Now this morning I thought about something I think hasn't been mentioned here.
Any missile ever that has taken off from land or sea has gone somewhere right? So if you launch a missile you also have to recover it or let it fall down as is usually done when testing new missiles with the latest exceptions of Falcon etc where they try to reuse it to increase it's commercial viability.
Now suppose you have a chemically launched nuclear in flight powered ramjet type of a missile , so you launch the missile and what then? You essentially have a speeding nuclear "dirty bomb" even without a warhead in place that flies at mach 2 or greater speeds , where do you land such a test missile??
You can't let it crash in international waters or neighboring countries for the risk of giving away your secrets and pollution and an international scandal, so you crash it somewhere silent and remote in your own territory and which country in the world has the biggest luxury of having a place like that... Russia ofcourse.
You see where I am going with this?
Now I will try to give some links later, but right now here is my thinking.
The Russians already have a working chemically launched nuclear missile but they are tweaking it and probably testing a good enough recovery mechanism for the rocket. Because having a rocket like this also requires some way of recovering it if used in peacetime.
Also what strikes as odd is the place of test because the Russians have even more remote areas like the famous "Nowaya Zemlya" or "New Land" which is a large very far north located land mass that is virtually empty of humans or other "intruders" , also the place where they tested the largest thermonuclear bomb ever the "Tsar" bomb.
It has been reported that they have made some tests of this same 9M730 missile there and close by among other things have been a special nuclear waste and radiology ship named "Serebryanka"
Now guess what? I found on some Russian blogs that at the latest spot in the Dvinsky gulf the same ship has been spotted hours before reports of any explosion took place. Now thinking logically the Russian scientists are among the best in the world surely they would take some backup precautions while testing a nuclear powered missile.
PS. a flashback they would have also told the operators of the RBMK units of how dangerously unsafe they were when used in a low power range but they were not allowed to do so.
Also someone there posted a link to a police escort of some 3 and more ambulances with drivers in full bio-suits and the cars themselves wrapped in plastic film. Now this doesn't seem like an accident to me but a planned emergency in case the rocket dumping goes wrong.
So here is what I think they did, another test fire of the rocket, but as in all other cases they needed a safe spot where to dump the rocket after flight tests were done, probably something went wrong in the trajectory of the rocket and they now had a nuclear missile heading for civillian territory so they activated the emergency self destruct function of the missile and it blew up in mid air near the towns where the short spike in radiation was noticed. (I suppose they have such controls built in such a rocket as it would only seem logical)
I think they probably would have wanted to dump the rocket in sea originally and do it in a controlled fashion and then the specialists could pick up the remains (why the special purpose ship Serebryanka was there)
but as they blew it up the remains of it crashed near the platform (not sure what it's purpose was) and in the result some people were killed.
As
@mfb and others said here earlier the only radiation that could travel far enough from source for a short time is gamma, so maybe the gamma background was elevated because of the disintegration of the rocket some 40km from the shore , as the fragments fell into sea the gamma background dropped as the source of radiation was now not only far away but mostly underwater or covered.Surely without any normal information this is just speculation but to me it seems highly probable.
