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Author Topic: Tokamak produces radioisotopes  (Read 2718 times)

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Enthalpy

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Tokamak produces radioisotopes
« on: July 09, 2017, 03:13:14 AM »

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
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marquis

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Re: Tokamak produces radioisotopes
« Reply #1 on: December 02, 2017, 02:39:35 PM »

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
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Enthalpy

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Re: Tokamak produces radioisotopes
« Reply #2 on: December 03, 2017, 12:35:24 PM »

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.
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