Reply To: Barack Obama on Energy

[Brian H]

Axil wrote:
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A good neutron moderator must efficiently thermalize colliding fast neutrons. This thermalization process occurs by neutron-nucleus elastic collisions. It can be shown from a simple consideration of Newton’s laws that maximum energy loss per collision occurs when the target nucleus has unit mass, and tends to zero energy loss for heavy target elements. Low atomic weight (Z) is thus a prime requirement of a good moderator. The maximum energy is always lost in a head-on collision. However, elastic collisions occur at many scattering angles, and thermalization takes place over numerous collisions. Therefore, a useful quantity in characterizing the scattering properties of a moderator is the average logarithmic energy loss per collision, E, which is independent of energy. Values of E and n, , the average number of collisions to thermalize a 2 MeV fast neutron to 0.025 eV, are given as follows:

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But you’re using that bad word: thermalize. When you’ve got your heat, then what? You must run it through a steam generator, and you’ve just reversed a primary advantage of FF: no boilers and turbines!
Also, you’ve introduced that horrible concept of a containment vessel and its walls, with all the associated mass, expense, and materials degradation issues that implies.

The FF idea is to avoid neutron and heat flux, not maximize and exploit them. I get the image, when talking of FF “hybrid” designs, of turning a sportscar into an armored vehicle. Possible, but it makes for a lousy sportscar and worse armored car.