Rick Has A Word or two for sceptics.

[TallDave]

I was boggled by that for a bit when I first ran across it too.

It's like burning a gallon of gasoline and getting half a gallon back. Seems like it ought to be impossible.

It may have big implications in a couple hundred years, if we don't have an economic method of fusion yet. It seems hard to believe we'll have any new sources of fossil fuels in the 23rd.

[blaisepascal]

I was boggled by that for a bit when I first ran across it too.

It's like burning a gallon of gasoline and getting half a gallon back. Seems like it ought to be impossible.

It may have big implications in a couple hundred years, if we don't have an economic method of fusion yet. It seems hard to believe we'll have any new sources of fossil fuels in the 23rd.

The only reason we aren't building breeder reactors for power is political. You see, a breeder reactor (or it's close kin) is the only way we have of producing Pu-239 in large quantities. The US, the USSR/Russia, China, England, France, India, Pakistan, South Africa, Israel, and probably a handful of other nations have been making Pu-239 in large quantities for 65 years now, using the functional equivalents of breeder reactors. Converting "fertile" U-238 into "fissile" Pu-239 is old-hat.

The problem with a U-238-based breeder reactor is that Pu-239 is too useful for making bombs. Attempting to make a U-238 breeder power reactor looks indistinguishable from attempting to make a Pu-239 production plant. Attempting to make a Pu-239 production plant is the type of thing that can get you looked at funny by the international community.

The Th-232 based breeder cycle has a couple of differences. First, while the generated fuel (U-233) is fissible, and the US has made a test bomb based on it, it also generates a significant quantity of U-232, which isn't fissible. The quantity is small, but is "significant" because U-232 rapidly breaks down into strong gamma-emitters. You can handle manufactured Pu-239 in a isolation box with gloves; it's just an alpha emitter. If you tried that with U-233 you'll get fried by the gammas. So from a "proliferation" standpoint, it's much nicer. It's harder to make a bomb, and if you don't have big expensive facilities obviously dedicated to it, you'll kill yourself trying.

But there's another engineering problem with Th-232. While the conversion of U-238 + n to Pu-239 happens fast with two beta decays, the corresponding conversion of Th-232 + n to U-233 doesn't happen so fast. There are two beta decays, but instead of having half lives in the fractions of seconds, the two decays have half lives in the minutes to days range. So designs for Th-232 breeder reactors try to come up with some way to physically separate the Pa-233 from the neutron flux until it has decayed into U-233.

[Soylent]

Can someone give me an explanation how breeder reactors work? I'm floating somewhere between magic and neutron bombardment, and neither is a terribly satisfying explanation.

Thorium-232 and Uranium-238 won't sustain a chain reaction. The only isotope suitable for a chain-reaction you can find in reasonable amounts in nature is uranium-235.

When you fission U-235 you get between 2 and 3 neutrons on average depending on the speed of the neutron. When U-238 or Th-232 absorb a neutron you get U-239 and Th-233 respectively, which if you wait a little while eventually decay to plutonium-239 and uranium-233. These will support a chain reaction, so they can gradually replace the U-235 you've used up if you can produce them faster than the U-235 you originally put in.

Because of the need to limit the number of unproductive neutrons that neither cause a fission reaction or produce new fissile Pu-239 or U-233, you are forced to adopt some strange constraints on reactor design.

When you use the plutonium-239 fuel cycle you are more or less forced to use a fast neutron spectrum reactor, typically cooled by some liquid metal(lead-bismuth or sodium). Operating in a fast spectrum forces you to have a rather large fissile inventory which makes it hard to deploy as many reactors as rapidly as you might want(but there's not necessarily any rush since once-through reactors produce some plutonium in spent fuel that you can use for starting up IFRs etc.).

With thorium it turns out that a liquid fluoride thorium salt reactor can be a breeder reactor if you continually remove fission products(especially short-lived gaseous xenon-135 that soaks up neutrons like nothing else). Because the core is liquid you don't need to do any conversion or fabrication like you do with solid fuel elements, which has the potential to make reprocessing really cheap.

[Soylent]

The only reason we aren't building breeder reactors for power is political. You see, a breeder reactor (or it's close kin) is the only way we have of producing Pu-239 in large quantities.

That's a bit of fib(not necessarily through any fault of yours since this is the information that gets repeated over and over again).

Plutonium for weapons is only any good if it's mostly Pu-239. If there's too much Pu-240 in there it throws off a lot of extra neutrons(there's a small chance for plutonium to decay by spontaneous fission, 1 kg of Pu-239 undergoes 10 spontaneous fissions per second, while 1 kg of Pu-240 undergoes 415 000 spontaneous fission per second). If you have too many background neutrons it's difficult to make the bomb reliable. Tritium boosting and advanced neutron generators where invented to try and increase reliability, yields and resistance to attacks by overwhelming the weapon with neutrons(from another nuke).

Plutonium-241 is also a problem because it has a short half-life and gives off a lot of heat; that's problematic when you have a lot of precisely crafted, temperature-sensitive high explosives. It's probably not an insurmountable problem, but it means you sacrifice storage life and have to skip directly to some advanced design that is sufficiently miniaturized.(from publically available information I believe it is some variation on the linear implosion design; for thermonuclear weapons the primary is just there to compress the secondary, it has to be small and lightweight, not efficient).

The way to limit the formation of Pu-240 and Pu-241 is to have very little Pu-239 in the reactor that can be exposed to neutrons; you accomplish this by changing the fuel very frequently. It's rather telling which reactors have been chosen for producing weapons grade material; it's the ones that let you irradiate whatever you want(i.e. heavy water research reactors for producing medical isotopes, testing fuel elements etc.) or really crude air-cooled graphite reactors where you just push in a uranium slug and one of the irradiated slugs fall out at the back, ready for reprocessing.

If you have to shut down the reactor to refuel and you have these big, pesky cooling towers; you're essentially sending smoke signals to spy satellites telling them that you're shutting down the reactor and refueling every few weeks.

If you're not producing the fuel indigenously you're also going to have the russians(or whomever) wonder why you're refusing to return it; did you perhaps strip of the cladding, chop it into bits, disolve it into hot nitric acid and extract the plutonium by yourself even if you promised not to?

[Helius]

Which brings us 'round to blaise's first sentence.

The only reason we aren't building breeder reactors for power is political.

The most powerful dynamic is that the power density of Nuclear Power is so great, that'd simply blow the doors of any other type of power source out there. If you want to know why something is either pursued or avoided, look first at it most powerful dynamic.
We have a DOE that is really towing the minimalist line, and is thus avoiding this ever more obvious solution of Thorium or depleted Uranium breeder reactors.

So Drink your snake oil, and buy your windmills, no real solutions will be pursued until India or China gets this ball rolling.

[chrismb]

I agree - for what it's worth [to the thread] I do not believe the power density of fusion power will ever be as great as that possible with fission. (yeah, I know the claimed power density for Polywell....).

We might well get there [fusion power] but once it gets into the unit watts per cc it looks to me with any cursory calculation that there are some highly unstable and/or 'high density' ions going around that won't last too long in that state.

A GW sized nuclear power station looks like no more than a small office block. It is a technical marvel that fusion technologies will never match.

If we get to 'fusion', all well-and-good, but fission power is here to stay and will always be part of the energy mix now, come-what-may, and in my opinion should always be so. So let's get on with it and develop those Super Phenix type fast breeders and reprocessing safety, thorium processes, &c., to fruition and stop p*ssing around wishing for a perfect solution before anyone lifts a finger and being too timid to get stuck into some known technologies that have not yet been taken through to their ultimate implementation.

[MSimon]

I agree - for what it's worth [to the thread] I do not believe the power density of fusion power will ever be as great as that possible with fission. (yeah, I know the claimed power density for Polywell....).

We might well get there [fusion power] but once it gets into the unit watts per cc it looks to me with any cursory calculation that there are some highly unstable and/or 'high density' ions going around that won't last too long in that state.

A GW sized nuclear power station looks like no more than a small office block. It is a technical marvel that fusion technologies will never match.

If we get to 'fusion', all well-and-good, but fission power is here to stay and will always be part of the energy mix now, come-what-may, and in my opinion should always be so. So let's get on with it and develop those Super Phenix type fast breeders and reprocessing safety, thorium processes, &c., to fruition and stop p*ssing around wishing for a perfect solution before anyone lifts a finger and being too timid to get stuck into some known technologies that have not yet been taken through to their ultimate implementation.

If you include the steam plant the numbers are not near as good as the reactor alone.

If an aneutronic machine can be made to work I think the overall balance might come out in favor of fusion.

[blaisepascal]

If you include the steam plant the numbers are not near as good as the reactor alone.

If an aneutronic machine can be made to work I think the overall balance might come out in favor of fusion.

I think you mean an aneutronic direct conversion machine. Otherwise I think you're back to needing the steam plant.

[KitemanSA]

I agree - for what it's worth [to the thread] I do not believe the power density of fusion power will ever be as great as that possible with fission.

The SF author David Weber seems to agree with you. In order to have a small, effective stellar war-craft he had them use those re-discovered, antequated fission reactors rather than the huge, mega-interstellar-ship sized fusion reactors.

[jmc]

Posted by: WR Jonas
Jun 19, 01:18 PM

I have spoken out here about my skepticism based on a provable dynamic and truth . There will always be ample reasons to spend other peoples money. To give this research or any other some noble purpose or cause does not necessarily make the aims correct or worthwhile .
If we were still shooting rockets at the moon and coming up empty or failed we would have stopped it a long time ago. This canard of ,try until we run of money, is the basis for continuing a proven failure. Because it is Navy project doesn't give it any greater chance of success.
So , how about we put the fusion research industry on a time, results or dollar limit to see if it is ever going to produce anything . Any takers?

Back to the original post. I don't like the attitude of having a finite number of attempts and then agreeing to give up for ever more.

Should we have put Leonardo de Vinci on a tight budget with heavier than air flight and if he failed to deliver declare it impossible and ban all further research into the subject.

Should we have established success and failure criterion for the computer developed by Charles Babbage and then after he failed ban all further research into the development of computers.


Some things in this world are worth striving for such as nuclear fusion, economic spaceflight, cancer and AIDS research, delaying the aging process and producing more food for the world through Genetically engineering higher yield crops.

These general nobel goals aren't just things we should try once while establishing arbitrary failure criteria and then if those arbitrary failure criteria are met give up forevermore and never try again.

There's alot to be said for the perseverance that motivates a man to pick up the torch from where his predecessor has failed and carry on, its the spirit that gave us the industrial revolution.

[taniwha]

There's alot to be said for the perseverance that motivates a man to pick up the torch from where his predecessor has failed and carry on, its the spirit that gave us the industrial revolution.

I'd be inclined to say it's the spirit that gave us the stone axe, are maybe even that blade of grass stuck into the termite hill. If it wasn't for that spirit, we wouldn't have a torch to pick up!

[chrismb]

I'd be inclined to say it's the spirit that gave us the stone axe, are maybe even that blade of grass stuck into the termite hill. If it wasn't for that spirit, we wouldn't have a torch to pick up!

hmm....

which came first... instruments of war, or instruments of agriculture?

Tools are a means used by great thinkers to advance our understanding by ingenious use of said tools, but they are financed and constructed at the behest of politically motivated warfarers. We do not yet appear to have moved away from that model, but, perhaps, one day we may and we will then justify the title of civilised.

We are not currently civilised, the Western world remains significantly militarised. I think this situation has changed somewhat over time, but whether being civilised will be a sufficient calling that we no longer have a need for military motivations has yet to be seen.

[jmc]

I think there's a lot more money going into pure research and peaceful industrial research financed by corporations now then ever before, but I guess there still an awfully large research budget from the military.

An unlimited source of money and the ability to concentrate large quantities of wealth comes from taxation, the ability to tax comes from power, power comes from fear and fear comes from the ability to kill. I suppose that why the large expensive high risk projects that required a steady stream of concentrated wealth tend to be of a military nature.

Having said that, there's always the LHC..

[chrismb]

An unlimited source of money and the ability to concentrate large quantities of wealth comes from taxation, the ability to tax comes from power, power comes from fear and fear comes from the ability to kill. I suppose that why the large expensive high risk projects that required a steady stream of concentrated wealth tend to be of a military nature.

Exactly. Uncivilised.

Having said that, there's always the LHC..

According to some, not only uncivilised, but an actual abomination to God!

Yes, LHC is a good example of what we can do, and shows the way...

[scareduck]

Back to the original post. I don't like the attitude of having a finite number of attempts and then agreeing to give up for ever more.

Things cost money. If something's repeatedly failed, especially if it's been an expensive failure, it's not likely to be retried (although war seems to be an exception to this rule).

Remember, the reason we're all here is to find a path to cheap energy. There's plenty of paths to expensive energy. We don't care about them, for a good reason.