So here's a mystery. I was skimming an old AEC list of reactor proposals for article ideas, and I came across an entry for a reactor called "BRENDA", that was going to be built by the Societe Nationale D'Etudes et de Construction de Moteurs D'Aviation (SNECMA) and the Commissariat à l'Energie Atomique (CEA) in Cadarache, France. The reactor was gas-cooled, used ceramic-clad enriched uranium oxide fuel, and would be moderated by beryllium oxide. 1 MWth power, 1300 F temperature. Purpose: aircraft propulsion prototype.
Now that's certainly something.
Part of what makes this really interesting is that the document claims they had actually started construction, although they didn't finish. Plenty of countries did paper studies of A-planes, but I had previously thought only the US and USSR had actually produced any hardware. The question naturally arises, was this real or just a bizarre typo?
The original document didn't have any more details, but I found an article in a trade journal indicating that BRENDA was cancelled in 1958 after tests of the hot-pressed beryllium oxide moderator revealed it powdered when exposed to high radiation and temperature. (Kronberger, H. "The Role of Dispersed Fuels in the Further Development of the Advanced Gas-Cooled Reactor." Journal of Nuclear Materials, Vol. 14 (1964), pp. 41-48.) I also found another article from 1959 saying they still hoped to get the machine to work, possibly by switching to a graphite or water moderator. ("The Plan at Half-Time". Nuclear Power, Vol. 4, April 1959, p. 82). I also found it in a list from the second UN Peaceful Uses of Atomic Energy conference in 1958, which claims its power output was actually going to be 12 to 17 MWth.
None of these three articles say that this was an aircraft reactor, nor they do they say that they had actually started construction. They also, however, don't say that it wasn't going to be an aircraft reactor.
Finally, I found a fourth article, a paper from a UN conference in 1961. The article doesn't mention BRENDA specifically (except in the abstract, and it says nothing there), but there is a section that appears - at least through Google translate - to indicate they were examining the use of beryllium oxide as a moderator in gas-cooled reactors for maritime propulsion. (Parker, E. "Etude D'une Filiere de Piles a Moyenne Temperature Utilisable pour la Construction de Centrales a Moyenne Puissane." Small and Medium Power Reactors, Proceedings.) But this was 1961, after BRENDA was no longer a live option, so the fact they don't mention aircraft propulsion may not mean anything. I've found other mentions here and there but nothing with any further information.
I think the claim the reactor was actually under construction was probably incorrect. The choice of moderator material is a pretty important design consideration, so if that hadn't been nailed down yet, then they probably weren't ready to actually build the thing
Whether it was really supposed to be an aircraft reactor I'm on the fence about, but leaning against. It's at least somewhat plausible that someone at the AEC read an article calling BRENDA a "propulsion reactor", noticed it was being designed by a group with "aviation" in the name, and assumed it was for airplanes. However, I haven't found anything else saying specifically what it was for, and beryllium oxide and uranium oxide ceramic are what you would want to use in a direct-cycle atomic turbojet. Although they were used in a few other reactor concepts as well, e.g. the AEC's Experimental Beryllium Oxide Reactor. From searches on the Google patent server, it does seem SNECMA had an interest in nuclear energy, but all of these proposals seem to be of the terrestrial variety. So at this point I just don't know, but I think the odds are in favor of BRENDA being a maritime propulsion prototype that was misunderstood by someone in the US. It's terribly tantalizing, though.
If I find anything more, I'll post it, but at this point I've exhausted my usual methods. I don't really have any good sources for French atomic energy stuff, and I'm sadly monolingual. If you have any suggestions - or know what the real story of BRENDA is - please let me know in the comments.