I thought they said that when it was first reported?
In comments published on the Kremlin’s website, Shoigu told President Vladimir Putin
...President-for-Life of Russia. He gets along well with other presidents for life. He is credited with bringing political stability and re-establishing something like the rule of law, which occasionally results in somebody dropping dead from poisoning by polonium or other interesting substance. Under Putin, a new group of business magnates controlling significant swathes of Russia's economy has emerged, all of whom have close personal ties to him. The old bunch, without close personal ties to Putin, are in jail or in exile or dead from poisoning by polonium or other interesting substances...that the incident that killed 14 sailors was caused by a fire in the battery compartment and that the nuclear reactor on board had been completely isolated.
The blaze marks the most serious Russian naval accident since 2008, when 20 crew members died aboard the nuclear-powered Nerpa submarine in the Pacific Fleet when a firefighting system was accidentally initiated.