Horizon - Fusion HELP

[Hysteresis]

I watched the Horizon program on BBC last night. Its subject was material science.
One feature was that of one of the astronaughts who landed on the Moon had determined that there was evidence of Helium trapped in the rocks of the moon. He had set up a company to eventually harvest this Helium as the element was scarce on Earth and Helium was a prized element required for the eventual Fusion program for energy production, (whenever that problem resolution may be).
My problem is this. My university physics of the 70's was that the fusion process was that of the fusion of the first isotope of Hydrogen, Deuterium, which PRODUCED Helium. Therefore Helium is a stable by-product of the fusion process NOT a requirement for it. Deuterium is in almost limitless supply in the oceans of the world and as such whenever the Fusion problem is cracked, the material to to supply it is readily available.
SO what on earth is the BBC claiming that this astronaught is wanting to bring Helium which is a by-product of the fusion process from the moon and not a requirement for it. My understanding was that the fusion process will produce helium which we will have to dispose of somehow.
Has the fundamental science of fusion changed in the last 40 years and I have missed the revelation or has the BBC and this astronaught got it all wrong by wanting to import Helium when in fact we would want to dispose of it IF man made fusion ever happens.
My understanding of the fusion process was rather confirmed in the program by the suggestion that the helium arrived on the Moon from the Sun and carried on the Solar wind and as the Moon has no atmosphere or magnetic field the Helium arrived at the Moon surface but could not get to the Earths surface due to atmosphere and magnetic field. As the source of helium from the Moon is a direct result of Fusion then surely the BBC and the astronaughts reasoning is Wrong.
I am sure Joe 90 can put me right here.

 

[mysteryman]

I didn't see the programme, but have I understood this?

They are proposing to harvest helium on the Moon and bring it back to Earth? To save energy?

 

[EddieM]

you are indeed correct helium plus a neutron plus energy are the products of fusion of deuterium and tritium. deuterium and tritium are used rather than hydrogen as fusion of these isotopes of hydrogen occurs at a lower temperature.[/img]

 

[snico]

There is very little Helium produced annually from nuclear fusion.

There is a huge ammount of it on the moon, 25 tonnes of helium could power the US for a year.

 

[EddieM]

how does helium power things ? ah, looked it up, guess they are going on about helium 3 ?

 

[Hysteresis]

The programme must have been referring to Helium 3 although to be fair, I did not notice a reference to it, only Helium was mentioned.
I have to admit, the Helium 3 reactions are new to me and Good Old Wikipedia was very informative.
My formal education ended with the Deuterium/Tritium fusion process. The second and third generation fusion technology is very interesting although as elusive as the first generation (D-T) process.
Thanks for the education everybody.

 

[Space cat]

Most helium on the moon will be a product of radioactive decay, just like the stuff here on earth. Heavy radioactive nuclides, notably U235, U238 and Th232, emit alpha rays. (The name is historical because that 'ray' is a fast moving helium nucleus.) Those elements were made in one or more long-dead stars whose remains condensed into our solar system.

Most of the original U235 and about half of the U238 have gone - along with virtually all of a fourth nuclide, Np 237 - but there's still plenty left under your feet, slowly and quietly spitting out helium until it finally decays to bismuth or lead. The same thing is happening on the moon.

helium plus a neutron plus energy are the products of fusion of deuterium and tritium. deuterium and tritium are used rather than hydrogen as fusion of these isotopes of hydrogen occurs at a lower temperature

Although deuterium-tritium fusion is the easiest to achieve, tritium is a non-starter as a fuel because, with a half-life of about 12.5 years, it doesn't occur in nature. It has been made at huge expense for use in bombs and also for neutron radiotherapy. The first fusion bomb used lithium-deuterium fusion and, since we have plenty of lithium, this is the most promising mix for a fusion reactor.

how does helium power things ? ah, looked it up, guess they are going on about helium 3 ?

The sole advantage of using He3 for fusion is that you don't get any free neutrons, which are insidious things to have flying around. They pass through matter like a ball in a bagatelle game, sometimes bouncing off atoms and sometimes being captured - a process that can make the host atom radioactive.

The problem with He3 is that it's rare here on Earth (most of what we have has come from the decay of man-made tritium) and it's not particularly common on the moon either.

 

[Hysteresis]

Hi Space Cat,
My understanding that the Alpha Ray emission was the Nucleus of He4, but I believe the requirement for Fusion is He3. SO where does the He3 Come from?.
The Horizon program to which I originally referred talked of harvesting Helium from the Moon as there was an abundance of it there which was a product of the Solar Wind carrying it from the Suns fusion and not radioactive decay in the Moon itself. This Helium was not present on Earth due to the Atmosphere and Magnetic field.
The suggested harvesting from the Moon suggests that Helium is quite common on the Moon and presumably that source of Helium is He3 and not He4. I think it is He3 which is the form required for Fusion???
As you are from Newcastle, are you a graduate of Newcastle University as indeed I am? But my graduation was before any mention of second and third generation fusion. Do you remember Dr Littlefield and Dr Thorley if you were a Newcastle Physics Graduate of the 60's or 70's?

 

[Space cat]

I believe the requirement for Fusion is He3.

There are many possible fusion reactions, the simplest of which is H + H = D. This is the starting point for a star but it's difficult to achieve and doesn't produce much energy. The good news is that, for the foreseeable future at least, we can bypass this step because we already have plenty of deuterium sloshing around in the oceans.

For power generation, the aim will always be to make He4 which has an anomalously high binding energy for such a light element, so high in fact that it is not possible to make a stable nuclide with mass number 5 of 8. The logical reaction would appear to be D + D = He4 but, for reasons that elude me, it doesn't work. Maybe it's something to do with quantum numbers but the two possible outcomes of D-D fusion are He3 + n or T + H. As with H-H fusion, the reactions are difficult and the output is poor.

With so much hydrogen available in a star, the second step is D + H = He3 - hence the He3 in the solar wind - followed by He3 + He3 = He4 + H + H + lots of energy. He4 is so stable that it won't accept another nucleon and neither will two of them fuse together (beryllium needs a fifth neutron) so it's a sticking point in the life of a star - which is good news for us!

The interest in He3 fusion stems from the fact that it's aneutronic (no free neutrons). I think this preoccupation may be misplaced. Despite what I said about free neutrons above, they can be managed; they can even be put to good use for transmuting elements. (Fission reactors are awash with free neutrons and the early ones were built for the sole purpose of turning uranium into plutonium. ) Hydrogen (in the form of water) is a good neutron shield, it's plentiful and cheap and the neutrons turn it into deuterium. Neat huh!

The suggested harvesting from the Moon suggests that Helium is quite common on the Moon and presumably that source of Helium is He3 and not He4.

There is more He3 on the moon than we have here but it still doesn't amount to much. We would have to mine and process 150 million tons of moon rock to obtain a single ton of He3 then somehow bring it back. This link:

http://en.wikipedia.org/wiki/Helium-3

has loads of information on the subject. It sounds like a non-starter to me but a fusion reactor built on the moon is a different story. There would be no arguments with environmentalists and you wouldn't even need a vacuum chamber! If you want to build a starship, possibly powered by anti-matter, the moon is the place to start.

-- are you a graduate of Newcastle University --

Yes, but my first degree was in mathematics. Disillusioned with the jobs available to mathematicians - none of which I was prepared to spend a lifetime doing - I drifted into electronic engineering. (What actually happened was that I got a job as a lab technician at Newcastle Polytechnic (as was) and did the part-time degree in physical electronics.) The rest, as they say, is history.

 

[Hysteresis]

Yes, but my first degree was in mathematics.

Funny how careers develop. My first degree was in in Power and Electrical machines, went into the Fission Nuclear generating industry (Hence my interest in fusion) and then 'Drifted' into the oil industry after the decline in Fission Generation. I think we may all have taken different paths given another chance.