Fukushima nuclear power plant: 1760 tons of spent nuclear fuel

[Paradoxical]

I am going to significantly alter my stance on the current nuclear disaster unfolding in Japan. It appears as though a SIGNIFICANT amount of spent fuel is stored in pools within the reactors (contrary to my prior belief).

http://criepi.denken.or.jp/result/event/seminar/2010/issf/pdf/6-1_powerpoint.pdf

As of March 2010:

3450 fuel assemblies were stored in pools inside the reactor buildings

408 fuel assemblies were stored in dry casks

6291 fuel assemblies were stored in a common storage pool.


-----------------------

The dry casks are almost certainly safe as they are stored in a separate building and none of the major buildings seem to have suffered structural damage from the tsunami.

Similarly, the common storage pool also appears to be in safe condition.

HOWEVER, almost 600 tons (1.2 million pounds) worth of spent fuel are stored in pools inside the individual reactor buildings. This is a major cause for concern given the recent explosions that appear to have caused significant damage to at least two reactor buildings.

If the distribution of spent fuel is equal between the 6 reactors, that would lead us to believe that almost 200 tons of spent nuclear fuel is currently at risk of being exposed to the open air.

Safety of Spent Nuclear Storage Pools: from 2006 report requested by Congress

The study provided a probabilistic risk assessment that identified severe accident scenarios and estimated their consequences. The analysis determined, for a given set of fuel characteristics, how much time would be required to boil off enough water to allow the fuel rods to reach temperatures sufficient to initiate a zirconium cladding fire.

The analysis suggested that large earthquakes and drops of fuel casks from an overhead crane during transfer operations were the two event initiators that could lead to a loss-of-pool-coolant accident. For cases where active cooling (but not the coolant) has been lost, the thermal-hydraulic analyses suggested that operators would have about 100 hours (more than four days) to act before the fuel was uncovered sufficiently through boiling of cooling water in the pool to allow the fuel rods to ignite. This time was characterized as an “underestimate” given the simplifications assumed for the loss-of-pool-coolant scenario.

The overall conclusion of the study was that the risk of a spent fuel pool accident leading to a zirconium cladding fire was low despite the large consequences because the predicted frequency of such accidents was very low. The study also concluded, however, that the consequences of a zirconium cladding fire in a spent fuel pool could be serious and, that once the fuel was uncovered, it might take only a few hours for the most recently discharged spent fuel rods to ignite.



http://www.nap.edu/openbook.php?record_id=11263&page=44

[aquart]

1. Which would mean what?

[Paradoxical]

5. Well, the spent fuel is stored in a giant pool of water.

Assuming the pool is intact and still full of water, the fuel is safe. The water is an excellent barrier against radiation.

If the pools are not intact, there is a very possible risk of EXTREME radiation leakage.

[aquart]

9. Which would mean what?

To the immediate area?

To Japan?

To other nations?

To ME? Here in NY with a sister in San Diego.

[Paradoxical]

17. I am not educated on the volatility of spent nuclear fuel.

It will decrease in temperature over time to a steady state and that is usually when they place it in dry casks.

If the spent fuel is relatively "new", there is a possibility of it heating up if it is taken out of water. And it may heat up to a temperature at which it will begin to burn. Once it begins to burn, it will basically allow for a large portion of the fuel to be transported in smoke. But, like I said, I do not know what kind of state the spent nuclear fuel is in.

Also, if the reactors exploded as violently as it appears, there is a possibility that the spent fuel was broken up and carried out within the smoke clouds.

[joshcryer]

19. That is my biggest fear about #3 explosion.

[Paradoxical]

34. Reread the OP with updated information on the spent fuel pools.

[joshcryer]

2. Not at risk, almost certainly exposed. The explosions at both reactors was significant enough...

...to empty the pools of water, particularly the #3 explosion.

I think that is why they are constantly trying to keep the reactors deluged in sea water.

You can see the storage pools in this image, near the top of the reactor:

EDIT: this is not the exact design but this design was common in that era and it's a very good analog!

[kristopher]

7. You'd better look at that second explosion again, hoss.

And then ask yourself why we have no close ups of the buildings that have exploded.

[joshcryer]

10. We got a closeup of #1 actually, we don't have one of #3 that I have found yet.

That's reactor #1. We'll see if we get one of #3, you need one hell of a telephoto lens to get that picture.

[aquart]

12. Before or after?

[joshcryer]

15. After, this photo shows before and after:

http://en.wikipedia.org/wiki/File:2011-03-12_1800_NHK_Sōgō_channel_news_program_screen_shot.jpg">clicky

[aquart]

20. Wowza. What is that surviving lattice made of?

[Rex]

24. I believe it is steal.

Pretty strong structure for such a big blast.

[Hannah Bell]

42. not a closeup but

[Hannah Bell]

11. it's only the top level (at the level of that orange thing) that blew off.

[joshcryer]

13. I know, look at the storage pools, they don't have caps or anything.

I would have a difficult time believing that a good portion of the water in those pools wasn't blown out and possibly even some of the spent material.

[PoliticAverse]

45. That was reactor # 1. The explosion at reactor # 3 appears to have caused more damage

More of the reactor # 3 building appears to be damaged than was the case for reactor # 1:

[reformist2]

64. My God. How can the storage pool still be intact... the top half of the building is gone!

[leftstreet]

3. When you say 'exposed to the open air,' what are the implications?

Dumb question here...but what's the chemical composition? I mean - things like oxygen are heavy, so they drop when airborne. If that makes sense

[JVS]

16. Spent fuel is heavy stuff. Mostly uranium, a small portion of plutonium

Basically the stuff mined from the earth is primarily U-238 and a small amount of U-235. This is enriched to get a higher percentage of U-235 because it's the fissionable stuff. U-235 splitting turns some of the U-238 atoms into Pu-239 and Pu-240.

But the other side of the coin is that these heavy things are incredibly poisonous, highly radioactive, and have long half lifes. There is a reason people wanted to put this stuff in long term storage.

[kristopher]

4. You will need this link

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=439x639155

Thanks. That is part of the puzzle.

[Rex]

6. Well you did say it was just a hobby.

[joshcryer]

8. At least he admitted being wrong. He probably should apologize for calling this a lie.

[aquart]

14. Who "he"? What "this"?

[joshcryer]

18. In kristopher's link in post #4 he denied this fervently.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=439x639155

[kristopher]

35. What are you blathering about now?

[joshcryer]

36. Read?

:shrug:

[kristopher]

40. Explain your comments please. They are not aligned with your link.

[Paradoxical]

41. I wrongfully accused another poster of posting fallacious material.

And now it turns out that they were completely right and I'm an asshole.

[kristopher]

43. No problem.

We are all tired and full of passionate feelings.

[Ignis]

63. +1

[bananas]

53. You should post a retraction in that thread so people know you changed your mind

I think this is the one you're talking about: http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=439&topic_id=639155&mesg_id=639275

[themadstork]

56. Respect

Your explanations have been great for the science newbs like me, and then the intellectual integrity to admit when you're wrong? You are an awesome dude.

[Hannah Bell]

21. map of facility (fukushima #1 plant)

[Paradoxical]

22. Do we have a post-photo of the entire facility?

The one I saw was relatively zoomed in.

[Hannah Bell]

23. after the #1 explosion, which i believe is on the far right of the group of 4 buildings

[Paradoxical]

26. We need a shot zoomed further out so we can see the dry cask facility.

The common pool appears to be in good shape, though.

[Hannah Bell]

31. where is the common pool? i can't make out through the smoke.

[Paradoxical]

33. It is directly behind the first two reactors.

The t-like shaped building. That is the common pool according to your map.

[Hannah Bell]

37. ok, i see now.

[csziggy]

58. Here is one After shot

http://www.businessinsider.com/google-maps-shows-tsunami-devastation-2011-3#the-fukushima-nuclear-power-plant-after-the-flood-18

Not sure when it was taken.

[Paradoxical]

62. The common pool is obscured by clouds.

[Lucinda]

25. Would that be possible with Google Earth?

Or are those facilities blocked?

[Paradoxical]

27. They may be blocked. Google Earth does not have up to date photos though.

We need photos of the facility from as recently as possible (like within the past 24 hours).

[snagglepuss]

28. Safety of Spent Nuclear Storage Pools: from 2006 report requested by Congress

The study provided a probabilistic risk assessment that identified severe accident scenarios and estimated their consequences. The analysis determined, for a given set of fuel characteristics, how much time would be required to boil off enough water to allow the fuel rods to reach temperatures sufficient to initiate a zirconium cladding fire.

The analysis suggested that large earthquakes and drops of fuel casks from an overhead crane during transfer operations were the two event initiators that could lead to a loss-of-pool-coolant accident. For cases where active cooling (but not the coolant) has been lost, the thermal-hydraulic analyses suggested that operators would have about 100 hours (more than four days) to act before the fuel was uncovered sufficiently through boiling of cooling water in the pool to allow the fuel rods to ignite. This time was characterized as an “underestimate” given the simplifications assumed for the loss-of-pool-coolant scenario.

The overall conclusion of the study was that the risk of a spent fuel pool accident leading to a zirconium cladding fire was low despite the large consequences because the predicted frequency of such accidents was very low. The study also concluded, however, that the consequences of a zirconium cladding fire in a spent fuel pool could be serious and, that once the fuel was uncovered, it might take only a few hours for the most recently discharged spent fuel rods to ignite.



http://www.nap.edu/openbook.php?record_id=11263&page=44

[Paradoxical]

29. I'm making this part of my OP. Thank you.

[joshcryer]

30. The problem is during the explosions, you can be sure they're heroically keeping water in the pools.

[Paradoxical]

32. Yes, but what happens if they lose the ability to pump sea water?

Not good.

[Lucinda]

38. I've been wondering where the seawater is going in #3

I have seen statements saying they have been pouring sea water in, but not getting the level to rise as expected. That sounded like some sort of breach to me, or possibly steam evaporation?

[Paradoxical]

39. Almost certainly steam evaporation.

The core is already EXTREMELY hot. a lot of the water they are pumping in to cool it down will be vaporized. What I am hoping is that this is a closed loop. Otherwise, they are basically letting evaporated radioactive sea water boil off into the open air.

[Hannah Bell]

44. in one of the briefings the nuke guys explained that the reactors had

3 levels of cooling backup, the third of which didn't require power.

it was basically the water turned to steam, rose, went through a pipe where it cooled & turned back to water & reentered the housing at the bottom.

so i guess so unless there's a leak.

[jtuck004]

47. That was one of the processes they thought was taking

place at Chernobyl. But the water didn't circulate as steam pockets developed and blocked it (same thing happens in radiant hot water systems in homes), and for the same reason the instruments didn't show the pressure buildup accurately, and it came apart.

I would guess that the instrumentation design and piping has been rectified to either avoid or take this into account, since these are far more modern and different reactors.

Reports would indicate that part of the way they are controlling this is to vent the steam when the pressures become too great, which would require periodic water replacement. That makes me wonder if the construction of these next to the water included large intake pipes which could take in water via gravity (As you said, without power).

[Hannah Bell]

48. at one point in the #1 saga they realized that pressure had equalized

which is why they vented. but then that lowers water level i guess.

[jtuck004]

50. Yes. Boilers on board ships and in other facilities

act the same way. We would produce fresh water and fill the tanks, then it would be heated to high pressure steam and sprayed through nozzles to run turbines, similar to a nuclear electricity generator (but ours was hooked to a shaft that had a propeller on the other end instead of a generator). The steam would then flow into a condenser, a series of pipes where it cooled back to water, and was re-circulated through the boilers to be turned into steam again. Very similar to a nuke, but conventional ships use fuel oil to heat the water instead of uranium.

In some respects like a car radiator. As long as it is closed it works pretty well, but if you get a leak (loose cap) the high temp causes everything to flash to steam and you can melt your engine. With all the little explosions at the reactors I wouldn't be surprised if there are cracks in what should be a pressured system, and that means real trouble.

We had instruments and sight glasses to monitor the water level so we could refill it. In that environment, there was a bit of loose steam where we had to pack material around valves, etc. Very powerful and dangerous stuff in its own right, steam.

I have an awful lot of respect for those people, probably volunteers, doing the job of trying to keep those reactors cool right now.

[kristopher]

46. I wouldn't be so sure of that.

The trend has been consistent and yesterday morning Edano was genuinely puzzled. Here is the transcript:

"About #3 reactor in Fukushima Power Plant. A short while ago they started the sea water injection into the reactor and the level of water has risen. It has risen to a certain level and then it seems that the gauge is showing the level of water is not going up however the supply of water continues. We do not know what to make of this fact. Yesterday ever since the explosion in the #1 reactor the situation like this is continuing, now #3 reactor vault might be showing some failure. And the failure in the vault has to be solved and the air pressure inside has to be lowered (said forcefully). And currently the radiation monitor hasn't shown any change. That is the situation in reactor #3."

[kristopher]

49. self delete dupe

[Junkdrawer]

51. When you say "This is a major cause for concern"....

It a signal for the rest of us to crawl in a corner and start sucking our thumbs.

Video of the blast at Reactor 3:

http://www.youtube.com/watch?v=2bPi6aHmd88

[Paradoxical]

54. It's not the nuclear apocalypse by any stretch of the imagination.

It is, however, a disaster of historical proportions.

[JVS]

52. Does this mean that the CS-137 could be from the spent fuel rather than the core?

[roamer65]

55. I am praying to God tonite that it does not result in a radioactive fire...

in the spent fuel pools. I honestly don't know how they would deal with it.

[Poll_Blind]

57. I don't think you can. Maybe dump liquid graphite on it?

I have no idea.

PB

[Paradoxical]

59. This may require the quick construction of a protective dome.

Following the extinguishing of the fires, they need to seriously consider similar actions taken at Chernobyl

[nadinbrzezinski]

60. Welcome to the significant event band wagon if two days late

[Paradoxical]

61. The difference is I actually care about facts.