I wonder if they had a problem with the nuclear powered cruise missile they are developing[0]. It's interesting that they are recommending taking iodine pills though, because that might imply a release of radioactive iodine, a fission product.<p>[0]<a href="https://en.wikipedia.org/wiki/9M730_Burevestnik" rel="nofollow">https://en.wikipedia.org/wiki/9M730_Burevestnik</a>
I wonder if this spike could be explained by dispersal of depleted uranium commonly used in bullets and other kinetic weapons for its high density. The article is very light on detail though, it's not clear whether this was an engine on a test stand, or a launch test.