(Reuters) Two dead in Russian rocket engine explosion; radiation spikes, shipping shut. Quoting,

The brief spike in radiation was reported by authorities in the nearby city of Severodvinsk, which has a population of 185,000. This apparently contradicted the defense ministry, which was quoted earlier by state media as saying radiation was normal.

With one exception, the nuclear ramjet, a rocket engine is not a source of radioactivity.  Things which are not radioactive stay that way, because chemical reactions do not create radioactivity. If something is subject to intense or prolonged irradiation by something that is radioactive, typically with neutrons, then a nuclear reaction occurs, creating new radioactive material.

If the Russians tested a rocket without bothering to remove the nuclear warhead, or left it nearby, that would indicate a level of alcohol consumption that is not possible, even in Russia.  That implies that whatever was radioactive could not be removed from the test article before the test was performed.

This implies that Russia’s nuclear ramjet, to power their nuclear cruise missile, was involved. The ramjet contains a small, air-cooled nuclear reactor that replaces chemical fuel. It heats air admitted by a duct in the front of the engine, causing the air to expand out the back.

The radiation spike indicates that the reactor was disintegrated by an explosion  inside the ramjet, or nearby.

• If the ramjet reactor is not a fail-safe design, or is defective, the rate of atomic fission could spike, causing it to melt. Nearby organic materials, if confined by the missile housing, could result in explosive disassembly. This is not like a “high explosive” detonation, but enough to kill a few bystanders.
• Even a nuke powered ramjet has to be boosted to a pretty high speed before it will start producing thrust. So the cruise missile it is mounted on a conventional, chemical booster stage. If the booster explodes, it can destroy the ramjet reactor.

The ramjet reactor core is not very radioactive before use. Like a commercial power reactor, the radioactivity of the core increases drastically with use. So if the explosion is caused by a fission spike, more radioactivity is released than by a booster explosion.

The fuel for a ramjet reactor is at very high temperature when the ramjet is operating.. It is encapsulated to withstand this stress for the short time it has to work. The town of Severodvinsk reported a brief radiation spike, so the explosion lofted radioactive materials into the air. The briefness of the spike indicates that packaging remained mostly intact, so the fuel was not widely dispersed.

There is real danger here.  The ramjet reactor itself, independent of the warhead, is a source of radioactivity, which increases  with every minute of run time. A nuclear powered cruise missile has the danger of a nuclear weapon, even with no warhead.

Vladimir Putin has expressed pride in this nuclear powered cruise missile. He may not understand that the danger of this weapon: It can slip the leash of the most careful testers. It may fail so that it cannot be controlled from the ground. It may spontaneously change course. Perhaps scarring Russia’s earth is what Stalin would have deemed  an acceptable cost. But even in testing, this ill-conceived weapon could deal nuclear death outside of Russia.

This is one reason why the U.S. cancelled a nuclear cruise missile program, Project Pluto. It was too provocative.

Vladimir Putin, in provisioning your country with a nuclear deterrent, it is vital to eliminate the chance of self-inflicted harm. Nuclear weapons are hellish enough without it.