[ RadSafe ] Absurd? Oh, the irony!

[Dale Boyce]

This isn't quite correct, or rather it is incomplete. Proton-proton fusion 
is rate limited by the weak reaction since the strong force is insufficient 
to make He2 stable it must simultaneously beta(positron) decay to deuterium 
at the time the "fusion" occurs.  However, all of the energy release in p-p 
fusion is from the strong force, and is equal to the binding energy of 
deuterium minus the energy that goes into the positron and the neutrino. You 
have to subtract the decay energy in this case because you have to "make" 
the positron and neutrino and the only energy source to do this is the 
released binding energy of the proton and the neutron that make the 
deuterium.

It is believed that in the innermost part of the sun the carbon cycle 
dominates the energy production. However, outside that zone the p-p, p-d, 
and He3-He3 -> He4 +2p and so on dominates.

I agree that in most fusion reactors or bombs we start with different fuel 
than in the reactions that take place in the sun.  However, almost all of 
the energy produced is due to the strond interaction. Even at its very basis 
the energy from the weak force decays comes from the strong interaction. The 
energy in beta decay is due to the difference in the strong interaction 
between neighboring isobars.

On the subject of radioactive waste from fusion reactors, one would expect 
it to be similar to that produced by low energy proton accelerators scaled 
by the relative power (input in the case of the accelerator, and output in 
the case of a fusion reactor).  I say this because in low energy proton 
machines very few things actually see the protons as they get stopped very 
quickly in the machine components. You get 1 or 2 percent of the proton flux 
appearing as neutrons from the nuclear reactions that take place. So there 
is another fudge factor to consider in scaling from the accelerator side.

Now from the fusion side. A lot of fusion reactions do not produce neutrons. 
What fuel is being used to produce the neutrons we are hearing about? 
Depending on the fuel, neutron yield could be very low. This leads to a 
fudge factor on the fusion reactor side of the equation. In fact producing 
neutrons is probably detrimental in a fusion reactor. It means you lose 
several MeV of the binding energy of the neutron in the reaction.

We tend to think of neutrons being important from the weapons concept where 
the fusion fuel needs to produce high energy neutrons for a ternary device 
to work.

Dale

daleboyce at charter.net


----- Original Message ----- 
From: "Franta, Jaroslav" <frantaj at aecl.ca>
To: "Radsafe (E-mail)" <radsafe at radlab.nl>
Sent: Thursday, June 30, 2005 10:22 AM
Subject: Re: [ RadSafe ] Absurd? Oh, the irony!


> >As a public issue, quantities are apparently irrelevant.
>>So I don't see the difference between fusion
>>and fission radioactive wastes as a public issue.
>>This is a strange world we are dealing with!
> =============
>
>
> Indeed !
> The public issue appears instead to be that ITER "seeks to mimic the way 
> the
> sun produces energy," or "reproducing the sun's power source" (warm & 
> fuzzy
> image), while NIF & other inertial confinement fusion schemes "simulate
> fusion reactions that occur in hydrogen bombs" (horror!) -- and of course
> fission reactors "split atoms, like A-bombs."
> In fact, our fusion reactors are very much UNLIKE the sun, in both 
> operating
> conditions and fuel type, fusion marketing propaganda notwithstanding.
>
> Fusion reactors and the Sun don't even operate on the same physical force,
> and there aren't any D-D or D-T reactions in the Sun -- both accounting 
> for
> the fact that the Sun burns for billions of years, instead of blowing up.
>
> The Sun *depends* on reactions using the weak nuclear force, while 
> reactors
> & bombs use fuels that can be fused quickly & relatively easily using the
> strong nuclear force only.
>
> In his seminal book "Principles of Stellar Evolution and Nucleosynthesis,"
> Donald Clayton writes concerning p-p fusion that the weak nuclear
> interaction is so exceedingly rare, that the deuterium (D)  that has been
> formed never actually encounters another D.
> As Clayton explains, "after the deuterium has been formed [in the p-p
> fusion], one could imagine that He-4 might be produced by the reaction D + 
> D
> --> He-4 + u.
> This reaction, however, suffers from..... the fact that the deuterium
> abundance is kept very small by its interaction with protons [in the
> reaction D + p --> He-3 + u, following which the helium nuclei fuse
> according to He-3 + He-3 --> He-4 + p + p ].
> .....That these are the major reactions comes about because..... D can 
> build
> up only to a very small abundance." [ie. two Ds never bump into each other
> in the sea of protons....]
>
> According to
> http://www.shef.ac.uk/uni/academic/N-Q/phys/people/vdhillon/teaching/phy213/
> phy213_fusion3.html , "This [p-p] reaction occurs via the weak nuclear 
> force
> and the average proton in the Sun will undergo such a reaction 
> approximately
> once in the lifetime of the Sun, i.e. once every 10 billion years" (the
> sun's life) ...this in spite of the fact that the protons undergo
> approximately 10 billion collisions per second with other protons in the
> solar interior.
>
>
> Jaro
> ^^^^^^^^^^^^^^^^^^^
>
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