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Nuclear Powered Submarine FAQs

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The following answers are drawn from the experiences of a 'Chief Petty Officer Marine Engineering Artificer in Her Majesty's Royal Navy Submarine Service'.

In other words, 'a slightly glowing glorified spanner monkey doing the 'Scottie' bit down the back end of the boat1'.

Isn't it very claustrophobic?

No. The boats are roomy enough to preserve your personal space. The corridors are wide enough to pass without touching. Your bunk space is yours (once qualified)2 and has curtains for privacy. The bunks are designed for sleeping and work very well. The worst job involves having to go into the dark sleep-smelly bunk spaces and try to raise the next watch. A stick is used to insert into the curtained bunk to prod a response from the unfortunate next on watch. Some people will hit out when woken and the stick provides distance and protection.

Whilst at sea only a third of the crew are in any one place at a time. The watch system dictates that a third of the crew will be 'on watch', a third will be asleep and the rest will be in the mess or the makeshift gym or just hanging around the control room or sonar room in case something interesting happens. There were times when the mess was empty.

A strange effect is that the space slowly seems to grow. This is perceptual but quite useful. An oddity is that we were advised, after a long time at sea, not to drive within 24 hours of leaving the boat. This was because the eyes have not had to focus on anything further away than a few feet and take time to adjust. However, try telling that to a matelot just docked and on his way to see his girlfriend/wife/promise!

What can you see out of the window?

This question is due to the type of submarines designed in Hollywood. In reality there are no windows at all on a military boat. They are reserved for tourist and research submersibles. Imagine what a liability a relatively weak window would be if the enemy started dropping depth charges on you or loosed a torpedo at you.

Another good reason not to have windows is that they are completely useless down below 30 metres because it is pitch black. The light does not penetrate below this sort of depth. A modern boat will operate at over 300 metres.

If there are no windows how do you know where you are going?

The main method of navigation on a dived submarine is dead reckoning. This is where three key pieces of information are required. The starting point, the speed the submarine has been travelling and the direction in which the submarine has been travelling. Putting these pieces of information together will give you the current position. If this information is displayed on the correct chart, the submarine shouldn't go bumping into things such as underwater mountains, wrecks or the bottom.

A collison at sea can ruin your entire day.

Back in the old days this information was gathered by a spinning propeller dragged through the water, a compass and lots of paper and pencils.

In more modern times the submarines carry two very accurate, very expensive gyro compasses, a GPS system and a chart table with a moving red dot. Computers recieve the signals from the gyros which sense every slight movement of the boat and they cross reference this with the chart displayed and move the little red dot to exactly indicate the current position.

Whenever possible and 'safe' to do so the boat will come to periscope depth, raise a communications mast and obtain a GPS fix. This is fed into the navigation system computers and the postion of the boat updated.

Why do they make that pinging noise all the time?

Hollywood again. That pinging noise is a sonar3 pulse. It is actually a very loud noise blasted out from a submarine which then listens to the echo in an attempt to locate objects around it.

Reality. A submarine's role is usually that of intelligence gathering, spying, sneaking about in places it shouldn't be. To do this it must be stealthy and very quiet. The last thing a submarine would do is announce its position by making a loud noise. Submarines listen. It's called Passive Sonar. They are bristling with hydrophones (underwater microphones). They even put them (along with other sensors) into long flexible tubes. The tubes are stowed in housings attached to the side of the boat or under the casings on large spools. When the boat is at sea and dived these tubes are paid out and towed behind the boat. Hence the name 'towed array'. They do this to be free of any noise interference from the submarine itself.

So a submarine down in the dark, noiselessly slipping through the water, is aware of everything around it. Shrimps, fish, dolphins, whales, fishing boats, merchant ships, tankers, warships and even other submarines. They know the types and names of the ships, how fast they are travelling and their heading. They are all called 'targets'.

How long can you stay down?

Nuclear powered submarines have only one limiting factor to their dived endurance. They are limited by the amount of food that can be stored. If it is properly stored and used, enough provisions to last about 3 months can be loaded.

Dry goods - potatoes, carrots etc are stored under false decks in the corridors and flats along with tinned foods and any thing else that does not require refrigerating or freezing. The crew literally eats its way through the boat.The other two staples, namely water and air, have no limits as they are produced on demand by the submarine.

Sea water is used to produce both drinking water and oxygen. Water is made by evaporators. The raw seawater is let into a vessel which is kept under a vacuum. The vacuum is produced by the main engine steam turbine condensers. Water boils at a much lower temperature when under a vacuum. This saves considerable amounts of energy. Waste steam (from the turbine sealing system) is used to boil the sea water. The steam produced is condensed and pumped away to fresh water storage tanks. The water produced is used for both drinking and 'hotel services'.

The air requires two separate systems. One to produce oxygen and one to remove the carbon dioxide. The oxygen is produced by an electrolyser. Water is made from oxygen and hydrogen joined together. The trick is to break the join. If you stick a pair of wires in some water and connect them to a battery, bubbles appear on the wires. Oxygen on one wire and hydrogen on the other. If you can arrange to collect them separately you can throw the hydrogen overboard and breathe the oxygen. The more electricity you pump into the water the more gases you get. A nuclear reactor plant can produce plenty of electricity.

Once you have breathed the oxygen in, you breathe out carbon dioxide. There are lots of chemicals that will absorb carbon dioxide. One of them will absorb large quantities of it when hot. So if you bring the air thick with carbon dioxide into close contact with this chemical when hot it will absorb the carbon dioxide. If you then move the chemical into a sealed vessel and cool it down the carbon dioxide comes back out of solution. The carbon dioxide can then be compressed and pumped overboard.

There are lots of other gases produced by the crew which if left to build up could become a nuisance or dangerous. The majority of these gases can be oxidised to produce carbon dioxide or water or both. Air from the submarine atmosphere is pumped through an orifice across which are two electrodes. The electrodes produce a powerful spark. Any unwanted gases coming into contact with the spark are oxidised and the resultant gases dealt with as described above. On a few occasions the correct ratio of oxygen/CO2/nitrogen was not maintained and produced some odd effects. If the oxygen is too high it affects your ability to sleep. You might be bone tired but when you close your eyes nothing happens and you are lying there still wide eyed and tired. If there is not enough oxygen then it is almost impossible to keep your eyes open. Arms and legs become intolerably heavy. Not much fun and many complaints to the wrecker4.

What do you do with the rubbish?

Anything that is dry and contaminate free is compressed and stored on board until docking. Stuff that needs to be got rid of is sent to the 'gash gun'. This is actually a downward pointing torpedo tube. The gash is sealed into a tin can about 20cm in diameter and about 25cm long. The tin cans are made from flat sheet blanks in a machine. The cans are weighted and then filled and sealed and loaded into the gash gun. Permission is then sought from the ship control officer to 'ditch gash' and just like a torpedo tube, the gun is flooded and equalised and the can ejected. The cans must sink so as not to give away any trace on the surface of the submarine's presence.

What do you do when it all goes wrong?

A submarine is designed with as much redundancy as possible. This means there is always a back up system. With vital systems there are back ups for the back ups.

Any warship has a creed to follow. 'Move and Fight'. This was true even when the first sailor hurled rocks at another sailor's boat. If you can't move you can't fight. If you can't fight you are a spectator or worse, a target.

On a submarine there are two primary power supplies: two steam generators (boilers) both powered by the nuclear reactor. Each steam supply can be sent to either side power plant or both. The steam is used for both propulsion and power generation. The other primary supply is a very large rechargeable battery. The battery is also used for propulsion and power generation. Normally the reactor is used to provide steam used by both the propulsion turbines and the generator turbines.

A clutch between the turbines and the main electric motor is engaged and the propellor turns. If the steam should be lost then the main battery is used to provide some essential power supplies and the main electric motor is used for propulsion once the clutch has been disengaged. The battery is large enough to propel the submarine considerable distances and hopefully out of harm's way. It also allows the submarine to fight.

Once the battery is exhausted it can be replenished by running two diesel generator sets. This can be done either on the surface or at perescope depth by use of a snorkel or 'snort' mast. If you find yourself in this position it must have been a very big mistake or you were lucky enough to survive enemy action.

Finally you could end up sitting in one of the escape compartments wearing a once only survival suit, breathing oxygen supplied by an oxygen candle5 and purified by CO2 canisters6. The survivors would be waiting for rescue in the form of the Deep Sea Rescue Vehicle. This is a mini submarine that can dock with the stricken boat and transfer the survivors to the surface. If this is not possible then they would be calculating how long they can last until forced to escape from the boat using the escape hatches. All submariners are trained for this, but not many would look forward to it.

Isn't it dangerous to be so close to a nuclear reactor?

No. The submarine reactor compartment is designed to shield the crew from all harmful radiation. There is less radiation in the accommodation areas of the boat than on the high street in Aberdeen7. The reactor compartment is fully shielded with lead across the top of the reactor. Think of it like a saddle. The shielding reaches down to just below the waterline. Below this the water acts as a shield. Imagine the radiation as a light source. The light is prevented or shielded from shining upwards. Very strict safety routines govern entry into the reactor compartment. The only time anyone could become contaminated is during the reactor coolant sampling procedure. To keep everybody safe during this procedure it is carried out in the 'tunnel', a heavily shielded access route from for'd to aft across the top of the reactor compartment. The operator is locked inside the tunnel whilst the sample is taken. If the worst happens and the operator has a spill, the whole submarine goes into a special routine to handle the 'spill'.

A plastic sheet 'tunnel' is taped over the tunnel door and leads down to the showers in the heads. A trained health physics chap then comes and lets the unfortunate operator out of the tunnel. They would normally be completely naked having used their clothes to soak up the spill. They then shower and are checked with meters for contamination. If they still have any contamination on their skin the health physics chaps scrub them vigorously until they are completely clean - everywhere! They also gather up the contaminated clothing and either double bag it and store it or wash it thoroughly. This usually gives much entertainment to the rest of the crew, and leads to much good natured banter.

The public have some deep-seated fears about nuclear reactors and radiation fuelled by the equally ignorant media. It seems cruel to prey upon these fears but we are discussing submariners. During a family day, when the submarine was full of loved ones, some of the crew decided to don the white overalls used for reactor compartment entries. They put on anti-flash hoods and gloves. Using a long pair of tongs they held out a chemical light stick, emitting its green glowing light. They emerged from the tunnel and proceeded through the boat shouting 'stand back - reactor refuelling'. The ensuing panic was a rare sight to see, evidently.

There are, of course, many other questions, and the above only the most common.

The submarine service is and has always been made up from heroes and villains and saints and sinners. All deserve a moment's consideration for their efforts.

1Boats are small vessels carried by and launched from ships. In the very beginning of submarine history they were carried on and launched from ships.2Qualification means being awarded one's dolphins, the submariners badge. On joining a submarine for the first time, a new recruit (of any rank) has to prove to the rest of the crew that they are competent throughout the submarine. Until the recruit can do this he has no bunk and no mess privileges; he is a passenger and sleeps with the torpedoes.3SOund Navigation And Ranging.4The wrecker is the chief who looks after all the systems on the boat other than propulsion and weapons.5A mix of chemicals that when burnt give off more oxygen than they consume.6A tin can containing a chemical that will absorb CO2, fitted to a circulating fan.7The local geology of Aberdeen is largely granite. Some granites can contain 15 - 20 ppm of uranium. The natural decay of uranium emits both gamma radiation and radon gas.

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