Propulsion development

Discuss life, the universe, and everything with other members of this site. Get to know your fellow polywell enthusiasts.

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MSimon
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Postby MSimon » Tue Aug 05, 2008 11:27 pm

Submarines need about 100 MWth to propel them.

They run about 10,000 tons. As do most destroyers these days.

Polywells will power the fleet if we get them working. Not just CVs and BBs.
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wizz33
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Postby wizz33 » Thu Aug 07, 2008 1:16 am

tom can i get a link to that story?

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Postby MSimon » Thu Aug 07, 2008 5:44 am

wizz33 wrote:tom can i get a link to that story?


Say what?
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Postby Aero » Thu Aug 07, 2008 5:53 am

Simon,
wizz33 is referring to the final post on page one of this thread.
Aero

Tom Ligon
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Postby Tom Ligon » Thu Aug 07, 2008 3:53 pm

Wizz,

I've never posted those stories on-line.

I might be sweet-talked into sending .pdfs of them to interested parties as long as they won't be posted on a website. Once they're posted, it is unlikely any publisher would be willing to pay for them. Analog won't publish a story previously published or posted.

I've gladly posted my two fact articles because they support the cause, but the story that was intended to accompany the first fact article might still be revived, and I don't want to prevent it from being published one day.

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Postby TallDave » Thu Aug 07, 2008 7:47 pm

Simon,

Sure, based on the raw power reqs that makes sense. But I'm doubtful that can actually happen, given a Polywell's complexity, cooling reqs, and the need for a 5-10MW input to run the reactor.

My guess is this only goes on something that already has one or more diesel/fission engines.

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Postby cuddihy » Thu Aug 07, 2008 10:32 pm

TallDave wrote:Simon,

Sure, based on the raw power reqs that makes sense. But I'm doubtful that can actually happen, given a Polywell's complexity, cooling reqs, and the need for a 5-10MW input to run the reactor.

My guess is this only goes on something that already has one or more diesel/fission engines.


Well, a 1 MW aux diesel, with large capacitor and battery banks, are doable even in a small hull.
Tom.Cuddihy

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Postby MSimon » Fri Aug 08, 2008 6:46 pm

TallDave wrote:Simon,

Sure, based on the raw power reqs that makes sense. But I'm doubtful that can actually happen, given a Polywell's complexity, cooling reqs, and the need for a 5-10MW input to run the reactor.

My guess is this only goes on something that already has one or more diesel/fission engines.


Dave,

Look up DLGN - 25 the Bainbridge. My ship. The cooling will be easier (no condensers) with much higher water discharge temps. 150 to 180 deg F. On nukes any discharge temp over 100F (IIRC) required a reduction of maximum output. The input to the reactors is on par with the primary loop coolant pump(s) energy rqmts in a nuke. And start up power can be stored in rotating machinery (enough for 1 to 10 seconds of start up power).

A 1 MW DG could store the start up power over a two to twenty minute period (10% of the DG load) so you could do a restart every 2 to 20 minutes (depending on rqmts) on a dead reactor (assuming the other 90% of the DG power went for the auxiliaries). If you had 2 DGs (one for the aux machinery and one for the storage) or one twice as large a start up a minute should be possible. Limited more by personnel factors than the machinery.

Let me add that a BFR is a LOT less complicated than a nuke plant. And multi rack cabinets of control eqpt (my ship) can be reduced to a crate. Of course the racks will be replaced by DC conversion eqpt so no net change in volume.

Think about coolant pumps (electric for start up changing over to steam for operation). Oil pumps for the rotating machinery. And a gazillion other rqmts (shop air for some aux eqpt for instance).

Most likely CVNs will be the first converted. then CGs. Followed by smaller ships as experience is gained and operators trained and eqpt size reduced.

I have gone over all this before. Maybe you missed the thread.
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Postby TallDave » Sun Aug 10, 2008 7:05 am

Hrm. I don't see how the cooling can be easier; you don't have to maintain a superconducting magnet at ridiculously low temps. You don't have the concentrated heat loads, which are going to test the limits of existing materials. You also don't have to maintain a vacuum in a fission reactor. And you'll need a big honking power source to start all that up.

And let's not even get into alpha sputtering and the other engineering issues we have to solve for a p-B11 reactor.

I don't know, it just seems optimistic to think this can go on something smaller than a carrier anytime soon when we're not even sure it will be a non-mobile source withing 10 years.

A 1 MW DG could store the start up power over a two to twenty minute period (10% of the DG load)


What are you going to store it in? Are we talking giant capacitors here? A flywheel?

Let me add that a BFR is a LOT less complicated than a nuke plant.


But also far more dynamic.

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Postby MSimon » Sun Aug 10, 2008 8:13 am

What are you going to store it in? Are we talking giant capacitors here? A flywheel?


A flywheel. Also good for things like pulsing a high powered laser or a rail gun.

The cooling problem is trivial for a pBj BFR operationally. That is once you figure out how to do it it will not have much effect on plant operation. Or size.

Think of it this way: a nuke or any steam plant operates at a 20F (10 degC) delta T sea water cooling loop. The BFR burning pBj can operate at a 100 deg F delta T. That means 1/5th the sea water flow and a correspondingly smaller heat exchanger.

The #1 problem is: can the reactor be made small enough?

So the deal is: start with the bigger ships (CVs ) and then work your way to the smaller ships as the technology improves and experience is gained.

As to the dynamics: the control is all electronic. No moving mechanical parts like control rods or delays from heat diffusion. So it all balances out. You do have delays from fuel injection but in a large reactor you have a few seconds of fuel inventory so the control loop for fuel injection will be a slow loop - on the order of 100 ms.

In addition the bigger ships have steam plants so you can do them with D-D until you figure out how to make pBj work - if you are in a hurry.

The biggest problem will be the design. Once that is done the rest is relatively trivial.
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Postby Jeff Peachman » Tue Aug 12, 2008 9:00 pm

The cooling problem is trivial for a pBj BFR operationally.


A peanut butter and jelly fusion reactor....
- Jeff Peachman

MSimon
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Postby MSimon » Tue Aug 12, 2008 10:52 pm

Jeff Peachman wrote:
The cooling problem is trivial for a pBj BFR operationally.


A peanut butter and jelly fusion reactor....


It is an old joke around here it stands for:

protons
Boron
joules
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Postby MSimon » Tue Aug 12, 2008 11:07 pm

Let me add that keeping the magnets superconducting should take about a few KW. That is easy to do and the technology is well understood. Think MRI magnets. I think they currently have to move a few watts of power per magnet (up a very steep hill) to keep them at 4K.

If the water jacket next to the LN2 cooling loop is at room temp the problem is nearly identical to an MRI magnet.

The toughest deal is absorbing neutrons which will present an unacceptable thermal load to the superconductors. I know how to do that in principle. Thermalize the neutrons. Absorb them in B10. Reducing the flux by 1E20 is not hard (about 5 or 10 mm of B10 will do the trick). It just requires working out the trade offs. The hardest part is making sure the water jacket is thick enough. To figure that out we will need to know the energy spectrum of the neutrons.
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