NRC: No Water In Spent Fuel Pool Of Japan Plant

by The Associated Press
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WASHINGTON March 16, 2011, 03:54 pm ET

The chief of the U.S. Nuclear Regulatory Commission said Wednesday that all the water is gone from one of the spent fuel pools at Japan's most troubled nuclear plant, but Japanese officials denied it.

If NRC Chairman Gregory Jaczko is correct, this would mean there's nothing to stop the fuel rods from getting hotter and ultimately melting down. The outer shell of the rods could also ignite with enough force to propel the radioactive fuel inside over a wide area.

Jaczko did not say Wednesday how the information was obtained, but the NRC and U.S. Department of Energy both have experts on site at the Fukushima Dai-ichi complex of six reactors. He said the spent fuel pool of the complex's Unit 4 reactor has lost water.

Jaczko said officials believe radiation levels are extremely high, and that could affect workers' ability to stop temperatures from escalating.

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http://www.npr.org/templates/story/story.php?storyId=134600420

I heard last night that in No.4 building there could be enough spent rods in the pool for EIGHT reactors.

So, how many are in buildings 1,2,3,5,6 ?
My guess is that we're looking enough rods for 20+ reactors.

This is going to be a HUGE catastrophe, most of which we haven't even heard about yet!

Also somemewhat ironically reactor fuel can't achieve criticality without water. The neutrons from fissile material are too fast to split other fissile atoms. They bounce off without causing fission. You need a substance that slows them down (called moderator). In US reactor designs water is the moderator. Neutrons traveling through water get slowed down enough that they are at the right speed to cause fission and generate a chain reaction.

Now without achieving criticality the fuel rods can still burn and release radioactive material but a moderator is needed to create a critical mass.

Thanks for the response. So we're not looking at a scenario where there is a hiroshima-like explosion or multiple such explosions? Instead we're looking at a consistent release of radiation or "core on the floor" type scenario? How long will the spent fuel rods leak radiation without intervention?

I do know they should never be left uncovered. My guess would be they have hours not days.

There would be no nuclear detonation.

If there is no criticality then the spent fuel would simply burn conventionally and the smoke would contain radioactive ash. How far it goes depends on a lot of factors like weather, rate of burning, humidity, etc.

If there is a criticality event then the water in the pond would get very hot very very very fast. A lot of it would instantly flash to steam and you could have a steam explosion. If the rods are partially exposed in water they can react with the water vapor and remove the oxygen leaving explosive hydrogen.

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Too add water safely they need to add a neutron poison like boron which absorbs neutrons and prevents any fuel from achieving criticality. I have no idea how much boron they have onsite, hopefully a love.

All of the reactors have been shut down, and by that I mean stopped the fission.. There is some residual heat but I don't understand how they can continue heating...

and water is needed to keep them cool. Without fission reaction they drop to 7% heat emission. That's what I read anyway.

They decay to more stable isotopes according to their half life and in the process release heat.

You can stop fission (it is actually hard to achieve fission) but there is no known process to halt, slow, or prevent nuclear decay.



This is the decay chain of uranium. As you can see it has a lot of steps and it takes a very long time.

possible? Are the radiation levels going to be getting in the way of humans doing the necessary work? Could the radiation leak for thousands of years without intervention?

This isn't a situation that will solve itself (like a fire that burns itself out).
If they don't get the rods under water soon it will be very very bad. A worst case scenario.

"Are the radiation levels going to be getting in the way of humans doing the necessary work?"
From the limited info we are getting that seems to be the problem. It doesn't matter how they do it, or who has to die they have no choice the rods must get back under water and then the water continually added to ensure they remain covered.

hamper rescue efforts?

I'm not clear why this is being judged as potentially less calamitous than Chernobyl. It seems to me that the overall disaster (earthquake/tsunami) encompassing the nuclear damage can't help but exacerbate the nuclear issue since resources as far more scarce, roads are destroyed, etc. I keep hearing worse case scenario, but I don't know what that means. I'm not fear-mongering but rather the opposite. I want to know the full extent of what's possible because I want to know the truth so that I can relay information accurately and without hysteria or confusion to students, colleagues, friends on the West Coast, etc.

Maybe it wouldn't be exactly but a disaster of that magnitude.

The pond without water is very very bad because if not cooled the rods WILL eventually ignite and start pumping huge amounts (like thousands times more than the small amount already released) of radioactive material into the atmosphere. Remember radiation is energy, radioactive material is a contaminate and it constantly bombards whatever it is near with radiation.

I don't think that is likely yet but if they can't get the fuel rods under water it will get very bad.