Questions about lost Russian submarine Kursk

[Sarevok]

1. Why could not the submarine empty it's ballast tanks and attempt to surface after the accident ? Was it lack of power from the reactors ?

2. Why did the crew run out of breathable air so quickly ? Diesels and AIP boats could stay submerged for weeks if needed. Is a nuclear boat dependent on power from the reactors to operate the machinery that keeps air inside breathable ?

3. What happened to communications equipment ? Submarines have short range acoustic telephones that permit short range underwater communications.

[Sephirius]

The whole front of the sub being blown open may have something to do with it. If I remember correctly most of the torpedoes went up, blowing the nose off the sub and damaging/compromising the ballast tanks.

EDIT: and the crew had plenty of oxygen, the problem was the buildup of CO2, as the scrubbers were obviously not functional.

[Sarevok]

That sounds pretty horrible. How did anyone manage to survive an explosion of the torpedo magazines ? Russian double-hull design must be pretty tough even to survive just one torpedo going off near or inside the sub.

[Sea Skimmer]

Only about 20% did survive the blasts

1. Why could not the submarine empty it's ballast tanks and attempt to surface after the accident ? Was it lack of power from the reactors ?

The explosion had enough shock to incapacitate men in the control spaces, and all control spaces then rapidly flooded killing everyone who might have attempted to blow ballast. Immediate flooding would have rapidly exceeded the reserve buoyancy of the submarine, its very doubtful surfacing was ever possible.

It’s worth noting that reserve buoyancy on Russian submarines is in fact vastly higher then on US submarines which have only a slim margin. Like 30-40% margin vs. 5-10%. This advantage, while very significant in the event of a collision or even a lightweight torpedo hit, made no difference when three or four torpedo warheads exploded onboard. One torpedo exploded initially, and touched of several others in a secondary explosion that completely destroyed the bow and damaged all the forward compartments. Each type 65-76 torpedo that exploded had a roughly 1,000lb warhead.

In fact the Oscar class, like all Soviet submarine designs of its generation incorporated a escape pod capable of holding the entire crew. This pod system is a very advanced safety feature compared to the west which has nothing like it, but could not be used because it was located in the conning tower, and all spaces from which it could be accessed flooded immediately.

2. Why did the crew run out of breathable air so quickly ? Diesels and AIP boats could stay submerged for weeks if needed. Is a nuclear boat dependent on power from the reactors to operate the machinery that keeps air inside breathable ?

All compartments up to the reactor spaces flooded. All normal power and life support systems would have been disabled. Only 23 men survived the initial explosion and flooding and locked themselves in the furthest aft compartment which was still partly flooded. Nuclear submarines have main reactor power and backup battery power for life support but it is highly unlikely that the complicated systems required to maintain the atmosphere were still functional. You don’t count on them in an emergency. Rather the backup system to this on pretty much all modern subs is a system of manually opened CO2 absorber cartridges and special candles which emit oxygen as they burn; they also provide heat which is important as the deep ocean is very cold.

The men did not suffocate because they ran out of these supplies; rather burn damage to the compartment and the bodies of some of the men showed that at some point after several days to a week of elapsed time a fire started in the last compartment and would have asphyxiated the men. The chemicals the Russians used in the CO2 absorbers would catch fire if they touched oil, and it is assumed that one was dropped or otherwise made contact with the water in the compartment which was bound to have a film of lubricating oil on it. Result is a flash fire and everyone in the compartment would have been dead in minutes.

This compartment had an emergency escape hatch, but it has never been made clear as far as I’ve heard if it was still functional after the explosion or not; when it was forced opened from the outside the rescue team found the wet/dry compartment already flooded. That likely means the chamber had leaked from the explosion and was unusable. It would be dry normally, and the crew would have had no reason to flood it without attempting an escape. I'm pretty sure that's the official Russian story to this day, the chamber was in fact damaged but many random people don't believe them. I tend to believe them.

The depth of the sinking was on the lower edge of what was survivable for an escape in Steinke hood style escape suits, but such an escape was physically possible, if they could get out. Nobody exactly knows why the men did not attempt to escape in this manner but it seems the flooding in the compartment, and the angle of the sub on the bottom meant that the men's remaining air pocket did not allow direct access to the chamber even if it wasn't broken. So the situation likely was completely hopeless. Several men left final letters, and wrote stuff on the sides of the compartment but as far as I know only a small amount of this was very made public. They may have written an answer and the Russian government has suppressed it. I looked into some stuff to remind myself of details to write this, but it doesn't look like much has changed in the public domain since the early 2000s. In any event, such an escape would have been very dangerous and likely would have killed at least some of the men. So they had reason to wait and hope for an outside rescue.

For political reasons the Russians have been deceptive about the detail details and conditions of the last compartment; which tends to suggest the men did survive long enough that a prompt request for western aid might have saved them. The Russians have generally maintained that all men died quickly. They also of course have massive culpability even if they did die quickly before any rescue could have been possible, since the 650mm torpedoe which exploded was just inherently a massive safety risk due its use of a Hydrogen Peroxide oxidizer. The Soviets accepted extremely dangerous torpedoes in ordered to have maximum performance for wake homing, which require a long tail chase. That means you need lots of performance to run the enemy down. The Russians just kept on using these weapons, which required lots of dangerous maintenance because its Russia. Hydrogen Peroxide was completely abandon by western navies (one British 1950s test sub was nicknamed HMS Exploder) and even the Soviet fleet abandon it as a means of AIP (AIP isn't an new thing...) submarine propulsion, but not as torpedo propulsion.

3. What happened to communications equipment ? Submarines have short range acoustic telephones that permit short range underwater communications.

All relevant spaces flooded. Had the Russians not delayed asking for help for so long, having no operational rescue submarines themselves at the time, a prompt rescue effort might have detected the crew banging on the hull sides. That’s how you normally find survivors on a sunken submarine and it works well enough.

[cosmicalstorm]

Thanks Skimmer, all very interesting!

[Thanas]

I am intrigued about those special candles - how do they work?

[starslayer]

My guess would be that they are similar to how airline oxygen canisters work. Those simply store a bunch of sodium chlorate. When ignited, the chlorate decomposes and gives off free oxygen and heat.

A quick look on Wiki reveals that by combining an alkali metal (doesn't have to be sodium) chlorate with iron powder, you can create a self-sustaining candle that will burn quite hot (~600 C).

[Sea Skimmer]

Yeah that'd be the jist of it, chlorate based plus other compounds depending on specific application, some for example make much less heat then others at the price of less liberated O2. Keep in mind they usually don't have an open flame, but some did in the past. In addition to having piles of cans of them for use on submarines, which dates back (at least, could be earlier) to the invention of submarine escape suits in-between the world wars, navies also use small man portable versions linked to face masks for both submarines and surface ship crews. In the USN these are called OBA for Oxygen Breathing Apparatus. They allow you to escape from compartments completely filled with smoke and fumes to the point that a mere gas mask would be worthless because no oxygen is left. Very similar devices are used by coal miners. OBA style devices typically contain about 1 hour of oxygen for the user.

Back in WW1 they actually used candles in dugouts to extend the time men could remain sealed up in them against massive gas barrages that could go on for days. Talk about horrible. Often these days they are just called 'oxygen generators' like that wiki link does and I'd assume technical papers would, but that can give a mistaken impression of a mechanical device so the term candle is in a lot of ways more appropriate and still very persistent. The O2 candles themselves can also be a fire hazard and an explosion hazard if oil contaminated but apparently the CO2 absorbers used on Kursk were a lot worse, and needed more handling and that's they they are suspect no.1 for the fire that killed her last men.

[Thanas]

Thanks for the answer.

[aieeegrunt]

I worked with hydrogen peroxide for my uni thesis. It's frustrating stuff, I mean it would make an awesome fuel (with oxygenated steam exhaust!) but it's just so damn unstable and unpredictable.

[Sarevok]

Thank you for the detailed response Sea Skimmer. It told me so much more than I expected !

[Sea Skimmer]

I worked with hydrogen peroxide for my uni thesis. It's frustrating stuff, I mean it would make an awesome fuel (with oxygenated steam exhaust!) but it's just so damn unstable and unpredictable.

Its a bad sign when LOX is considered a safer and lesser explosion hazard! The British submarines powered by it actually just had firefighting deluge systems rigged over the tanks; which had open tops, because it caught on fire that much. The open tops then allowed dust and oil specs to get into the fuel causing regular fires. Great stuff.

The German walther turbine boats stored the fuel externally in plastic bags which reduced the fire hazard at the expense of a whole new range of problems. The USN had one HTP submarine X-1, which was converted to diesel engines after it blew up. RN had a HTP torpedo explode in 1955 on HMS Sidon leading to loss of the vessel with 13 men killed, but she was lucky enough to be on the surface inside a harbor moored next to her tender. That incident put an end to RN HTP program. The only place HTP seems to have been really successful is spacecraft, and that's related to the ultra high quality standards. The Russians went a long time with HTP torpedoes, but it caught up to them badly.

[aieeegrunt]

Contact with just about any organic material will set it off, that's the problem. So it has to be kept in inorganic non-reactive containers, lines etc. at all times and it all must be spotlessly clean at all times. Even then it will spontaneously decompose on it's own just sitting there, so you have oxygen and heat slowly building up in whatever container it's in.

[Sky Captain]

I have question about the reactors used in Kursk and other subs. After torpedoes exploded all control ststems and most of the crew to operate them were lost. Reactors were operating at the time of explosion. Why there were no meltdown?
I suppose some sort of failsafe shut down reactors after explosion, but reactors still generate decay heat after shutdown and need operational cooling systems to prevent meltdown and no such systems could possibly remained operational after the blast.

[starslayer]

I'm pretty sure the reactor spaces all flooded with seawater, which would have prevented even a hint of a meltdown.

[Stark]

The reactors were almost certainly automatically scrammed anyway.

[Sea Skimmer]

The reactors did scram and are on a fail safe system. The Russians had a lot of experience with nuclear submarine disasters going into the design of the third generation submarines, but even the earliest nuclear submarines had safety systems like this. It is open to question that compartment flooding would completely prevent a meltdown if they somehow did not scram.

You need serious high volume water circulation to deal with the 190 MW of heat each atomic pile on the boat produces at full power. Even if they were not at full power, say 100 MW is still quite a lot and the reactors are directly side by side. The layers of shielding and sealing of the reactor compartment would preclude much natural circulation of water, especially circulation within the pressure vessel itself which is what is key. It seems to me that probably the water within the pressure vessel would quickly boil and cause at least a partial meltdown, but the extent of the meltdown would depend on the depth of the sinking, which would govern how much the steam pressure can resist the inflow of ocean water by whatever access is possible. Much would also depend on the extent of the damage to the reactor compartment itself.

Worth noting that several Soviet submarines that did suffer meltdowns either sank, or were later scuttled still fully fueled, as were a number of fueled reactor compartments. The US threw at least one fueled reactor into the ocean as I recall. I also recall that one of the sunken commie wrecks was later sealed up by pumping clay into it, because it was right in the middle of major European fishing grounds. The lonely Mike class I think that was.

[Sky Captain]

It seems to me that probably the water within the pressure vessel would quickly boil and cause at least a partial meltdown, but the extent of the meltdown would depend on the depth of the sinking, which would govern how much the steam pressure can resist the inflow of ocean water by whatever access is possible. Much would also depend on the extent of the damage to the reactor compartment itself.

So the natural flooding of reactor compartment is enough to prevent full meltdown from residual decay heat causing breach of reactor vessel and leading to melted nuclear fuel coming into contact with ocean water? I'm curious because land based nuclear reactors would suffer full meltdown if all post shutdown cooling failed and reactor were left on its own.

[Sea Skimmer]

So the natural flooding of reactor compartment is enough to prevent full meltdown from residual decay heat causing breach of reactor vessel and leading to melted nuclear fuel coming into contact with ocean water?

It should be enough to prevent a meltdown, if the reactor scrams and hopefully and indeed likely the emergency cooling system will function for at least a short period. Scram reduces thermal output to 5-7% of the original full power rating, less if the reactor was not running at full power to start with and this will quickly drop down to about 1%, then taper off to very little over a period of weeks and months. On 190 MWt sub reactor 7% is 13.3 Mw, this is no small amount of heat but it’s plausible to conduct it away into the ocean. Fuel rods however will still come into contact with the ocean because seawater is going to get into the core at some point, but as long as the rods don't melt only very small amounts of fission products will leech into the water. The exact details would determine what really happens, for example if the reactor compartment is directly hit by a heavyweight torpedo you could have serious fission product release without a meltdown because the fuel just got blown apart.
In fact the emergency cooling systems for some new generation reactors like AP1000 actually involve just dumping cooling water, via gravity from a big tank above the reactor, onto the external surface of the reactor containment. Evaporation then removes the heat; as long a you still have water for conduction inside the core proper. Fukushima was so bad in part because we have high reason to believe that the cores directly leaked cooling water as a result of physical quake damage, reducing effective cooling even before all power was lost to the tsunami.

I'm curious because land based nuclear reactors would suffer full meltdown if all post shutdown cooling failed and reactor were left on its own.

Well, we are assuming the reactor compartment floods with unlimited access to makeup water from the ocean should any of it boil; that doesn't happen to a totally broken land power reactor unless you have the Godzilla handy to crack it out of the containment and throw it in the ocean (or a passive cooling system as found on only a few existing reactors). Also typical land power reactors are simply much larger and more powerful, vastly increasing the heating density. Those reactors at Fukushima for example, unit 1 was rated for 460 MW electrical and unit 2 and 3 for 784 Mw electrical. Nuclear plants are only around 35% efficient at thermal-electrical conversion so the thermal power of these reactors is about three times higher. 784 x 3 = 2,352 MW approximately. That’s twelve times the thermal power of each of Kursk’s reactors. Those Fukushima reactors that exploded and burned are all on the smaller scale of land power reactors too, plenty exist which are rated for well over 1,000 MW electrical and indeed about 1,000 MW is about normal, though few are above 1,300 MW. The most powerful nuclear reactor ever run were Soviet RMBK-1500s (50% more powerful version of what blew up at Chernobyl HELL YEAH!) which had 4,800 MW thermal output. That’s only 25 times the power of each Kursk reactor! The US built an even more powerful 5,000 MW thermal reactor for a nuclear rocket engine, but never ran it at full thermal power. It did run at 4,400 MW making around 220,000lb of thrust. Full power would have been 250,000lb. So puny.