Talk-Polywell.org

I was hoping someone here could answer a question for me (which in turn would allow me to explain this to someone else.)

What exactly is the major benefit of using Boron (PB-11) as a fuel?

Or, to phrase it the way my friend asked,
"Doesn't it run on hydrogen?"


Could a BFR use both?



Please forgive my ignorance in advance.

Read the following FAQ. It is basic, but valuable.


http://www.ohiovr.com/polywell-faq/inde ... l_ideal%3F

Didn't see that.



Danke.


Not answered on the wiki: Which would be a better fuel for long-term space flight, a D-T or PB-11 reaction? (lol)

Seriously, anyone got thoughts on this?

PB11. The weight of the boron is rather inconsequential, and the neutron flux is much smaller, meaning much less shielding, which is consequential weight. Of other interest are the He3 reactions, which would allow easier scavenging of fuel. Not sure how much boron is out there, but we know that there's a fair amount of He3. D+T could be scavenged, but again, we also need to look at the neutrons.

Aside from the neutron issue, P-B11 fuel has the advantage that practically all of the fusion energy produced is carried by charged particles, which allows for direct energy conversion at high efficiencies (~80%). D-T and D-D reactions also produce charged particles, but onlly ~ 50% of the energy is in this form. The rest is in neutrons. Also, the charged particles from these reactions have a wider range of kinetic energy- increasing the difficulty of direct conversion. The energy in the neutrons not only cause more radiation concerns for the crew, they damage structures, and produce more waste heat (per unit of usefull power obtained). Waste heat is a major concern for a spacecraft. At least some of the heat energy deposited from the neutrons can be recovered through thermocouples, or a heat engine (steam or sterling type engine), but these are far less efficient (more waste heat) than direct conversion.
As a hypothetical comparison. A P-B11 reactor might produce 1.2 GW raw power, and deliver 1 GW usefull power. A D-D reactor would need to produce ~ 2 GW of raw power to deliver the same amount of usefull power. That means the P-B11 reactor can be half the relative size (help to offset the increased difficulty of fusing P-B11) and ~800MW less waste heat would need to be handled. In some regards the D-H3 reaction would be superior to P-B11 (more energy per reaction, easier to fuse, perhaps easier direct conversion, neutron load is much worse than P-B11 but much better than D-D or D-T) except that the difficulty and cost of obtaining He3 is daunting.

Dan Tibbets

Thank you, Dan and Kunk.

Actually, H3 is easy to get. Start with 10 tons of moon dust, ...

Yeah. Copper is easy to get too. Start with ten tons of ore...