debu -
Immediately following the accident would this might have been a remote possibility due to the fuel cells most recently removed for the maintenance shutdown of Unit 4 (I think 4), but this is no longer the case. We know that for some amount of time there was no ability to add and recirculate water to the storage pools - and temperatures did indeed rise, 90C is the highest I recall reading about. Well below the point of zircalloy cladding breakdown and even further below the ignition point of zirc. We also know that the pools were and are still intact.
As far as damaging a cell? These aren’t fragile things like light bulbs. They are basically flat, rolled sheets of metal. They won’t just "break open" if something falls on them. After a 9.0 earthquake and follow-on tsunami, a 35 ton crane isn’t much to worry about - which is precisely while you will read about it because the press has no idea what to make of real information so they will sensationalize everything. Hence the doomsday scenario being kicked around.
While it’s not a zero chance event (like the Cubs winning the World Series in my lifetime), the total meltdown, ignition, degradation and release of fission products from the spent fuel scenario is pretty remote. Even the fuel matrices inside the once recently operating reactor vessels have cooled and stabilized (somewhat). Those reactors are still the primary threat and issue facing the Japanese response teams going forward with stabilization and clean-up efforts.
Samuel -
Of course Gunderson has to change his tune. The rest of the band was in the key of G and he was singing in the key of D flat.
I think you are confused with the scenario you propose…there is very little decay heat left in the spent fuel cells. It’s not negligible, but it’s very manageable. Even with a loss of recirculation ability like we had in the initial days following the accident the zircalloy cladding (I think that is what you really mean by "shielding") on the fuel cells didn’t melt or burn. Without a serious breach of structural integrity of the fuel cells, there is no way for entrapped fission products and fission product poisons to escape the fuel matrix and enter the environment.
The scenario the press seems to be very fond of lately is the earthquake that will "toss fuel cells about the grounds" Any earthquake that large is going to be much more of a concern than what gets tossed. And as I have addressed in earlier posts, the fuel cells are spent - there is no plausible way for an earthquake to spill these fuel cells out where they arrange themselves in any kind of geometry where they will start fissioning again. Let’s not forget that they are SPENT FUEL CELLS. They might be laying on the ground, but they are not surrounded by a neutron moderator so they won’t fission. At all. They won’t melt either. They will simply be picked up and removed in the world’s largest game of nuclear pick up sticks. Not a trivial tasking, but certainly not the Doomsday event still being chattered about today.
[quote=Dogs_In_A_Pile]I think you are confused with the scenario you propose…there is very little decay heat left in the spent fuel cells. It’s not negligible, but it’s very manageable. Even with a loss of recirculation ability like we had in the initial days following the accident the zircalloy cladding (I think that is what you really mean by "shielding") on the fuel cells didn’t melt or burn. Without a serious breach of structural integrity of the fuel cells, there is no way for entrapped fission products and fission product poisons to escape the fuel matrix and enter the environment.
The scenario the press seems to be very fond of lately is the earthquake that will "toss fuel cells about the grounds" Any earthquake that large is going to be much more of a concern than what gets tossed. And as I have addressed in earlier posts, the fuel cells are spent - there is no plausible way for an earthquake to spill these fuel cells out where they arrange themselves in any kind of geometry where they will start fissioning again. Let’s not forget that they are SPENT FUEL CELLS. They might be laying on the ground, but they are not surrounded by a neutron moderator so they won’t fission. At all. They won’t melt either. They will simply be picked up and removed in the world’s largest game of nuclear pick up sticks. Not a trivial tasking, but certainly not the Doomsday event still being chattered about today.
[/quote]
Yes, thanks for correcting me: the cladding.
Look, they picked up 73 Sv/h when moving a bot around inside Unit 2. Do you seriously expect anyone to believe that if the whole batch of "spent fuel" gets yanked to the ground that it will not emit at 73 Sv/h anywhere over the pile of fuel cells? I would seriously like to understand what I am missing here because I don’t see how anyone would ever be able to get close to that pile…
Samuel
[quote=guardia][quote=Dogs_In_A_Pile]
I think you are confused with the scenario you propose…there is very little decay heat left in the spent fuel cells. It’s not negligible, but it’s very manageable. Even with a loss of recirculation ability like we had in the initial days following the accident the zircalloy cladding (I think that is what you really mean by "shielding") on the fuel cells didn’t melt or burn. Without a serious breach of structural integrity of the fuel cells, there is no way for entrapped fission products and fission product poisons to escape the fuel matrix and enter the environment.
The scenario the press seems to be very fond of lately is the earthquake that will "toss fuel cells about the grounds" Any earthquake that large is going to be much more of a concern than what gets tossed. And as I have addressed in earlier posts, the fuel cells are spent - there is no plausible way for an earthquake to spill these fuel cells out where they arrange themselves in any kind of geometry where they will start fissioning again. Let’s not forget that they are SPENT FUEL CELLS. They might be laying on the ground, but they are not surrounded by a neutron moderator so they won’t fission. At all. They won’t melt either. They will simply be picked up and removed in the world’s largest game of nuclear pick up sticks. Not a trivial tasking, but certainly not the Doomsday event still being chattered about today.
[/quote]
Yes, thanks for correcting me: the cladding.
Look, they picked up 73 Sv/h when moving a bot around inside Unit 2. Do you seriously expect anyone to believe that if the whole batch of "spent fuel" gets yanked to the ground that it will not emit at 73 Sv/h anywhere over the pile of fuel cells? I would seriously like to understand what I am missing here because I don’t see how anyone would ever be able to get close to that pile…
Samuel
[/quote]
Samuel -
Now you have changed the scenario. While the spent fuel cells can no longer be used in an operating core to generate heat to run the steam turbines - hence the term "spent fuel", they are still very highly radioactive, and that would be the issue to deal with if the cells were to somehow get ‘tossed’ all over the place. They would be point source emitters (possibly plane source emitters depending on the dimensions of the pile) - for a point source emitter, the radiation exposure falls off at a 1/r squared function. It would be nearly impossible for humans to work right up against the fuel cells for any amount of time, but the cells could be picked up by robotics or long boom cranes and placed in shielded containers. It would (still) be a localized event and situation. Not an ideal situation by any means, but this whole discussion about earthquakes tossing them to the ground with burning and melting and fissioning is utter nonsense.
[quote=Dogs_In_A_Pile]Now you have changed the scenario. While the spent fuel cells can no longer be used in an operating core to generate heat to run the steam turbines - hence the term "spent fuel", they are still very highly radioactive, and that would be the issue to deal with if the cells were to somehow get ‘tossed’ all over the place. They would be point source emitters (possibly plane source emitters depending on the dimensions of the pile) - for a point source emitter, the radiation exposure falls off at a 1/r squared function. It would be nearly impossible for humans to work right up against the fuel cells for any amount of time, but the cells could be picked up by robotics or long boom cranes and placed in shielded containers. It would (still) be a localized event and situation. Not an ideal situation by any means, but this whole discussion about earthquakes tossing them to the ground with burning and melting and fissioning is utter nonsense.
[/quote]
Yes, I am talking about that: spent fuel getting tossed over the ground and not being able to do anything about.
I guess we can choose to believe that we are smart enough to come up with the kind of technology needed to pick up that mess, but it doesn’t prove that we actually can.
So, what if we can’t? Can this cladding resist rain, erosion and radioactivity for 10000 years? What if a couple of those claddings crack? Stuff comes out right? And where is it going to end up?
That’s what I’m talking about. Nobody’s talking about what we could do if that happens. We are just praying very hard that it does not happen over the course of the next 30 years, the minimum amount of time they expect to wrap up Fukushima, in the relative good state that it is now…
Samuel
[quote=guardia][quote=Dogs_In_A_Pile]
Now you have changed the scenario. While the spent fuel cells can no longer be used in an operating core to generate heat to run the steam turbines - hence the term "spent fuel", they are still very highly radioactive, and that would be the issue to deal with if the cells were to somehow get ‘tossed’ all over the place. They would be point source emitters (possibly plane source emitters depending on the dimensions of the pile) - for a point source emitter, the radiation exposure falls off at a 1/r squared function. It would be nearly impossible for humans to work right up against the fuel cells for any amount of time, but the cells could be picked up by robotics or long boom cranes and placed in shielded containers. It would (still) be a localized event and situation. Not an ideal situation by any means, but this whole discussion about earthquakes tossing them to the ground with burning and melting and fissioning is utter nonsense.
[/quote]
Yes, I am talking about that: spent fuel getting tossed over the ground and not being able to do anything about.
I guess we can choose to believe that we are smart enough to come up with the kind of technology needed to pick up that mess, but it doesn’t prove that we actually can.
So, what if we can’t? Can this cladding resist rain, erosion and radioactivity for 10000 years? What if a couple of those claddings crack? Stuff comes out right? And where is it going to end up?
That’s what I’m talking about. Nobody’s talking about what we could do if that happens. We are just praying very hard that it does not happen over the course of the next 30 years, the minimum amount of time they expect to wrap up Fukushima, in the relative good state that it is now…
Samuel
[/quote]
Samuel -
I understand your concerns, but rest assured there is plenty we can do about them The technology already exists to safely handle spent fuel cells. The short answer is we can pick up that mess.
Zirc cladding is very, very resistant to corrosion and the elements. Remember, it was manufactured to operate under extreme temperatures and pressures, and in a neutron flux. I think you mean corrosion instead of erosion, and yes, a fuel cell is more than capable of standing up to the elements. Remember, the fuel cells aren’t like eggs or light bulbs, nothing will "leak" out if there are surface cracks. There is a good reason why zirconium cladding is used - zirc 4 alloy is used for the outer layer because it is very resistant to pitting, corrosion and steam crevice corrosion. It develops an extrememly thin (nanometers thick) passivation layer of zirc oxide that all but shuts off further oxidation and corrosion. Zirc 2 alloy is rolled inside the zirc 4 cladding - it does a great job of holding the fuel particles together and is also corrosion resistant. Both zirc 4 and zirc 2 have a very low neutron absorption cross sections so they are ideal for use in nuclear fuel cells. Zirc 2 and zirc 4 are subject to hydrogen embrittlement if subjected to steam for prolonged periods of time. It will absorb hydrogen if present and may with time cause blistering and cracking of the zirc 4. This could lead to release of fission product daughters. But since the spent fuel cells weren’t subject to steam, the chances of them having residual hydrogen blisters or bubbles from previous normal operations is slim. So even if they were on the ground, they would remain intact and corrosion resistant for quite some time.
Trust me, people are talking about what to do if the building collapses and you can be confident that contingency plans for such an event are at least being discussed if not already in place. If it did happen, it will be an issue to deal with, but it certainly won’t be the "Mass Extinction" event that has been flying around cyber space the past couple of days.
Keep the questions coming - I want to make sure you and others are as well informed as possible within the scope of my knowledge and experience. If I know the answer, I’ll tell you. If I don’t know the answer, I’ll find it out for you. If I am maing an educated guess, I’ll let you know that as well.
Take care…
[quote=Dogs_In_A_Pile]I understand your concerns, but rest assured there is plenty we can do about them The technology already exists to safely handle spent fuel cells. The short answer is we can pick up that mess.
Zirc cladding is very, very resistant to corrosion and the elements. Remember, it was manufactured to operate under extreme temperatures and pressures, and in a neutron flux. I think you mean corrosion instead of erosion, and yes, a fuel cell is more than capable of standing up to the elements. Remember, the fuel cells aren’t like eggs or light bulbs, nothing will "leak" out if there are surface cracks. There is a good reason why zirconium cladding is used - zirc 4 alloy is used for the outer layer because it is very resistant to pitting, corrosion and steam crevice corrosion. It develops an extrememly thin (nanometers thick) passivation layer of zirc oxide that all but shuts off further oxidation and corrosion. Zirc 2 alloy is rolled inside the zirc 4 cladding - it does a great job of holding the fuel particles together and is also corrosion resistant. Both zirc 4 and zirc 2 have a very low neutron absorption cross sections so they are ideal for use in nuclear fuel cells. Zirc 2 and zirc 4 are subject to hydrogen embrittlement if subjected to steam for prolonged periods of time. It will absorb hydrogen if present and may with time cause blistering and cracking of the zirc 4. This could lead to release of fission product daughters. But since the spent fuel cells weren’t subject to steam, the chances of them having residual hydrogen blisters or bubbles from previous normal operations is slim. So even if they were on the ground, they would remain intact and corrosion resistant for quite some time.
Trust me, people are talking about what to do if the building collapses and you can be confident that contingency plans for such an event are at least being discussed if not already in place. If it did happen, it will be an issue to deal with, but it certainly won’t be the "Mass Extinction" event that has been flying around cyber space the past couple of days.
Keep the questions coming - I want to make sure you and others are as well informed as possible within the scope of my knowledge and experience. If I know the answer, I’ll tell you. If I don’t know the answer, I’ll find it out for you. If I am maing an educated guess, I’ll let you know that as well.
[/quote]
Thanks for the technical info! Technically I suppose there are good chances of getting out of that mess, but only if we’re actually serious about it. Although I’m not convinced we have the technology, I think we could probably come up with hacks if we’re motivated enough (as was the case with the Macondo blowout, for example).
My main concern are the Japanese government/TEPCO and the international community. IMO, they’re not motivated.
http://ex-skf.blogspot.jp/2012/04/reporting-by-fukushima-local-newspaper.html
So, forgive my paranoia, but I seriously doubt anyone with any sort of authority in Japan is thinking about what to do if the spent fuel pool finds its way to the ground. (They’re too busy debating tax increases and quantitative easing.) I also seriously doubt that TEPCO has any intention of following up on their plans to build an underground wall to stop polluted underground water from contaminating the rest of Honshu (the main Japanese island).
Suffice to say, I won’t be buying land or real estate anywhere on Honshu.
Samuel