Are nuclear power plants just a sort of steam engine?

 Essentially, yes.

The nuclear fission produces enormous amounts of heat and you use the heat to produce steam to drive a steam turbine which in turn drives the alternator.

It’s basically a conventional coal powered plant on steroids. A conventional coal powered plant uses coal to heat the water instead of nuclear fission.

Apart from photovoltaics, electricity is generated by driving the alternator ( electric generator) using a mechanical device such as a steam turbine, hydraulic turbine, gas turbines, diesel engines or IC engines or just about any device that will output mechanical energy.

A steam turbine converts thermal energy from high pressure and high temperature steam into mechanical energy which is outputted at the shaft of the turbine which in turn drives an alternator ( short for alternating current generator ) that produces electricity.

Similarly a hydraulic turbine converts hydraulic energy into mechanical energy that drives the alternator.

The difference between a coal powered plant and nuclear plant is how the water is heated and made into steam to drive the steam turbine. A nuclear plant uses nuclear fission which can generate enormous heat and that is used to generate the steam that drives the steam turbine. The only difference is the source of the heat for the steam.

And for people commenting that Beta Voltaics, Magneto Hydrodynamics, Fuel cells, batteries etc can produce electricity without a mechanical prime mover with the exception of photovoltaics, can any of them power an electric grid or produce enough power to do so? This specific answer pertains to power generation for an electric grid and other than photovoltaics, most others are incompabale of generating power to supply a grid and batteries are for low power devices ( cars with Li-Ion or NiMH batteries have to recharge through the electric grid mostly powered by conventional electric power generation and some from photovoltaics.

Can astronomers' research on stellar physics truly contribute to advancing nuclear fusion technology?

 Probably not.

I believe the nuclear fusion power plant experts have enough data on how the actual fusion process works.

The problems are almost all with how you build some kind of containment system that can withstand the crazy amount of heat, radiation and pressure while maintaining continuous fusion reactions and while extracting that heat for generating electricity.

But building a system that doesn’t melt or erode or have dangerous oscillations or become too radioactive to maintain are the stumbling blocks here.

What’s frustrating here is that they’ve been trying to do this since about 1960 - and after 65 years of trying and eyewatering amounts of money thrown into the research - they’re STILL saying “We’ll have it perfected in 25 years…which is the precise time estimate they gave back in 1960.

But the problems they have simply don’t exist inside a star.

• Within a star, the pressure can be held with nothing more than gravity.
• The heat doesn’t have to be contained - it just radiates outwards in all directions
• The radiation also doesn’t have to be contained. Stars are radioactive as all hell.

…and when the star starts to run out of fuel - it simply explodes - often wiping out everything withing a light-year or more!

WHAT THEY’RE TRYING TO DO:

(WARNING: This is going to be an incredibly naive - and possibly outdated explanation - but it’ll give you a feel for what the problems actually are.)

Basically, the fusion reaction itself - if scaled up to a useful level and run continuously - will melt literally ANYTHING it touches - there is no possibility of a material that won’t be destroyed by it.

So you have to somehow prevent your mini-star from touching anything. (Which is also good advice for actual stars! :-)

You can do this with a powerful magnetic field - but if you can’t make a spherical (or cuboidal, or tetrahedral or shaped like a cute bunny…) magnetic field - the laws of physics don’t allow that.

You can, however, make a cylinder - with a simple coil of wire in fact.

But then the fusion reaction just blasts out of the ends of your cylinder and - you lose “containment” and that’s very, very, bad!

So what they try to do is to use very carefully placed magnetic fields to bend that cylinder into a donut shape (a “torus”) - that’s like bending a cylinder until the flat ends touch each other.

The purple stuff is the fusion reaction the dark blue and light blue things are insanely powerful electro-magnets.

…and this is what it looks like for real…

So now you have a magnetic field with no “ends”…

This seems like the perfect solution! Problem solved!

But the devil is in the details. The insanely hot, insanely high pressure plasma wants to leak out. It doesn’t stay stable - it wobbles about, forms kinks and so forth.

This means that it can (possibly briefly) touch the side of the containment vessel - and if that happens, you’re going to have a VERY bad day!

So now you need fancy computer tech to carefully futz with the magnetic field microsecond-by-microsecond to keep the plasma contained within the torus.

As computers have gotten better - and the designers have gotten smarter about predicting and preventing those kinks…they seemed to be getting better at this. But every time anyone ever asks - it’s always “We’ll be generating power within 25 years”…with literally no end in sight.

Periodically - the researchers will demand another billion dollars to build a better machine…and sometimes some government someplace will give it to them…but (as you can imagine) the patience and the money tends to wear thin when you build a new machine - and we’re still 25 years away.

But the facility doesn’t end with the torus…here is a more complete picture…

The next problem is that the energy required to keep the plasma inside the magnetic field is crazy-high…and it can be MORE than the energy the plasma itself produces.

So now you have a power plant that needs more energy to run than it generates!

There are other ways to make fusion power - like shooting lasers at a pellet containing hydrogen gas - but these don’t generate continuous power - and have numerous problems of their own. It doesn’t seem like those are THE ANSWER TO OUR PROBLEMS - because the majority of work is going into those toroidal systems - suggesting that researchers are still seeing that as the best hope.

CONCLUSION:

I think that fusion power plant researchers already know all they’ll ever need to know about what happens during the fusion process.

It’s all about containment - and that’s something that we can’t learn from stars (which, quite honestly, do an absolutely TERRIBLE job of doing that!!)

I’m not optimistic about fusion energy. I was 5 years old when they first started to work on it - and now I’m collecting my pension. I don’t think I’ll live to see a practical fusion reactor…but we have hope.

Why do nuclear power plants have such wide chimneys?

These are not chimneys. They are called cooling towers. Large power plants produce huge amount of heat, but use up only about half of it. They must release the remaining heat to avoid melting, so they blow it into the environment.

How do they release it?

If there is a big enough river nearby, they use the water. But if not, they build these big chimney-LIKE towers to release heat by EVAPORATING WATER. Yes, these chimneys release steam and vapor, not smoke or radiation. And why such big towers? The hot water raining down in the bottom section of the tower causes the air to heat up and start rising inside the tower, similar to why a hot air balloon rises. This “natural draft” pulls fresh air in through the zigzag openings at the bottom, which cools the falling water by evaporation, leaving the remaining pool of water at the bottom nice and cool for return to the power plant. The tower needs to be so big to allow the huge amount of air in that's required to cool the huge amount of water heated by the plant.

Water, in the amounts the power plants use it, is not cheap, also since it is highly purified. In most cases, it’s cheaper to reprocess it than to get more of it.