Are Fusion-Reactors Possible?

Mars_B4_Moon · 2021-06-02 02:32:26

The tech keeps getting better every few years.

China's artificial sun brings nuclear fusion energy closer
https://www.spacedaily.com/reports/Chin … r_999.html

The United States, Russia, Germany, France and Japan have also worked on these experiments, the reversed field pinch and magnetic confinement experiments which help produce brief moments of fusion.

Spaniard · 2021-06-02 05:18:48

In physical terms, it is proved.

In technological terms, a fusion reactor that generate more energy that needed to function for long periods, it's yet to reach that goal, but there is progress on that research.

In economical terms, maybe it works, maybe not. It is soon to know that. But it will be harder that just meet the technological goal. At first sight, nuclear reactors seems they will be very expensive. Even if the fuel is cheap, the amortization and maintenance costs could make the economical goal unfeasible.

Like in most economic situations, the key to reach cheap energy could be the scale of deployment.

It's not the same deploy one of a kind reactor that fifty standard reactors.

But standardization could take time. So... more wait.

louis · 2021-06-02 07:30:23

Fusion is one of those technologies that we are always told is 20 years away.

On the other hand I think it is one of those technologies where there could be a sudden breakthrough. I find the Low Energy Nuclear Reaction (LENR) type technologies more interesting.

Calliban · 2021-06-02 07:39:42

Yes, they are possible. In fact there are desktop scale electrostatic confinement fusion reactors that have been produced by hobbyists. These units do not achieve breakeven and consume orders of magnitude more energy than they generate. But electrostatic confinement has been discussed as a useful neutron source.

Most fusion research focuses on magnetic confinement of De-T plasma. The problem is that in order for plasma to be stable, plasma pressure must be about 10 times smaller than magnetic pressure (Beta = 0.1). This limits plasma pressure to 100-200KPa. Reactor power scales with the square of particle density, therefore power is proportional to square of pressure. The low plasma density achievable in a tokamak severely limits power density and in fact, the only way to achieve breakeven at all appears to be to either build extremely large tokamaks or to find a way of increasing magnetic field strength or operate at a higher beta, which raises plasma stability problems. To achieve economical power generation, the energy yield must be ~30 times the driving energy. It is presently, less than one. The low power density of a tokamak raises the possibility that even if breakeven were achieved and greatly exceeded, a tokamak fusion reactor may not be an economical source of energy.

In inertial confinement approaches, plasma density is billions of times greater. But it is difficult to inject sufficient heat at achievable plasma density to ignite pellets.

Another problem (and potential useful attribute) of fusion stems from the fact that about 80% of energy is released as high energy neutrons. Of the ~17MeV released by De-T fusion, about 13MeV is carried away by the neutron yielded by the reaction. This collides with the reaction vessel internal walls, rendering them brittle and radioactive. So energy conversion into electricity is problematic. However, the abundance of fast neutrons makes a fusion reactor a potentially very useful driver for a sub-critical fission assembly. In fact, the 13MeV neutrons yielded by fusion are capable of fast fission of 238U or 232Th, without the need for intermediate breeding of 239Pu or 233U. Each 13MeV driver neutron could ultimately yield several fission events in the blanket, each yielding 200MeV. So a fusion-fission hybrid does not need to achieve breakeven in its fusion section in order to provide a high net energy yield. Likewise, a tiny micron sized piece of fissile material could allow ignition of fusion in inertial confinement, if placed at the centre of imploding pellets, in a fission-triggered inertial confinement device.

An interesting concept would be a hybrid inertial confinement reactor, in which fission both triggers pellet detonation in lithium deuteride pellets and yields net energy in surrounding fissionable blankets. Such a reactor should be able to function using a fraction of the laser driver energy input of conventional IC fusion. The driver should therefore be compact. The natural uranium or thorium blankets around the core would also be extremely compact and high power density. Maybe a useful power source for a Mars base, that requires only small amounts of fissile or fissionable material delivered from Earth. No real radiological consequences, even if the payload accidentally burns up in Earth atmosphere. As the reactor is able to fast fission both uranium and thorium, it would neatly circumvent the need to import large amounts of fissile materials in starter cores. Native Martian fuel resources could be relied upon at an early stage. Later, hybrid reactors would generate abundant fissile fuel for Martian fission reactors. These could be light water, molten salt, sodium cooled, gas cooled, etc. The fusion energy source, in providing an abundant source of neutrons, allows very fast breeding of fissile material, which can then be used to fuel more conventional nuclear reactors.

Last edited by Calliban (2021-06-02 08:03:25)

tahanson43206 · 2021-06-02 07:56:29

For Calliban re #4

First, thank you for picking up on B4's new topic!

SearchTerm:Fusion summary of current status by Calliban
http://newmars.com/forums/viewtopic.php … 32#p180632

Second ... Thanks for adding the text explaining in greater detail how fusion and fission can supplement each other, on Earth and on Mars.

(th)

Calliban · 2021-06-02 08:56:52

Interesting paper by Winterberg on the use of small amounts of fissionable material to trigger IC fusion.
http://icc2006.ph.utexas.edu/uploads/13 … _paper.pdf

His concept avoids the need for enormous petawatt scale lasers and could work using much smaller electrostatic ion accelerators. Slightly different to what I had proposed, but roughly along the same lines. A tiny amount of uranium or thorium can be used to trigger a fusion microexplosion under the right conditions.

Last edited by Calliban (2021-06-02 08:59:03)

tahanson43206 · 2021-06-02 12:14:33

For Calliban re Post #4

Most fusion research focuses on magnetic confinement of De-T plasma. The problem is that in order for plasma to be stable, plasma pressure must be about 10 times smaller than magnetic pressure (Beta = 0.1). This limits plasma pressure to 100-200KPa. Reactor power scales with the square of particle density, therefore power is proportional to square of pressure. The low plasma density achievable in a tokamak severely limits power density and in fact, the only way to achieve breakeven at all appears to be to either build extremely large tokamaks or to find a way of increasing magnetic field strength or operate at a higher beta, which raises plasma stability problems. To achieve economical power generation, the energy yield must be ~30 times the driving energy. It is presently, less than one. The low power density of a tokamak raises the possibility that even if breakeven were achieved and greatly exceeded, a tokamak fusion reactor may not be an economical source of energy.

Would you be willing to consider lining a tokamak with U238 (or similar material such as Thorium) to protect the vacuum wall?

What I'm curious about here is if your hints about hybrid approaches might offer a path forward, if the tokamak is designed from the outset to provide neutrons to impact the liner material.

Related questions would be ...

1) What thickness of liner would absorb neutrons and thus protect the vacuum wall?

2) Does U238 have any properties that would inhibit magnet fields developed outside the vacuum wall?

There are probably other questions I don't know enough to ask.

Edit: by "design from the outset" I meant ... designed to split the vacuum chamber for periodic removal of exhausted liner and replacement with fresh.

Such a design could (presumably) allow for permanent installation of magnetic coils.

Word picture: a donut cut in half along the central axis .... ( <<== left side vs right side ==>> )

For SpaceNut ... could you (perhaps?) find an online image that shows the cut donut (torus)

(th)

Calliban · 2021-06-02 17:01:43

tahanson43206 wrote:

For Calliban re Post #4
Most fusion research focuses on magnetic confinement of De-T plasma. The problem is that in order for plasma to be stable, plasma pressure must be about 10 times smaller than magnetic pressure (Beta = 0.1). This limits plasma pressure to 100-200KPa. Reactor power scales with the square of particle density, therefore power is proportional to square of pressure. The low plasma density achievable in a tokamak severely limits power density and in fact, the only way to achieve breakeven at all appears to be to either build extremely large tokamaks or to find a way of increasing magnetic field strength or operate at a higher beta, which raises plasma stability problems. To achieve economical power generation, the energy yield must be ~30 times the driving energy. It is presently, less than one. The low power density of a tokamak raises the possibility that even if breakeven were achieved and greatly exceeded, a tokamak fusion reactor may not be an economical source of energy.
Would you be willing to consider lining a tokamak with U238 (or similar material such as Thorium) to protect the vacuum wall?
What I'm curious about here is if your hints about hybrid approaches might offer a path forward, if the tokamak is designed from the outset to provide neutrons to impact the liner material.
Related questions would be ...
1) What thickness of liner would absorb neutrons and thus protect the vacuum wall?
2) Does U238 have any properties that would inhibit magnet fields developed outside the vacuum wall?
There are probably other questions I don't know enough to ask.
Edit: by "design from the outset" I meant ... designed to split the vacuum chamber for periodic removal of exhausted liner and replacement with fresh.
Such a design could (presumably) allow for permanent installation of magnetic coils.
Word picture: a donut cut in half along the central axis .... ( <<== left side vs right side ==>> )
For SpaceNut ... could you (perhaps?) find an online image that shows the cut donut (torus)
(th)

To answer your first question, one would need to calculate the macroscopic fission and scattering cross section of 238U for 13MeV neutrons. I = I0 x e^-kx, where k is macroscopic cross section and x is thickness. The neutron flux will have have a half-thickness for any specific energy. The wall would experience an increase in total neutron fluence, due to build up resulting from fission. But the much lower energy of fission neutrons will result in less damage.

Uranium metal is a conductor, with generally poor permeability. That may complicate its introduction into a tokamak. Uranium oxide, as a non conducting ceramic should avoid any problems.

Winterberg comes out strongly in favour of inertial confinement approaches to fusion, as opposed to magnetic confinement concepts like the tokamak. His main reasoning appears to be the enormously greater plasma density that can be achieved in an imploding pellet and potentially greater resulting power density. In a fusion-fission hybrid design, this would have the advantage of allowing a uranium blanket to be exposed to extremely high neutron flux in which case, cooling would probably be accomplished using liquid metal. This has economic advantages, as a very compact core region can generate large quantities of power, from a small quantity of fissionable material. Fuel rating - the amount of power generated per tonne of heavy metal - is an important economic driver in breeder reactors. In an IC design, the uranium blanket would effectively be a single cast uranium metal slug, with a steel lined void in the middle for the pellet explosions with various ports running into it to allow pellet and ion beam injection and cooling portstgrough the slug for heat removal. Heat removal would be accomplished via high pressure sodium-pottasium, with the liquid metal forced through the slug using magnetodynamic pumps. The cast slug would sit within a tank of liquid sodium-pottasium, which would contain S-CO2 heat exchangers (for power generation) and a passive decay heat removal loop. The slug would have diameter of ~50cm and would weigh about 500kg, with a volume fraction of about 50% uranium metal alloy. Power density would average 1GW.m-3 within the slug, for a total power of 65MWth. Refuelling would take place after ~10HM atom fission, with the entire slug effectively replaced with a new one. The old slug will be electrorefined into metallic reactor fuel for conventional fast reactors.

In this way, a single fusion-fission hybrid reactor can provide the seed material to begin a breeder reactor programme, using Martian fissionable resources, to meet the power demands of a rapidly growing population.

Last edited by Calliban (2021-06-02 17:08:27)

tahanson43206 · 2021-06-02 17:41:13

For Calliban re #8

Thank you for your follow up, and for addressing several of the questions I offered ...

The conductive property of U238 was/is something I'm glad to know, along with the non-magnetic property of uranium-oxide.

I would assume heavy neutron flux would damage a significant number of Oxygen atoms ... I did a quick check with Google and did not find anything definitive, except a passing comment that oxygen is a relatively light atom and (the text seemed to imply) less likely to be damaged by neutrons passing through.

***
Thank you for your description of the design of Winterberg. My observation about Tokamak designs was motivated more by the significant investment already made in that concept by a number of nations, including Great Britain.

Google came up with this:

https://www.nature.com/articles/d41586-019-03039-9

Over the next four years, scientists at the Culham Centre for Fusion Energy near Oxford will produce a detailed design for the Spherical Tokamak for Energy Production (STEP), a plant capable of generating hundreds of megawatts of net electrical energy that would be up and running by the early 2040s. If the decision is made to go ahead and build the facility, the bill would stretch to billions of pounds.

My recollection is that a precursor to ITER in France was built and tested in Britain.

The point I'm trying to make is that psychological momentum appears to exist in the Tokamak realm, while the intertial fusion efforts I've heard about are just the one, in the US at Berkeley, where there is an attempt to focus multiple laser beams on little pellets of fusion fuel.

Thus, if someone were to think up a way to use the existing Tokamak design to produce fission from non-radioactive material such as U238, then perhaps all that investment can yield a positive return.

***
Today's news feed included an item about an initiative to build advanced (sodium cooled) small reactors in [correction: Wyoming].... this is a digression from the immediate topic, but I bring it up because a hybrid concept might appeal to those who are funding fission research.

Edit next day: An article about Uranium is available from an EU site:

https://www.radioactivity.eu.com/site/p … 38_235.htm

The article is accessible by older computer systems.

The article about Plutonium includes mention of discoverer Glenn Seaborg and the wartime production of quantities of the metal at plants constructed for the purpose.

Since the suggestion of Calliban is/was that U238 might be converted into fissile material in a fusion device, I presume that Plutonium would be the likely output. The EU article explains that Plutonium can emit an alpha particle and drop back to U235, which itself is fissionable.

One impression I came away with is that the equipment that might be used for such a hybrid operation would need to be highly/entirely automated, and all the security precautions associated with weapons production would be required.

Edit: https://currently.att.yahoo.com/att/1-w … _test=1_11

(th)

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#1 2021-06-02 02:32:26

Are Fusion-Reactors Possible?

#2 2021-06-02 05:18:48

Re: Are Fusion-Reactors Possible?

#3 2021-06-02 07:30:23

Re: Are Fusion-Reactors Possible?

#4 2021-06-02 07:39:42

Re: Are Fusion-Reactors Possible?

#5 2021-06-02 07:56:29

Re: Are Fusion-Reactors Possible?

#6 2021-06-02 08:56:52

Re: Are Fusion-Reactors Possible?

#7 2021-06-02 12:14:33

Re: Are Fusion-Reactors Possible?

#8 2021-06-02 17:01:43

Re: Are Fusion-Reactors Possible?

#9 2021-06-02 17:41:13

Re: Are Fusion-Reactors Possible?

#10 2024-10-03 19:03:21

Re: Are Fusion-Reactors Possible?

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