I read some of the old United Aircraft Corporation reports about the nuclear light bulb reactor the other weekend. The design parameters are delightfully extreme. You can see why it wasn't tested in later years. By the 1970s there was already much diminished tolerance for experiments that ejected fission products into the environment, and effective release prevention for testing this design would be expensive.
Here's one of the reports, from 1969: https://core.ac.uk/download/pdf/85241637.pdf
Some highlights from this report:
- The fully gaseous core would operate at a pressure of 200 atmospheres. This is somewhat higher than the pressure in a pressurized water reactor core.
- The vapor/plasma fuel temperature would be 42000 Rankine. That's about 23300 Kelvin, roughly 4 times as hot as the surface of the Sun.
- The fiberglass pressure vessel was projected to last about 6000 seconds (100 minutes) of full power operation before its strength was compromised by neutron irradiation.
- The preferred fuel was uranium 233, which does not exist to any considerable degree in nature. It has to be bred from thorium. Since U-233 never had significant use in civil or military nuclear applications, the US has not produced any U-233 since the 1980s [1]. Highly enriched uranium 235 or plutonium 239 would also work, just not as well. All fueling options needed "bomb grade" fuel purity. That was the only way to make the reaction zone so compact.
Other details that I recall from other reports -- sadly not ready to hand:
- Later iterations of the design kept thinning the quartz envelope to maintain adequate transparency to UV radiation after accounting for color centers induced by radiation damage. This required aggressive/optimistic estimates of how perfectly pressure could be equalized on both sides of the envelope, particularly during start-up.
- The optimal core fuel temperature would have been even higher except that it was difficult to find materials that would be adequately transparent to even shorter ultraviolet radiation.
- Fission products were supposed to be separated from the fuel centrifugally before the fuel recirculated into the reaction zone. This seems chemically optimistic to me.
- There was little consideration of chemical factors in any of the reports I read. Given that the environment was extremely hot, rich in fluorine, and would soon contain most elements of the periodic table from fission products, this seems like an oversight. One that would probably be testable only by actually building and operating test reactors.
[1] https://www.world-nuclear.org/information-library/current-an...