There are good grounds to believe that this project is, in whole or in part, a strategic deception by Russia [Maskirovka in Russian parlance], to gain the benefits of developing and deploying such a weapon without enduring the costs and hazards that an actual program would entail.
Russia has a national history of strategic deception, surely dating to the Potemkin Villages of the 1780s. More recently, a series of Red Square parade deceptions in the early years of the Cold War helped fuel The Bomber Gap and the Missile Gap. This is not to say that the Russians are uniquely deceptive. All clandestine and covert operations entail deceptions. Classified weapons programs are by their nature deceptive in restricting the publicaion of information, and highly classified programs would typically have a cover story to further confuse the inquisitive.
The recently [May 2018] appointed Deputy Prime Minister, Yuri Ivanovich Borisov, who is responsible for defense issues, has been pretty explicit in advocating a Khrushchev-style strategic deception campaign to facilitate reduced military spending.
The Burevestnik was unveiled at Putin's March 2018 show and tell that was substantially deceptive.
Moscow has never released a photograph of anything that was unambiguously an atomic powered cruise missile - the few images released in conjunction with this project are generic cruise missiles, with no functionally related observable differences indicating nuclear propulsion.
It is reported that by mid-2018 tests were conducted four times, from November 2017 to February 2018. In all four cases, the test ended in failure. The longest of the tests lasted about two minutes. The rocket flew about 35 kilometers and fell, according to TASS. These numbers are about what one would expect from the solid rocket motor booster stage, with a complete failure of the nuclear power plant to function. According to another source, as of early 2019 only one of 13 known tests of the missile had been moderately successful to date. This is backwards. The US conducted a number of ground tests of Pluto, and they generally "worked". The scenario here is that the Russians are tossing the thing into the air on the off chance that it might work.
No one has offered a coherent concept of what this thing is supposed to look like. The Pluto reactor was quite large relative to current GLCMs, and there are physics limits to how small the things can be made. It is not simply a question of the core, but all the stuff that the core is wrapped in. The naive notion is that one can just take a GLCM, and replace the small turbofan with a reactor, but it probably doesn't think it works that way. It is plausible that the Burevestnik is big, along the lines of Navaho or Buran, but no one has suggested this.
If there was indeed a launch site flight accident on 08 August 2019 with the SSC-X-9 as popularly conceived, the reactor would have been cold, or very nearly cold, else the missile would be off the test range and over water. Either way, it is hard to see how there would have been a fatal radiological accident. There could have been such an accident in conjunction with a ground test, but ground testing of the SKYFALL is not previously attested at this site, and would have almost certainly been conducted at some regular polygon out in the boonies, for safety reasons.
TASS quoted Rosatom "The rocket tests were carried out on the offshore platform. After the tests were completed, the rocket fuel ignited, followed by detonation." Possibly this was a ground test, and the reactor was contaminated. But generating the air flow needed to simulate fight conditions was a major challenge for Pluto, and required a pretty vast installation that is not in evidence. And there is still no statement here of a radiological accident.