Nuclear/etc. Power: Steam turbines the best choice?

[McC]

I'm hoping some of the brilliant minds here at SDN can help me understand a concept that has been bugging me for a long time. I apologize in advance if this comes off as incredibly naive or misinformed. It is that very sense that leads me to post, seeking enlightenment.

As I understand it, nuclear and most other forms of power generation go something like this:
Nuclear Fission Heat Water Steam Turbine Alternator Electricity

If I understand the process correctly, then it seems so very wasteful. Some questions, in no particular order:

• Is capturing the heat of the reaction and then using it to make steam that spins turbines really the best way we have of generating electricity?
• Are there really no better ways of converting the products of a nuclear reaction into useful electricity?
• Is heat the only product we care about capturing or are there other products that might be converted into useful electricity that we currently ignore?

I'm approaching this mostly from a practical POV, but also from a science fictional one. Would this be the same process employed to generate electricity on a capital-scale spacecraft, regardless of initial source? For example, is there any information on how Star Wars ships capture the resultant energy from a hypermatter reaction? In Trek, the assumption seems to be that the the M/A reaction creates some kind of plasma stream (the "Electro-Plasmic System"), which is then directly tapped for power. Does this actually make any sense?

Please help fill in this blank for me.

[Singular Intellect]

Just my two cents, but it seems that it's rather a given that there does need to be a process of turning energy into 'work'.

A nuclear reactor initially generates heat. Since all desired and wasted energy is heat, the goal is to capture and utilize this as much of this as possible. Water is one of the most abundant elements on Earth that can absorb a great deal of heat energy, and we know how to put water/steam to 'work'.

I'd say the nuclear reactor process isn't that ridiculously complicated, it just takes some understanding in order to do something useful with it.

Edit: Also, water is part of the cooling process, thus I have no doubt there's likely several other very productive uses it contributes to a nuclear reactor.

[Fleet Admiral JD]

Edit: Also, water is part of the cooling process, thus I have no doubt there's likely several other very productive uses it contributes to a nuclear reactor.

But as I understand it, the cooling water and the generating water never mix or come into contact--both are in closed loops.

[Singular Intellect]

Edit: Also, water is part of the cooling process, thus I have no doubt there's likely several other very productive uses it contributes to a nuclear reactor.

But as I understand it, the cooling water and the generating water never mix or come into contact--both are in closed loops.

I didn't say or imply so; my point being that water is both an excellent coolant and a means of absorbing energy to be used for work.

[Fleet Admiral JD]

Edit: Also, water is part of the cooling process, thus I have no doubt there's likely several other very productive uses it contributes to a nuclear reactor.

But as I understand it, the cooling water and the generating water never mix or come into contact--both are in closed loops.

I didn't say or imply so; my point being that water is both an excellent coolant and a means of absorbing energy to be used for work.

Sorry--my bad then.

[Beowulf]

There's not really any better system for high temperature energy production. Example:
Coal/Oil Heat Water Steam Turbine Generator:arrow: Electricity

The only real difference is the volume of fuel going in, the amount of exhaust going out, and the lack of a heat exchanger between coolant loops.

It's possible to use some other type of coolant loop to let you run the reactor even hotter, but you still end up with some sort of heat engine to turn the generator.

[Pinjar]

It always seems wrong that something as flashy as a nuclear reactor would basically be a steam engine.

This wikipedia page
covers or links to the alternatives.
Which today boast 10% efficiency. The best of which might someday approach 23% efficiency. Links from that same page say that the steam engine approach gets 50%+ efficiency today.

[Kanastrous]

Is it possible in principle to generate electricity by just dumping the heat into a thermocouple (don't the radioisotope power generators on spacecraft basically work that way..?)

Is it possible to produce thermocouples efficient enough, for use in industrial electrical power generation?

[Ender]

If I understand the process correctly, then it seems so very wasteful. Some questions, in no particular order:

• Is capturing the heat of the reaction and then using it to make steam that spins turbines really the best way we have of generating electricity?

Yep.

[*]Are there really no better ways of converting the products of a nuclear reaction into useful electricity?

Nope, none. Because aside from the relatively high efficiency, this method provides a built in feedback stabilizing the reaction rate as power demand varies, allows for easy maintenance, allows for simple pressure control, behavs in a normalized fashio at varying high temperatures and pressures, etc.

[*]Is heat the only product we care about capturing or are there other products that might be converted into useful electricity that we currently ignore?[/list]

Well, I suppose if you did away with the cladding you could get the kinetic energy of the fission fragments themselves instead of just the gammas and neutrons we get now, but the whole "open fission core" thing is regarded as a bad idea for some reason. Other then that, what you are losing are the neutrons that leak out during the neutron life cycle and the gammas that aren't absorbed, and there really isn't a feasible way to turn those into useful work.

We use steam because it is a well understood technology with good efficiency. While there might be other solutions, they are unlikely to provide all the benefits our current water cooling method does on top of being more efficient.

I'm approaching this mostly from a practical POV, but also from a science fictional one. Would this be the same process employed to generate electricity on a capital-scale spacecraft, regardless of initial source? For example, is there any information on how Star Wars ships capture the resultant energy from a hypermatter reaction?

I'd imagine that they apply some kind of shield technology so that the can safely absorb everything. Given the energy levels involved in that scenario, the slight inefficiency posed in our reactors would be enough to destroy the ship at theirs.

I'd say the nuclear reactor process isn't that ridiculously complicated, it just takes some understanding in order to do something useful with it.

Edit: Also, water is part of the cooling process, thus I have no doubt there's likely several other very productive uses it contributes to a nuclear reactor.

I love how you declare that this is easy in one sentence and then prove you are a fucking idiot in the next one. Yes, any concept is readily grasped if you oversimplify it so that anyone can understand it. "Hot rock make steam, turbine go roundy-roundy" is about the level of understanding you declare to be not "that ridiculously complicated". Refusing to acknowledge the oversimplification to arrogantly claim it isn't that tough would be amusing if it weren't the source of so much anti-intellectualism today.

By the way homes, if the water you are using to moderate the core is also being released into the environment so as to cool the core, you are having what we in the biz like to call a "nuclear reactor accident", a term we yell at the top of our lungs as we sprint away as fast as we can to minimize our exposure from everything you just released.

Is it possible in principle to generate electricity by just dumping the heat into a thermocouple (don't the radioisotope power generators on spacecraft basically work that way..?)

Yes they do

Is it possible to produce thermocouples efficient enough, for use in industrial electrical power generation?

Efficiency of the thermocouple isn't the problem. The problem is that there is a fixed cap on how big you can make it before you hit sufficient mass of the material to have the reaction self perpetuate. AKA "Critical Mass". For this rather important reason RTGs can't be bigger than a few kW. and building a few hundred thousand/million of them to match the output of the regular core will be very inefficient.

[McC]

Thanks for the information, everyone. Ender, your post in particular was very informative.

I'd imagine that they apply some kind of shield technology so that the can safely absorb everything. Given the energy levels involved in that scenario, the slight inefficiency posed in our reactors would be enough to destroy the ship at theirs.

Point well taken.

What would the situation be in a more hard sci-fi scenario? Would a spacecraft powered by a nuclear fission reactor have a steam turbine generating its electrical power as well?

Also, is the same water-based method the one employed by current fusion reactor designs? If so, what does the heating in this instance? Is the water exposed to the fused plasma itself, or is the heat transferred to the water via some other mechanism?

[Sky Captain]

A way to get higher efficiency is to raise temperature of the reactor core. That can be done by abandoning water cooled reactor designs and switching to gas cooled reactors which can have core temperature above 1000 degrees and still operate safely.

Wikipedia article on pebble bed reactor claims this type of reactor could achieve 50 % efficiency, far more than todays water cooled reactors which is around 30% efficient
http://en.wikipedia.org/wiki/Pebble_bed_reactor

For hard sci-fi spacecraft I would probably use some sort of gas cooled reactor and make it as efficient as possible to minimize waste heat problems. Also this type of reactor can be much lighter because gas turbine can be fed directly from reactor without the need of separate coolant loops.

Other potential candidate for sci-fi spacecraft could be a fusion reactor running some form of aneutronic fusion and generating electricity directly from charged fusion products without the need of turbine.

However if I had to design an interplanetary warship for hard sci-fi setting I would use Orion nuclear pulse propulsion as main drive giving my ship terawats of propulsive power and multi G acceleration (very useful when enemy missile spam is incoming) and relatively small (~1 GW maybe) highly efficient reactor to power energy weapons, pulse unit ejection, life support, sensors, etc. Small emergency reactor for most essential systems also would be onboard in case main reactor breaks down.

[Admiral Valdemar]

How about eventually getting fusion to work and using MHD as a means of getting electricity instead? No turbines required, and better efficiency, potentially.

[Singular Intellect]

I'd say the nuclear reactor process isn't that ridiculously complicated, it just takes some understanding in order to do something useful with it.

Edit: Also, water is part of the cooling process, thus I have no doubt there's likely several other very productive uses it contributes to a nuclear reactor.

I love how you declare that this is easy in one sentence and then prove you are a fucking idiot in the next one.

Oh? Where did I say this is 'easy'?

Yes, any concept is readily grasped if you oversimplify it so that anyone can understand it. "Hot rock make steam, turbine go roundy-roundy" is about the level of understanding you declare to be not "that ridiculously complicated".

So you are saying is the simplied version of how a nuclear reactor works provided in the OP is in fact still too ridiculously complicated?

That's strange, I figured out the idea pretty damn quick despite knowing there's a shitload more to it than the simplication stated.

Refusing to acknowledge the oversimplification to arrogantly claim it isn't that tough would be amusing if it weren't the source of so much anti-intellectualism today.

Just want part of acknowledging a simplication of a concept as 'not ridicously complicated' therefore asserts the details aren't in fact much more complicated?

By the way homes, if the water you are using to moderate the core is also being released into the environment so as to cool the core, you are having what we in the biz like to call a "nuclear reactor accident", a term we yell at the top of our lungs as we sprint away as fast as we can to minimize our exposure from everything you just released.

And your point here is...what? The more you learn about how a nuclear reactor works, the more complicated it gets? No shit sherlock.

[Pinjar]

How about eventually getting fusion to work and using MHD as a means of getting electricity instead? No turbines required, and better efficiency, potentially.

The plasma in a fusion reactor is a Magneto-Hydrodynamic system. Nice link.

I think the main idea is to leave that all well alone to maintain fusion and then salvage any heat that leaks out. If you mean this then that isn't that just another way to get extra energy from your working fluid?

At 6:24 on the second of these one, two videos by the European Commision there is the implication that the intention is to eventually use turbine engines.

Isn't it true that anything more direct needs a linear fusion reactor? To quote from the introduction to fusion energy on iter's webpage

In the early days a number of different confinement schemes were tried out. Initial investigations were on linear devices, but loss of particles from the ends of these machines quickly led to experiments which wrapped the field round to form a torus.

Of course in a spaceship the loss from the end of a linear machine is your thrust.

[Lord of the Abyss]

Here's an alternative method of extracting energy : Link

Materials that directly convert radiation into electricity could produce a new era of spacecraft and even Earth-based vehicles powered by high-powered nuclear batteries, say US researchers.

Electricity is usually made using nuclear power by heating steam to rotate turbines that generate electricity.

But beginning in the 1960s, the US and Soviet Union used thermoelectric materials that convert heat into electricity to power spacecraft using nuclear fission or decaying radioactive material. The Pioneer missions were among those using the latter, "nuclear battery" approach.

Dispensing with the steam and turbines makes those systems smaller and less complicated. But thermoelectric materials have very low efficiency. Now US researchers say they have developed highly efficient materials that can convert the radiation, not heat, from nuclear materials and reactions into electricity.

Power boost
Liviu Popa-Simil, former Los Alamos National Laboratory nuclear engineer and founder of private research and development company LAVM and Claudiu Muntele, of Alabama A&M University, US, say transforming the energy of radioactive particles into electricity is more effective.

The materials they are testing would extract up to 20 times more power from radioactive decay than thermoelectric materials, they calculate.

Tests of layered tiles of carbon nanotubes packed with gold and surrounded by lithium hydride are under way. Radioactive particles that slam into the gold push out a shower of high-energy electrons. They pass through carbon nanotubes and pass into the lithium hydride from where they move into electrodes, allowing current to flow.

"You load the material with nuclear energy and unload an electric current," says Popa-Simil.

Space probes
The tiles would be best used to create electricity using a radioactive material, says Popa-Simil, because they could be embedded directly where radiation is greatest. But they could also harvest power directly from a fission reactor's radiation.

Devices based on the material could be small enough to power anything from interplanetary probes to aircraft and land vehicles, he adds.

"I believe this work is innovative and could have a significant impact on the future of nuclear power," says David Poston, of the US Department of Energy's Los Alamos National Laboratory. However perfecting new nuclear technologies requires years of development, he adds.

Popa-Simil agrees, saying it will be at least a decade before final designs of the radiation-to-electricity concept are built.

A paper on the new nuclear power materials was presented on 25 March, at the Materials Research Society Spring Meeting 2008 , San Francisco, California, US.

[Sky Captain]

Of course in a spaceship the loss from the end of a linear machine is your thrust.

Hmm this sounds interesting, never knew something like a fusion torch drive is in fact on a drawing board. I have always liked drive systems which can directly use nuclear power to generate thrust without complicated power conversion steps. Hopefully something useful comes out of this. Although problem is this thing is too big to be launched into space with any existing or near future chemical rocket, so large scale orbital assembly work will be needed.