More On Burevestnik

This is really down in the weeds, but I think there are a half-dozen or so readers who will be interested.

Last night, Decker Eveleth, who identified a possible Burevestnik launch site, asked me about a quote. I was in the middle of watching the Harris-Trump debate, so I said I’d post something later. This is that something.

First, the quote:

The primary issue with this discovery is that a nuclear-powered cruise missile is hardly possible, with the main obstacle being physics. A nuclear reactor cannot be light-weight and compact enough to fit on a missile with all the cooling and control systems necessary to provide sufficient power for both a missile engine and onboard equipment. This would mean that the Kremlin is either conducting a strategic psychological operation to convince the West that it has developed disastrous nuclear weapons other than intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and old-fashioned strategic bombers, or it believes in these mythical technological theories and is spending Russia’s limited intellectual and financial resources on their research and development—good news for the West if true.

This is from an article by Pavel Luzin that Eveleth says also makes no sense about its interpretation of the site.

In my previous posts, I haven’t gone into detail on the necessary tradeoffs to design a nuclear rocket, although I might have done a bit of that in my large 2018 post. I’ll do that here.

Luzin makes several strong claims in that paragraph. They are similar to things I’ve said, but he goes further. I have been more cautious about saying that such a reactor cannot be built, because I am not an engineer and have been impressed by the creative solutions that engineers come up with. But yes, a nuclear rocket engine faces many constraints. I’ll discuss them quickly, without the links I might have wanted to supply, but that 2018 post contains many of them.

The Nuclear Reactor. Any propulsion system for a missile must trade power and weight. Nuclear reactors are heavy for what they are, and they do not supply power as rapidly as do chemical systems. They also have size requirements related to power and criticality. Make the system too small, and it may go critical when you don’t want it to, in a deadly burst of neutrons.

The photo at the top of the post shows a missile whose diameter is very small for a critical system. The Rover reactor was about four feet in diameter and four feet long. The fuel was weapons-grade U-235 in a graphite matrix. I don’t have a dimension for the Tory reactor of Project Pluto; that fuel was a uranium-beryllium oxide, probably with the uranium enriched to weapons grade. Incidentally, I’d love to know where and how that fuel was fabricated.

Criticality control in the Rover reactors was by a rotating reflector outside the core. The design did not allow for control rods. It has occurred to me that the 2019 Burevestnik accident could have been a result of a reflector accidentally moving into a position where it caused criticality, sort of an inadvertent KIWI-TNT experiment.

Of course, we don’t have any firm information about the design of the Burevestnik reactor. All we can do is compare it to Rover and Tory. Recently, a new design for US space nuclear reactors was released. It is very small and, IIRC, made of uranium metal, probably highly enriched. But such reactors are for electrical power for satellites, which is a much lower requirement than for propulsion. Additionally, they would need a heat exchanger.

Propellant and Heat Transfer. A propulsion system depends on expanding hot gases. The reactor supplies that heat. The easiest way to do that (Reader, it is not easy) is to send the gases through the reactor. That means that the reactor must have holes through which the gas passes. That means a larger diameter than a reactor without those holes. During the discussions of Burevestnik a few years back, there were suggestions of a compact reactor with a heat exchanger. But a heat exchanger is additional weight and space requirements, and it slows down the heat flow. I never did see a proposal for a heat exchanger beyond words.

Here is a cross-section of fuel elements for a space nuclear propulsion reactor. The report that it is from considers how small a reactor might be. I haven’t read it yet. A quick scan suggests that “small” is in the range of a Rover reactor.

Bottom line: If the partly covered object in the photo is a Burevestnik, as the Russians have claimed, they have achieved some remarkable things in nuclear rocket design. The problem with that is that we would likely have heard some things about the engineering or, say, fabrication of Be-U oxide if they had. No such information has leaked, which could indicate tight security or that there are no remarkable things. I would not say that a nuclear-powered Burevestnik is impossible, but I would want more information than we now have.

A Strategic Psychological Operation. I had thought of this only in terms of an Edward Teller-like scientist convincing Vladimir Putin of his pet project, but it could be that Putin is in on it and trying to scare the West.

Cross-posted to Nuclear Diner