[Klaustrophobia]

So as not to derail the other thread with an actual topic, let's do this here   Mods could you delete/merge posts as necessary?

I'm an enthusiastic amateur, and I appreciate your insights.

I am a bit confused by your comments on fuel rod degradation, though.  My impression was that the build-up of fission products can cause the rod itself to crack and release by fuel and byproducts directly into the coolant.  Does the reaction get poisoned by fission products before integrity becomes an issue, then?

While I do see the difficulties of dealing with liquid fuel, it seems to me that the advantages ought to outweigh them.  Even assuming fuel rod degradation is a non-issue, you are still going to have to remove a huge quantity of unburned fuel because of fission product build-up which eventually poisons the reaction.  Again, I'm no expert, so I only have a couple examples to throw out there, but Xe-135 is the one I'd been warned about.  In a liquid fuel system, separation of these byproducts from the still burnable fuel would be child's play by comparison.  Some of it will gas off (collect at the top of the reactor), some will become insoluble and fall out of solution (a bit more tricksie, but not insurmountable), some would still be liquid, but could be separated chemically or through differences in density.

I had not given much thought to the fact that you'd have to kick start the reaction with something else.  That is very good point.  Nominally, you'd be using U-233 in the kernel and Th-232 in the blanket, but in order to get to get the U-233 you'd have to make it in a fast breeder reactor.  Once you get the fuel cycle started in earnest, this problem would go away, but it does present a significant hurdle.  One would think, however, that the breeder reactors we already have for production of weapons-grade isotopes could be put to this task?

As far as proliferation goes... my issue with it is mostly that it has been made an issue.  I would probably sleep a little better knowing we weren't making more weapons-grade materiel, but at the end of the day, it is the fact that "proliferation" is being used as an excuse not to reprocess our fuel or burn it in a more efficient manner that really sticks in my craw.  If it were possible to side-step the proliferation issue by saying, "Look, we've got a fuel cycle that doesn't produce anything that could be used to build a nuclear bomb," my hope is that some of the resistance to nuclear in general, and more long-term sustainable fuel cycles specifically, could be overcome.

Fuel rod degradation:
You are quite correct that fission products (especially the gasses) expand, and this WOULD cause the fuel rod to crack, but this effect is known and they are designed around that.  A fresh fuel rod has a gap between the fuel and the clad that allows the fuel to creep out during operation.  Eventually this gap closes (for the most part), which has some benefits for thermal performance of the rod.  The gasses eventually escape the fuel into the gap, and are channeled up to the top of the rod where there is another gap and some springs and such to relieve that pressure.  Fuel rod degradation that we have to worry about comes from two sources.  The first and generally most limiting is the temperature and chemistry of the coolant water.  High temperature water his more corrosive, and tends to build up deposits on the zircalloy cladding.  (Fun fact:  the word "crud" is actually a nuclear acronym, from "Crystal River Unidentified Deposits."  They saw gunk on the rods, and didn't know what was causing it.)  The other is accidents, where large, sudden temperature gradients can crack the fuel.  Radiation damage (the neutrons, gamma rays and such) DOES degrade metal structures, but this is quite a slow process, much slower than the fuel cycle. 

The life of the fuel isn't so much determined by poisons as it is simply the depletion of fissile material.  There are dozens of "poisons" that pop up during operation, but really only two that contribute enough to concern ourselves with.  One is samarium-149, which has the considerably smaller reactivity effect of the two.  This one is essentially stable, and is only removed from the reactor by burnup (instead of also by decay).  Samarium builds up to an equilibrium level in about 40-50 days and pretty much stays there, so it is just accounted for as part of the fuel.  The other is the one you identified, Xenon-135.  This is the one we actually have to account for.  It has a non-negligible reactivity effect, but it DOES decay.  It will also build up to an equilibrium level based on the reactor power, but after shutdown it will decay away.  When we operate the reactor, we have nice little graphs that tell us the reactivity contribution of the xenon based on operation time and time since shutdown.  Xenon is the only one we worry about when operating the reactor.  The bottom line for poisons as far as fuel lifetime is concerned, is that they don't continually build up.  They reach a maximum level during operation, and the larger of the two even decays away after shutdown.  The reason the fuel becomes unusable is because the U-235 and the Pu-239 that is bred from U-238 during operation have depleted to the point where the reaction can't be sustained any longer.  Technically you COULD squeeze a drop more power out of the core at end-of-cycle by shutting down and letting the xenon decay away, but you can imagine how horribly uneconomical that would be.  Startups and shutdowns of commercial plants aren't the trivial matter like it is at our research reactor. 

Now I'm about out of time for right now, so I'll have to come back later to the liquid fuel and other stuff, but you've raised some good points there.  Keep asking/commenting, I'll answer as much as I can.

[perihelion]

Actually, I was wondering if/when we'd hit the split threshold.

I need to dig out some older articles or find a decent text on the subject.  I don't have any of this in front of me and I'm going off my rather suspect memory.  What I remember is a chart that detailed raw tonnage of fuel required and waste produced at various stages in the fuel cycle for both LWR and LFTR reactor designs.  That chart made it look like you were going to be able to get a lot more energy per unit mass of fuel in a thorium fuel cycle than you do in a LWR design.  Like, by nearly two orders of magnitude.  I was given to think this is because more of the fissile / fertile fuel gets burned in the thorium cycle, not that there is inherently more energy to be had in one cycle versus the other.

What I'm hearing from you, though, is that there isn't that much fertile / fissile material left in the fuel rods by the time they are taken out of service.  Is it that, or is "critical mass" just a significant percentage of total fuel mass in a fuel rod?

[Klaustrophobia]

I wrote this last night, but the internet in this dorm is wack and it wouldn't let me post it. 

Part two.  I'll respond directly to your latest post in the next installment .

Liquid fuel:
Maybe this is something that will be looked at in the future, maybe not.  It does remove the first step of reprocessing, which is dissolving down the waste, but chemically separating it from there is probably the harder of the two steps.  After giving it some more thought since my last post, I've identified other potential problems.  A big tank of this liquid solution would not work for a reactor.  The heat needs to be carried away to the turbines by a coolant, and you can't pass a coolant through a tank of liquid fuel without taking the liquid fuel with it.  This means the liquid would still have to be contained in some sort of enclosure, at which point there isn't a whole lot of benefit left over solid fuel.  You also loose the ability to distribute the fuel loading optimally.  Believe it or not, a homogeneous core arrangement is NOT ideal.  Enrichment actually does vary throughout the core, both axially and radially, to even out the flux profile and reduce peaking (important for even fuel burn across the core, and more overall power output).  And then back to my original thought, that radioactive liquids are just really nasty stuff.  An extremely high-level waste liquid, and a ****load of it, is frankly terrifying.  Just the other day I had to handle a very low-level source of liquid cesium for a lab, and even that made me a bit uncomfortable.  You run into worries about spreading and ingestion that aren't a problem with encapsulated solids.  It can get on your hands and inadvertantly get rubbed around your mouth, nose, and eyes.  Disposal of it is a great big headache also. 

There is one fundamental design that is something of a happy medium though, the pebble-bed reactor.  The fuel is still solid, but instead of rods, you have tennis ball sized spheres of fuel just dropped into the moderator/coolant.  I haven't seen a lot of detail about any of these designs, but I'm most excited for this gen-5 design.  The fuel isn't tied down, so you can do stuff like refuel without shutting down by dropping burned up spheres out of the bottom of the reactor and tossing fresh ones in the top.  With the solid balls, we still retain that important first barrier to release.  Just as an intuitive guess, I would think they are probably more corrosion and crack resistant than rods due to their smaller size and different flow paths, but I have nothing to back that up. 

I had not given much thought to the fact that you'd have to kick start the reaction with something else.  That is very good point.  Nominally, you'd be using U-233 in the kernel and Th-232 in the blanket, but in order to get to get the U-233 you'd have to make it in a fast breeder reactor.  Once you get the fuel cycle started in earnest, this problem would go away, but it does present a significant hurdle.  One would think, however, that the breeder reactors we already have for production of weapons-grade isotopes could be put to this task?

Certainly that is a possible, and I would think probable source of plutonium.  We could get even more from current LWRs if we ever get the green-light from the government to reprocess.  But then, if we went that far, we wouldn't really even need the thorium fuel.  The thorium fuel concept is primarily to address the concern of running out of U-235.  If we started actually running reprocessed plutonium as fuel, and modified LWR designs to be more efficient at breeding it from U-238, our fuel supply becomes effectively limitless even without thorium.  On the flip side, if the US continues to insist on screaming "non-proliferation", the thorium fuel cycle can be used with U-235 as the catalyst.  The reason Pu-239 is used in the current on-paper designs is that it has a naturally higher reactivity than uranium, and therefore you need less of it and can use more thorium.  One final note about the thorium fuel that makes it not attractive as of now is the thermal issues that arise with a heterogeneous fuel rod of two different fuels.  Obviously, the easiest way to fabricate a thorium-plutonium (or whatever) rod would be to have a core of one surrounded by a clad of the other (called duplex fuel).  The design team I mentioned earlier looked into exactly this, and as it turns out, the thermal gradients involved across the different metals is VERY poor and can lead to unacceptable fuel centerline temperatures.  The solution to this is to use multi-plex fuel, which is several alternating layers of either fuel.  This drives the cost up rather substantially.  We very well may see thorium used eventually.  It's not a BAD design, but it's not better than what we currently have at this time.  This will be decided economically by the individual vendors/utilities if or when uranium prices climb to the point where thorium is viable.

Proliferation:
I think we're basically on the same page here.  It would be nice if we didn't have to deal with it at all, but as it stands, we do, and I really think we need to not let it hold us back this much.  Most of the other nuclear states have already cleared this hurdle, I just don't see what is taking us so long.  Actually I do see EXACTLY what it is, but that's an issue for another thread.

Alright, done for tonight.  Off to GE's fuel fabrication plant tomorrow, so probably nothing else until saturday.  But if you're tired of reading me anyway, I can shut up whenever 

[Kosh]

If liquid cores are such a problem why not just skip to gas core?

[Klaustrophobia]

... No.  Every problem I just described with liquid fuel would be WORSE with a gas.

[perihelion]

I have to agree with Klaustrophobia here.  The whole point of a liquid fuel reactor is that you can operate without pressure.  The pressure in the reactor is the same as the pressure out of the reactor: 1 atm.  In a LWR the water is under pressure to keep it from boiling so you can achieve higher core temperatures (among other reasons).  The risk of leaks, the difficulties of maintaining 100% integrity, and much higher when the reactor is under pressure.  All containment vessels must have very thick walls.

In a liquid fuel reactor (liquid salt or liquid metal) the coolant and the fuel are one and the same.  The liquid chemistry is selected with a lot of goals in mind, but one of the biggest is that it have a very high boiling temperature.  Liquids are essentially incompressible (their volumes change so little with changes in temperature that the change is frequently neglected in engineering calculations).  So, you do not need a huge reactor vessel capable of holding in several atmospheres of pressure.

If you switch to a gas core, then you have the negatives of liquid fuel (radioactive fluid that will, by its very nature, be strongly resistant to containment) AND you have all the negatives of a pressurized core, because gas is very compressible.  Pressure will vary quite a bit with temperature.  In a fixed volume, that should mean that density of the gas does not change, but I still wonder what the increased pressure would do to neutron absorption cross-section.  I fear the thing would be a ***** to control.

There's also the small detail that, in the event of a containment failure, gravity will insure that it will go down.  Spilling liquid fuel could be caught in a catchment device beneath the reactor core that spreads it out to the point where it cools and solidifies.  (I read an article that detailed this exact technique in American Scientist V98 No. 4.)  In the case of a pressurized gas, who the hell knows where it would go?

[Kosh]

So, in other words a liquid core could allow the reactor to be miniaturized. Isn't that a good thing? In the event of a catastrophic systems failure or leak of some kind, as scary as it might be there should be procedures to clean up the mess.

[perihelion]

That is exactly it, yes.  Many of the liquid fuel designs I've seen being proposed have been small enough that the entire reactor could be fit into a standard shipping container.  The wattage runs the gammut from a couple MW up to a couple GW.  It is far more scalable than LWR designs.  Hyperion Power Generation has been trying to commercialize these miniature designs for several years now.

And to me, as long as the melting point of the fuel / coolant is above, say 100°F, at least some of the concerns of radioactive liquid ought to be mitigated.

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

[Klaustrophobia]

Ok, I think I see the root of misunderstanding here.  That design is not liquid FUEL, it is liquid metal COOLANT.  If the design you linked isn't one of the liquid fuel ones you are talking about, please link one (preferably not a wikipedia page).  I don't have time right now to go into a detailed response, but I haven't forgotten this thread.

[perihelion]

You are right.  I had missed that the fuel wasn't carried by the coolant in the Hyperion design.  I knew it was uranium nitride, but somehow the fact that a nitride is practically guaranteed to be solid slipped my notice.

The main article I've been reading on the LFTR design is "Liquid Fluoride Thorium Reactors," by Robert Hargraves and Ralph Moir in the current edition of American Scientist from the Sigma Xi Research Society.  It isn't the same as a technical journal (it is very obviously dumbed down to layman's terms), but it is peer reviewed.  Unfortunately, it is also only available in hard-copy or paid online subscription.  I scanned the bit with the fuel cycle comparison diagram.  It sounds like it won't be anything you haven't seen before, though.

[attachment deleted by ninja]

[Klaustrophobia]

if this is a legitimate attempt at a liquid fuel design, it would be the first i've ever heard of.  that being said, there is a LOT of stuff published that is just far-reaching theoretical ideas with little chance of ever being implemented or even developed in the relatively near future.  for example, a recent design project here was a reactor for the moon.  there are likely hundreds of reactor designs that currently exist on paper that haven't been and may never be constructed, for a variety of reasons including materials limitations or just plain lack of practical/economical use for it.

[perihelion]

Well, I can tell from the article I cited that there at least was an experimental molten salt reactor that ran for four years at the tail-end of the 1960's that proved out the concept.  The thorium blanket wasn't included, but the liquid fluoride U-233 core was run all that time.  Online refueling was demonstrated (no weeks-long turnaround required).

I'm not sure I've made this clear yet, but just in case, the Hyperion Reactor is liquid metal-cooled fast neutron reactor.  That is entirely separate from the liquid fluoride thorium reactor in the article.  I only brought the Hyperion reactor up because I was attempting to show liquid fuel reactor designs that were approaching commercialization.  Unfortunately I missed the detail that the fuel was not actually liquid after all.

[Rand al Thor]

Interesting stuff. The general public definately needs to be coaxed out of it's (unfortunately somewhat deserved) fear of all things nuclear. Much as I'd like fusion to be ready for switch on, nothing other than fission plants offer a reliable steady alternative to fossil fuels and the 3rd and 4th generation plants, from what I've read, seem to be fairly foolproof.

I said 'fairly'.

[Kosh]

Interesting stuff. The general public definately needs to be coaxed out of it's (unfortunately somewhat deserved) fear of all things nuclear. Much as I'd like fusion to be ready for switch on, nothing other than fission plants offer a reliable steady alternative to fossil fuels and the 3rd and 4th generation plants, from what I've read, seem to be fairly foolproof.

I said 'fairly'.

As long as they listen to environmentalists that will never happen.

[Klaustrophobia]

Which is why we need to go straight to the enviornmentalists and gently explain that we're on their side 

[Klaustrophobia]

I have to agree with Klaustrophobia here.  The whole point of a liquid fuel reactor is that you can operate without pressure.  The pressure in the reactor is the same as the pressure out of the reactor: 1 atm.  In a LWR the water is under pressure to keep it from boiling so you can achieve higher core temperatures (among other reasons).  The risk of leaks, the difficulties of maintaining 100% integrity, and much higher when the reactor is under pressure.  All containment vessels must have very thick walls.

The pressure of a reactor is determined solely by the coolant.  A liquid fuel reactor that uses water for coolant would still have to be pressurized.  I don't know the fluid properties of sodium for liquid metal coolant, but I would guess that it could operate at much lower pressure.  *googles boiling point of sodium* ~1600 F.  No pressurization would be NEEDED, but it still might be used for efficiency/economic considerations.  However, by using liquid metal coolant, you trade for other problems.  Sodium is a nasty corrosive, and liquid metal is a b!tch to pump.  It also needs to be kept above its melting point (~200 F) at all times.  The containment vessel isn't there just because of the pressurization.  It's there to contain radiation release in the event of an accident, and serve as a missile shield for the reactor.  You'd still have a containment building with very thick walls even with an atmospheric pressure reactor. 

In a liquid fuel reactor (liquid salt or liquid metal) the coolant and the fuel are one and the same.  The liquid chemistry is selected with a lot of goals in mind, but one of the biggest is that it have a very high boiling temperature.  Liquids are essentially incompressible (their volumes change so little with changes in temperature that the change is frequently neglected in engineering calculations).  So, you do not need a huge reactor vessel capable of holding in several atmospheres of pressure.

The coolant and the fuel CANNOT be the same.  The very principle of how power plants operate is that the coolant carries heat away from the source (core, coal burner, whatever) and to the turbines and then the condenser.  The fuel CAN'T cool anything, it is SUPPLYING the heat.  This would be analogous to a coal plant trying to use flame to carry away the heat from the burning coal (ok that was a really poor analogy, but do you see what I'm trying to say?).  I've been wracking my brains for a bit trying to think how some radical design may try to make this work, and I've only come up with one possibility.  If you have the chance, could you show me any such design you have seen?  For my idea, there would be a giant tank or vessel full of the liquid fuel, with inlet and outlet much like the hot and cold legs currently.  The big tank would serve as the core, with enough mass and density of fuel to sustain the reaction.  The mass of liquid outside of the tank would have to be small enough such that it cannot be critical, and the reaction only occurs in the "core".  This sort of design, if it would even work, is just LOADED with problems that make it anywhere from economically/operationally undesirable to downright dangerous.  Controlling this thing would be a nightmare.  Again, the radiation containment is at the forefront of my mind.  You've got pipes carrying HIGHLY radioactive liquid out of the core and all over the plant.  Workers CANNOT be around that, so maintenance work becomes damn near impossible.  Which is unfortunate, because you're going to need a lot more of it.  A lot more radiation damage will be done to components, and I would venture to guess your chemical treatment options for the liquid to ease corrosion issues is going to be severely limited.   
I mentioned that the reaction would only occur in the tank.  However, 7-10% of the power from the fission reaction is delayed.  Unstable fission products that further decay supply the remaining 7-10% of the power, which occurs from a few seconds after the fission event up to several minutes.  I.e., the fuel is still essentially active in the pipes, at 7% or so of full power.  That doesn't sound like a lot, but 7% of 3400 (typical thermal power of a 1000 MW electric plant) is 238 MW.  Our ENTIRE reactor here is 1 MW. 

If you switch to a gas core, then you have the negatives of liquid fuel (radioactive fluid that will, by its very nature, be strongly resistant to containment) AND you have all the negatives of a pressurized core, because gas is very compressible.  Pressure will vary quite a bit with temperature.  In a fixed volume, that should mean that density of the gas does not change, but I still wonder what the increased pressure would do to neutron absorption cross-section.  I fear the thing would be a ***** to control.

Cross sections vary with density, not pressure.  Pressure isn't really a big deal at all to a reactor.  You can set the pressure to whatever you need it at (via pressurizer or simply throttling valves), and under normal conditions the reactor operates with no temperature fluctuations.  Pressure vessels are a bit expensive, but they aren't THAT bad.  And they can certainly handle 2200 psi with ease.  It would be nice to get them smaller to cut costs, but as far as safety goes, the pressure vessel is among the least worrying things in the plant.

There's also the small detail that, in the event of a containment failure, gravity will insure that it will go down.  Spilling liquid fuel could be caught in a catchment device beneath the reactor core that spreads it out to the point where it cools and solidifies.  (I read an article that detailed this exact technique in American Scientist V98 No. 4.)  In the case of a pressurized gas, who the hell knows where it would go?

Spilling liquid fuel that solidifies is nothing to brag about.  This is essentially what happened at TMI, and that mess is STILL sitting sealed up in its containment building.  A pipe break in that design, something the NRC requires to be analyzed, would pretty much be game over.  You instantly get the results of a meltdown of a solid fuel reactor.

[perihelion]

This is not the LFTR, but it is similar. 

http://nuclear.inl.gov/gen4/msr.shtml

I am not having good luck finding a diagram of the LFTR that actually depicts it in the way the American Scientist article described.  That article included a picture showing both the kernal of liquid fluoride-salt bearing U-233, and then a "blanket" of salt bearing Th-232 with chemical processing loops move U-233 from the blanket into the core and separate out waste products that could not be burned up.

The diagram did not specify the method by which heat would be extracted.  It was only depicting the reactor itself.

I'm confused by your confusion regarding coolant versus fuel.  Surely I'm preaching to the choir when I state that there are usually multiple cooling loops?  In most LWR's you've got the primary cooling loop that runs through the reactor.  The secondary loop runs through a heat exchanger and then goes to the turbine.  The condenser normally has yet a third cooling loop.

In LWR, the primary coolant does not have fuel dissolved in it, but it does "contain" the fuel.  In a liquid fuel reactor, the primary coolant contains dissolved fuel.  Obviously, there is another coolant loop (or two) before you reach the turbine.  No one is talking about expanding radioactive liquid through a turbine!

I fear I'm bungling explanations here.  I wish I had better online articles to direct you towards.  Unfortunately, almost everything I've read has been in physical periodicals, most of which I recycled years ago.

[Klaustrophobia]

PWRs have primary and secondary loops for power generation, the tertiary is the lakewater or whatever for the particular site that is the coolant for the condenser.  A BWR has only one loop plus the condenser.  Obviously (at least I really hope) the liquid fuel wouldn't be boiled, so you're quite right that it wouldn't pass through the turbine.  I shouldn't have said or implied that or whatever I did, but it was late and I was tired .  We still have the problem of sending the fission products all over the primary side and through the steam generators though.  In LWRs, the coolant does pass through the fuel, but it does not contain any fuel or fission products unless there are any leaker fuel rods (which there is an industry-wide initiative to completely eliminate by the end of this year). The only radioactivity in the primary loop coolant water is oxygen that is activated to N-16, which has a 7 second half-life and decays away essentially within one minute.  Impurities could also activate, but tight control over that is kept by the Chemical and Volume Control System.  In a liquid fuel/coolant design, the fission products that are usually cooped up in that first barrier of the fuel rod would be deliberately spread outside of the reactor vessel.  While it would remain inside the containment building, on-site dose levels would be astronomical.  I sure as hell am not getting next to a pipe that has fresh fission products flowing through it.  Not to mention if you get a leak in the steam generator tubes and have crossover.  You can see how that might be problematic.

The fact the article did not mention heat removal suggests to me that this was probably a design to replace JUST the solid fuel; I would guess contained in tubes and arranged in a similar lattice type array.  I guess the liquid could be flowed through the tubes and connected up to those chemical processes, but the idea of flowing fuel in and out of the core like that sill makes me a bit uneasy. 

I'm really intrigued by this now.  I'll ask the professor I'm working with for the camp if he knows of anything like it on monday.

[Iss Mneur]

The guys that run the Google Tech Talks seem to rather interested in LFTR and they now have three videos about LFTR on youtube.  It is sort of assumed that you have watched the three in order, but all three videos explain the history of LFTR and do have a diagram of the proposed fuel design of the reactor (but I do suggest watching all three, as the three different speakers cover slightly different areas).

http://www.youtube.com/watch?v=AHs2Ugxo7-8
http://www.youtube.com/watch?v=VgKfS74hVvQ
http://www.youtube.com/watch?v=AZR0UKxNPh8

The third video also talks about how LFTR can be used to burn down the current stock pile of long term radioactive waste. As well they talk about because both the blanket and the fuel are liquids they can easily remove the poisons, and the interesting lighter radioactive materials. 

The fluoride salts that everything is dissolved in boils at some 2000 degrees Celsius (and solidifies about 200 degrees Celsius) and the LFTR reactors are designed to run around 800-900 degrees Celsius.  These properties allow for the reactor to be load following because as the fuel heats up it becomes sub-critical causing the fuel to cool, as the fuel cools the it becomes super-critical causing the fuel to heat up. 

These properties also allow the reactor to have, what I personally think to be the coolest feature, the fluoride salt drain plug.  You have a fan keeping a drain plugged (by keeping the salt below the freeze point) so if the power in the reactor building fails (or you want to stop the reactor) you let this plug melt (because it is not being cooled) and the fuel drains into a non critical shape and solidifies.  When you want to start the reactor up again, you heat the storage area up, and pump the fuel back up to the reactor and away you go.  The great thing about this, is we know it works because the research version of this reactor (didn't have the thorium blanket) at Oak Ridge was shutdown every weekend for (IIRC) four years because nobody wanted to stay and monitor the reactor.

[perihelion]

http://www.youtube.com/watch?v=AHs2Ugxo7-8
http://www.youtube.com/watch?v=VgKfS74hVvQ
http://www.youtube.com/watch?v=AZR0UKxNPh8

Thanks!  That works great!