# Nuclear energy at sea

On nuclear powered aircraft carriers/submarines/icebreakers, do the crew have to follow similar precautions as people who work in nuclear power plants such as clothing, film badges etc? Also, how much more protection does the reactor core have compared to a civilian power plant?

mgb_phys
Homework Helper
On nuclear powered aircraft carriers/submarines/icebreakers, do the crew have to follow similar precautions as people who work in nuclear power plants such as clothing, film badges etc?
You think the Navy wants to cut corners on safety on a $Bn sub? If there is an alarm you can hardly run away! Also, how much more protection does the reactor core have compared to a civilian power plant? Generally more - people tend not to fire 18" shells at civilian reactors. Do searches on 'Admiral Rickover' the man behind the US's nuclear navy Last edited: You think the Navy wants to cut corners on safety on a$Bn sub? If there is an alarm you can hardly run away!

Generally more - people tend not to fire 18" shells at civilian reactors.

Do searches on 'Admiral Rickover' the man behind the US's nuclear navy

What I meant was is it nessecary go through the 'everyday' precautions for radioactivity for the whole crew, as I imagined (as you pointed out), that the reactor would be well protected, and also that the majority of the crew do not go in that area. I also can't imagine that there would be as stringent precautions on a 100000 tonne aircraft carrier or an icebreaker which can (in some cases) carry passengers.

mgb_phys
Homework Helper
I would expect everybody on a sub to wear film badges (or TLDs nowadays) since a leak of any radioactive gas might go everywhere.
Possibly only engineering wear them on a ship. Generally you keep crew compartmentalized so non-engineering staff don't get near the reactor - you don't want idiots playing with knobs!
Even on land you wouldn't normally wear bunny suits for anything other than waste handling / isotope reprocessing where everyone also wears TLDs. People are a good way of finding spills.

Morbius
Dearly Missed
On nuclear powered aircraft carriers/submarines/icebreakers, do the crew have to follow similar precautions as people who work in nuclear power plants such as clothing, film badges etc? Also, how much more protection does the reactor core have compared to a civilian power plant?
James,

On US Navy ships, most of the crew never goes anywhere near the reactor. Only the members of the
engineering department are in the engineering spaces containing the reactor. Additionally the crew is
not anywhere where they would need special clothing when the reactor is operating.

As far as protection of the reactor core - a commercial nuclear power plant has MUCH, MUCH more
protection for the reactor than would a US Navy ship. Take a look at the following graphic courtesy
of the Nuclear Regulatory Commission that shows what the interior of a nuclear power plant looks like:

http://www.nrc.gov/reactors/new-reactors/design-cert/apwr.html

The reactor is the red object in the middle. the containment building is the domed tan colored building,
the walls of which are several feet thick. However, in the interior of the containment building surrounding
the reactor is the reactor shielding colored green in the graphic.

That shielding is made of high density concrete. A nuclear power plant doesn't have to float - so it can
have LOTS and LOTS of concrete around the reactor. A US Navy ship can't have that much concrete.

There are lots of constraints on the design of a Navy ship - it has to float; space on a ship is expensive,
while land is cheap; the Navy ship's main purpose is not to generate energy - but to be a warship - so
most of the ship is going to "airport" / hanger for a carrier, for example. So a civilian power plant can be
designed with MUCH BETTER safety systems than a ship - and they are.

A commercial power plant has MUCH better protected for the reactor than does a US Navy ship.

Dr. Gregory Greenman
Physicist

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mgb_phys
Homework Helper
That shielding is made of high density concrete. A nuclear power plant doesn't have to float - so it can have LOTS and LOTS of concrete around the reactor. A US Navy ship can't have that much concrete.

A commercial power plant has MUCH better protected for the reactor than does a US Navy ship.
On the other hand a submarine reactor is inside a steel or titanium tube designed to withstand 200-1500m of water pressure.
Naval reactors are smaller and simpler than civilian models and are generally sealed units that aren't refueled during their life. They also need to be tougher to take the mechanical beating of a ship moving at sea.
Reactors on naval surface ships are similarly well protected by lots of armor plate, rather like the ship's magazine, a direct hit on the reactor would really spoil your day

Morbius
Dearly Missed
Generally more - people tend not to fire 18" shells at civilian reactors.
mgb_phys,

By FAR - a civilian power plant has MUCH BETTER protection than a US Navy ship.

US Navy ships are not designed to withstand 18" shells anyway. For example, a carrier
just flat out will not let an enemy warship come within range so that it could use 18" shells.

A carrier has a lot of jet fuel aboard - and it would be problematic attempting to protect that.
So the philosophy is not to make a carrier that can take hits from the enemy. The philosophy
is to NEVER let the enemy get into a position where they can put that type of armament into
the carrier.

It's like in the movie "Top Gun" - "Air Boss" Johnson gets upset when the enemy planes are
200 miles away. That's the type of "buffer" the US Navy keeps around its carriers.

Dr. Gregory Greenman
Physicist

When the nuclear submarine 'Kursk' sank in 2000, there was a large explosion onboard due to a very large torpedo stored onboard. When the ship was discovered, the nuclear reactor was still intact. I was aware that civilian power stations have a lot greater quantity of protection around them in the form of concrete, but I thought that as a naval power plant would inevitably be much smaller, It would be able to have protection around it sufficient to withstand a greater impact.

mgb_phys
Homework Helper
Subs tend to be pretty strong, the Russians lost one of their nuclear powered titanium hulled subs boats in the 80s in water >1mile deep and the reactor didn't leak (so far).
As morbius said no ship is going to survive a missile carrying a 1000kg warhead at mach 2 but the reactors are deep inside the hull and you would expect them to go to the bottom in one piece.

Most (all?) naval reactors are also PWRs which have a bunch of inherent safety features and are relatively small. The US has had no naval reactor accidents in 50 odd years , the Russians haven't been quite so lucky (or careful) but none of the reactors in sunk submarines have exploded - or even significantly leaked.

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mheslep
Gold Member
mgb_phys
Homework Helper
"They point to a history of naval and nuclear accidents in Russia and the former Soviet Union, including the Chernobyl disaster of 1986."

This is a PWR not an RBMK - it's hardly a comparison.
Why does nobody object to gas powered generating stations? Bhopal was a gas leak and it killed 25,000 people.

mheslep
Gold Member
"They point to a history of naval and nuclear accidents in Russia and the former Soviet Union, including the Chernobyl disaster of 1986."

This is a PWR not an RBMK - it's hardly a comparison.
Why does nobody object to gas powered generating stations? Bhopal was a gas leak and it killed 25,000 people.
Agreed, the accident comments in the news links are a distraction. I'd like to concentrate on the exposure of HEU that these floating reactors present. There is some US or international official body (IAEA ?) that has a near term goal the elimination of all commercial use of HEU - completely zero it out - and this move by the Russians would seem to fly in the face of that goal.

mgb_phys
Homework Helper
There is some US or international official body (IAEA ?) that has a near term goal the elimination of all commercial use of HEU - completely zero it out - and this move by the Russians would seem to fly in the face of that goal.
I suppose they have to balance the safety of an existing proven sub reactor design with developing a new LEU model and they must have a bunch of HEU around from weapons disarmaments.
I can't see the Iranians capturing a Russian power station and sailing it to Iran without the Russian navy noticing - as an alternative to enriching their own fuel.

mheslep
Gold Member
I suppose they have to balance the safety of an existing proven sub reactor design with developing a new LEU model and they must have a bunch of HEU around from weapons disarmaments.
I doubt they're reusing weapons HEU. Probably making more.
I can't see the Iranians capturing a Russian power station and sailing it to Iran without the Russian navy noticing - as an alternative to enriching their own fuel.
Not the Iranians, they would then be subject to retaliation. More likely some non-state actors - something like the Taliban-Pakistani gang that hit Mumbai - direct attack or infiltration. Appears this would be manned by a commercial oil/gas drilling rig crew - ie anyone - and not Russian military.

mheslep
Gold Member
Chinese are also using commerical / civilian HEU.
http://www.nti.org/db/heu/china.html [Broken]
Cochran from NRDC has an HEU ban brief here. Caveat: Cochran has a reputation as a an anti-nuclear advocate.
http://www.nti.org/db/heu/china.html" [Broken]

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Morbius
Dearly Missed
S
Most (all?) naval reactors are also PWRs which have a bunch of inherent safety features and are relatively small.
mgb_phys,

ALL naval reactors in current use are PWRs. One certainly would NOT send a BWR to sea -
because a BWR has a "free surface" - the water / steam interface. You don't want to have a free
surface moving around in a naval reactor. One would like the power distribution to be static.

The US Navy did send one liquid sodium cooled reactor to sea in the original Seawolf (SSN 575):

http://navysite.de/ssn/ssn575.htm

USS SEAWOLF was the Navy's second nuclear-powered attack submarine and the first submarine to be
equipped with a S2G sodium-cooled nuclear reactor. But due to the difficulties of running a sodium-cooled
reactor, the Navy decided to replace SEAWOLF's sodium-cooled reactor with a water-cooled one and use
only water-cooled designs in the future.

Dr. Gregory Greenman
Physicist

Morbius
Dearly Missed
When the nuclear submarine 'Kursk' sank in 2000, there was a large explosion onboard due to a very large torpedo stored onboard. When the ship was discovered, the nuclear reactor was still intact. I was aware that civilian power stations have a lot greater quantity of protection around them in the form of concrete, but I thought that as a naval power plant would inevitably be much smaller, It would be able to have protection around it sufficient to withstand a greater impact.
James,

NOPE - space is at a premium on a ship. A US Navy nuclear-powered ship doesn't have the big
containment building that a commercial power reactor has - you couldn't get even a carrier to float
with THAT much concrete / steel.

Again - the reactor compartments are NOT designed to withstand attack. The philosophy is to keep
the battle far away from the carrier. As for a sub - if something breaches the hull - the ship and its
contents are lost. No armor plating is going to withstand the shock - the air in the sub essentially
turns to a multi-thousand degree plasma.

Dr. Gregory Greenman
Physicist

mgb_phys
Homework Helper
ALL naval reactors in current use are PWRs.
I didn't know if there had been some other possibly secret designs.
I thought somebody might have tried AGRs, to get higher power and perhaps the gas coolant could be made quieter (for subs) than the cooling pumps on a PWR.
I don't know if you could make a gas cooled where the gas was hot enough to efficiently run a turbine without a steam pant?

The US Navy did send one liquid sodium cooled reactor to sea in the original Seawolf (SSN 575):
I had heard of Rickover doing a Feynman type demonstration with sodium in a water glass at a meeting to explain why he didn't want any more sodium cooled reactors on a boat!

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Morbius
Dearly Missed
So this why Russia's pending deployment of 70MW KLT-40 reactors for oil and gas drilling in the Arctic are troubling. KLT-40's apparently use 90% HEU. I am not concerned about waste, or even accidents, but proliferation. I'm unaware of a more exposed use of HEU.
mheslep,

The only proliferation risk would be once every 3 years when the reactor is refueled with fresh fuel.
I would hope that the Russians would guard that fresh fuel until it is safely installed in the reactor.
Once HEU starts to be used as reactor fuel - then it becomes UNUSABLE as a bomb fuel.

There are two university research reactors in the USA that still use HEU. The concern is not about
the HEU that is actually in the reactor - but fresh fuel. Neither university keeps a supply of fresh
fuel in reserve. Fresh fuel is delivered "just in time" to be loaded in the reactors.

Dr. Gregory Greenman
Physicist

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Morbius
Dearly Missed
I didn't know if there had been some other possibly secret designs.
I thought somebody might have tried AGRs, to get higher power and perhaps the gas coolant could be made quieter (for subs) than the cooling pumps on a PWR.
mgb_phys,

I would think that the gas coolant would be noisier. The gas has a lower density, hence lower heat
capacity per volume. That means the flow rate for the gas is going to be higher than the water -
hence noisier. In fact, that's the reason they tried sodium. For quiet operation, you don't go to a
gas - you go the OTHER way - you want as DENSE a coolant as possible. Something with a high
density and high heat capacity like sodium - doesn't have to be pumped as fast as water and most
certainly a LOT slower than a gas.

Dr. Gregory Greenman
Physicist

QuantumPion
Gold Member
90% HEU is still far off from being weapons grade. If you had the technology to enrich 90% HEU to 99+% then you could go from natural to 99% anyway.

mheslep
Gold Member
90% HEU is still far off from being weapons grade. If you had the technology to enrich 90% HEU to 99+% then you could go from natural to 99% anyway.
Multiple sources report the Hiroshima weapon was 80% HEU. And the topic at the moment is not the ability to enrich, but to steal or divert existing HEU, especially from platforms at sea.

Criticality is a function of geometry and material composition, bombs need high criticality. My friends and I once joked about having a bomb made out of natural uranium if you had enough of it, not sure if that is possible though.

Morbius
Dearly Missed
Criticality is a function of geometry and material composition, bombs need high criticality. My friends and I once joked about having a bomb made out of natural uranium if you had enough of it, not sure if that is possible though.
Candyman,

One can certainly calculate the "k-infinity" of natural uranium - in fact it is easier to calculate with a
reactor code than doing a reactor.

You put zero-current boundary conditions on a mass of uranium, and you have effectively described
an infinite reactor of U-235.

Dr. Gregory Greenman
Physicist

Morbius
Dearly Missed
90% HEU is still far off from being weapons grade. If you had the technology to enrich 90% HEU to 99+% then you could go from natural to 99% anyway.
QuantumPion,

WRONG - as pointed out 90% enriched HEU is good "weapons grade" material. The "average"
enrichment for Little Boy was 80%:

http://en.wikipedia.org/wiki/Little_Boy
http://www.cartage.org.lb/en/themes/Sciences/Chemistry/NuclearChemistry/NuclearWeapons/FirstChainReaction/FirstNuclWeapons/LittleBoy.htm [Broken]

The pit contained 64.1 kg of highly enriched uranium. By the time Little Boy was assembled,
50 kg of uranium enriched to 89% had been produced by Oak Ridge, and an additional 14 kg of
50% enrichment uranium was on hand. All of it was used in the bomb, giving an average enrichment of 80%,...

Dr. Gregory Greenman

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