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Captain Slow
I just thought I'd post this...found it on another forum, and thought it was really well done. Always found Chernobyl a fascinating case study - amazing how the right combination of ignorance, poor planning, and simple gauge malfunction can completely change the world.
Both posts from this thread:
http://forums.vwvortex.com/showthre...e-graveyard.-some-hauntingly-beautiful-photos.
91gti_wolfsburg said:I did a lot of research on chernobyl when I was in college.
I was very much into nuclear power back then.
I gotta warn you -this is a long read, so if you have ADHD, or simply cant be bothered with long posts, skip this one.
@ the time Radiation was measured in Roentgens. A lethal dose (mortality=100%) to the average human being is 400 Roentgens. (these days I think they use RADS, Seiverts, or REM depending on the institution -converting back and forth sucks too)
When measuring levels of radiation at a given time, it was usually taken in Roentgens per Hour.
There are 3 different kinds of ionizing radiation, Gamma, Alpha, and Beta.
Gamma is a high frequency form of electro-magnetic energy (the most deadly)
Alpha is an atom of Helium stripped of its electrons (not as deadly)
Beta is electron radiation (almost harmless)
Each is harmful, but not equally.
Different radioactive isotopes of compounds, Iodine 131 (big offender @ Chernobyl), Cesium 137, Cobalt 60, and a myriad of others all emit one or more forms of ionizing radiation.
Iodine tablets were issued to prevent the body from taking in and storing I 131. The iodine tablets do not protect you from any other isotope except I 131.
Gamma will go through pretty much anything but lead, Alpha can be stopped cardboard or wood, and beta can be stopped by a sheet of paper. Radiation shielding usually has all 3 of these (or equivalent) components as gamma can produce Alpha if it strikes a lead surface in just the right way.
IIRC acceptable levels for radiation were around 50 millionths of a R per hour. (only slightly higher than background radiation)
Ill effects of radiation show up in blood chemistry at about 2R, blood chemistry starts to change, the Iron in the Hemoglobin goes hot, making your blood slightly radioactive, this would severely damage your bone marrow in the worst case, resulting in a marrow transplant in an attempt to reverse the effect.
From there on in terms of dose, Nausea, vomiting, loss of hair, internal bleeding, and general organ failure, followed with a mortality directly proportional to dose in varying combinations all the way on up to the lethal dose.
Currently:
The picture of the person holding the meter in front of Reactor #4 (a couple pages back) showed 7/10ths of a R. In other words, you could stand there for about 3 hours before you got ill.
In other areas levels are much less, thousandths of a R, do the math. Is it safe to go there? Yes. Would you want to live there? No.
Back then:
The highest levels of radiation ever encountered by a human being on the face of the planet, were found on the roof of reactor #3. When the lid blew off #4, it sent chunks of moderating graphite into the air, much of it landing on the roof of #3.
This moderating graphite is the stuff that directly surrounds the nuclear fuel. When Uranium decays one increment, the following happens:
one neutron fired into an atom of--> U235-->U236-->Kr 92 + Ba 141 + 3 neutrons. Kr 92 and Ba 141 further decay into many other isotopes. The 3 neutrons spewed from that decay need to go somewhere. Ideally in a self sustaining reaction 2 of them are supposedly captured by the control rods, the remaining one passes through the moderator, and is slowed down enough to initiate another nuclear decay.
This graphite moderator from #4 ended up on the roof. Radiation levels were estimated to be up above 12,000R/hour.
At that rate, a lethal dose is received in less than 2 minutes.
Usually when anyone mentions nuclear power, they automatically think of Chernobyl, and rightly so. That was the worst nuclear disaster ever. Worse than Hiroshima and Nagasaki. People live there at the A-bomb grounds-zero nowadays.
Some of the radioactive isotopes expelled from the chernobyl reactor will not decay to safe levels for a hundred thousand years. The exclusion zone around chernobyl will be there permanently for the foreseeable future.
Usually radioactivity is inversely proportional to half life. In other words, the most dangerous stuff only lasts for a few years, while the least dangerous stuff (while still dangerous) lasts for a very very long time.
Why did chernobyl melt down? A good question, which lots of research has been done on.
What I have gathered from what I have read:
The disaster was caused by a number of things (in descending order by blame) :
Design Flaw
Faulty Instrumentation
Operator inexperience
When it happened, the operators were doing a test on an emergency system to keep the reactor cool in the event of a turbine stall. Turbine stalls happen when the power grid goes into a blackout. The steam to the turbines must be shut off so that they stop producing power, since there is nowhere for the power they produce to go otherwise.
Even though after the turbines stop and the reactor SCRAM happens, the reactor is still immensely hot from the decay heat and it needs to be constantly supplied with coolant.
The other edge of the sword here is that the coolant pumps of the reactor are also powered by the same electricity that the turbines produce, so when the turbines stop, they need diesel generators to run the pumps. Well, they take some time to start up and actually produce power.
The operators were testing to see how long the turbines could power the coolant pumps on their spin down momentum with no steam going to them, to see if it would be long enough to allow the diesels to take over from a cold start.
When the operators started the test, they brought the reactor to minimum power. Soviet RBMK reactors are/were very unstable (difficult to keep going) at minimum power. I am not sure of the exact physics, but RBMK's get "poisoned" at low power.
The operators fearing that the reaction would stall (due to instrument malfunction), disabled the safeties and withdrew all of the control rods. (when regulations prohibited removing a certain percentage of them more than another certain percentage -a boundary for safety)
This is when the instrumentation failed them. Water level instruments were reading high, temperature instruments were reading low, and in an attempt to bring things back to normal, they let a bunch of coolant out of the reactor.
When the temperature and coolant level instruments started reading properly again, the operators realized what had just happened and they hit the reactor SCRAM button. This automatically inserts all of the control rods to stop the reaction.
During the instrumentation mishap, the graphite moderator had become so hot that it deformed and prevented the control rods from going in all the way -thus starting the runaway power excursion
Speaking of design flaws:
RBMK reactors are graphite moderated (modern ones are water moderated), have graphite control rods, and have inefficient coolant flow.
When graphite is irradiated, it builds up something called Wigner Energy. (Another concept that is somewhat nebulous to me, something about the crystal lattice of the carbon atoms getting warped) The short version is that when this energy builds up high enough, it will dissipate with a very intense burst of heat.
When graphite control rods are inserted into a graphite moderated reactor, the output spikes for a few seconds -adding insult to injury in this case.
The coolant of an RBMK (or any commercial reactor for that matter) must be kept at extreme pressure to prevent it from boiling inside the pressure vessel, steam does not absorb heat as well as water and steam pockets could cause melted fuel.
As the reaction ran away, the coolant in the pressure vessel boiled, causing air pockets, more heat, more steam, more pressure, and it simply blew the lid right through the roof.
Once all of the water had boiled away, the graphite started to burn. As the graphite burned, it melted the uranium further, making it burn faster and hotter. Nothing could put the fire out. All the while spewing massive clouds of contamination all over the world.
Another design flaw of chernobyl RBMK's is that they are physically massive. Building a containment structure for a single RBMK would have been such an undertaking that the USSR simply didn't bother. Now we have to build one anyways because of that oversight.
Modern PWRs (like three mile island) and BWRs (vermont yankee) are small enough that a containment shelter can be made around them, so that even if they do blow -which is unlikely, the radiation is contained within the building.
91gti_wolfsburg said:The red forest did not actually "glow."
The radioactive blast simply killed the trees surrounding the plant, many of them coniferous (pine-type trees).
Have you ever seen a dead pine tree with needles still attached to it? It probably looked a lot like that, only thousands of acres of trees as opposed to one or two trees
As far as the gasses coming from the reactor during the initial explosion, I read a first had account of the moment of the blast from one of the operators in the turbine hall.
He said that after it popped its lid, the stream of steam glowed with all the colors of the rainbow. Red, blue, violets, teals. He said that it was "beautiful."
Colors like that are probably due to the extremely hot and ionized gas vapors coming from the vessel acting on their surroundings, much like the ion storms of the auroras in the extreme north.
Another misnomer that I find is common, is that many believe that things that are radioactive have a green glow.
This is utterly false, and a result I can only assume of the opening credits of the Simpsons.
Extremely Radioactive things can emit an iridescent blue glow, much like a white shirt under a blacklight, but much more vivid and deep blue. This is called Cherenkov Radiation. It is commonly seen in the cooling pools for spent fuel assemblies.
If you actually see Cherenkov Radiation in the air, you are a dead man walking.
The blue glow can be compared to a sonic boom in the way that it forms. When an aircraft moves faster than the speed of sound, it produces a sharp and very loud crack.
The blue glow is the result of electrons (and possibly other particles? someone help me here..) moving at a speed greater than that of light in the medium it is viewed. The blue glow is the visual version of the crack that supersonic aircraft makes.
How can something move faster than the speed of light? Very easily if in water. Light slows down to a fraction of its speed in a vacuum--> (~186,000 miles per second), in water. Particles ejected from radioactive materials move extremely fast.
If you were to see Cherenkov in the atmosphere, the source of the radiation is extremely intense and you are way too close to it, at this time however it is far too late. You have about 48 hours (likely much less) to live.
Both posts from this thread:
http://forums.vwvortex.com/showthre...e-graveyard.-some-hauntingly-beautiful-photos.
