Panic limitation, been reading the news and had a drunken argument last night regarding what's going on with the ~~~ashima Daiichi reactor site.
First off some low brow physics lessons.
A nuclear reactor is a very simple device, think of it like a high pressure beer keg (only on a far larger scale)
This is called a pressure vessel (its under enormous pressure for the majority of the time)
This is housed inside another vessel called the primary vessel.
Think of a beer keg inside a nice concrete and lead case.
Inside the beer keg is water, its filled up with the stuff and there's a steam pipe coming out the top and a water pipe coming in to refill the boiled off steam.
The steam pipe connects to big motors which produce the electricity then to the cooling system then back to the pressure vessel. everything is contained in one big loop.
Now there's two types of rods in the water, Fuel Rods, made from uranium pellets housed in zirconium. then Control Rods made from boron.
The fuel rods are radioactive the control rods aren't, its their job to absorb neutrons and control the reaction (they become radioactive through their lifespan by this absorption)
take your hand and open your fingers like your sign languaging four, these would be Fuel Rods, now do the same with the other hand and place it over the top interwoven with the four and you get the idea of how things work, drop the control rods lower the reaction slows, take them back up and the reaction speeds up.
The Fuel rods decay and give off some heat and neutrons.
If the radioactive material gets struck by a neutron it splits at an atomic level and gives off two more neutrons and more heat, these two neutrons hit other rods and cause the atoms in them to split and you wind up with 4 neutrons and even more heat, then 8,16,32,64,128,256,1024,2048 and so on.
This happens very quickly doubling again and again till the reactor goes bang like a nuclear bomb.
Hence the control rods which take neutrons away from the fuel rods and stop things happening too quickly and getting too hot.
Thats all a reactor does, day in day out, its as simple as that!
If something starts to go wrong you simply drop all the control rods down and the reaction effectively stops because the bulk of the neutrons flying around are absorbed.
So WTF is the big deal?
When a disaster happens this is what happens, and its exactly what happened in Japan, the rods dropped and the reactors went into sleep mode.
Crisis averted...
Mostly...
The real problem is that if you strike a uranium atom with a neutron it breaks down into other elements that whilst less radioactive (in an order of days to weeks lifespan instead of a LOT of years like uranium) it also gives off heat.
Usually even this isn't a problem, the water still gets cycled, steam out cool water in and every things happy.
With the reactor stopped power comes into the pumps from the local region.
The local power got screwed by the quake though.
Not a problem, the diesel backup generators kicked in and kept the coolant running... till the 23m wave broke past the 20m high tsunami defence wall and well... diesel generators don't much like breathing seawater and promptly decided to take their ball and head home pissed off.
But AH HA! the batteries kicked in to cover the gennies spitting the dummy out the pram, I don't know if the electrics fried or if they operated normally till they ran out of juice, either way they didn't buy much time and the pumps stopped pumping, things got hot.
HEAT, PRESSURE AND EXPLODY STUFF
without the pumps to cool the system several things start to happen.
1: things get hot and start to boil and melt.
2: depending on the part depends on the seriousness.
Control rods
These melt at fairly low temperatures, when they melt they pool at the bottom of the beer keg and stop "controlling" the reaction. causing other parts to melt.
the upshot is that whilst they gradually melt the reactor gets hotter and other parts begin to melt, this is good because if the fuel rods melt they prevent themselves from making a very big bang
Fuel rods
A couple of things happen with fuel rods when the fit hits the shan, none of them pleasant.
Firstly if Zirconium gets exposed to steam it starts to produce Hydrogen. Hydrogen under heat and pressure likes to get all pissed off and explody.
The uranium begins to dribble out and pool at the bottom of the reactor and get very hot, melting like magma through everything, the beer keg floor, the lead and concrete lining and eventually the top soil, rock all the way down, releasing radioactive shit as it parties on down, this can contaminate a wide area and cause all kinds of bad stuff.
The beer keg pressure vessel.
These are built for pressure, its in the bloody name, but like anything else it can only tolerate so much before it pops like a balloon.
omfg wtf we do?
The solution to it all is simple, cool shit down.
The complication lays at the feet of the pumps being off-line, they cant get back on-line cause there's no juice, you cant get at the equipment because, well, theres radiation everywhere. radiation isnt friendly towards people and its spiking at rates where after a few hours people get all kinds of messed up.
you wanna wander into an invisible nightmare with a toolbox be my guest.
so the next option is to flood stuff with seawater.
The decision to do so isn't as clear cut though, seawater is corrosive, ask any boat hull, its full of salt.
Salty steam even more so, so whilst it cools things it might make them worse.
Its also hard to contain, radioactive water sloshing around isnt ideal.
neither is a rather large bang so screw it, they've started dumping in seawater with boron powder.
This in turn boils and introduces more pressure int0 the system, the solution is to vent the pressure, this releases some of the secondary waste that's only slightly radioactive(the short lifespan shit) again not ideal but in this case necessary. the problem is whilst venting they vented hydrogen and gone and blown the roofs off the reactor huts. looks scary but surprisingly the 1960s reactors don't seem to troubled by the explosions, they're still by and large intact.
It's also why people are freaking out, things going bang is scary as is the newspapers printing panic pieces like "Exposed Fuel Rods" this sounds nightmarish but as you've learned it doesn't mean out in the open, it just means not covered in water, theres nothing out in the open air, everything is still contained in the reactor vessels.
so all that's left to do now is keep on dumping in water and hoping to hold out for a few says till stuff cools enough to, you know, not melt itself and cause worse things to happen.
So yeah radiation is being vented, its only the less harmful stuff though, as opposed to letting things go and watching another Pripyat.
People are dumping as much water as they can, venturing into places that are very inhospitable, you've got under an hour near the reactor at this point before you hit your yearly dosage of 50 miliSieverts or 5 REM.
anything over an hour and your risking all kinds of bad things and long term problems.
So all thats left now is to chopper in more water and hope the people holding conventional fire hoses dont wind up seriously mutated.
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