This is a followup to a prior question I asked about gaseous nuclear fission. What is the lowest nuclear fuel density required to initiate fission? This is critical for a gas core reactor with a solenoid magnetic bottle containment system in terms of how strong the magnetic field should be keep the fuel at a high enough density to trigger fission. Of course, the reactor vessel would be a cylinder with an inner jacket made of beryllium to reflect neutrons back into the core.
There is always something new to learn from the questions here.
These gaseous reactors are being studied
The document is in PDF and is hard to copy figures, but, the gases used are :
Density does not have much relevance for gases, it is the temperature pressure curve that is important at page 9 and it seems to work from quite low pressures up to tens of atmospheres .