So far reports of 20 dead:
Moscow, 08 November - RIA Novosti. More than 20 people dead as a result of an incident on a nuclear submarine in the Pacific Fleet according to the Navy Public Affairs officer, K1R Igor' Dygalo.
A malfunction of the automatic fire supression system during sea trials on one of the Pacific Fleet submarines killed more than 20 people today. Among the dead were shipyard workers and servicemen.
The boat wasn't damaged. THe reactor compartment is normal. Background radiation on the boat is within standards.
The Commander in Chief of the Navy has ordered a halt to testing. The decision to return the boat to its temporary base has been made.
Comment: The commenters at Live Journal user U-96's blog seem to think that the boat was Akula II K-152 Nerpa based on the fact that it was 1) during sea trials, and 2) shipyard workers were among the dead.
I'm sure we'll hear more about it later.
Update from U-96:
The incident which killed 20 people on board a Russian Pacific Fleet nuclear submarine occured in the bow of the boat. There is no threat to the reactor, which is located in the stern section of the boat a source in the Pacific Ocean Fleet Headquarters told RIA Novosti.
There were 208 people on board the submarine, 81 of them military. The BPK Admiral Tributs and the salvage tug Sayany are escorting the boat. Twenty one injured have been evacuated to the Tributs in various states of health.
U-96 comments: Two hundred and eight on board instead of the 73 normally assigned. Of course there weren't enough EBAs to go around. "In the bow section" must mean compartment one. Torpedo room.
Update 2: Novosti reports on the types of fire suppression systems found on Russian submarines:
Now there are two fire suppression systems on board nuclear submarines: air-foam and chemical.
The air-foam system is designed to extinguish local fires and consists of two stations located at either end of the boat. The foam reserve supports six foam stations. Each station can produce one cubic meter of foam which can be applied by means of a 10 meter long hose. The stations are placed such that they can deliver foam to any corner of the compartment.
The chemical system is designed to extinguish any type of fire in a space except for fuel and ammunition fires and consists of a fire supression station located in all compartments except the reactor compartment. The reactor compartment is covered by stations located in the 5th and 7th compartments.
The extinguishing agent is Halon 114B2. The system can deliver three shots of extinguishing agent to each space. The system can be activated remotely from the central command post or from a local control panel as well as manually from the station in the compartment.
Update 3: The traditional Russian reflex to find and punish the guilty kicks in as a criminal investigation is launched into the tragedy under Article 352 of the Criminal Codex - hazarding a military vessel leading to death.
Lots of cool shots of of Akulas underway in this video clip along with word that it was an accidental Freon discharge:
Update 4: Looking at the casualty list, except for two unidentified, it doesn't look like there were any Indian specialists on board.
Update 5: Footage purporting to be K-152 returning to port. The audio recaps what is known about the incident so far, adding that there will be a special commission to investigate the incident and that the President Dmitriy Medvedev is on top of making sure that families get help and compensation.