Blue Fuel Cells

[sefrick]

OK, I was not the strongest on nuclear physics, I was more like to grunt that knew how to rig the main condenser manhole cover off in less than 10 minutes or turn the cooldown knocker valves the fastest, but anyway, Beer Court had me look at some pictures posted on this site. I'm curious what causes the fuel cells to glow blue. Also I'm wonding about outages. I know, from what Beer Court posted that cell replacement is frequent, but what about decay heat, exposure etc. I decommissioned my first boat which required removing the fuel cells. I don't remember what the mechanism was called that lifted the cells out, but I remember that it took about 3 hours per fuel cell and the basics on how it worked. I'm wondering how it is done in a commercial plant and where the "spent" cells are transported or stored. And how the heck where those pictures taken???

Sorry guys, even though I was the M-Div grunt, I always wanted to know EVERYTHING.

[Already Gone]

Okay, let's start with the blue color.  It is the result of something called the Cerenkov Effect.  It's been a long time since I've studied this, so I can't be very technical.  Essentially, the blue light is the emitted radiation from Beta particles rapidly slowing to sub-light velocity.  The speed of light in water is much slower than the speed of light in air or in a vacuum (c, as in E=mc2, is speed of light in a vacuum).  Anyway, this means that it is possible for a particle to exceed the speed of light in water.  As the particle loses kinetic energy, part of that energy is converted to visible light.  Due to the wavelength of the light, it is always the same color of blue.
The longer a bundle has been in the core, it will accumulate more beta-emitting fission products.  As the bundle sits in the fuel pool for a long time, the fission products decay away, as does the intensity of the blue glow.

Now, if you look at more of those pictures, you will notice that the reactor head is removed.  The flange at the top of the vessel is at the botom of a cavity which is flooded with water.  The bridge which travels over the cavity has a manipulator crane that lifts the assemblies out of the vessel and transports them to the Spent Fuel Pool.  In a PWR, this takes two cranes and a shuttle, which moves the bundle through a tube that connects the reactor cavity ant the SFP.  In a BWR, the SFP and cavity are next to each other, and it only takes one manipulator to move the fuel between them.

It takes and average af around 10 to 30 minutes to complete a move of one bundle.  If all the machinery is working well, and the bundles are cooperating, it is closer to 10 than 30.  It is also faster to shuffle a bundle from one place in the core than it is to remove one and replace it.  The average refuelling outage requires the replacement of around 100 bundles.  But, sometimes all the fuel has to be totally offloaded and then reloaded, depanding on what maintenance and inspections are being done.

The fuel is visible because the water in the cavity is about 25 feet deep.  The SFP is about 40 feet deep, with at least 25 feet to the top of the fuel.  You don't want to see one of those out of the water, you'd never live to talk about it.

Due to decay heat, the bundles have to stay in the Spent Fuel Pool for about ten years, before they can be loaded into shipping containers for final storage.  Due to political reasons, they have to wait until the second coming of Christ before there is going to be a place to put them for final storage.  Lots of sites have temporary facilities to store the casks until that happens.

[sefrick]

That' s heavy, I knew you would be the one to reply. I became very curious after I peeked at the pictures on this site. The cells appeared to be dry and I was wondeing how on earth that was possible, that was my main question. I'll try to look up some info on the Cerenkov Effect.Thanks

[sefrick]

OK, I've convinced that you can find anything on the net these days...the following was found as a result of a web search for cerenkov effect; good stuff.

http://www.nightscribe.com/Science_Technology/Nuclear/db_rx_cerenkov1.htm

...and I thought the blue water in K-19 was hollywood hype!

[Tina]

  OK Beer Court...

Maybe I missed something in your explination, but I have a question now 

I've seen fuel rod manipulations in progress and watched the pretty blue glow and crane work here at Clinton Power Station...  I've seen the long boxes that fuel rods come in for delivery and shippments.  So I guess my question is How do the fuel rod bundles get pulled and placed in these boxes for shippment I thought they stayed in the cool pool like you previously said for an awful long time.    but for the sake of argument... lets say it their time to be shipped  now how dose a fuel rod bundle get from being lifted by crane through the water and placed in a box/cask  I do realize that they are bundles of fuel rods , not just single rods being transfered...

I luv it when an intellegent speaks 
:

[MrHazmat]

The bundles are placed in a fuel cask under water.

[Tina]

  AAAhHHAAA

[Phurst]

I've seen the long boxes that fuel rods come in for delivery and shippments.  So I guess my question is How do the fuel rod bundles get pulled and placed in these boxes for shippment

:

The fuel in boxes is new fuel being delivered and as such are low in radioactivity. Once they are placed in the core and begin the fission process then they get 'hot'. It is the results of fission, the fragments, that decay at a high rate that causes the 'glow'. The fuel that you see manipulated is stuff already used. When they are used up they are transfered underwater to the spent fuel pool. When the pool is full they get loaded in special casks underwater and stored elsewhere. Hope that helps. There are a number of sites that explain the fuel cycle really well, I just can't remember the names, Google them up.

[Already Gone]

I think he's right.  You're probably seeing the new fuel coming in and the empty shipping containers being returned for re use.  Nobody has had a reason to put any significant amount of spent fuel onto a truck since West Valley was halted in the '70's. 
Anyway, spent fuel casks come in two types - shipping and storage.  The storage casks are bigger, but both have multiple components designed to contain the fuel and dissipate heat.  They have some parts in common, so you can move fuel from storage to a shipping cask and into storage again.
Those big blue metal containers with bolts around the middle are the new fuel containers.  New fuel is usually less than 5 mR/hr on contact.

[Roll Tide]

I think he's right.  You're probably seeing the new fuel coming in and the empty shipping containers being returned for re use.  Nobody has had a reason to put any significant amount of spent fuel onto a truck since West Valley was halted in the '70's. 

Not to nitpick, but CP&L requested a license of one of their unfinished units SFP, with the specification that it could hold fuel from any of their sites. I haven't heard if it was approved yet.

[Already Gone]

I thnk that some of the decommissioned sites have also shipped fuel to intermediate storage too.  Shoreham (and maybe some others) have actually sold fuel that had been only slightly used.  But, I don't think any operating units have shipped anything offsite as yet. 
That CP&L thing sounds like a fallback plan to me.  Why would you take fuel out of a cask and put it back in the water when you'll just have to take it back out and repack it to ship (someday)?

[Tina]

  Yep Beer Court I think you and Phurst is right

So just how much fuel will a cool pool hold   before something else will has to be done  

What will their next option be  

[Nuclear NASCAR]

Yep Beer Court I think you and Phurst is right

So just how much fuel will a cool pool hold  before something else will has to be done 

What will their next option be 

It depends on a particular plants design.  Some have modified their fuel pool racks to hold more since Yucca Mountain isn't going to be done as soon as was thought back in the 70's & 80's.

[Masterlee RF]

there are alot of plants that have reracked and others have started on site cask loading and storage, Palo Verde loads more casks than anywhere else.

[Phurst]

Right across the mountains from me, the Goshuts want to store spent fuel, the dry cask storage area. What a fight here in Utah. They got nothing else to complain about so they moan and groan about the place. Steal every decent arce of land from the Native Americans and then bitch when they find a decent use for it.

[sefrick]

Good Stuff!!

I'm glad to see so many people jumped on this thread. When I decommed Sand Lance our spent fuel cells went straight from the grappling mechanism into a train car that was basically just a drum filled with water with fins to dissapate heat. I'm sure that there was plenty of lead shielding in that car as well. I have no idea where they were shipped to. This was at the Puget Sound shipyard.

Does anyone have any idea what a realistic contact rad level (or how far away the 1mR/hr line would be from an exposed rod) would be on a typicall S5W spent fuel rod. I'm pretty sure that our fuel rods are wayyyy more enriched than the cells in commercial plants. Just curious.

[Already Gone]

It's hard to say.  Navy fuel is enriched at least 30 times as much as commercial fuel, but it contains far, far less fuel in total.  The majority of material in Navy fuel is the cladding and other non-fuel components, while commercial fuel is mostly uranium inside cladding tubes.  Even though most of that Uranium isn't 235, it is still active.
Commercial fuel also "burns" a lot more than Navy fuel.  Consider that it is at full power almost constantly.  The fission product buildup is huge.  Full power is a lot more in a commercial reactor than in a Navy reactor.  A 500MWe commercial plant (about the smallest there is) is the equivalent of around 1750 MW thermal.
Commercial fuel is also much, much bigger.  A bundle is ablout 12 feet long, with an active fuel area of 8 to 10 feet.  It is also subjected to a much greater neutron flux.

Depending on the size, power history, and time since removal of a particular bundle, commercial fuel ranges from 500,000 to a couple of million Rem per hour on contact.  The highest actual meter reading I have ever gotten on a bundle in the transfer tube is 200 Rem/hr, but that was a very thin beam shining through a gap in the shielding from several feet away.
The highest contact reading I ever got on a Navy reactor was maybe 50 Mr/hr on contact with the Rx head at about 10,000 EFPH.
Anybody else have any good numbers?

[Phurst]

Good place for nuke info http://www.nucleartourist.com/

[RDTroja]

I stuck an RO-7 underwater probe into the Cherenkov glow from a freshly removed bundle and got a reading of just over 400,000 R/hr (I cannot vouch for the calibration of the probe, but it was still very impressive) around 6 inches from contact with the bundle -- under water, of course. Beer Court had the numbers about right -- it varies from half a million R/hr to about 4 Million R/hr estimated dose.

It is estimated that if you put a fresh bundle (right out of the core after its effective lifespan) on the 50 yard line of a football field and you came out from behind a 'perfect' shield at the goal line and ran toward the bundle as fast as you could, you would be dead by the time you hit the 30 yard line. If you drove past the bundle on a motorcycle at 60 mph you would not reach the opposite goal line alive. No volunteers for the test run as yet.

As for the fuel storage issue, several plants have built dry storage facilities (Calvert Cliffs has one that is fairly large) and some plants have toyed with storing other plants' fuel, but I think so far no one is doing it. Imagine how entertaining it would be in the room with the corporate lawyers when that subject comes up...