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Old May 19th, 2011, 07:37 AM   #21
K_
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Quote:
Originally Posted by Jay View Post
Aircraft Carriers use nuclear reactors for example, it seems like a more practical way of moving something weiging 1000s of tons like a freight train rather than burning massive amounts of fossil fuel or electricity.
How do you propose to move a train using nuclear power that does not involve using that power to produce electricity first?
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Old May 19th, 2011, 10:35 AM   #22
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neat.

I guess a nuclear powered train would effectively be a steam train as well. Only instead of burning a fuel, there would be a reactor supplying heat to the boiler instead. Of course it would probably be some kind of turbine powering electric traction motors, so no pistons or choo choo sounds But yeah, shovel some more uranium in there, casey jones.

Retrofuturistic in more ways than one, really. Also, it should totally look like that black armor train from Goldeneye.

Last edited by zaphod; May 19th, 2011 at 10:47 AM.
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Old May 19th, 2011, 04:19 PM   #23
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Quote:
Originally Posted by K_ View Post
How do you propose to move a train using nuclear power that does not involve using that power to produce electricity first?
Well, the same way as in the large US aircraft carriers, I guess... The nuclear
reactor produces heat, which is used to generate steam, which is used to
make turbines rotate, which, after suitable speed reduction, rotate the propeller shafts. Change "propeller" into "wheel", and you have indeed a nuclear-powered loco that does not use electricity.

Whether that would be feasible remains to be seen. But it would definitely
be less expensive than using electricity : with that solution, all the steam
gear has to be kept, and the turbines rotate generators which themselves
power electric motors.

To evaluate the cost and complexity of such a system, one often uses the
ratio between installed power and output power.

In a diesel-electric locomotive, the ratio is 3 : the output power is the power
of the traction motors, and the installed power is 3 times that : diesel engine
+ generator + traction motors.

For a "direct steam" nuclear loco, the ratio is 2 : the output power is the
power of the turbine, and the installed power is 2 times that : nuclear
reactor + turbine (you may argue it is 3 and not 2 because of the
presence of the speed reduction gear).

For an "electro-nuclear" loco, the ratio would be 4 : the output power is the
power of the traction motors, and the installed power is 4 times that :
nuclear reactor + turbine + generator + traction motors (again, you may
argue it's 5 and not 4 because of the unavoidable speed reduction gear
between the turbine and the generator).

The ratio between installed power and useful power is a very important
indication on how heavy, how complex, and how expensive a system will
be. As cost, wheight, and complexity are things to be avoided, specially
on a locomotive, then we may assume that if it is technically feasable,
the "electro-nuclear" solution will be avoided on locomotives... like it has
been avoided on aircraft carriers and other nuclear vessels.
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Old May 19th, 2011, 05:22 PM   #24
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Also, Jay, next time you start a thread, please post a link to it in the thread finder. It makes my job of archiving all discussions in this part of the forum much easier. Thanks.
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Old May 20th, 2011, 08:19 AM   #25
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Quote:
Originally Posted by MarcVD View Post
Well, the same way as in the large US aircraft carriers, I guess... The nuclear
reactor produces heat, which is used to generate steam, which is used to
make turbines rotate, which, after suitable speed reduction, rotate the propeller shafts. Change "propeller" into "wheel", and you have indeed a nuclear-powered loco that does not use electricity.
Steam is far less controllable than electric power. Which is the reason by which, way before diesel engines came around, many railways were electrified so they could provide better service than steam locos.
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Old May 20th, 2011, 08:27 PM   #26
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Originally Posted by Suburbanist View Post
Steam is far less controllable than electric power. Which is the reason by which, way before diesel engines came around, many railways were electrified so they could provide better service than steam locos.
Sure... But here you would have steam anyway, like in any thermal
power plant. So why would you want to insert an electrical transmission
between the turbines and the wheels while the turbines could make the
wheels rotate directly ? Remember also that each transformation of
power introduces its own losses... Why would you do thermal-mechanical-
electrical-mechanical while thermal-mechanical could perfectly do it ?
If that had any interest, dear US Navy would for sure have done it
for its aircraft carriers, wouldn't it?
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Old May 20th, 2011, 10:01 PM   #27
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Quote:
Originally Posted by MarcVD View Post
Sure... But here you would have steam anyway, like in any thermal
power plant. So why would you want to insert an electrical transmission
between the turbines and the wheels while the turbines could make the
wheels rotate directly ? Remember also that each transformation of
power introduces its own losses... Why would you do thermal-mechanical-
electrical-mechanical while thermal-mechanical could perfectly do it ?
If that had any interest, dear US Navy would for sure have done it
for its aircraft carriers, wouldn't it?
Losses on those 2 conversions are much lower than losses on the deploying of pressurized steam on wheels. It is a matter of mechanical engineering: use of steam as conveyor of energy in industrial processes was largely overtaken by use of other hydraulic and electric systems that offer greater control, though it still have many applications.

For starters, you can't have multiple-units, where apparently the future of high-speed trainsets is laid.

Then, you have the whole issue of synchronizing wheels. Remember that any potential problem with the reactor leaking into the boiling system would mean an automatic, outright nuclear contamination. Not safe, for sure.

Finally, you'd still need to generate electricity for all the systems in the train anyway. Surely, a minor part of overall consumption, but you still need it as you don't want to run trains without electricity onboard.
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Old May 21st, 2011, 04:00 AM   #28
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Quote:
Originally Posted by MarcVD View Post
Sure... But here you would have steam anyway, like in any thermal
power plant. So why would you want to insert an electrical transmission
between the turbines and the wheels while the turbines could make the
wheels rotate directly ? Remember also that each transformation of
power introduces its own losses... Why would you do thermal-mechanical-
electrical-mechanical while thermal-mechanical could perfectly do it ?
If that had any interest, dear US Navy would for sure have done it
for its aircraft carriers, wouldn't it?
Here is something I wrote in another thread concerning the demise of steam locomotive which I believe have some relevance to this subject.

Quote:
It is said that it was the greatest invention in the industrialized era revolutionizing the way we travel reaching stellar peak with the development of the 4468 Mallard but at the same time the introduction of electric locomotives at the turn of the 20th century and later diesel-electric locomotives spelled the beginning of the end for steam locomotives which was considerably less thermal efficiency than modern diesels, requiring constant maintenance and labor to keep them operational.
Water was required at many points throughout a rail network and becomes a major problem. The reciprocating mechanism on the driving wheels of a two-cylinder single expansion steam locomotive tended to pound the rails, thus requiring more maintenance.
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Old May 21st, 2011, 03:54 PM   #29
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Quote:
Originally Posted by MarcVD View Post
In a diesel-electric locomotive, the ratio is 3 : the output power is the power
of the traction motors, and the installed power is 3 times that : diesel engine
+ generator + traction motors.

For a "direct steam" nuclear loco, the ratio is 2 : the output power is the
power of the turbine, and the installed power is 2 times that : nuclear
reactor + turbine (you may argue it is 3 and not 2 because of the
presence of the speed reduction gear).
Your ratios aren't correct. For one thing, the efficiency of nuclear plants is usually quite low (because the heat they produce is so cheap there is no need to be efficient). The Nimitz class aircraft carriers have two 500MWt reactors, for a shaft output of 168MW...
And diesel electrics are more efficient than you mention here. The electric drivetrain is quite efficient (or everyone would be buying diesel hydraulics.).
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Old May 22nd, 2011, 11:30 PM   #30
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Quote:
Originally Posted by Suburbanist View Post
Losses on those 2 conversions are much lower than losses on the deploying of pressurized steam on wheels. It is a matter of mechanical engineering: use of steam as conveyor of energy in industrial processes was largely overtaken by use of other hydraulic and electric systems that offer greater control, though it still have many applications.
The same losses apply when you deploy pressurized steam on turbines
coupled to generators to produce electricity.

Quote:
Originally Posted by Suburbanist View Post
For starters, you can't have multiple-units, where apparently the future of high-speed trainsets is laid.
Why is that ? And by the way, the need for multiple units is essentially
caused by the impossibility to produce a powerful enough diesel engine.
With a nuclear reactor, you will certainly end up with a unit that has enough
power to work solo.

Quote:
Originally Posted by Suburbanist View Post
Then, you have the whole issue of synchronizing wheels. Remember that any potential problem with the reactor leaking into the boiling system would mean an automatic, outright nuclear contamination. Not safe, for sure.
You are anyway under the same risk with the steam used to extract
energy from the reactor to produce electricity.

Quote:
Originally Posted by Suburbanist View Post
Finally, you'd still need to generate electricity for all the systems in the train anyway. Surely, a minor part of overall consumption, but you still need it as you don't want to run trains without electricity onboard.
Sure, but that's only a very small part of the total power output, for which
reliability is far more important than efficiency. If the loco used electrical
transmission, the generation of electricity for on-board systems would
probably be separated from the generation of traction current anyway.
Simply because you need 3-phase variable voltage & frequency for traction, and 1-phase fixed voltage and frequency for auxiliaries. This is how it is
made in modern diesel units today.
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Old May 22nd, 2011, 11:43 PM   #31
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Quote:
Originally Posted by K_ View Post
Your ratios aren't correct. For one thing, the efficiency of nuclear plants is usually quite low (because the heat they produce is so cheap there is no need to be efficient). The Nimitz class aircraft carriers have two 500MWt reactors, for a shaft output of 168MW...
And diesel electrics are more efficient than you mention here. The electric drivetrain is quite efficient (or everyone would be buying diesel hydraulics.).
It doesn't matter. You use that to make comparisons, so the result remains
the same.

Efficiency of nuclear power has nothing to do with what you say. Every
machine using heat has an efficiency limited by Carnot's formula, which,
for usual operating conditions, amounts to approximately one third. You'll note
that 168 is approximately the third of 500. So the nuclear kettle of US aircraft
carriers have indeed been engineered to extract the maximum possible...

I never said that diesel electrics are not efficient. The efficiency of a couple
generator + electrical motor is about the same as the one of an hydraulic
transmission. Railroads do not buy these for road engines simply because
nobody can build an hydraulic transmission that can whitstand the power of
the diesel engines we can build today. For shunting engines, the
story is different, because the power required is less important. In Europe,
almost all shunting locs are diesel hydraulics.

The complexity factor I mentioned does not in fact drive the total efficiency,
but it drives the wheight, and the cost.
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Old May 23rd, 2011, 07:36 AM   #32
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Quote:
Originally Posted by MarcVD View Post
Efficiency of nuclear power has nothing to do with what you say. Every
machine using heat has an efficiency limited by Carnot's formula, which,
for usual operating conditions, amounts to approximately one third. You'll note
that 168 is approximately the third of 500. So the nuclear kettle of US aircraft
carriers have indeed been engineered to extract the maximum possible...
Well, the thermal power of the Nimitz's reactors is 2x500MWt, so the efficiency of the plant is only about 15%. Nuclear plants are engineered for safety and reliability, not for thermal efficiency as they produce huge amounts of heat for next to nothing anyway.

The thermal efficiency of big Diesels however is starting to get close to 50% though.
The Thermal efficiency of a large thermal power plant is also higher, with modern gas fired plants getting almost 55% nowadays.
So if you are going to power trains using nuclear power, the best way to do this is the way the French do it.

Interestingly diesel-electric propulsion is becoming more common in cruise ships (and navy ships) these days.
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Old May 23rd, 2011, 07:58 AM   #33
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Why is that ? And by the way, the need for multiple units is essentially
caused by the impossibility to produce a powerful enough diesel engine.
With a nuclear reactor, you will certainly end up with a unit that has enough
power to work solo.
I don't think you could build a more powerfull unit that way, nor would it be desirable. A major reason for running engines in multiple unit is not to get enough power, but to get enough powered axles, to get enough traction.

I doubt designing a nuclear powered engine would enable you to get a compact powerful engine anyway. On problem is the cooling requirement. If you have a 40MWt reactor powering a 6MW locomotive you need to get rid of about 34MW in heat. And that alone will entail a couple of cooling trailers...
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Old May 25th, 2011, 08:34 PM   #34
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WOW.

When I first saw the title of this thread and that it had 2 pages of comments, I was a bit blown away and thought "Oh my what a ridiculous topic. Everyone must be expressing their disdain."

Lo and behold, I was quite surprised to find out that it is kind of realistic to have a nuclear reactor on a train, just that it might be a tad controversial, to say the least. Well, you learn something new everyday
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Old May 25th, 2011, 10:59 PM   #35
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Originally Posted by stingstingsting View Post
WOW.

When I first saw the title of this thread and that it had 2 pages of comments, I was a bit blown away and thought "Oh my what a ridiculous topic. Everyone must be expressing their disdain."

Lo and behold, I was quite surprised to find out that it is kind of realistic to have a nuclear reactor on a train, just that it might be a tad controversial, to say the least. Well, you learn something new everyday
Well, technically I think it's certainly possible. But I doubt it would be economical in any way...at least when using it for normal freight services.

However maybe this would be something for the military, like setting up mobile bases in the middle of nowhere and the reactor in the train generates the electricity for the whole base
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Old May 28th, 2011, 12:18 AM   #36
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Well, technically I think it's certainly possible. But I doubt it would be economical in any way...at least when using it for normal freight services.

However maybe this would be something for the military, like setting up mobile bases in the middle of nowhere and the reactor in the train generates the electricity for the whole base
Well, in USSR it was a project to use a nuclear loco together with a ICBM-launching train (last one was actually build and can be seen in S.-Peterburg railway museum, AFAIK). The scope was to provide the maximal autonomous operation time - with a nuclear loco it was possible to keep the entire complex operational for years without refuel, while classic diesel-electric traction provided only 28 days.

But s project of nuclear locomotive was considered unsafe, thus never built.
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Old May 28th, 2011, 05:09 AM   #37
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Ahhhh, aren't many trains, especially in France, already nuclear-powered?



What percentage of France's electric power consumption comes from nuclear power plants?

Mike
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Old May 28th, 2011, 05:46 AM   #38
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Old May 28th, 2011, 06:45 AM   #39
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As was sort of touched on before, weight is also an issue with this method of power production. It's why nuclear-powered planes and (non-military, with the exception of some icebreakers) naval vessels never took off. For every extra pound of its own weight a vehicle has to move, there's a correspondant reduction in maximum payload capacity. The weight of all the shielding that would be necessary to make such a train passably safe would significantly reduce the weight of the cargo (or passengers) that could be moved at whatever speed, ergo reduced revenue.

As much as the pro-nuclear and retro-futurist in me loves the idea of nuke-powered everything, I can't disagree with the issues that others have brought up, issues that make that Googie dream unfeasible.

And btw Railfan, I love that poster.
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Old May 28th, 2011, 10:40 AM   #40
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Quote:
Originally Posted by mgk920 View Post
Ahhhh, aren't many trains, especially in France, already nuclear-powered?



What percentage of France's electric power consumption comes from nuclear power plants?

Mike
That's a point. The rise of mass high speed trains both in France and Japan tightly linked with cheap nuclear energy. But we hold discussion about on-board nuclear reactors.
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