Japan earthquake/tsunami

[Saltheart]

Here's an analogy most fisherman may understand.

If you have ever melted lead to make sinkers , you know you can smell the lead. If you are a little above the melting , the lead smell is evident but if you screw up and get that lead a few hundred degrees above its melting point , the lead smell just reeks.

No heres why.

Atoms are always bouncing around and above the large masses there are actual atoms of the material that are in the air. Now we don't think of it as a vapor but in fact , there is some amount of vapor above even solids at room temp. Now as the materal nears its melting point , the amount of atoms as vapor above the solid surface goes up. When the material melts , there is a huge jump in the number of atooms that are vapor above the liquid , many times more than above the solid. Now as the liquid gets hotter and hotter above it original melting point , the vapor pressure (amount of atoms that are vapor) goes up at some exponential rate.

THe really bad Nuke stuff is the fuel itself that can melt (meltdown) if the control rods cannot slow the fission reaction and if the water cannot take away the heat. Too much heat and the uranium , etc melts and then its vapor pressure sky rockets. The vapor pressure can easily be envisioned as number of atoms , each one highly radioactive and deadly.

Now if you can keep the stuuf from actually melting , you can avoid the huge jump in the vapor pressure but remember , there is still some vapor pressore above the solid and its more , the hotter the solid , just like its more the hotter the liquid. So you do everything you can to keep those temps from going so high the stuff melts. Water is the coolant. However , its not going to cool the whole blob of fission material evenly. Some places are very hot , hot enough to first form steam , then the steam breaks down to H and O and then Boom. You have to take the risk of these H explosions (Actually are explosions) and steam explosions (too much water pressure in a sealed vessel and it bursts , what many would call an explosion too) because you have to try to keep everything cool as possible and try at all cost not to have molten uranium with no water on top of it because molten uranium without the water cover is going to be boiling off the most radioactive vapor aotms.


The whole thing is a nightmare as you risk lives and small explosions to prevent the big meltdown.

Now I don't think there is any way the reactor core can actually explode like an A bomb if that is what people are worrying about. That is actually something that is pretty hard to get started even when you want it to happen. . The biggest worry is the spread of the radioactive metals , etc if the core melts with a failure of both coolant and containment structures.

Now other stuff pics up radiation from the uranium. Th8ngs like the salt and other solids in the water. I'm not sure but I believe the water can actually get irradiated. Most of the time , this is a low level of radiation compared to the actual uranium . Some things , particularly heavy atoms , can pick up a lot of radiation. Its likely at this point that the radiation picked up by the Navy is from escaping water vapor and the contaminents in the water. Hopefully there isn't too much actual uranium atoms getting out.

[JohnR]

Scratch facility fire at Reactor 4

http://www.nytimes.com/2011/03/16/wo...uclear.html?hp

That fourth reactor had been turned off and was under refurbishment for months before the earthquake and tsunami hit the plant on Friday. But the plant contains spent fuel rods that were removed from the reactor, and experts guessed that the pool containing those rods had run dry, allowing the rods to overheat and catch fire. That is almost as dangerous as the fuel in working reactors melting down, because the spent fuel can also spew radioactivity into the atmosphere.

Pressure in 2 Reactor basically at nil? Game over.

[Van]

Originally Posted by Saltheart

Water is the coolant. However , its not going to cool the whole blob of fission material evenly. Some places are very hot , hot enough to first form steam , then the steam breaks down to H and O and then Boom. You have to take the risk of these H explosions (Actually are explosions) and steam explosions (too much water pressure in a sealed vessel and it bursts , what many would call an explosion too) because you have to try to keep everything cool as possible and try at all cost not to have molten uranium with no water on top of it because molten uranium without the water cover is going to be boiling off the most radioactive vapor aotms..

Good stuff.

And yes people think a plant can blowup like a nuclear bomb--NOT--.

In the case of the rods used in this older plant, they are coated with an alloy call zircalloy (sp?). This coating is supposed to help scavange hydrogen. Many plants that are this type (BWR) boiling water reactors have hydrogen problems ie. keeping it as low as possible and have various systems to midigate the gas.

But now that this reactor is superheating, the coating itself is breaking down, and oxidizing. That reaction creates even more hydrogen than breakdown of the cooling water. The explosion yesterday that blew the dome off was a hydrogen gas explosion.

Modern plants are (PWRs) pressurized water reactors. Much easier to control and less chance of environmental contamination as they are two separate systems, one for the reactor, one for the turbines.

I'm not sure yet, but I think they are calling this the worst nuclear disaster in history. If not yet they will......