Speculations on the Nenoksa Explosion

On the morning of Thursday, August 8, something exploded at the Nenoksa Naval Base in Russia, not far from the city of Severodvinsk. This article is a good summary of what we knew by Friday. Since then, the Russian government has said that a radioactive source was involved in the explosion, along with liquid rocket fuel. Reports have gone back and forth on whether radiation detectors in Severodvinsk detected anything. Five more people have been reported dead. Sarov/VNIIEF, one of the Russian nuclear weapons laboratories, has released a statement, which some folks are rushing to translate.

Update: Sarah Bidgood has translated the video. Here’s the start of her thread. No additional information about what was being done.

Here are some things that we know. Jeffrey Lewis and the OSINT group at MIIS are doing a good job with the small amount of information we have. I mostly agree with them, although I tend to be slightly more conservative in my confidence in the interpretations. They are publishing mainly on Jeffrey’s Twitter feed. Here’s a recent thread.

Almost exactly a year ago, when Burevestnik was announced, I wrote up what the United States had done with nuclear rocket and cruise missile engines. I saw the Rover program up close and personal and knew a number of people involved in it. One of the conference rooms I used had an unloaded Rover fuel element to be used as a pointer. Fun.

On Twitter, I’ve been a bit of a naysayer. I’m not disagreeing that Russia is testing what they believe will become their Burevestnik. I’m saying I think they’ll never have an operating system.

I think that what has happened is that someone sold a program to Putin. The visuals are cool, and the idea of a cruise missile that can just keep cruising obviously appealed to him. “Nuclear-powered” sounds good. The promoter of the program may even believe in it.

Programs have been sold this way in the United States. We are still working on the missile defense that Edward Teller bamboozled Ronald Reagan into. I recall a Labor Day weekend in which the proof test for laser isotope separation was to be completed. It wasn’t. People get overenthusiastic about their ideas or just are selling something they think would be fun to work on or to make their status higher.

But there are basic and fundamental engineering considerations that suggest that a nuclear-powered cruise missile with a very small power source, will be very difficult or impossible to build.

All flying machines trade off between power and weight. Nuclear reactors have another couple of tradeoffs, between size and critical mass and between ways to do heat transfer. With the announcement that a radioactive source was involved in Thursday’s explosion, speculation has swung to the many isotopic thermoelectric power sources. But they are not powerful enough for propulsion.

Burevestnik is supposed to be a ramjet, which means that it takes in air, heats it, and rapidly expands it out the back for propulsion. That was how the Tory reactor of Project Pluto worked. The Rover reactor, which was designed to operate outside the atmosphere, used hydrogen as a propellant gas. More details about both in my earlier post.

The reactor heats the propellant gas. That requires a fair bit of area between the heat source (reactor) and the gas. Tory and Rover accomplished this by having fuel elements with holes through them, aligned so that the gas could come in one end and go out the other. The gas went through the reactor.

The reactor could be small and transfer heat to the gas via a heat exchanger, possibly two heat exchangers. Jeffrey Lewis sent me a patent from 1979 (actually 1965, but declassified in 1979) that describes such a system. I doubt that this system was ever built, although there are some tantalizing details that suggest that some parts of building it were looked into. However, not much is said about the heat exchangers, nor the fluid that would be used in them. Since the patent is for a fast reactor, it is tempting to believe that the primary heat exchange fluid would be sodium.

[Update (8/16/2009): I read the patent incorrectly. It is a flowthrough design like Tory and Rover. But the discussion about compact reactors, if one is proposed, and heat exchangers still stands. For more, see here.]

When you are concerned about weight, as a cruise missile designer must be, the places to look in these designs would be the moderator and reflector for the reactor. Highly (above 90%) enriched uranium is the only possible fuel; plutonium is too hard to handle, and lesser enrichments add too much weight. The moderators in the Tory and Rover reactors also served as structural elements.

The air gaps in a Tory-type reactor require more fissile material than a solid reactor would for criticality. A reactor with external heat exchangers requires less fissile material, but the heat exchangers are additional weight.

Some of the smaller reactors now being developed for space applications have been suggested, like the KiloPower reactor. But, like the isotopic thermoelectric sources, these small reactors are for electrical power generation. They must be bigger, and therefore heavier, to provide the power necessary for propulsion.

The Tory and Rover reactors, in their containers with subsidiary equipment, were around ten feet long and 3-4 feet in diameter. The 1979 patent doesn’t give dimensions, but they would likely be similar. That’s small for a reactor, but larger than photos of the Burevestnik suggest. Here’s one for comparison.

800Burevestnik-nuclear-powered-cruise-missile

Both liquid propellant and a radioactive source are mentioned in Russian government press releases. It is not clear how these come together for cruise missile propulsion. A nuclear reactor could not get a cruise missile off the ground, and a chemical engine would be needed for starting (more weight), but solid fuel was previously mentioned for Burevestnik. This is where we might go back to the possibility of a sodium coolant.

What if the Russians found a big breakthrough? I’ve been thinking about this for a year or more, and I can’t come up with anything that makes sense. I don’t see a way around the constraints – heat transfer requirements, critical mass – and nobody has suggested one.

Unless it’s red mercury. Or cold fusion.

 

Cross-posted to Balloon Juice

18 comments

  1. Jones · August 11

    Just a couple of thoughts, and a slightly expanded background. Your scepticism of the packaging size of SKYFALL is well founded. Project PLUTO-Vought SLAM was a silo-launched, ICBM-sized weapon with a payload of some 16-28 lay-down five megatonners. It used a direct cycle ramjet with a hex cell ceramic reactor core built by Adolph Coors.
    It was huge. it was to cruise at M=3-3.5 @ 100ft on a terrain-matching guidance system. It’s shock wave and exhaust plume were well up in the lethal range; after expending it’s primary load, it would continue to trail destruction until something broke. The problems in just testing one are apparent, and help it’s merciful demise along.
    The other air-breathing ANP were direct and indirect cycle versions of extant gas turbines, also very large bit’s of machinery sized for large aircraft.
    Our Hot russian friend here has a very subsonic airframe, sized for existing tubes.It pretty much has to be an air-breather, I don’t see room for a worth-while reaction-mass.
    A semi-informed guess says they’re noodling an RTG with lots of juice on tap, X-ray pumped Hafnium has been punted around, but, what ever. All they have to get is the calorie equivalent of X pounds of jet fuel/hour.
    If and when anybody talks about what comes up radiation monitors will be a helpful clue about the nuts and bolts.
    The ‘Why On Earth Are They Doing It’ is, as you noted, somebody’s air-starting Vlad, and the blat is reaching the right pockets.

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  2. Raybender · August 11

    Didn’t the USA work on a fast-reactor-powered turbojet (J87)? You seem wedded to the idea of a secondary loop with something like sodium. Why not just run air through the core where it gets heated? You may (turbojet) or may not (ramjet) have compressors and turbines wrapped around that core. Seems physically plausible at least, if not particularly sane…

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    • Cheryl Rofer · August 11

      Clearly you haven’t read the post.

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    • ajay · August 12

      From the post, it seems that you have a choice: either you run air through your reactor (direct-cycle) in which case you need a big Tory-size reactor, or you run air through a heat exchanger (indirect-cycle), in which case you can have a smaller reactor but you need a separate heat exchanger (and some sort of working fluid such as sodium). The post implies that the Burevestnik airframe is too small to hold a Tory-size reactor. Hence assumption that it is the smaller though potentially heavier indirect-cycle approach.

      The experiment you’re thinking of was the GE Heat Transfer Reactor Experiment-3 (HTRE-3) which used a couple of J47 turbojets ducted into the core of a reactor (direct cycle). P&W tried an indirect-cycle approach around the same time but didn’t get as far as testing.

      The reference to a “liquid propellant” could mean that they’re launching it up to ramjet speed off a liquid-fuelled booster (because why not strap your experimental nuclear ramjet cruise missile on top of a couple of big tanks of, ooh, nitrogen tetroxide and unsymmetrical dimethylhydrazine WHAT COULD GO WRONG?) and the booster blew, as liquid boosters tend to, up. I don’t think it can mean a liquid propellant for the nuclear stage because that’s a Rover engine and running a Rover engine in atmosphere is just daft.

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    • ajay · August 12

      “The reactor could be small and transfer heat to the gas via a heat exchanger, possibly two heat exchangers. Jeffrey Lewis sent me a patent from 1979 (actually 1965, but declassified in 1979) that describes such a system”

      I am not a reactor engineer but that patent doesn’t seem to involve a heat exchanger – the air flows directly through the reactor core. The words “heat exchanger” only appear twice in the patent and in both cases they seem to be describing heat exchange between the reactor and the airflow.

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  3. gosnold · August 12

    Interesting. What makes you think highly-enriched molten salt reactors, like Space Molten Salt Reactor (https://therestlesstechnophile.files.wordpress.com/2018/03/eadesjbis2011.pdf), would not make this technology possible? The authors claim it can deliver 7MWe in a 300kg package (reflector included).

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    • Cheryl Rofer · August 12

      This is getting into the range of possibility. But nuclear electric propulsion can only be used in space. So the reactor would have to be used with a heat exchanger as I discuss in the post.

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    • ajay · August 13

      7 MWe of electricity would power quite a punchy ducted fan engine. Basically you’re building an enormous jet-powered electric RC aircraft.

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    • ajay · August 15

      And hey, according to this thread https://twitter.com/sovietologist/status/1161856776603443200 the Soviets were researching indirect-cycle turboprop aircraft right up to the 1970s.

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  4. gosnold · August 12

    Indeed, making the heat exchanger work with a low mass and volume would be tricky.

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  10. BLVCK NVTIXN · September 2

    Excellent 😉

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