Chernobyl, dangers of nuclear, environment, nuclear, nuclear accident, nuclear disaster, nuclear power, nuclear waste, nuclear weapons, Putin, radiation levels, radioactive waste, risk management, Russia, Ruthenium 106, Spent Nuclear Fuel, Yaroslavl, Yaroslavl Region
“The prerecorded warning, which aired at about 9 a.m., alerted residents to what it said were high levels of radiation in the atmosphere in the region 250 kilometers northeast of Moscow. It advised people to protect themselves, tightly close their homes or offices and stay inside, and secure food and water from possible contamination by radiation.” (RFE/RL)
The orange skulls correspond to nuclear reactors-facilities, but may not be complete. Yaroslavl is bottom center-right on map. It could also have been an accident in transport of nuclear waste (including spent fuel), nuclear weapons, or other nuclear materials.
Remember the apparent Russian radioactive ruthenium release which ended up in Europe: “This report concludes that the release of a significant quantity of Ruthenium, located between the Volga and the Urals, and which would have occurred at the end of September 2017 during an operation using spent fuel cooled for approximately two years, is the hypothesis that best explains the measurements taken from atmospheric radioactivity monitoring stations in different European countries. IRSN speculates on the age of the fuel due to the detection, in some measurements, of Ruthenium 103 with a ratio relative to the Ruthenium 106 characteristic of a spent fuel removed from a nuclear reactor since about 2 years. ” (ISRN) 
Press Release from the Ministry of Emergency Situations of Russia for the Yaroslavl Region:
“The Main Directorate of the Ministry of Emergency Situations of Russia for the Yaroslavl Region asks the population to remain calm, Today 09:21
Today, around 9.00, a regional warning system about the threat of radiation hazard has been launched. On this fact verification is carried out. At the moment, the radiation background corresponds to the norm. In the city of Yaroslavl, it is 0.11 μSv / h.” 
In the town itself, the wind was calm and from the north: https://www.timeanddate.com/weather/russia/yaroslavl/historic
“‘False’ Radiation Alert Causes Scare In Russia
February 13, 2018 11:08 GMT, RFE/RL
Residents of Russia’s Yaroslavl region got a scare when local TV and radio stations broadcast a radiation warning, but the Emergency Situations Ministry said the broadcast was a mistake.
The prerecorded warning, which aired at about 9 a.m., alerted residents to what it said were high levels of radiation in the atmosphere in the region 250 kilometers northeast of Moscow.
It advised people to protect themselves, tightly close their homes or offices and stay inside, and secure food and water from possible contamination by radiation.
In a statement, the regional branch of the Emergency Situations Ministry said that a technical glitch caused the “false” warning to be broadcast.
It urged residents to “remain calm” and said radiation levels were “within the norm.”
In a short video statement, the senior regional emergency official, Yevgeny Shumilin, said the authorities were investigating what caused the message to be broadcast.” With reporting by RIA Novosti. Copyright (c) 2018. RFE/RL, Inc. Reprinted with the permission of Radio Free Europe/Radio Liberty, 1201 Connecticut Ave NW, Ste 400, Washington DC 20036. https://www.rferl.org/a/russia-yaroslavl-radiation-scare/29037176.html
 Google translate of ” Главное управление МЧС России по Ярославской области просит население сохранять спокойствие , Сегодня ” 09:21, http://76.mchs. gov. ru/pressroom/news/item/6482471/