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Author Topic: Tokamak produces radioisotopes  (Read 664 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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