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Thread: Nuclear submarines vs nuclear power plants

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    Nuclear submarines vs nuclear power plants

    Hi
    Last night I watched a documentary about the Seawolf class submarines. I thought it was very generic in that it didn't really touch any technical aspects but then again maybe the most interesting ones might be classified.

    But this made me wonder how it is possible to cram 100+ people into a 110m steel tube together with a small nuclear power plant, some rockets and lots of other hardware - and make it run on 4kg of Plutonium (at least that's what I think they said.) Are there significant differences between reactors used on subs vs. those used to make electricity on land? Is there a different safety threshold? It would seem to me that the submarine variety would need better engineering. Is it simply the scale factor? Seems the submarine produces about 45,000hp = 33kw while nuclear power plants are in the 1000mw range, 30,000 times more output? Are my numbers way off?

    Which of course raises the question about nuclear space propulsion.

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    I thought that submarine reactors ran on ca. 90+% U235.

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    i served on the USS California
    it had 2 small Pressure water reactors...
    one forward and one aft..
    it was very safe.
    it was not uncommon for us to have drills where we would "SCRAM" the reactors (drop the control rods into the core to stop the reaction)
    we had to wear TLD (total dose meters)
    if you wore one to my home in the mountains of Colorado, the TLD would read above the safety threshold for total radiation dose when it was checked the next time onboard.

    i had always thought that having a reactor buried in the backyard would be a really cool thing to have.

    but the more i learned, i discovered that over time, neutron bombardment will actually harden the surrounding container and make it brittle and be susceptible to cracking.. (not what you want inside of a reactor core.)

    i know what material the control rods were made of, but i do not know if that information is still classified even after the California's decommission..

    here is some information on the PWR core used in the vessels

    http://en.wikipedia.org/wiki/Pressurized_water_reactor

    enriched the uranium dioxide fired into cermanic pellets is used a fuel..

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    Plutonium, NOT

    Mike

    I am sure you are right about it NOT being Plutonium. Four kilos would be rather a lot, too. I watched that show when I was pretty tired.

    That size reactor would supply how many residences?
    20? If you are frugal. I guess that could be rather expensive.

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    well
    1 horsepower = 746 watts
    assuming the avarage home uses 10k watts
    that equals 13 horse power per home.
    if this thing puts out 45,000 horse power,
    you can run about 3460 homes off of one reactor.

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    i was wrong..
    Each boat is powered by a single S6W nuclear reactor, delivering 52,000 hp (39 MW)
    http://en.wikipedia.org/wiki/Seawolf_class_submarine

    that comes to 4000 homes tha can be run from a 39 MW reactor..

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    that is a lot of energy...

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    I think you're also wrong about the power consumption of a household. According to what I can find (CIA World Factbook), average US electricity consumption is about 1,500 watts per person, and I think the average household size is less than 3, so per house electricity is about 4,000 to 5,000 watts.

    39 Megawatts of electrical power should be able to supply 26,000 Americans, or ~8,500 houses. Of-course the US has one of the highest energy consumption rates in the world, if we go by the average for a European; about 700 w, then it would power about 56,000 people or ~19,000 houses.

    If we were to go by the world wide average electrical consumption of less than 300 w, that would be 130,000 people. And if it were the average Indian, who uses only about 60 w, that would be 650,000 people. The number of Africans supplied would be in the millions, etc...

    BTW the Seawolf's is by no means the biggest, according to Wiki the Typhoon class submarine has "2 OK-650 pressurized-water nuclear reactors, 90 MW (120,700 hp) each", so 180 MW of power.

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    Quote Originally Posted by mike alexander View Post
    I thought that submarine reactors ran on ca. 90+% U235.


    IIRC, it's more like 40% enriched. 90% would be weapons grade uranium. But yes, it is indeed significantly more enriched than the stuff normally used in commercial reactors, which is normally around 2-3% in your garden variety PWR.

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    The sub I was on had a reactor rated at 78 MW, I believe. The fuel was 93% enriched U235 and the control rods were made of hafnium (not a classified fact).

    A submarine PWR is very similar in basic design to a commercial PWR. There are obvious differences in auxiliary systems and the greater size of the commercial core makes the the reactor physics quite a bit different.

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    Quote Originally Posted by geonuc View Post
    The sub I was on had a reactor rated at 78 MW, I believe. The fuel was 93% enriched U235 and the control rods were made of hafnium (not a classified fact).

    A submarine PWR is very similar in basic design to a commercial PWR. There are obvious differences in auxiliary systems and the greater size of the commercial core makes the the reactor physics quite a bit different.
    Okay, I repeat.

    Do NOT - I repeat - do NOT roll up those rods into a ball and play baseball with it and another fuel rod as the bat. The crowd will go wild!

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    Angry

    Hmm. I will have to do some reviewing of my website. It looks like I'm okay for the moment because I don't discuss marine nuclear propulsion it seems.

    I was under the impression marine reactors generally operated on 40% occasionally going up to 60% in some Russian designs. It looks like I got things a bit back to front. I will take action on this.

    As everyone knows, no-one is more pro-nuclear on this site than me, but even I am not sure this is good practice.

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    By 'good practice', I assume you mean using highly enriched uranium in military reactors. Maybe not from a proliferation risk viewpoint, but these reactors are nuclear hotrods. I'm not sure it can be otherwise--the reactors have to be highly responsive to power changes and they have to be compact. I think those two factors restrain the design and require that kind of fuel. But I'm not a nuclear engineer.

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    Quote Originally Posted by Glom View Post


    IIRC, it's more like 40% enriched. 90% would be weapons grade uranium. But yes, it is indeed significantly more enriched than the stuff normally used in commercial reactors, which is normally around 2-3% in your garden variety PWR.
    One of my college professors was involved in USN reactor design; USN reactors do use very highly enriched -- near-weapons grade -- uranium, so the reactor can be operated for something like 30 years, so naval reactors need not be refueled during a ship's expected operational life.

    The brouhaha about utility reactors is kind of humorous to somebody who lives within a couple of dozen miles of a dozen or so naval reactors, which tend to go completely unnoticed.
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    Specifically weapons grade uranium rather than HEU in general, which I don't have an issue with.

    I wonder if accelerator driving would help provide the performance at reduced enrichment.

    Those powerplants must be horrendously expensive.

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    Quote Originally Posted by Glom View Post
    Specifically weapons grade uranium rather than HEU in general, which I don't have an issue with.

    I wonder if accelerator driving would help provide the performance at reduced enrichment.

    Those powerplants must be horrendously expensive.
    They are. It is, of course, impossible to directly compare the cost of nuclear powered vs fossil-fired submarines, as the latter are individually much less capable than nuclear boats, but I believe the unit cost of the USN's latest class of fast attack submarines is about $2,000,000,000.
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    Quote Originally Posted by swampyankee View Post
    ...but I believe the unit cost of the USN's latest class of fast attack submarines is about $2,000,000,000.
    Yes, but for that price, your nuclear power plant comes equipped with a completely operational submarine.

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    Quote Originally Posted by Glom View Post


    IIRC, it's more like 40% enriched. 90% would be weapons grade uranium. But yes, it is indeed significantly more enriched than the stuff normally used in commercial reactors, which is normally around 2-3% in your garden variety PWR.
    No, U.S. naval reactors use U-235 at over 90% enrichment. IOW the entire reactor is full of bomb-grade uranium.

    This provides a reactor of small volume and which can change power levels quickly, which is important for a warfighting vessel.

    The S6G naval reactor has a thermal output of about 130 megawatts, and an electrical output of about 26 megawatts. By comparison a utility power reactor might produce 1,000 megawatts electrical, or 38 times as much.

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    Quote Originally Posted by Murphy View Post
    I think you're also wrong about the power consumption of a household. According to what I can find (CIA World Factbook), average US electricity consumption is about 1,500 watts per person, and I think the average household size is less than 3, so per house electricity is about 4,000 to 5,000 watts.

    39 Megawatts of electrical power should be able to supply 26,000 Americans, or ~8,500 houses. Of-course the US has one of the highest energy consumption rates in the world, if we go by the average for a European; about 700 w, then it would power about 56,000 people or ~19,000 houses.

    If we were to go by the world wide average electrical consumption of less than 300 w, that would be 130,000 people. And if it were the average Indian, who uses only about 60 w, that would be 650,000 people. The number of Africans supplied would be in the millions, etc...

    BTW the Seawolf's is by no means the biggest, according to Wiki the Typhoon class submarine has "2 OK-650 pressurized-water nuclear reactors, 90 MW (120,700 hp) each", so 180 MW of power.

    i did say "assuming that the avarage household uses..."

    and yes, hafnium is what is used in the control rods.

    the reactors onboard the California were D2G General Electric nuclear reactors each
    Rated for a maximum thermal output of 150 megawatts, the reactors were designed to last 15 years with normal usage. The Navy's nuclear cruisers were outfitted with two reactors per ship, each having the ability to cross-connect the steam and condensate systems between plants to power both engine rooms from a single reactor. With both reactors running and the steam plants split, the average cruiser could reach 32 knots (59.2 km/h).
    http://en.wikipedia.org/wiki/D2G_reactor

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    http://en.wikipedia.org/wiki/List_of...Naval_reactors
    if anybody is interested, here is a list of the reactors used by the navy..

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    Quote Originally Posted by Murphy View Post
    I think you're also wrong about the power consumption of a household. According to what I can find CIA World Factbook), average US electricity consumption is about 1,500 watts per person, and I think the average household size is less than 3, so per house electricity is about 4,000 to 5,000 watts...
    The average U.S. residential electric consumption is about 936 kilowatt hrs per month, not 4,000 to 5,000: http://tonto.eia.doe.gov/ask/electricity_faqs.asp

    You have confused total electrical consumption across all sectors -- residential, commercial, industrial, etc with purely residential consumption.

    The U.S. uses less electricity per capita than Iceland, Norway, Finland, Canada and Sweden: http://www.nationmaster.com/graph/en...ion-per-capita

    Even this over-states U.S. per-capita electrical consumption. Why? Because U.S. workers are the most productive in the world. Thus it takes less workers to produce the same goods and services than just about any other country. Per capita electrical consumption will of course be high, since GDP per worker is high. If you divide the total national electrical consumption by the small, efficient workforce (relative to GDP produced) per-capita consumption appears artificially high, but that's a side effect of high worker productivity.

    Likewise in a country with lower worker productivity, it takes more bodies to produce the same GDP. Thus if you divide that country's total electrical consumption by a workforce size which is larger than necessary due to lower productivity, it looks like they're individually thrifty. But it's an illusion.

    E.g, 2008 U.S. GDP is about $14.4 trillion, produced by 152.6 million workers, or $94,364 per worker per year.

    By contrast the U.K. GDP is $1.448 trillion, produced by 29.4 million workers, or $49,251 per worker per year.

    http://stats.oecd.org/Index.aspx?DatasetCode=LEVEL

    In addition the U.S. has large electricity-intensive manufacturing sectors such as aluminum production. This increases the total national consumption but is unrelated to residential consumption.

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    Quote Originally Posted by geonuc View Post
    Yes, but for that price, your nuclear power plant comes equipped with a completely operational submarine.

    Exactly

    I've read (on the Web, for what that's worth) that the propulsion plant is about 20% of a USN nuclear submarines cost.
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    Quote Originally Posted by swampyankee View Post
    Exactly

    I've read (on the Web, for what that's worth) that the propulsion plant is about 20% of a USN nuclear submarines cost.
    I imagine the "Boom" in Boomers aren't cheap. And the delivery systems to get the rounds where you want them when you finally do get mad enough to burn several million people to death in an instant.
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    (John, not the other one.)

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    Quote Originally Posted by BigDon View Post
    I imagine the "Boom" in Boomers aren't cheap. And the delivery systems to get the rounds where you want them when you finally do get mad enough to burn several million people to death in an instant.
    The Virginia class boats aren't boomers; they're attack submarines, which means that they can shoot non-nuclear weapons at things. However, the gist of your comment is valid: the stuff that makes a submarine a useful weapons platform isn't cheap.
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    Humility has a nasty taste to it.

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    Quote Originally Posted by peterkienle View Post
    Hi
    Last night I watched a documentary about the Seawolf class submarines. I thought it was very generic in that it didn't really touch any technical aspects but then again maybe the most interesting ones might be classified.

    But this made me wonder how it is possible to cram 100+ people into a 110m steel tube together with a small nuclear power plant, some rockets and lots of other hardware - and make it run on 4kg of Plutonium (at least that's what I think they said.) Are there significant differences between reactors used on subs vs. those used to make electricity on land? Is there a different safety threshold? It would seem to me that the submarine variety would need better engineering. Is it simply the scale factor? Seems the submarine produces about 45,000hp = 33kw while nuclear power plants are in the 1000mw range, 30,000 times more output? Are my numbers way off?

    Which of course raises the question about nuclear space propulsion.
    The reactor in the sub boils water the same way the power plant's does. The major difference between the two is the the size of the fuel assemblies in the reactors, say around 100 pounds in the submarine but in a nuke plant may have 60 tons in 400 fuel assemblies just in one reactor! most plants have multiple reactors and with those come spent fuel ponds that increase in size over the plants lifetime. I read that 1/3 of the fuel is replaced every 1 and 1/2 years and sent to cool in the pond, 20 tons! Much of this can be reprocessed and used again but moving it around on trucks and trains for reprocessing scares folks.

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    Quote Originally Posted by joema View Post
    The U.S. uses less electricity per capita than Iceland, Norway, Finland, Canada and Sweden ... In addition the U.S. has large electricity-intensive manufacturing sectors such as aluminum production. This increases the total national consumption but is unrelated to residential consumption.
    I think you might find that this situation is even more true of the other countries you mention. They have large quantities of hydroelectricity in comparison to their population size, and geothermal also in Iceland.

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    The reactor used in NERVA nuclear rocket was a cylinder about 1m in diameter and 1m in height. It had thermal output of about 1000MW and could operate for 60 minutes.

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    Quote Originally Posted by Glom View Post
    Hmm. I will have to do some reviewing of my website. It looks like I'm okay for the moment because I don't discuss marine nuclear propulsion it seems.

    I was under the impression marine reactors generally operated on 40% occasionally going up to 60% in some Russian designs. It looks like I got things a bit back to front. I will take action on this.

    As everyone knows, no-one is more pro-nuclear on this site than me, but even I am not sure this is good practice.
    iirc, from when I took my reactors course in college, it was "common knowledge" that USN shipboard nuclear reactors used highly enriched fuel. When the USN decided to have the reactors redesigned to avoid fueling (no bolts; they use welds), the fuel needed to be enriched to weapons-grade. So, yes, most naval PWRs use weapons-grade fuel. The exception, I've heard, is France, which designs its naval reactors to be readily refueled.

    Doesn't particularly bother me, and I live about 80 km from the yard where a good chunk of the USN's nuclear-powered submarines are built (on one side of the Thames River) and based (on the other).

    Incidentally, the river in the UK is pronounced "Tems," but the one in the US is pronounced just like it's spelled: "Th" as in "Thought" and rhymes with "aims." Ain't English fun?
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    Quote Originally Posted by swampyankee View Post
    The brouhaha about utility reactors is kind of humorous to somebody who lives within a couple of dozen miles of a dozen or so naval reactors, which tend to go completely unnoticed.
    That may be true where you live but here, it seems that a lot of people are concerned about the reactors on nuclear-powered ships at Yokosuka, for example.
    As above, so below

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