[Enthalpy]

Hello dear friends!

I'd like to propose to produce radioisotopes using the D-D reaction in miniature Tokamaks, especially for medicine.

Tokamaks (including stellarators) top the rate of permanent nuclear fusion reactions for a given size and input power
https://en.wikipedia.org/wiki/Tokamak
https://en.wikipedia.org/wiki/Stellarator
so big machines fed with D-T claim to produce net energy (present) at affordable cost (uncertain future)
https://en.wikipedia.org/wiki/ITER

As a neutron source instead, the machines would

• Not try to produce any energy, even less net energy;
• Receive only deuterium (²H or D) without the scarce 50% tritium (³H or T);
• Be 10×10×10 times smaller than Iter with the same operating conditions:
  Φ=1.2m and 50kW input and 20M€ (...err);
• Emit neutrons to irradiate fertile material like ⁹⁸Mo.

Their activity or misuse would produce little plutonium, tritium and radioactive waste. From my estimates, the isotopes production would be naturally good - maybe at a lower cost than the other alternatives to fission reactors.

---------- Figures

Welcome to double-checkers, even more as usually, as a 3.7×10¹⁰ factor may well lack somewhere!

Iter is to produce 500MW heat (over 400s, let's forget that) from a 17.6MeV reaction, that's 1.8×10²⁰/s. At the same induction, density and 150MK, the D-D reaction is 0.012× as frequent as D-T and the machine is 1000× smaller, for a reaction rate of 2.1×10¹⁵/s. Every second D+D reaction produces ³He+n, the other T+p, but T is consumed 80× faster in a D+T reaction that produces one neutron too: ⁴He+n. So 2.1×10¹⁵/s neutrons as well.

The target shall catch all neutrons (how?) and consist of pure ⁹⁸Mo (that costs) in the example I choose. Something (Nitrogen behind graphite and molybdenum? Heavy methane?) shall thermalize the 4kW neutron flux to 77K=6.6meV:
http://www.nndc.bnl.gov/sigma/index.jsp thank you!
(n, total) 6.07b http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15091&mf=3&mt=1&nsub=10
(n, elastic) 5.79b http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15091&mf=3&mt=2&nsub=10
(n, γ) 0.26b http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=15091&mf=3&mt=102&nsub=10
I heavily overinterpretate curves made by models and don't integrate over the energy distribution. Then, the inelastic collisions section is 0.28b and (n, γ) make 90% of these or 1.9×10¹⁵/s. Still 60% at 300K so money shall decide.

Over a 5×24h week, the tokamak produces 8.3×10²⁰ atoms of ⁹⁹Mo. 2.75 days half-life = 343ks exponential decay mean 2.4×10¹⁵Bq = 65 000 Ci produced per week.

⁹⁹Mo decays fully to ^99mTc used for medical imaging. The worldwide demand is 12 000 Ci per week according to Aiea
https://www.iaea.org/About/Policy/GC/GC54/GC54InfDocuments/English/gc54inf-3-att7_en.pdf
satisfied by one mini-tokamak - rather several ones, since ⁹⁹Mo must be transported swiftly. This allows for:

• Correction of limited errors in my estimate;
• Account for limited design constraints;
• A smaller machine, or if possible less strong fields;
• Production of other radioisotopes;
• Work during daytime.

Produce and sell two mini-tokamaks per continent for redundancy.

Marc Schaefer, aka Enthalpy

[marquis]

Ok, I'm totally outside of my specialty.  So forgive my ignorance.

The problem with the tokamak and other such devices is containing the plasma.  It takes powerful magnets and much electric force to do that.

But if I read correctly, that MAY have already been done by mother nature in the form of ball lightning.  Would a better approach be to further investigate ball lightning for possible easier ways to contain plasma?

Regards

[Enthalpy]

Hi marquis, thanks for your interest!

Ball lightning has long been denied because it's difficult to observe, despite there were so many consistent testimonies, including from people of very different culture. About 3 years ago, a Chinese research team could measure a spectrum emitted by a lightning ball and found it consistent with the soil that had been hit by lightning. So the prevalent direction for theories is presently that lightning ejects a plasma from the struck object. No mention about confinement nor magnetic fields - but I didn't study the topic. My vague impression is that the plasma ball just dissipates freely.

Tokamaks begin to work presently. They do need strong magnetic fields, for which the oldish superconductors suffice, especially at the most recent attempt, ITER. Fusion is long achieved, fusion sustained for tens of seconds too, and the ancestors already produced more heat (...not electricity!) than the injected energy. The remaining problems are more
- How to produce tritium in proper amount?
- How to produce it cleany? [I do see a fundamental flaw here: to me, the operation is as dirty as uranium fission]
- What materials shall survive the neutron irradiation over years?
- How to stabilize the plasma safely for months?
And many more.

As compared with electricity production by D-T (deuterium-tritium) fusion, what I propose is much simpler in many aspects:
- I fuses D-D. No worry about T production.
- The tokamak is 10*10*10* smaller hence it's cheaper and easier. I suppose the magnetic field can decrease if the volume is less small.
- The reaction rate per volume unit is 80* slower, so the neutron flux is 80,000* smaller.

I have still to describe how to capture the neutrons efficiently by the target material, typically ⁹⁸Mo to produce ⁹⁹Mo and ^99mTc. I see more or less how but must put figures on it and write it cleanly.

[pcm81]

Neutron sources other than fission based nuclear reactors are usually spallation driven. A 1Gev energy protons are smashed into heavy metal target breaking up its atoms and releasing neutrons. Look up SNS at oak ridge. So far that is the cheapest way the world found to produce neutrons. What you ae suggesting is still allot more expansive per neutron if yo do the math.

[Enthalpy]

What you ae suggesting is still allot more expansive per neutron if yo do the math.

Can you show us your maths? The SNS has already cost 1.4G$, while the tokamak I suggest is 1000 times smaller than the existing ones.

[pcm81]

What you ae suggesting is still allot more expansive per neutron if yo do the math.

Can you show us your maths? The SNS has already cost 1.4G$, while the tokamak I suggest is 1000 times smaller than the existing ones.

To make fusion work you need He atoms moving at very high speeds. The tokamaks contain plasma in a torus. The speed going around the torus is fixed by energy needed to sustain fusion. If you make torrus smaller you are increasing centrifugal force needed to keep plasma inside the torus. There is a reason why LHC is 16.6 miles in diameter. You can't just say: "Let's make a tokamak that is 100x smaller in every dimension".

MIT is trying to create a small tokamak, but it's still much bigger than what you are suggesting: https://www.computerworld.com/article/3028113/sustainable-it/mit-takes-a-page-from-tony-stark-edges-closer-to-an-arc-fusion-reactor.html

Here is another article talking about smaller tokomak: https://physicsworld.com/a/smaller-fusion-reactors-could-deliver-big-gains/

And once ain, the idea is not bad, it is possible to have stable fusion in a smaller reactor; but we have to invent a way to make much stronger magnetic fields.

[Enthalpy]

To make fusion work you need He atoms moving at very high speeds. The tokamaks contain plasma in a torus. The speed going around the torus is fixed by energy needed to sustain fusion. If you make torus smaller you are increasing centrifugal force needed to keep plasma inside the torus. There is a reason why LHC is 16.6 miles in diameter. You can't just say: "Let's make a tokamak that is 100x smaller in every dimension".

Sorry to be so direct, pcm81, but you ignore the topic: about every of your sentences above contains a basic misunderstanding, which I won't comment individually. I'd suggest to you not to be affirmative on subjects you ignore.

[P]

I saw a youtube video a couple of years back about magnetic bottling and plasma containment in tokamaks using modern supermagnetic materials. It was presented by the Russians who were confident that their new materials would shield a tokamak and give it the fields it needed to contain a plasma on something of the kind of scale that would fit on a lab bench.  I can no longer find the vid - I do not know if was just boasting and fibs or propaganda or a serious breakthrough, but they seemed confident of cracking it soon.

It reminded me of the Mr Fusion, blender sized device, used at the end of Back To The Future.

[pcm81]

To make fusion work you need He atoms moving at very high speeds. The tokamaks contain plasma in a torus. The speed going around the torus is fixed by energy needed to sustain fusion. If you make torus smaller you are increasing centrifugal force needed to keep plasma inside the torus. There is a reason why LHC is 16.6 miles in diameter. You can't just say: "Let's make a tokamak that is 100x smaller in every dimension".

Sorry to be so direct, pcm81, but you ignore the topic: about every of your sentences above contains a basic misunderstanding, which I won't comment individually. I'd suggest to you not to be affirmative on subjects you ignore.

Don't be sorry about being direct. I got tough skin. I survived grad school in Russia... with lions and tigers and bears... and snow; oh my.

Back to the subject at hand. It all boils down to inventing a super conductor that can do the job. What I vaguely remember from my superconductivity course at moscow state (13 years ago) is that temperature as well as strong magnetic field have adverse effect on super conductivity.  In a tokomak you are trying to have something very hot, plasma, reasonably close to something very cold, super conducting magnet. Meanwhile by making the unit smaller you are increasing the magnetic field strength requirement. All this is putting a tall order on super conductor used to make a magnet. There are other issues like stability of plasma, leakage etc etc etc, most of which can probably be overcome if we can just invent the magic super conductor.

Oh, and as far as costs are concerned. Tokomak in europe is running north of $15bln so the $1.5bln for spallation source is chump change in comparison.

EDIT:
Don't get me wrong, i am all for fusion research and if you can design a working system, which actually does what you describe, that would be a great news for the world, because you would have also invented the technologies to power the world. I recall my undergraduate nuclear physics instructor doing a calculation on energy content of sea water. As i vaguely recall 1 gallon of sea water, if fusion was possible, has the same energy content as 400 gallons of gasoline used in combustion. So yeah, you would probably get Nobel prize in every category that year if you could invent the technologies required to make possible what you are proposing.

[wildfyr]

pcm,
I feel that I should remind you that Enthalpy's concept isnot for doing fusion for energy, but rather for element synthesis. Its an entirely different branch of fusion reactor technology.

As a neutron source instead, the machines would
Not try to produce any energy, even less net energy;
Receive only deuterium (2H or D) without the scarce 50% tritium (3H or T);
Be 10×10×10 times smaller than Iter with the same operating conditions:
Φ=1.2m and 50kW input and 20M€ (...err);
Emit neutrons to irradiate fertile material like 98Mo.

[pcm81]

pcm,
I feel that I should remind you that Enthalpy's concept isnot for doing fusion for energy, but rather for element synthesis. Its an entirely different branch of fusion reactor technology.

As a neutron source instead, the machines would
Not try to produce any energy, even less net energy;
Receive only deuterium (2H or D) without the scarce 50% tritium (3H or T);
Be 10×10×10 times smaller than Iter with the same operating conditions:
Φ=1.2m and 50kW input and 20M€ (...err);
Emit neutrons to irradiate fertile material like 98Mo.

I understand that, however not producing power does not take away the requirement to be able to be build it (still need to invent the magic super conductor that can survive in those magnetic fields) and producing neutrons cheaper than competing sources like spallation per neutron. And I am not even mentioning that D-D reactions have much lower cross section than D-T reactions.  Don't get me wrong, i am all for fusion and in physics la-la-land this would work wonderfully, but in real world the technology does not exist to make this design possible or competitive with alternative means.

The baseline need in this concept is a cheap neutron source. The world has a good demand for neutron sources, ranging from medical needs like boron therapy to research needs like neutron scattering. When i did my grad research in russia, the nuclear reactor that was used there was producing 0.5 grams on neutrons per year with an operating budget on $1M/year. And that is when the lead engineer on that reactor was making $300/month (my science advisor). The point is, neutrons are in demand and they are expansive, even in the countries where labour is dirt cheap. Many people thought long and hard about how to make cheaper, more efficient neutron sources. Yes, small fusion reactors could do the job, if only someone can invent the technologies needed to make them work.

[pcm81]

Also, something that is actually on topic of my masters thesis:
The target shall catch all neutrons (how?) and consist of pure 98Mo (that costs) in the example I choose. Something (Nitrogen behind graphite and molybdenum? Heavy methane?) shall thermalize the 4kW neutron flux to 77K=6.6meV:

Really to get to thermal range you just need water. Methane or heavy methane are needed to go to e-5 energy range. The advantage of methane is that it has a low excitation level, which means neutrons of low energies can still loose energy by hitting methane and sending it into spin, even though these neutrons already have too low of an energy to interact with hydrogen or deuterium as free gas.

[Enthalpy]

Better superconductors would make tokamaks more compact, everyone agrees, and at least one team in the US tries that direction.

The size of a tokamak doesn't result from centrifugal force and induction like in an accelerator. Tokamaks before ITER were smaller. The size results from the need to keep the heat in the plasma to achieve a net energy gain, which I don't want
https://en.wikipedia.org/wiki/Lawson_criterion

Because I don't seek energy production, the reaction can use D-D which is available in the Ocean. Tritium, for D-T that would produce energy, is not.

It is my hope that the size can scale down like the neutron production, if energy is provided from outside. 10³ smaller than ITER, despite the D-D reaction rate is 0.012× as much as D-T at identical conditions.

I did not try to provide cost estimates... Dividing the cost by 10³ like the volume was a joke, I hope everyone noticed my "...err". ITER, which runs out of financial control, is over 15G€. Other tokamaks are less expensive: Wendelstein 7-X cost 0.37G€ to build (it's a stellarator, or improved tokamak) for the same plasma temperature and density, using standard Nb-Ti superconductors for 3T rather than 5T
https://en.wikipedia.org/wiki/Wendelstein_7-X
and reducing the size a lot will make it cheaper - by how much remains to see.

It's been a year and I still haven't described how ⁹⁸Mo shall catch the neutrons. Thermalize for sure. I have ideas in mind but must put more figures on them. Size / 10³ supposes most neutrons serve; if this proves unrealistic, the size can shrink less.

[P]

This is from a couple of years back - Smaller tokamaks with high temp superconducting magnets:-  https://physicstoday.scitation.org/doi/full/10.1063/PT.3.2941

I still can't find any of the Russian stuff I saw a few years back.

[Enthalpy]

Thanks P!

A smaller tokamak thanks to stronger induction would also ease the capture by ⁹⁸Mo of the emitted neutrons, one more advantage.

Whether having 5T, 10T or 20T, a tokamak to produce radionuclides rather than electricity is easier on several points, not just the size. For instance the neutron flux is much smaller, so the materials are reasonably stressed, and the heat production shrinks too. Both ease the design of the magnets. Not fully optimizing the energy efficiency relaxes many design constraints too. And the arguably highest hurdle for electricity production, the regeneration of tritium, is removed.

So it is my hope that the production of radionuclides is a much easier, useful, and economically sensible goal for small tokamaks. If I didn't put nonsense and if one or few teams get interested, it would be a first, nice and graspable goal for tokamak designers, including stellarators.