Nuclear fusion waste products

paulhunn

I have managed to find out that waste products from fusion reactions are far less dangerous than those from traditional fission reactions but i cannot find anywhere that states what the waste products actually are. Can somone please tell me what the waste products from a deuterium and a tritium reaction are?

Thanks

Paul

Morbius

Paul,

We can't really say that right now.

First, the deuterium - tritium or D-T reaction that you are referring to is:

1D2 + 1T3 --> 2He4 + 0n1 + 17.6 MeV

That is deuterium + tritium --> Helium-4 + a neutron + energy.

The direct "waste products" are Helium-4 and the neutron. The Helium-4 is
nothing to be concerned about - it's ordinary stable Helium.

What is of concern is that 14.1 MeV neutron - or more specifically - what
that 14.1 MeV neutron hits. That's where the "waste" of a fusion reactor
is going to come from - the radioactivity induced by the neutron that comes
out ot the reaction. Since the designs aren't finalized - we're still trying to get
the reaction to work - we don't know what will be used to stop that neutron.

So unlike fission - where the waste products are the direct result of the reaction,
in fusion, the waste products are an indirect result of the reaction - so we can't
really say what they will be with 100% certainty as of yet.

Dr. Gregory Greenman
Physicist

Astronuc

From the fusion reaction itself, there are no 'waste' products, in the sense that the products can be used. He (helium) can be collected and the neutrons provide energy in whatever they absorbed.

D + T -> n (14.1 MeV) + He⁴ (3.5 MeV).

The 14.1 MeV neutrons irradiate the surrounding structure, and when the neutron is ultimately absorbed, the absorbing nuclide generally becomes radioactive In this sense, fusion does produce waste products in the form of irradiated (and activated) structural materials, which ultimately have to be disposed in some appropriate facility.

In a DT plasma, there will like be some D+D reactions, of which half produce p + T and the other half produce n + He³.

T is radioactive by the way, and it must be kept out of the environment.

paulhunn

Thanks for the replies. I understand it now.

Orion1

My understanding is that the entire fusion reactor is a 'nuclear fusion waste product'.

darkar

How much Helium will be produce by fusion process in fusion power generator (assuming they are operational)? Will it be a lot? Because this might lead to increase concentration in atmosphere after a lot of year of running like CO2. High concentration of helium can be dangerous because helium is a simple asphyxiant(http://en.wikipedia.org/wiki/Asphyxiant).

What to do with those Helium after they are collected?

Related:
http://en.wikipedia.org/wiki/Helium#Precautions

Morbius

darkar,

If we assume a typical 1000 Mw(e) generator; meaning a 3000 Mw(t) thermal heat
source which is the fusion reactor; then in one year it will produce about 450 kgs
or less 1000 lbs of He-4.

This amount is TRIVIAL compared to the thousands of TONS of exhaust gases in
fossil plants.

Helium is non-toxic. The only way Helium hurts you is if the concentration is so high
that it displaces the oxygen you need.

Helium is a non-problem here.

Dr. Gregory Greenman
Physicist

chroot

The "waste helium" is not an issue at all, and certainly not because it's an asphyxiant. Futhermore, helium released to the atmosphere escapes very quickly into space.

If anything, helium is becoming a precious substance. Our current supply of helium is dependent upon fossil fuels (nuclear reactions in the somewhat radioactive oil deep underground releases helium, which becomes trapped in pockets with the oil and natural gas). When the fossil fuels are gone, so will be our direct source of helium.

- Warren

mheslep

Allow me to qualify for benefit of the OP: There are 'aneutronic' reactions, or reactions that do not produce any neutrons; the energy is released instead by alpha particles which can be captured by electromagnetic fields and in general are much less of radiation hazard. Examples include proton + Boron 11. Note that ITER type Tokamaks are not capable of burning these fuels because they require higher reaction energies, hence the reason one doesn't here much discussion of aneutronic fuels. Example ~110keV for P-11B vs ~15KeV for D-T.

Astronuc

Not to mention Z(B) = 5, which means fairly high brehmstrahlung losses for a given plasma temperature, and high electron pressures if one tries to fully ionize B, and also recombination and cyclotron rad losses. P-B¹¹ would be great, but for the limitations.

Another aneutronic reaction D-He³ still has other issues, such as there is still the D-D reaction which does produce He³+n in 50% of reactions and T+p in the other half. T+D would still lead to [tex]\alpha[/tex] + n.

Andrew Mason

Helium is a noble gas. How can it be an asphyxiant? If you breathe it, it just makes you talk funny. CO2, on the other hand, in sufficient concentration (eg. 5%) will interfere chemically with hemoglobin transport of oxygen in the blood. I don't see how Helium can do this. If you breathe nothing but He for long enough, of course, you will die from lack of oxygen.

AM

Morbius

Andrew,

You answered your own question. You don't need a chemical reaction to have an
asphyxiant. If the gas just displaces enough oxygen; it will asphyxiate you.

That's how a lot of fire-suppression systems protecting computers, electronic equipment...
whatever; work. The system pumps in enough nitrogen, CO2, ....anything but oxygen;
and the fire is "smothered" which is the analog to asphyxiation.

Asphyxia is merely the lack of oxygen that results in unconsciousness or death.

Dr. Gregory Greenman
Physicist

sunday

I found this forum looking for info on plasma physics, info that I need to understand a little the works of a IEC fusor of the Bussard type, i.e. a Polywell*. I think that Bussard claims that the Bremsstrahlung losses in the core of the polywell are very low, as the high electron density make the electron cloud (Wiffle Ball) in the center of the device to behave as a diamagnetic medium, and expelling the magnetic field used to create the virtual cathode. As I have formal education on nuke physics and technology, but not on high-energy nor plasma physics, I don't know if that claim is reasonable.

What are the thoughts of the forum?

Thanks a lot.

Caveat: I'm not sure about Bussard work, or its interpretation by his followers, not being junk science. There are rumors about Bussard preparing a 120-page paper to expose his last 11 years work.

* See http://askmar.com/ConferenceNotes/Sh...%20Nuclear.pdf for a transcription of his talk at Google, and http://askmar.com/ConferenceNotes/20...AC%20Paper.pdf for the paper presented in 57th International Astronautic Congress. The paper is very skimpy, as it doesn't contain the "hard" physics required to explain how the thing works.

Morbius

sunday,

It's GARBAGE!!!

Bremsstrahlung doesn't require magnetic fields; it only requires that the charge is
accelerated. With lots of electron-electron interaction at high electron density; there
certainly is going to be Brehmsstrahlung losses.

Dr. Gregory Greenman
Physicist

ensabah6

Could radioactive nuclear waste absorb these neutrons, becoming less radioactive or perhaps even be used as fuel?

Morbius

ensabah6,

YES - in fact one of the goals of the GNEP - Global Nuclear Energy Partnership is to
produce fast "actinide burner" reactors. A reactor along the road of the design of
Argonne's Integral Fast Reactor or IFR, which was cancelled back in 1994; would go
along way in reducing radioactivity of nuclear waste.

First, nuclear fuel should be reprocessed - it's really DUMB to have nuclear waste which
is 90+% U-238; no more radioactive than when it was dug out of the ground.

Secondly, plutonium in spent nuclear waste should be recycled to power reactors as fuel
to eliminate a constituent of nuclear waste with a 24,000 year half life.

Third, we should have "burner" reactors along the lines of the Argonne IFR concept.

This would alleviate much of the nuclear waste problem.

If the only waste that we have to dispose of is fission products; the longest lived fission
product of any consequence Cs-137; has a half-life of just 30 years.

For more on the Argonne IFR, see the transcript of an interview PBS's Frontline did with
Argonne's Dr. Charles Till:

http://www.pbs.org/wgbh/pages/frontl...iews/till.html

Dr. Gregory Greenman
Physicist

GTrax

It could be somewhat worse than that. The breathing mechanism is, I understand, not driven by lack of oxygen, (even if that is the body's crying need), but by level of CO2. A real good lungfull of any inert gas asphyxiant could leave one incapable of re-starting if partly overcome, and without resuscitation help.

Breathing Xenon to get the deep low voice effect is now questionable as a teaching experiment, though the same concerns maybe do not extend to squeaky-voice helium.

I am also not so sure about chroot's belief - though I don't know for sure..
Helium is lighter than air, but would only get to rise to the top of the atmosphere if enough were contained in a balloon or something to displace more than its weight in atmosphere. Released straight into the air, it seems to simply mix with it.

While leak testing a vacuum furnace, I was impressed how very little helium, less than needed for a party balloon, could ping around the whole 2 industrial factory units and the car park also, in less than a second. We had to wait 20 minutes for it to disperse before the mass spectrometer instrument stopped squealing!

I guess atmospheric gases are lost into space, but I don't think we will run out anytime soon.