Why aren't we using nuclear thermal rockets?

[DDE]

3 hours ago, 0111narwhalz said:

ITER is supposed to break net positive, and then some

ITER, unfortunately, is the SLS, but built by members of the ISS treaty... so that makes it the LOP-G? Not actually meant to demonstrate commercial fusion power, is already ten years behind schedule, in constant political jeopardy, and under threat of being leapfrogged by more dynamic competitors.

Don’t hold your breath they’ll ever finish it.

[0111narwhalz]

2 minutes ago, DDE said:

Don’t hold your breath they’ll ever finish it.

Eh, the components will come together eventually.

[Green Baron]

A lot of even basic questions are open, technology to be yet invented, until artificial fusion for energy comes into being. It can't be compared to a relatively "simple" thing like a rocket where the fundamental science is clear. In a (printed) interview i read lately, project scientists expressed the opinion that it will still take decades until fusion is a thing, maybe >2050 until the first reactor is making watts. More money will likely not accelerate things at this stage.

Iter is doing progress now since 2015, when the heads were exchanged www.iter.org . The very high complexity has slowed iter's progress in the past, and the construction of the "blanket" that covers the inner part of the reactor from the plasma is still making "theoretic" trouble.

The Wendelstein design is a test carrier, not meant to go productive. It has shown that it is indeed possible to confine a high temp/pressure plasma and do things.

A Chinese team is proposing a machine that could be started earlier (CFETR), but needs additional heating in comparison the self sustained plasma in the other designs.

The American proposed SPARC project is seen as a slight overstatement in the scientific community, from what i read. The effects of high temperature superconductivity may be overrated at the current stage of knowledge. The CFR project, proposed by Lockheed Martin, lacks a factual basis (yet).

The highest chance of success could probably result from an ITER/CFETR collaboration, but we may know more in 15 years or so :-) The Chinese CFETR may be the first that pushes watts into the cables. In principle Stellarators (Wendelstein) and Tokamaks (Iter, cfetr) are seen as the most promising designs.

So much to the luddite.

Edited December 25, 2018 by Green Baron

[0111narwhalz]

1 hour ago, Green Baron said:

In principle Stellarators (Wendelstein) and Tokamaks (Iter, cfetr) are seen as the most promising designs.

I'm told that the NIF got more heat out than direct laser energy in, on at least one occaision, but the result is somewhat dubious, and in any case they didn't account for the inefficiencies of the laser. Still, fairly interesting result out of inertial confinement.

1 hour ago, Green Baron said:

it will still take decades until fusion is a thing, maybe >2050 until the first reactor is making watts.

This is not surprising, considering that it'll take at least that long just to build the next reactor after ITER.

As I understand it, stellarators could well provide the answer before tokomaks. Their growth has been stunted, on account of the complexity of the physical models and geometry and their comparative lack of symmetry, but our computronium has improved substantially.

1 hour ago, Green Baron said:

the construction of the "blanket" that covers the inner part of the reactor from the plasma is still making "theoretic" trouble.

I'm not entirely sure what you mean by this. There's the diverter, but that only covers a small part of the surface, and as far as I've seen it's not causing any theoretical trouble at all. JET tested all-tungsten diverters, with positive results, and the industry standard is carbon-carbon, cooled if possible. Then there's the vessel walls themselves, which are definitely not problematic—it's pretty much just stainless steel, and in any case they don't contact the plasma during normal operation. I guess you could be talking about the confinement fields themselves? Those are causing problems, and always have, but they're the very problems ITER itself aims to solve.

[Green Baron]

This.

It shall convert the neutrons' kinetic energy into heat for power generation. Suitable materials are yet to be tested, if i understand them correctly.

 

Edited December 25, 2018 by Green Baron

[sevenperforce]

2 hours ago, 0111narwhalz said:

I'm told that the NIF got more heat out than direct laser energy in, on at least one occaision, but the result is somewhat dubious, and in any case they didn't account for the inefficiencies of the laser. Still, fairly interesting result out of inertial confinement.

Yes, the NIF achieved baseline positive energy balance, in that the net fusion output was greater than the energy delivered to the target. Of course the net fusion energy output was still only ~10% of the laser pulse energy and a smaller fraction of total system energy. Since none of the fusion energy was capturable, the actual energy balance was 0%.

Inertial confinement has always been the most direct approach to fusion; if you get something hot enough, it will eventually fuse. The challenge is achieving ignition and actual power generation; we are decades away from that, at best.

[DDE]

4 hours ago, Green Baron said:

This.

It shall convert the neutrons' kinetic energy into heat for power generation. Suitable materials are yet to be tested, if i understand them correctly.

 

So... it’s a moderator followed by a fission reactor-style heat exchanger.

[Green Baron]

Yes. Made from matchsticks and glued with white glue. Problem: when it is heated, it falls apart. That is why they are researching a different glue. Estimations are that by 2025 such miraculous stuff may be available.

Fusion needs no moderator, there is no danger of a runaway reaction. Here, kinetic energy is converted into heat. A heat exchanger has a different working principle, it transfers heat from one medium to another via contact surfaces. So there may be an exchanger at a later stage, to separate the fluid from the blanket from the one that may drive a turbine. I would expect such a separation for safety reasons, so that a leak at a turbine stage does not affect the plasma stage.

But i am sure there is more info on how they plan to produce electrical energy on the web site.

Edited December 25, 2018 by Green Baron

[DDE]

57 minutes ago, Green Baron said:

Fusion needs no moderator, there is no danger of a runaway reaction

Actually a moderator thermalizes neutrons to allow fission. Or conversion to thermal energy.

[Green Baron]

ikr ?

The blanket is no moderator, nor a "fission style" heat exchanger.

Edited December 25, 2018 by Green Baron