Footage of Fukashima reactor

FishmanGeertz

http://www.youtube.com/watch?v=fLE2n...embedded#at=17

Is the yellow structure at the end of this video the lid to the reactor?

Astronuc

That is the cap to the Primary Containment Structure, which surrounds the reactor pressure vessel (RPV).

FishmanGeertz

So the reactor pressure vessel is probably completely intact?

Astronuc

If they were doing service on the vessel then the moisture separator and steam dryer are in the pool, and the RPV head may very well be in the debris. Since the core was defueled, there would be no reason to have the RPV head on the vessel. There is a pool on the north side for placing radiologically hot components underwater.

FishmanGeertz

If you look closely, you can see steam coming from the reactor containment structure cap. Reactor boiling itself dry?

Astronuc

That may depend on air temperature. It's humid in the buildings, especially without cooling of the pools and reactor vessels. Unit 4 SFP should be warmer than the others since it contains the reinsert and discharge fuel assemblies.

The cores in Units 1, 2 and 3 are still generating decay heat.

FishmanGeertz

Ever since this disaster started, I have been wondering if any of the reactor cores in units 1-4 have melted through the vessel, breached containment, and possibly sitting on the reactor building floor as a giant mass of red-hot, glowing uranium lava.

Has there been any official word yet by TEPCO or the Japanese government on the exact condition of the reactor cores/fuel assemblies in Fukashima units 1-4? Is there any significant core damage?

The TMI (Three Mile Island) reactor suffered roughly 90% core damage.

Astronuc

Firstly, the core of Unit 4 was empty. It had been removed months ago.

As for Units 1-3, I do not believe there has been any core melt, assuming that the water levels were maintained in the bottom half or third of the core. I do expect that there is a lot of cladding damage and degradation so that the many fuel rods are broken - or fractured - and perhaps signficant loss of fuel pellets. I have seen speculation of between 50 to 75% core damage, and that's possible.

I'm am still waiting for more evidence.

FishmanGeertz

There was a fire in reactor building four. If the core was empty did not contain any fuel, what caused the fire? Spent fuel assemblies?

Astronuc

The current thinking it that the hydrogen from oxidation of the cladding (mainly the reinsert and discharge fuel from the last cycle) in the SFP resulted in the fire/explosion at Unit 4. The SFP water does contain considerable Cs and I, and the only source of that would be the irradiated fuel in the pool.

FishmanGeertz

What about the some roughly 600,000 spent fuel rods divided amongst the four reactor buildings? All of those burning up and catching fire would pose an even greater radiological hazard than the worst thing possible that could happen to the reactors.

jakekazoo

that's what i'm thinking. with two partially and/or completely destroyed fuel rod pools, and no way to cool them, this could only lead to more disasterous consequences. i was under the impression that reactor number 2 has been completely destroyed in the explosion.

FishmanGeertz

The Kyshtym disaster is an example of what can happen when nuclear waste loses it's cooling. Only Fukashima is much worse.

http://en.wikipedia.org/wiki/Kyshtym_disaster

NUCENG

Where did you get that number 600,000? Are you talking rods or fuel assemblies (bundles of rods)? If they are using 8x8 fuel there are about 64 rods per assembly. If they are using more recent fuel designs (9x9 or 10x10) there could be up to 87 full and partial length rods per assembly. Conservatively assume all 6 site reactors were 40 years old gives 240 reactor years. Assume they have a two year cycle and discharge 200 bundles every two years. That would mean there are up to 120 refuelings times 200 bundles per refueling or 24000 bundles on site. Assuming 18 month cycles would increase that estimate by 25% or 30000 bundles. The oldest unit on site (Unit 1) is close to 40 years old the others are newer. So there should be fewer bundles than that estimate. Bundles out of the reactor for 10 years can easily be transferred to dry storage and air cooled. Fukushima has some dry storage and other bundles are in a shared 7th fuel pool that has not been reported to have problems. Units 5 and 6 have also apparently escaped any serious damage to fuel in their pools.

So it looks like your number may be counting individual rods. I seem to remember that in one of their news releases, TEPCO or NISA released a specific bundle count in each reactor and spent fuel pool. If someone has a ready reference, please post. I will try to find it as well.
As to your conclusion, yes, if a large number of rods or bundles were damaged or burned and melted that would be a problem, But it would also be bed if even a few were damaged. I don't have good information that allows anyone to calculate how many in each location have been damaged or to what extent. I believe containments have been damaged and reactor buildings have been damaged so fuel pools are open to the environment, so there are ongoing releases of radiation. Right now the priority is to cool and stabilize fuel in all locations to end further damage and releases from the fuel. Then the prioriy is to reestablish some form of low pressure containments to stop offsite releases to air, land, groundwater, and the sea. It would be best if they can work on both of these priorities, but access for spraying and cooling may temporarily prevent containing some release paths.

Damage to a spent fuel rod is bad, but loss of containment and damage of recently irradiated fuel is worse on a one to one basis.

FishmanGeertz

What are the core temperatures of Fukashima units 1-4? I think someone posted a link showing graphs of the pressure and heat levels inside the reactors.

Dmytry

Damage to old fuel is much worse long term. At 240 reactor years, it would be something around 120 times long-term Chernobyl inventory. Let's say, 100 or 50 times.
How bad was Chernobyl? Well, 25 years after, some German deer / boar / other wildlife has up to 40 000 Bq/Kg of Cs-137 in meat, and the restrictions are in place on sheep farms as far as Ireland.
Mushrooms can get pretty hot too. It will go on for a long, long while, as the caesium goes from the soil into living beings and stays in living beings, and the equilibrium between decay and re-introduction can remain for a while or the levels in animals may even be rising.
That is not to say that this would necessarily be worse than Chernobyl, but to say that it does not take widespread damage to spent fuel to match or surpass Chernobyl's long term effects. It really is a sort of wake up call. How much worse can things be than Chernobyl - well, apparently, if humans were to walk away from a big reactor complex, after machinery fails, 100 times worse. Ditto for a war that'd destroy a nuclear reactor complex. If the civilization were to fail, living would be rather more tough than typically depicted. I wonder if in the event of nuclear war, reactors, not bombs, would be responsible for majority of long term contamination.

jakekazoo

interesting idea, i believe that nuclear reactors would be responsible for alot of radiation contamination for much of the entire planet.