Comment by azernik | Hacker News Reader

Comment by azernik | Hacker News Reader

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The hope is that fusion will, indeed, be less complex and expensive than fission. This is for a few reasons:

1. The fuel is much more common and easier to handle - uranium and plutonium are a pain to extract/transmute, handle, and package.

2. The radioactive contamination is limited to induced radioactivity in the structural materials of the reactor core; there aren't the safety concerns of radioactive neutron moderators and the like that you see in a fission reactor. Preventing the release of those materials in the case of accident is one of the big drivers of fission plant costs.

3. The core itself is fail-off, again reducing the cost and complexity of safety measures.

4. They are not dual-use (civilian/military) to the extent of the fission supply chain.

5. By comparison to the rather indirect method of using solar panels and wind turbines to extract energy from solar radiation, steam turbines are a simple and efficient way of extracting energy from a fusion reaction. The Sun is enormous, but a fusion reactor would be right here and we can extract energy from one with well-understood, efficient technology.

Such things are often claimed. But every single statement here is false:

ad 1) Nuclear fusion as we know it does not rely only on deuterium, it needs tritium. Tritium needs to be produced by uranium fission, and after having a hypothetical fusion power plant running, by a breeding process. The technology of that breeding process is today completely unsolved.

2) Fusion reactors, if they aver will exist. will be large and will have a very large neutron flux. The will have breeding blankets which need to be several meters in size. Anything within these structures will be activated by neutrons. That means common materials such as carbon steel can't be used, because the carbon would become highly radioactive. Also, the neutron radiation weakens all known materials so that the structures will probably need to be periodically replaced. This alone will probably lead to a higher amount of nuclear waste than uranium fission plants.

3) It is correct that the fusion reaction will stop to operate when the core is damaged. But this does not mean that the plant is safe then. It will contain substantial amounts of tritium and other radionuclides. By the way, you may have seen nice photos of scientists in white coats which stand in the vacuum vessel of a a fusion power plant. Except that, if there were actually fusion to happen in these devices, nobody could enter them before they have been decontaminated in a time-consuming and expensive process. Consequently, in experiments such as ITER, no fusion happens at all.

In addition, a fusion plant will be very complex, and especially it will work with extremely large magnetic fields which have by themselves a tremendous energy content. If there is any electrical or structural failure, it is likely that the whole structure just blows apart. And it will not safe to be standing nearby.

4) As said, tritium is a key ingredient in the fusion technology that is aimed for, and it also happens to be a key ingredient of thermonuclear weapons. In addition, the required breeding technology is also highly relevant for military uses, because if you can breed tritium from lithium, you can also breed weapons-grade uranium and plutonium.

5. Steam turbines are not physically simpler than wind turbines. Apart from that wind power converters, as well as photovoltaic energy converters, can come pretty close to the physically possible optimum, there is another problem: Large steam turbines need cooling for thermodynamical reasons. Lots of cooling. The amount of cooling required for today's uranium fission plants is already a problem. For one, they cannot be built in arbitrary places - they need to be at rivers or at the coast. As the fukushiuma plant has shown, having a nuclear plant at the seaside can be a bit risky. But cooling by rivers also has costs, heating up a river to much messes up its ecology. Also, France often has energy problems in the summer, and the reason is that the rivers are too hot to cool its numerous nuclear plants.

Here another article on further problems of nuclear fusion - see the article of Michael Moyer.

http://energyskeptic.com/2014/why-fusion-is-still-30-years-a...

As a closing remark, I am not saying that fusion power plants are impossible. Sometimes, technological break-troughs happen, similar to the advances which made airplanes and aviation possible. But today, we don't even know what is required to make it possible. We are in a similar position like people from 1800 were in respect to aviation. And also, we have more urgent problems to solve - we need clean energy within the next decade, not in the next century. And fortunately, we do have the technology for that, we just need to put it in march.

1. No. The current bulk of research focuses on this pathway because d-t is both energetically favorable, and occurs at lower temps than other energetically favorable pathways. Tritium is a key component of fusion as it is currently studied in many, but not all cases and is the most likely first reaction. If you had said that the bulk of current research focuses on d-t, I’d agree, but it’s definotely not “nuclear fusion as we know it.” D-3He is a thing, not to mention stellar fusion which we certainly won’t create in a power plant, but we do know about it.

2. No, although the kinds of reactors being dreamed of in the “short” long term do fit this bill. Again, the much more difficult to manage (not to mention fuel) D-3He reaction is aneutronic, and doesn’t require a breeding blanket. Another difficult reaction would be p-7Li, although the fuel would be easier to come by. I’m not claiming that we’re remotely capable of harnessing these reactions, but it’s important to point out that they exist. A high neutron flux, and the need for Trtium are not inherent to fusion in general.

3. A bigger issue would be sputtering from the neutrons and He infiltration of the vessel. Othereise, assuming d-t fusion... this is accurate.

4. We can already breed tritium, and plutonium... this is a reality we have to live with. Fusion won’t change that either way. We can also engineer plagues, and a lot of other nasty things, and every year it all becomes easier to do “out of the garage” so to speak. If we’re going to survive, we need a better solution than unspilling the milk. Maybe embracing fission energy and greatly raising quality of life around the globe would be a good first step?

5. Agreed, although it is worth mentioning that there are ways to harness energy without a turbine, they are also complex. Fusion won’t save us, it won’t save our kids or grandkids. We need fission, solar, and wind, and peobsbly a century or more of research into aneutronic fusion if we want to survive well.

You point out that alternative reactions like D-3He are theoretically possible.

But my argument is not that D-T (Deuterium-Tritium) fusion is theoretically impossible. It is practically impossible. While it is possible to generate very small amounts of Tritium in commercial reactors, a fusion power plant would need much much larger quantities before it could even be started. And while the D-D reaction is also theoretically possible, it is even more difficult to achieve practically.

This is similar to aviation in 1800: While it was theoretically possible to build a flying machine, there was, for example, no known engine which would have been able to power an airplane. And for somebody to say "we just go ahead and will solve the technical problem of having a low-weight power source within 20 years" would have been delusional. You can't summon technological break-throughs like a mythical ghost in a bottle.

So to sum up, your argument against that todays nuclear fusion research, which is dominantly based on the D-T reaction, will not lead to any energy reaction in foreseeable time, is that there are more exotic, more difficult, end less well understood reactions which are also theoretically possible but not even close to being practically usable in any way.

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