Are there any methods to harness atomic energy that are more direct than the heating of water to drive turbines? It feel to me to be a terribly inefficient and convoluted. Is there no method that would have no moving parts, and preferably, not rely on temperature differentials?
You can generate electricity with temperature differentials by means of a Peltier device. They’re not particularly efficient either, though. And they’re quite expensive to make. And they’d probably end up melting.
I assume you mean to generate electricity here. Pretty clearly you can make a bomb without steam and there are proposals for nuclear rockets that don’t heat water either
Deep space probes do it all the time, using something called a radioisotope thermoelectric generator, and IIRC those don’t use peltiers to generate the electricity needed (there’s a PDF on the linked page that has all the details, but my machine’s acting flaky at the moment, so I’m not going to open it).
No easy method to dispense with the temperature differential, and possibly not even a hard one.
The energy in a fissile atomic nuceus can be regarded as a ball of tightly coiled springs, just poised to blast the atom apart. And we can imagine some miniature device whereby the atoms are lined up and induced to split in the same direction, so the “push” of those atomic springs happens in an organised way and shoves a piston.
Unfortunately we can’t build such a device. We can’t manipulate atoms on that scale, and even if we could, we have no way to influence the directions in which the atoms split. And even if we could, you’d have to align a hell of a lot of atoms to get a decent push on your piston. Billions ain’t even close. And even if you could do that, the atom fragments are too lively to simply capture with a piston anyway - they’ll penetrate deeply into it, most of their energy being turned to heat despite all your efforts. But suppose you solved all of these problems. You have another one. Not all the energy released in the fission goes to accelerate the fragments. A fair bit of it is released as short-wavelength photons (gamma rays), and neutrons, and they tend to zip clean through things, including your entirely theoretical gamma-frequency photovolataic cells, and not-even-theoretical neutron KE converters.
Instead, we use a chain reaction that basically lets the atoms split every which way, and their fragments and neutrons smash through bulk material like a bowling ball through a forest of pins, generating heat. Their gamma rays are also converted to heat by sheer bulk of material they have to travel through. Heat is our starting point.
From there we go the heat engine route, which have to exploit temperature differentials. For large scale external heat sources, water boilers and a steam expander (turbine, or in another age, piston steam engine) are the most well established. There are other possible working fluids but water/steam is cheap, widely available, non-toxic and non-flammable. 'Fraid we’re stuck with it.
If you are going to get energy from heat, using water is a good way to go. Steam holds a lot of energy and water is cheap. As far as heat based power generation, steam can be pretty efficinet also.
I beleive they use thermocouples, which are just 2 dissimular metals which when exposed to a temp difference produce a voltage, and in reverse - when exposed to a voltage difference they transfer heat. I believe a peltier is a form of a thermocouple also.
Radioisotope heater units, used in space probes, generate a small amount of electricity for very long periods of time using decay heat from a chunk of plutonium.
To capture the energy from a critically fissioning nuclear reactor, though, you need a working fluid. The most common is highly purified water. This water tends to pick up microscopic bits of radioactive contamination, though, from the neutron flux activating metal components in the valves and piping, as well as activation of the oxygen in the water itself. It is therefore problematic to attempt to use this “primary” coolant to directly produce steam, but it has been done in civilian reactors.
One method around this is to use two separate loops of water that do not contact each other. The primary loop passes through heat exchanger(s) which boils the water in the secondary loop to produce steam to drive the turbines.
Other working fluids have been used for the primary loop as well. One actually was liquid (molten) metallic sodium. As a metal, sodium provided excellent heat transfer characteristics, but had downsides as well, such as the fact that it explodes if it contacts water, and if the reactor is shut down and allowed to cool, the sodium solidifies.
Another working fluid that has been used is actually a gas, such as helium, used in pebble bed reactors.