MadSci Network: Physics

Re: Is Neutron Fusion Feasible / Practical

Date: Thu Dec 21 21:49:02 2006
Posted By: Tony Gaglierd, Assistant Professor , Natural Science and Engineering Technology
Area of science: Physics
ID: 1166657051.Ph

Hi Jeremy.

You asked is Neutron fusion feasible or practical.

There are many different nuclear fusion reactions occurring in the sun 
and other stars, but only a few such reactions are of practical value for 
potential energy production on earth.

The easiest fusion reaction to make happen is combining deuterium with 
tritium to make helium and a neutron. 

Deuterium is plentifully available in ordinary water. 

Tritium can be produced by combining the fusion neutron with the abundant 
light metal lithium. 

The "D-T" reaction has the highest reaction rate at the plasma 
temperatures which are currently achievable; it also has a very high 
energy release. 

These properties make it the easiest reaction to use in a man-made fusion 

The proton-proton chain, the reaction process is the dominant fusion 
mechanism in light stars, including our sun. In the P-P chain, two pairs 
of protons fuse, forming two deuterons. 

Each deuteron fuses with an additional proton to form helium-3.

The helium-3 nuclei then fuse to create beryllium-6, which is unstable 
and disintegrates into two protons plus a helium-4 (alpha particle). 

In addition, the process releases two neutrinos, two positrons, and gamma 
rays. The positrons annihilate quickly with electrons in the plasma, 
releasing additional energy in the form of gamma rays. 

The neutrinos interact so weakly that they fly right out of the sun 

The p + p => D reaction rate coefficient in the sun is much lower than 
that achievable with a deuterium-tritium fuel mix. A proton in the sun 
will exist for an average of billions of years before it fuses. 

By comparison, a deuteron in a magnetic fusion power plant would only 
exist for about 100 seconds, and a deuteron in an imploding, fully-burned 
inertial confinement pellet only for 1.0E-9 seconds.

Neutron  Neutron fusion dose not appear to be feasible at any time in 
the near future. Though it is theoretically possible in the laboratory 
the main problem is that it suffers from an unattractive power balance it 
consumes significantly more power than it produces. So for now magnetic 
fusion research has focused on systems that produce a high fusion gain, 
producing more power than they consume.

The difficulty in producing fusion energy has been to develop a device 
which can heat the deuterium-tritium fuel to a sufficiently high 
temperature and then confine it for a long enough time so that more 
energy is released through fusion reactions than is used for heating.

I hope this answers your question.


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