How much nuclear fuel is in a nuclear sub?

pcvrx560

How much fissile material, in kilograms, would, say, an Ohio-class submarine carry?

If it's classified, what would be about a good estimate?

OmCheeto

e=mc^2

25 years between refueling.

If I said more, I'd be arrested, and shot.



we're not supposed to give out the answers to homework questions. PF is brutal regarding that rule.

statphys

I went to a public lecture on nuclear marine propulsion, the speaker talked for 45 minutes and told us nothing! It's all too classified.

nismaratwork

I for one, am pleased that this kind of technology is not openly shared. The power plant of a sub is key to its ability to function as a deterrent, or hunter-killer, and comparable only to its means of acoustic insulation and propulsion in importance. This SHOULD be classified.

Borek

There is a HUGE difference between "sharing" a technology and giving out parts of the information. Amount of fuel doesn't tell you much about boat capabilities - it lasts much longer than any other type of provision needed. Boat sea time is more limited by amount of potatoes on board than by amount of fuel.

minerva

I have heard the volume of the reactor core fuel in a US nuclear submarine described, by qualified people, as "fits under a desk".

It's not a particularly large volume.

Morbius

Borek,

The amount of sea time is not the sensitive information the Navy is trying to protect.

The real information the Navy wants to keep secret is how fast the sub can go.
If you knew the reactor power - that would give you a big clue to how fast it can go.

If you know the amount of fuel, and can estimate the heat transfer area, you could
get a pretty good idea of what the power of the reactor is.

That's why they don't tell you how much fuel is in the reactor.

E=mc^2 doesn't help - because you don't know the power and hence don't know
the energy that the reactor produces in the 20 years between refueling.

Dr. Gregory Greenman

Vanadium 50

Maybe not in that order.

russ_watters

Well....except that the peak power of the turbines is published, so it is a good starting point to figure on an average output of, say, 50% (though I don't know how well a reactor throttles...) and a plant efficiency of 30% and calculate from there.

nismaratwork

Wouldn't top speed have a lot more to do with the design of the drive and screws than the power plant? At some point you get cavitation, and therefore noise and loss of efficiency, and I would guess this occurs long before a nuclear pile "poops out", and its related batteries and fuel cells.

apeiron

http://www.nato.int/acad/fellow/99-01/maerli.pdf

In 1995, with 158 operating U.S. naval reactors, the annual burn-up of U-235 in the entire fleet was reported to be approximately 1.1 tons.117 Thus, as a crude approximation, on average each U.S. reactor used 7 kg of U-235 during that year of operation.

nismaratwork

...But the fleet is comprised of vastly different submarines, from hunter-killers to boomers, and of those there are different classes within each, different missions and therefore different depths and speeds.

Xnn

about a 1000 lbs

rod_worth

I'm probably the most qualified to answer this question because I was in the nuclear navy, albeit on an aircraft carrier. My schooling was set up to teach us about submarines however. Here is what I feel I can reasonably tell you:

Potatoes 'do' limit how long a ship is out to sea; a deployment is limited by how much food you can store on the boat.

Most of this material is 'confidential' or 'secret'. They can tell you the general science behind things, but the specific engineering aspects including fuel loading, enrichment, and materials is off limits.

The power output of the reactor will far surpass the boats 'speed limit' which is classified on its own (I don't know it, and if I did I certainly wouldn't tell you). Speed on a submarine is not limited by the power output of the reactor/steam-plants but by materials on the exterior of the hull that will begin to rip off because you're going too fast through the water.

Most of the highly secret aspects lie not on reactors and plant design but harmonics and propulsion plant design to keep the thing from being detected.

The reactor itself is very small, say the size of a bunch of refrigerators stacked on top of each other and side by side (and don't ask me how many, I'm not telling).

I've probably given you enough info to have myself shot and arrested too (and in that order) ;) However, the fact that you're asking a very specific question like that is border-line suspicious, and is probably enough to at least have this entire conversation flagged by the FBI.

pcvrx560

Wow, thanks fellas. Now I feel like I accidently tried to commit treason by asking this question, haha. But seriously, I think the biggest thing I got from this thread is a visualization of how much energy can be contained in such a small volume. I've always heard "E = mc^2" and that "c^2 is a very large number" but now I can sort of visualize the size of energy/mass equivalency.

Another question: are nuclear reactors 100% efficient, in terms of mass/heat-energy produced? If the laws of thermodynamics took a day off, would nuclear power plants be able to convert ALL fissile fuel into electricity?

rod_worth

Nothing I know of is 100% efficient, except for my Mom at remembering to mail out birthday cards on time; no, reactors are not 100% efficent. I 'think' in a real plant something like 15-20% of the energy/heat produced by the reactor actually is used to do work in the form of propelling a ship and/or producing electricity.

If the laws of thermodynamics "took a day off" I would create my own castle with 70 virgins and a built in Taco Bell from empty space because energy would no longer be conserved, cold would 'flow' to hot, I would break every piece of glass I could find to watch it spontaneously put itself back together, and then I would fly to the moon on a pink elephant that I gave birth to from the same nothingness as my awesome new bachelor pad!

My point is this, if thermodynamics "took a day off", I believe anything would become possible, which would probably include your 100% efficient nuclear plant! ;) You can consider c^2 as nothing more than a 'conversion factor' which equates a little bit of mass (m) to a lot of energy (E) capable of doing work. I too think it amazing at how much energy can be extracted from a well designed 'hot rock' (aka 'reactor'). Thank you Dr. Einstein for realizing that (1/2)*m*v^2 = (1/2)*(E/c^2)*v^2!!!

nismaratwork

You get thermodynamics to take the day off, and you build a taco bell? I'd probably start with something with a little more umph. ;)