In some prior speculation about the possibility of designing an environmentally acceptable and safe uranium fission reactor, which employs direct thermal to electric conversion and depends on "makeup" neutrons in the form of fully shrunken hydrinos, an idea was present by Robin van Spaandonk which is intriguing in the context of a particular manufacturing technique. Robin writes,
"It seems to me that the overall efficiency would be higher if you just used the electrons freed by the fission fragments directly [snip] This avoids losses involved in producing coherent light, and in transferring the energy of that light to free electrons." At first, this idea seemed attractive but did not seem possible in actual practice... at least not for the situation were a high multiplication ratio in a subcritical reactor must be maintained using only natural uranium. Even if several pounds of hydrinos can be produced in situ per day and an acceptable percentage of those result in virtual neutrons, one would still need several thousand pounds of unenriched uranium to achieve a high multiplication ratio. How do you get that much uranium thin enough and still use it as a cathode? Here is the Energy (in MeV) distribution in typical fission reactions Kinetic energy of fission fragments 161 MeV Prompt gamma 9 Kinetic energy of fission neutrons 8 Delayed Gamma (fission products) 8 Beta decay of fission products 7 Antineutrinos 7 total 200 MeV per fission The fission fragements are both around half the mass of the original uranium, therfore even with about 80 MeV each, they will not travel far in a solid fuel rod. I would suspect the the free-path would be submicron. If one wanted to engineer a situation where a substanial number of the fragments (or at least the electrons displaced by them) were to be able geometrically to actually exit the cathode of a thermionic fuel rod, then the prospect looks hopeless... at first it did anyway. How does one convert several thousand pounds of natural uranium into a form thin enough but with structural integrity for use in a thermionic situation at 2000 K or higher ? Here is a partial answer based upon a particular manufacturing techniuqe... which is close to some which are in use today in metal fabrication factories, but is not itself exactly like anything which has been done before. First, realize that pure U is very malleable and ductile, bur very reactive with O2. It can be rolled as thin as aluminum foil and stamped using common metal working equipment so long as this is done in a very dry and O2 reduced environment. IOW it is difficult but not impossible. It can then be easily anodized or nitrided into a very heat resistent ceramic, using normal nitriding techniques. This alos binds the layers into a structural unit. In mass production, therefore, one can imagine that a tubular cathode of U ceramic with a high porosity can be manufactured ( 70-90 % porosity and not just random porosity, but micro-channeled so that all the channels are aligned radial to the fuel pipe axis. It would involve rolling, stamping, stacking and annodizing very thin disks of uranium robotically. The resulting cathode pipe would have porous channels all radiating out from the central axis in the direction of an accelerating grid but OTOH it would also be a one-piece heat resistent structural cathode. What this might allow, in terms of added efficency could be very promising... but who knows... The $64 question is - in a geometry in which a high proportion of all fissions result in the expelling of ballistic electrons, due to the kinetics of the fission fragments, can this be highly efficent even without high-probability coupling of the emitted electrons to semi-coherent IR from the fuel pipe? I don't think any of the garage experimenters on vortex are equiped to find out the answer, but I wonder if the "not invented here" syndrome extends all the way throught the entrenched nuclear bureaucracy? A curious note. Uranium is the second most dense element, so even if it is manufactured in a form with a porous solid with a gazzillion aligned microchannels, so that it has a porosity of say 85% (IOW 85 percent open space and 15 percent cermet) it will still be as dense as solid aluminum. Jones
