8.9 Earthquake has struck Japan

[David Wolfson]

As I understand it the fuel rods are racked into arrays together with boronated neutron absorber material that makes the assembly solidly sub-critical until removed. In operation the circulating water itself helps regulate the fission because it acts as a neutron moderator and promotes the fission. The designs are hopefully somewhat fail-safe as a result since loss of coolant is supposed to stop the primary fission. Unfortunately there's a bucketload of other residual reactions going on that generate a lot of heat, especially if the core has been running for awhile.

I gather the fear with the spent-fuel pool is that the rack supports could be compromised and the fuel rods could conceivably collapse together like a fistful of straws into a critical pile. At any rate there will be enough heat to get the whole mass burning, smoking, and vaporizing in a nastily radioactive way. Fill it with water and you might both cool it and start the fission going which would result in something like the same effect as dumping water into a grease fire.

 

[B Ozanne]

So the simple, dumbed down answer is it has to do with the way they arranged.

 

[David Wolfson]

Simply put -- yes. Materials used, and the geometrical configuration of the materials. Then just let probability go to work.

 

[Jeff Piotrowski]

Break News: The US Nuclear Team arrived this morning in Tokyo and at the site Fukushima nuclear power plant late this afternoon reports no water in spent rods at #4. They have declared 50 Mile or 82KM evacuation zone around the site.

The Press conference at 5:10 PM CST said the radiation levels are so high he would not release the data. The Japan government and the TEPCO Utility have not told the truth on how bad it is.
Tokyo reported late this afternoon that levels are 20 times normal in Tokyo. I just saw a NBC reporter at the Tokyo airport where people are getting scanned for radiation before they are allowed to enter the airport for flights.
A NBC photographers are leaving Japan now one of the photojournalist shoes had set off the alarm for radiation scan at the airport. He was scrubbing his show with soap and water outside of the airport in order to be allowed inside to catch his flight.

FYI: When the winds switch to NE/E over the weekend at the site expect very bad news at that time. How do you Evac for 20 million people??

Must see video from US Nuclear Regulatory Commission said Wednesday: PLAY VIDEO!!!
http://www.cnn.com/2011/WORLD/asiapcf/03/16/japan.nuclear.reactors/index.html?hpt=T1

 

[Jim Saueressig]

Worse than Chernobyl??

 

[Nicholas_Scherber]

Say the worst possible happened here, what kind of area of danger are we talking? Then, has anybody been doing any looking into the impact of this on the global economy

 

[Darren Addy]

The Press conference at 5:10 PM CST said the radiation levels are so high he would not release the data. The Japan government and the TEPCO Utility have not told the truth on how bad it is.

A rather ironic two sentences to put beside each other.

 

[Darren Addy]

Worst case scenario at this point, which I've read is unlikely (like almost all the other things that have happened thus far) is that the spent fuel rods go re-critical, i.e., start fissioning again.

One slight correction to the above. The Spend Rod Pool in No. 4 reportedly contains all of the live (not spent) rods from the No. 4 (as you mentioned). It also reportedly has 3 times the number of rods in it, compared to the others. So Worst Case Scenario is that THIS pool of rods (No. 4) goes re-critical. You would then have fission occurring OUTSIDE of any sort of reactor or containment vessel. This is probably why the U.S. is freaking out about this pool reportedly being empty. Something is not right with this picture if the Japanese government is still giving priority to No. 3.

EDIT: Good news, if true and on time (and adequate amount of power):

The power supply to the stricken Japanese nuclear plant could partially resume in the afternoon, the Kyodo agency reports

EDIT: Here is a fuller explanation of the rods in No. 4 pool:

One of the cores that was in a refuel outage required a complete full core offload. Typically only 1/3 of the cores fuel is offloaded for a normal refueling to the pool. That 1/3 pf the fuel load is typically burned out for about 3 cycles/6 years. Most of the Uranium is utilized. A full core offload means the other 2/3 of the fuel which hasn’t been fully utilized (burned out) is also in the pool.

EDIT2: If you have been imagining an open swimming pool, you are wrong. First time I've read this:

HOWEVER, what about the covers?

The sliding covers on the top of the storage pool are probably closed. They would be much stronger. The problem may not be the roof, per se, but the covers.

The writer is talking about getting water into the pools from the outside.

 

[B Ozanne]

I've seen many photos on the web of wide open pools...with life preservers and no covers in sight. A reactor this old may not have covers. An article I read (link below, scroll down) jokingly noted that the water is so effective at containing the radiation that workers have taken illicit swims in the pool.

la hague

 

[Darren Addy]

ZAMG (Austrian central institute of meteorology and geodynamics) projection of Cesium 137 spread:

No coincidence that the U.S. has deployed more radiation counters to the west coast.

From what I am reading, the possibility of fission in the SFPs is very remote. But fuel igniting in them is a big enough fear. A nuclear expert the other day called that scenario "Chernobyl on steroids". One can only hope he is prone to hyperbole.

 

[Ryan McGinnis]

I see they're air dropping water on reactor 1 (why 1?). In the process they took radiation readings above the plant:

http://english.kyodonews.jp/news/2011/03/78796.html

Defense Minister Toshimi Kitazawa said Thursday he has given the go-ahead for Self-Defense Forces helicopters to drop water onto a troubled reactor at the Fukushima No. 1 nuclear plant as the radiation level was 4.13 millisievert per hour at an altitude of 1,000 feet.

The level comes to 87.7 millisievert at 300 feet, the minister also said.

==Kyodo

 

[JF Massicotte]

I see they're air dropping water on reactor 1 (why 1?). In the process they took radiation readings above the plant:

http://english.kyodonews.jp/news/2011/03/78796.html

There are 2 Fukushima nuke Plant, reactors no. 1-4 are at the Plant no. 1... I can see a source for confusion here.

 

[Ryan McGinnis]

Btw that appears to be closely obeying the rules for falloff from a point source (twice the distance = 1/4 th the intensity). So that's probably radioactivity emanating from the building itself, not radiation from flying in a plume.

The calculations work the other direction, too, which might explain why it's so dang hard to work on these reactors or add water to them. Whatever the source if that radiation is, getting within 150 feet of it would be a dose of 350 millisievets per hour which is quite hazardous. Getting to 75 feet from the radiation source would mean a dose of around 1,400 millisieverts per hour. Rather impossible to safely get inside those buildings.

 

[Ryan McGinnis]

There are 2 Fukushima nuke Plant, reactors no. 1-4 are at the Plant no. 1... I can see a source for confusion here.

No, I undersand where it is, it's just that the reactors are sealed, so dumping water on them makes little sense. Unless the spent fuel pool for #1 is boiling away, too.

 

[Darren Addy]

No, I undersand where it is, it's just that the reactors are sealed, so dumping water on them makes little sense. Unless the spent fuel pool for #1 is boiling away, too.

If you are referring to the information in your quote (and not something you saw on TV coverage) then JF is correct. Plant No. 1 does not equal Unit No. 1.

BoingBoing has the transcript of the latest press conference: http://www.boingboing.net/2011/03/16/japan-japan-official.html

Via BBC Live:

The temperature of Reactor 5 is now a growing cause for concern, a Japanese official reports. "The level of water in the reactor is lowering and the pressure is rising," he says

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Just keeps getting better and better...