Russian Nuclear Cruise Missile Accident Analysis; Reverse Engineering 9M730 Burevestnik

See Russia Lies About her Flying Chernobyl. The lying continues with (CNN) Russia nuclear monitoring stations go quiet after blast.

The reason is obvious: iodine-129, a tell-tale fission byproduct, was detected. Additional isotope information could make it possible to determine how the reactor core disassembled or exploded. It may be possible to classify the reactor type, which I expect to be molten salt. This could make a political issue for the  political opposition, who may be displeased with the semi-permanent contamination of “Mother Russia” by repetitive mini-Chernobyls with a ridiculous military rationale.

The iodine-129 contamination points to a reactor core that

  • was operating at the time.
  • may have contributed explosive force.
  • may have been the origin of the explosion,  rather than the amplifier of a chemical rocket accident.

As with Russia’s Hypersonic Missile; Reverse Engineering Secrets of Avangard, we are limited to open source, which includes the declassified Project Pluto proposal. The goal of  Project Pluto was to develop  a nuclear ramjet to power SLAM, the Supersonic Low Altitude Missile. It was every bit as evil as the current Russian project.

The Project Pluto ramjet was proof-of-concept, not a flyable engine. As with Russia’s Hypersonic Missile; Reverse Engineering Secrets of Avangard, we make assumptions that have a decent chance approximating the truth, based upon the similar problem solving skills of Russians and Americans:

  • The U.S. report describes  what is definitely possible.
  • The Russian nuclear ramjet is contained by what is possible.
  • So the U.S. report has some descriptive value for the Russian device.
  • Since half a century has elapsed, the Russian device is more advanced than the Project Pluto device.  Compared to a chemical engine, the power-to-weight ratio of Pluto was lousy.

The declassified Pluto ramjet proposal, with extensive design data, is (pdf, download) Tory IIA; A Nuclear Ramjet Test Reactor. It is likely that the Russian device is an improvement. The Tory-IIA was a massive device, weight > 20,000 lbs, mounted on a railroad flatcar.  A conventional cruise missile fan-jet engine weighs less than 100 pounds.  A miniaturized engine, requiring a miniaturized reactor, is highly desirable.

Some background info:

  • Critical mass is the minimum size/weight/shape of a lump of nuclear fuel that can be caused to chain-react. It’s not a fixed number. By surrounding the fuel with a neutron reflector, the weight/size of the reactor core can be reduced. There is no hard minimum size, only a bunch of practical considerations that make shrinking the core progressively more difficult.
  • The Tory IIA contained 71kg (157 pounds) of uranium -235, and 18,800 pounds of beryllium oxide moderator. The  stated power goal, as heat, is (page 41) 15 megawatts. In  Tory II-A: a nuclear ramjet test reactor, the stated goal is 160 megawatts.
  • Replacing the combustion heat of a conventional engine, the Tory  IIA heats incoming air to 2000F, via hollow tubes 4.5 feet long. The long narrow tubes create huge internal drag, a major drawback of the design. The Russian design likely innovates.
  • The Tory design had  a design lifetime of  somewhat more than a week. A shorter design lifetime facilitates miniaturization , while dangers accrue.

Critical mass is not a limitation in miniaturizing a reactor. Heat dissipation is. Melted fuel can still produce atomic energy, but the containers that hold it tend to fall apart. Miniaturization is limited by

  • Heat transport, how efficiently heat can be removed from the core to heat the air.
  • The usual requirement that the fuel not melt. Pluto was limited to 2000F by solid fuel.
  • If molten fuel is used, higher temperature reduces life of all the parts.  As far as performance goes, hotter is better.

So with 9M730 Burevestnik, the Russians innovated. A hypothetical list:

  • Ditch the 18,800 pounds of beryllium oxide moderator.  Pluto is a thermal-neutron reactor. The Russian gadget is a fast reactor.
  • Liquid fuel, a molten salt, facilitating heat transport. The Russians make a specialty out of molten salt reactors, which are handy for isotope synthesis.
  • A “secret material”, a new ceramic, to contain the molten fuel, retaining integrity at higher temperatures than thought possible, with high thermal conductivity typical of metals.
  • Alternatively, a way to quench the chemical reactivity of the air stream. Gas phase electrodeposition?
  • Advanced geometry. Pluto had immense internal drag compared to a chemical engine.
  • As with Pluto, moveable neutron reflectors are part of the control system.
  • The cost is paid in reduced stability.

The holy grail is passive stability, fail-safe. Most reactors are not, requiring a control system on pins and needles, and backup systems, to keep them from melting down. Every reactor has its quirks.  In some designs, loss of coolant causes the reaction to slow down. In others, it speeds up.

In the Russian design, as with Pluto, the coolant is air. The high air pressure inside a ramjet reactor has effects on the rate of fission not seen in land-based air cooled reactors. Pluto required 800 pounds of air per second.  If the air inside the reactor changes density, things happen:

  • If the air moving through Tory IIA becomes denser, fission speeds up, making more heat.
  • If the air moving through Tory IIA becomes thinner, fission slows down, making less heat.
  • The Russian fast neutron reactor may reverse the above, speeding up if the air intake is blocked.
  • If a  reactor heats up, it tends to slow down.
  • In an accident scenario, when the control system cannot function, combinations of the above, plus other effects, determine the likelihood of a runaway reaction. This is summarized by a coefficient. If it is greater than 0, the reactor has a tendency to run away.
  • Pluto had 18,800 pounds of nearly inert beryllium oxide to slow the rate of temperature change.
  • The Russian reactor is small and light. It gets hot fast, which makes control more challenging.

Now let’s go out to the floating launch platform, in a bay off the frigid Arctic ocean. You’re one of the launch engineers. The wind is fiercely cold. You want to light this candle and get the hell out of here. But with nuclear reactors, nothing is simple.

It is likely that the Russian design requires something a chemical rocket does not: pre-heat.  The uranium salt must melt to establish stable flow through the heat exchanger. Unlike the U.S. SLAM, the missile cannot be launched cold. We take as fact that It must be near operating temperature at launch, ready to catch the air when the booster cuts out, to blow it out the exhaust nozzle heated to 2000F or more. The reactor must be started on the ground.

You look at the launch manual, and it’s hopeless. You’re supposed to ramp the reactor power up in stages, while monitoring all the vitals, so it doesn’t go out of control, like Chernobyl. It could take an hour to work through all the steps. Your comrades are shivering uncontrollably. Then you remember a shortcut you picked up from living in this cursed climate.

The solution: You throw your coat, with a rope attached, over the air intake, and retreat behind the radiation shield. In just 30 seconds, the reactor will get toasty. A pull of the rope, and  it’s Stoli Time. But the rope  breaks. The reactor, now dangerously radioactive, cannot be approached. With little thermal mass to slow things down, and a possible positive thermal coefficient, temperature of the reactor zooms, hitting the red zone — and explodes.

Why didn’t the control system scram the reactor? Your coat caused a temperature rise so quick, it jammed the neutron reflector control vanes between sampling intervals. The rest is history.

So are you. I’ll stick with beer.

 

 

 

 

 

 

 

 

 

 

 

 

 

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