Fusion energy is dirty

westfield

Isn't it rather unfair to brand fusion power in general as "dirty" while only referring to tokamak designs?

Correct me if I'm mistaken as I'm not up on the very latest in fusion power research but at this point in time we really cannot say with any certainty which design\s will prove to be practical for fusion power production, let alone which technology\s will end up being commercially viable.

So it's a little premature to make such pronouncements and call for an end to research isn't it? Doesn't seem very scientific at all.

Joseph Chikva

Regardless the design more easy for realization D-T reaction requires neutron multiplying; its 14.1MeV neutron flux produces secondary radiation of first wall and support structures.
We already know that.
But as mentioned here those threats are much lower in comparison with existing fission reactors.
And instead of long-live high radioactivity wastes we will have lower quantity of short-live lower radioactivity.
Also fusion reactors will be less dangerous in case of accident if we take into account that fuel loading in fission reactors has a few years reserve and wastes also remain there till further reloading vs. in fusion reactor only current load of much less radioactive fuel is required and practically no wastes.
And so by realization fusion we can achieve the new much higher standard of industrial safety.

Renewable are not competitive to fusion as I mentioned earlier. Also wide usage of renewables would impact environment while fusion or fission reactors impact only in case of accidents.

Khashishi

The difference is that with fusion, the radioactivity will be gone in a few years, while with fission, you will still have radioactivity left over when the sun consumes the Earth.

Possibly, one of the alternative fusion devices will eventually use B11 + H reaction, which won't produce neutrons. But this seems pretty distant.

Joseph Chikva

• D+He3 gives 18.3MeV having cross section resonance at 250keV
• p+B11 about 9MeV and resonance at 500keV
But yes - B11 is more available than He3

Enthalpy

About production of tritium by uranium reactors, please refer to the other thread:
http://www.physicsforums.com/showthread.php?t=422576
Fission produces much heat and little tritium (limited by the absolute maximum number of neutrons), using this tritium in a fusion reactor would add very little electricity to what the uranium reactors already produce - hence not worth it.

That's why people want to regenerate tritium at tokamaks, using lithium blankets.

These blankets need neutron multiplication because of a simple neutron bookkeeping problem.

Hence neutron multiplication by lead, which is dirty - the subject of the present thread.

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Lead blankets were used against gamma rays, but aren't the natural choice against neutrons. 14MeV neutrons aren't as widely studied as fission neutrons or as thermal neutrons. Hence the PhD thesis by Peter Reimer, in 2002 - not so old.

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I took here two examples only of radionuclides produced in these blankets. For instance ²⁰⁴Tl would have a longer life. Compare with ¹³¹I which has 8 days half-life and is enough of a problem, so a quick decay isn't a good excuse.

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Aneutronic fusion is completely out of reach of tokamaks for now, as is D-D. They may exist in encyclopaedia and courses, but tokamak researchers don't even indicate a number of centuries to harness these reactions. Sorry for the nice dreams.

Laser inertial fusion doesn't publish much about using such reactions, but Z-striction does, yes. Though, I'm very cautious about the Z-machine's results, because exploring electricity production is not its aim, and because people there seem to like sensational results.

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ITER is sold to the public as "limitless and clean energy" and this doesn't fit with the huge radioactivity (not just "its own difficulties": please check the activity produced, it's equal to a uranium reactor!) produced when regenerating the lacking tritium.

Joseph Chikva

As i know Z-machine is more promoted as X-rays source. And not as fusion concept. A number of Tungsten wires gives very intensive pinch but due to high atom number very intensive braking radiation. I heard about idea to combine Z-machine with pulse light ions accelerators. But do not know will that idea be checked or no.

It would be difficult for me to speak more about other fusion concepts as I am proposing a new one. And sure in its viability. Even in more complicated D-He3 reaction case. That would not be a nice dream.

Drakkith

You must be misunderstanding something that was designed for the average person. ITER can LEAD to limitless and clean energy. It itself will NOT be producing any electricity for use. It is merely a stepping stone to future breakthroughs and such. In addition, it is already well known that D-T fuel produces a huge neutron flux. Materials are being researched and developed that can accommodate this flux while staying less dangerous than current materials.

You clearly show that your view of "clean" is NOT what is meant when fusion is referred to as clean energy. Looking at the long term situation fusion is MUCH cleaner than fission. Even the isotopes released in an incident are far less dangerous than fission is.

There is no such thing as "clean" energy in the absolute context. Making solar panels, windmills, dams, ETC all require the manufacturing of materials. None of this is perfectly clean.

Edit: After closer reading of your posts, it seems to me that nuclear power, whether fission or fusion, will never be clean enough for you as long as ANY radiation is produced. If that is your view then you should go away and stop posting this nonsense. This isn't a forum for your personal views, but for scientific fact. Evidence has shown that Fusion is MUCH cleaner than Fission in every realistic use of the term "Cleaner". Unless you have actual questions about something, then go away.

minerva

Could you elucidate exactly why the lead blanket is required?

For every tritium nucleus consumed in D-T fusion, a neutron is emitted, which can regenerate another triton in a reaction with Li-6 - or two neutrons, in a reaction with Li-7.

Li is less chemically reactive than Na, so the safety concerns with liquid Li are even less than those associated with the present use of liquid Na in fast-spectrum fission reactors, and we have plenty of experience with doing that safely.

Nonsense. There is no radioactivity left over from the 1.7 billion-year-old fission reactors at Oklo.

nikkkom

A CANDU reactor produces about a kilogram of tritium per year.