postby 4=5 » Sat Aug 04, 2007 4:46 am UTC

how dense is the spent fuel?

(I read somewhere about the possiblity sending a probe down to the earth's core rideing on an emense amount of iron, and so I was wonding if it was feasible with the radioactive waste instead)

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Postby Haploanddogs » Sat Aug 04, 2007 5:30 pm UTC

The Spent fuel itself is about 70% denser than lead, however it is suspended in a Ceramic matrix, which is much lighter. All of the spent fuel is kept within its fuel rods, which are in a 14x14 wide array (for a PWR).

No probe can be sent into the earth for a bunch of reasons, none of them having to do with the density of the material it is riding in. The pressure and heat inside the earth prevents anything of our current technology from surviving much below a few miles.

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Postby 22/7 » Sat Aug 04, 2007 8:58 pm UTC

Holy crap Haploanddogs, thank you.

What kind of time frame are we looking at until we have to develop another place to store waste?
Totally not a hypothetical...

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Postby Haploanddogs » Sat Aug 04, 2007 9:27 pm UTC

The fuel storage problem is entirely political. Our Current technology allows us to store the waste very safely. The long term geological repository would work for all our current storage needs using once through fuel until approximatly 2017.

However we can reuse the fuel we have approximatly 20 times before it is truly expended. This would create much much less long term waste per Tera-Watt year, and would allow us to have thousands, if not millions of years of power left.

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Postby DeadCatX2 » Sat Aug 04, 2007 9:38 pm UTC

I've read wiki and it indicates many different types of reactors. You even mention breeder reactors.

Are certain reactor types safer than others (for ambiguous definitions of safe)? If so, what is the safest reactor type(s)?

Which reactor type(s) most efficiently use fuel?

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Postby Solt » Sun Aug 05, 2007 6:06 am UTC

Ok, what the hell is up with breeder reactors?

Wikipedia says nothing more than, basically, "They create more fuel than they consume." What does this mean? That there is no radioactive waste? Can the resulting fuel be fed into breeder reactors indefinitely?

Since you said our current fuel can be reused approximately 20 times before being truly expended, I'm guessing what happens is that some percentage of the U-238 is turned into plutonium during every cycle in the reactor. When the plutonium is fissioned, more of the U-238 turns into Pu, and you repeat. You can do this almost 2 dozen times before the fuel's U-238, U-235, Pu, and potential to make any of those is completely exhausted. How correct is all that? Is the term "once through fuel" related to any of this?

Also, is it being done? I always read that breeder reactors can make fuel, but is anyone actually using fuel created by breeder reactors? Are the associated costs high, or much lower than acquiring new fuel?

Wiki also says that the world's nuclear energy reserves are about 2.5 YJ. Can you give some insight into whether that includes the extra energy gains offered by breeder reactors?



Also, you say nuclear fuel is hot and fatal to the touch. Has anyone explored the possibility of extracting extra power from this? Currently, is the heat radiated off of spent fuel just released into the environment?


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Postby Hawknc » Sun Aug 05, 2007 7:28 am UTC

Solt wrote:Ok, what the hell is up with breeder reactors?

Wikipedia says nothing more than, basically, "They create more fuel than they consume." What does this mean? That there is no radioactive waste? Can the resulting fuel be fed into breeder reactors indefinitely?

That struck me as a slight violation of some laws of physics (net output > net input? huh?), so I had to research that a bit more. Basically what it says is that it can produce more fissile material than it consumes, but it also has to consume fertile material. So while you're getting more fissile material than you're using, you still need a net input of fertile fuel such as thorium. Still way better than traditional reactors, though.

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Postby e946 » Sun Aug 05, 2007 9:11 am UTC

I'm also curious about breeder reactors, and if they're so great as far as resuing fuel, why don't we have more/any of them?

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Postby ZeroSum » Sun Aug 05, 2007 12:55 pm UTC

e946 wrote:I'm also curious about breeder reactors, and if they're so great as far as resuing fuel, why don't we have more/any of them?

Expensive, complicated, new technology that can aid in the production of weapons-grade plutonium.

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Postby Haploanddogs » Sun Aug 05, 2007 3:12 pm UTC

Alright so the deal with any nuclear reactor is that they have what is called a breeding precentage. That means the precent of fuel they create out of U-238 compared to the fuel they consume of U-235.

U-238 is not normally radioactive in a meaninful way as its half life is 4.5 billion years, however with a hot, non thermal, neutron introducted it becomes Pu-239. So a normal reactor, like mine, might have a breeding precentage of .2. That would mean that 20% of the energy it makes comes from the U-238 it is transmuting into Pu-239 and 80% comes from U-235. Using diffrent kind of reactors, and diffrent modulators it is possible to increase or decrese this precentage. If you increase this precentage above unity then the reactor has more fuel availible to it than it is consuming. However this process is using up the U-238, it is not creating energy from nothing. However as Nuclear reactions are millions of times more energy dense than a chemical reaction it can be difficult to see this at first glance. For example a reactor genarlly takes in Uranium enriched to about 4.7% and spits it out at at .875 precent enriched. So by fissioning only 3 precent of the fuel we can generate 3GW thermal for 3 years.

The United States does not use breeder reactors because they are more complicated, its really a trivial diffrence in cost as basically all the money goes into the cooling system and turbines, they do not use them because the can be used to produce weapons grade material if used improperly. U-235 is difficult to turn into a bomb as you need 90%+ enrichment, but Pu is the material of choice for a nuclear bomb. However is it not a simple task to take the spent fuel and create a bomb. The Russians had a lot of problems with this, and ended up killing a few of their scientist, as did the United states.

As for using the spent fuel in another reactor as it is still making a bunch of heat the problem is that the energy density has gone down enormasly. A heat flux that is dangerous to us, perhaps 1MW per unit, might not be enough to power a station where you need GW of heat. China is experimenting with doing this, but no one else has.

Terms.
Once Through fuel. This fuel is only used once at normal enrichment and is then put aside. It leaves inside it nearly all of the energy, eg the U-238 and some U-235

Breeder reactor. A reactor that creates more Pu out of U238 than it consumes of U-235. France uses them to great effect as do the Canadians to a degree with their CANDU reators.


The Safest reactors are the proposed Adv BWR and APWR1000 designs. They are passively safe. Eg if everything fails gravity will take care of keeping the fuel contained.

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Postby the Cow » Sun Aug 05, 2007 5:11 pm UTC

I worked for decade at Bailey Controls (now part of ABB), and while we mostly did coal fired power plants, we did have a nuke division. They talked a whole lot about disassembly costs and maximum lifetimes, etc... What is the industry doing to lengthen the life expectancy of the plants and reduce the disassembly costs?

At Bailey, they were quite frustrated that very few control systems were needed in the nuke side, because so few plants were being built or upgraded in the face of eventual regulatory shutdown. Of the two nearby plants where I live, one is never allowed anywhere near full capacity, and the other is virtually shutdown all of the time due to poor maintenance.

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Re: Nuclear Q&A with Industry

Postby Yakk » Sun Aug 05, 2007 6:34 pm UTC

Haploanddogs wrote:1. "The Spent Fuel is not a problem because we it now has less energy than it did when we mined it"
-This is false as the problem with spent fuel is that it now has many decay products of U-238 and U-235 in it that would not normally exist. It is, when pulled from the reactor, many thousands of times more radioactive than when it was mined. It is fatal to the touch, and also emits copious amounts of heat. It must be stored for many years in a pool to allow it to cool off and let the radioactivity approach a more reasonable level.


How does it compare to reactor-grade refined fuel, in terms of radioactivity?

If you sat the spent fuel in a pool for 10 years, then diluted by the same ratio as the original fuel was concentrated, would it be more or less radioactive than the original ore?

U-235 is difficult to turn into a bomb as you need 90%+ enrichment, but Pu is the material of choice for a nuclear bomb.


Is this correct: And Pu is relatively easy to extract, because it is chemically different than the substrate, while isotopes react chemically nearly identically, forcing you to use centrifuges and other trickier ways of separating them.

The Safest reactors are the proposed Adv BWR and APWR1000 designs. They are passively safe. Eg if everything fails gravity will take care of keeping the fuel contained.


I thought that heavy-water cooled and moderated reactors, like CANDU, shut themselves down if they overheat/lose coolant. Is the problem the breeder characteristics of CANDU?

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Postby Haploanddogs » Sun Aug 05, 2007 10:04 pm UTC

un-used Reactor-grade refined fuel is slightly more radio-active than the background Uranium Ore. However the fuel once it has been used it is orders of magnitude more radioactive. The fuel at first is safe enough to pick up and handle with thin gloves without getting much does, once it is out of the reactor it is deadly. The difference is between a few milli-rem an hour and tens of thousands of REM an hour.

After 10 years the radio-activity has plummeted to much lower levels but without reprocessing it will never (in thousands of years) be safe to handle again. Of course this is all assuming the fuel is unshielded which it never is. Inside the plant we really don't receive much does from the fuel itself. It is moved under 30 feet of water which takes care of the gamma and neutron rad pretty easily.

As for plant Up time it has increased enormously. It used to be that plants were down nearly 40-50% of the time. However once they were removed from government run control and moved to the private sector we have 90%+ uptime. Also nuke plants nearly always want to run at a very steady power rate and do not respond as fast as other sources of power.

The CANDU reactors are extremely safe, but are not as safe as the newest designs simply because they do not have passive water systems inside containment. The amount of decay heat they produce with no moderation is enough to destroy the fuel. However this would require many failures of completely separate system and would still not release to the outside. Remember that the most dangerous civilian plant in the United States is probably safer than any other source of power here.

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Postby Lester :P » Tue Aug 07, 2007 11:55 am UTC

What do you do with your coolant water once you've used it?
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Postby Haploanddogs » Wed Aug 08, 2007 3:59 pm UTC

The coolant water is used for the life of the plant. If there is a water loss or during the plants decomissioning the water can either be stored on site as a low yeild waste, or more commanly it is mixed with concrete in a slurry and sent off for burial as Low grade dry waste.

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Postby Yakk » Wed Aug 08, 2007 5:13 pm UTC

How much does heavy water cost? I've heard that on the order of 10% of the water in one's body can be replaced with DHO with no ill effects. ;)

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Postby Haploanddogs » Wed Aug 08, 2007 5:40 pm UTC

Plants in the united States do not use Heavy water as a moderator, they use "Light" or normal water.

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Re: Nuclear Q&A with Industry

Postby Marvo76 » Mon Nov 26, 2007 2:35 pm UTC

Ok how long does it take to "spend" a nuclear fuel rod. I notice with Iran saying they produced fuel pellets, how long would it take to reach a point where they can extract a meaningful amount of plutonium for use in a bomb?

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Re:

Postby oxoiron » Mon Nov 26, 2007 5:16 pm UTC

Yakk wrote:I've heard that on the order of 10% of the water in one's body can be replaced with DHO with no ill effects.

Where did you hear that and did you mean D2O?
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Re: Nuclear Q&A with Industry

Postby thoughtfully » Mon Nov 26, 2007 6:40 pm UTC

The funny/absurd/tragic thing is, advanced breeder reactors can burn off pretty much all the high level waste, solving the boogeyman problem of disposal. If the damn fuel was actually fully exploited, there's enough mined uranium to power the U.S. for a few hundred years. Counting the crap in ground, we'd have thousands of years to get that fusion thing perfected. It is really the only existing technology that is ready to replace fossil fuels in any serious way.

Proliferation can be an issue, but all we can ever do anyway is slow it down, countries like Iran will develop the bomb, and we can't really stop them. The best approach is to promote a peaceful atmosphere (haha, no pun intended), and global warming is going to cause a lot of political instability.

We could also use up a lot of the waste stored currently at nuclear plants, and avoid all the problems that the poor shmucks who get stuck with mining wate repositores are going to have when that starts to make economic sense. It's just silly to bury all that unused energy.

Which does raise a question. Now that we're starting to wake up and smell the burning ecosphere, nuclear power is getting more attention than it has since Three Mile Island / China Syndrome. Is anyone talking about breeder reactors or at least using fuel more efficiently than once-through?

Also, would this not reduce the cost of nuclear power? Or do the added reprocessing costs offset some of the gains, or is the fuel too small a component of the costs?
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Re: Nuclear Q&A with Industry

Postby Indon » Mon Nov 26, 2007 8:12 pm UTC

So, still-usable nuclear waste is buried rather than be fully exploited simply because it's cheaper to just chuck it and get new fuel?
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Re: Nuclear Q&A with Industry

Postby thoughtfully » Mon Nov 26, 2007 8:21 pm UTC

Indon wrote:So, still-usable nuclear waste is buried rather than be fully exploited simply because it's cheaper to just chuck it and get new fuel?


That's probably part of it, but I think it's also due in part to the design of the reactor. Designing a reactor that can reuse fuel introduces plutonium concerns. But I'm a little fuzzy on that.
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Re: Nuclear Q&A with Industry

Postby Gelsamel » Tue Nov 27, 2007 11:05 am UTC

What do you know of pebble bed reactors. The wiki article is good and all, but I'd like to hear from someone in the industry what problems there are (if any) + any other opinions.
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Re:

Postby Minerva » Tue Nov 27, 2007 4:24 pm UTC

Yakk wrote:How much does heavy water cost? I've heard that on the order of 10% of the water in one's body can be replaced with DHO with no ill effects. ;)


In the U.S. and Canada, non-industrial quantities of heavy water (i.e., in the gram to kg range) are routinely available through chemical supply dealers, and directly from the world's major producer Ontario Hydro, without special license. Current cost of a kilogram of 99.98% reactor-purity heavy water, is about $600 to $700. Smaller quantities of reasonable purity (99.9%) may be purchased from laboratory chemical suppliers at prices of roughly $1 per gram.

It's true, by the way, what you said about substituting a significant portion of the hydrogen in your body for deuterium. Not too much, though, or the isotope kinetics mean that you'll start to get sick.

Indon wrote:So, still-usable nuclear waste is buried rather than be fully exploited simply because it's cheaper to just chuck it and get new fuel?


Basically, yes. That and the whole proliferation concern thing. In the future, as easily accessible uranium deposits decline, and the price goes up, reprocessing will look more and more attractive.

Haploanddogs wrote:un-used Reactor-grade refined fuel is slightly more radio-active than the background Uranium Ore.


Correct me if I'm wrong, but I think that refined uranium fuel is less radioactive than the original uranium ore, because uranium isn't very radioactive, and the vast majority of radioactivity in uranium ore is the far more radioactive radium, polonium, etc - the daughter products. Once the uranium is processed, these are removed, and the result is less radioactive.
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Re: Nuclear Q&A with Industry

Postby Thunderbird4! » Wed Nov 28, 2007 2:39 am UTC

Since someone earlier mentioned replacing fossil fuels with nuclear power I can't help but ask what level of theoretical probability there is for a car/train/plane to run on nuclear power? Or what is needed to perform small scale nuclear power production?
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Re: Nuclear Q&A with Industry

Postby Hawknc » Wed Nov 28, 2007 2:52 am UTC

The only way I can think of using on-board nuclear power for transport (aside from things like aircraft carriers) is to make it a power generator and use the power from batteries or capacitors to drive the vehicle. Cars and even trains stop too often for nuclear power to directly drive the vehicle, because it's difficult to just change the rotational speed of the turbine that frequently, but if it were constantly pumping power into a bank of batteries, they are far more conducive to rapid changes in power requirements. It might possibly work for aircraft, I don't know how much a nuclear system would weigh.

Of course, there is the whole issue of carrying nuclear material in a car or plane. ;)

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Re: Nuclear Q&A with Industry

Postby Thunderbird4! » Wed Nov 28, 2007 2:53 am UTC

That was what I was really trying to ask Hawk. Just how (un)safe of a system could be devised for use as Hawk described?
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Re: Nuclear Q&A with Industry

Postby thoughtfully » Wed Nov 28, 2007 2:55 am UTC

Thunderbird4! wrote:Since someone earlier mentioned replacing fossil fuels with nuclear power I can't help but ask what level of theoretical probability there is for a car/train/plane to run on nuclear power? Or what is needed to perform small scale nuclear power production?


Trains would seem very feasible, they seem to be similar in size to a lot of submarines, although the nuclear ones might be bigger. The government was researching high power to weight ratio nuclear plants for aircraft, but I don't don't think it every really, umm, got off the ground. Hehe.

I dunno about cars. But you can produce hydrogen in nuclear reactors directly, or indirectly with the electricty. I'm not sure how small you can scale reactors down, but I imagine the weight would still make it problematic for passenger vehicles.
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Re: Nuclear Q&A with Industry

Postby Minerva » Wed Nov 28, 2007 3:58 am UTC

I don't know about cars. You'd need a really small reactor and powerplant, and you need to shield it...
...better to just have an electric car powered by clean nuclear electricity.

Ships and submarines, of course, it's proven tech.

Trains... well, sure, it would be viable, I think. Consider the usual diesel-electric technology, with the diesel engine replaced with nuclear, just like submarines evolved from diesel-electric to nuclear.

As far as small, scalable, novel nuclear power systems go, check this out: http://www.atomicengines.com/.
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Re: Nuclear Q&A with Industry

Postby Marvo76 » Wed Nov 28, 2007 4:53 am UTC

the problem with a nuke train is in having a reactor that can be diverted ( sabotage rails) and rupture. In the ocean, if it sinks due to a melt down, it will take the ship down to the bottom and encase it in a protective emmission shield (water). They did try a plane engine back int he 50's if I remember correctly from my readings of a few years back, but emmissions was once again the issue. Sattellite ractors are successful due to russian technology, but I don't think the US uses anything like that in their sattellites.

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Re: Nuclear Q&A with Industry

Postby Redem » Wed Nov 28, 2007 9:41 am UTC

The main problem facing the nuclear industry is the mere word brings up images of mushroom clouds.

Waste and cost are the other two big problems, both of which are political more than anything else.

So lacking any technical or financial problems that might slow down the acceptance of nuclear power, what's being done about the real problems? What's being done to combat the negative associations with nuclear power, and educate the public on the subject? And what's being done to counteract the efforts of "green" nay-sayers?

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Re: Nuclear Q&A with Industry

Postby thoughtfully » Wed Nov 28, 2007 1:07 pm UTC

Satellites don't use reactors, they use thermionic generators, which convert the heat from radioactive decay directly into electricity. They aren't very efficient, but they are extremely reliable. We don't use them in Earth orbiting satellites, but they are common in space probes, since solar panels don't work so well as you go further and further out.

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Re: Nuclear Q&A with Industry

Postby oxoiron » Wed Nov 28, 2007 4:51 pm UTC

thoughtfully wrote:Trains would seem very feasible, they seem to be similar in size to a lot of submarines, although the nuclear ones might be bigger.

The great advantage subs and ships have over trains is an unlimited supply of cooling water.
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Re: Nuclear Q&A with Industry

Postby Redem » Wed Nov 28, 2007 9:08 pm UTC

That, and they are staffed by highly educated people who put a lot of time and money into training people to run them correctly.

Mass production would remove that.

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Re: Nuclear Q&A with Industry

Postby thoughtfully » Wed Nov 28, 2007 10:28 pm UTC

One of the major manufacturers of locomotives is General Electric, which is also heavily involved in nuclear power. I think if the two or three giant railroad companies wanted to do this, they wouldn't have any trouble with expertise.

Redem, besides being a misanthropic sourpuss, you also haven't followed the rules posted prominently in every forum and posted in the intro thread. We'd all be pleased if you did so.

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Re: Nuclear Q&A with Industry

Postby TheStranger » Fri Nov 30, 2007 1:34 am UTC

Thunderbird4! wrote:Since someone earlier mentioned replacing fossil fuels with nuclear power I can't help but ask what level of theoretical probability there is for a car/train/plane to run on nuclear power? Or what is needed to perform small scale nuclear power production?


There was a brief period when a nuclear powered bomber was considered. Able to fly around the world without stopping several times it had a few problems... mostly that it could not be turned off once it was turned on, and that if it crashed / was shot down it would spread nuclear material across a wide area.
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