Today is the 27th anniversary of the Chernobyl Accident, so here's a documentary
9 replies, posted
So 27 years ago today, at 1:23 AM, a nuclear power plant in northern Ukraine underwent a fatal power excursion that destroyed the reactor, spreading radioactive contamination for miles and killing at least 31 people, possibly far more.
The explosion was a result of a botched safety test, operator error, and poor design of the reactor itself.
If you [I]really[/I] wanna rack your brain with info about the accident itself [url=http://www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf] here is the IAEA's write up on the accident, in full[/url]
This particular documentary has been posted before, a long time ago. It's one of the best.
[B]Surviving Disaster - BBC Documentary[/B]
Part 1
[media]http://www.youtube.com/watch?v=zyHvDhILYl8[/media]
Part 2
[media]http://www.youtube.com/watch?v=9ErRr1PD9IM[/media]
Part 3
[media]http://www.youtube.com/watch?v=qs55k58OPXo[/media]
Part 4
[media]http://www.youtube.com/watch?v=DS8d3ESsvEk[/media]
Part 5
[media]http://www.youtube.com/watch?v=KibJgOb0PM4[/media]
Part 6
[media]http://www.youtube.com/watch?v=4lE8Fr1PVKs[/media]
Let's just get this over with
[video=youtube;VHPltbD-4QA]http://www.youtube.com/watch?v=VHPltbD-4QA[/video]
I do not even remotely want to make any jokes about this, the aforementioned tragedy requires nothing but compassion and understanding, even considering the supposedly poor design of the reactor.
[QUOTE=genkaz92;40432386]I do not even remotely want to make any jokes about this, the aforementioned tragedy requires nothing but compassion and understanding, even considering the supposedly poor design of the reactor.[/QUOTE]
It's not [I]that[/I] drastically serious. I've seen jokes on way worse.
[QUOTE=michaeldim;40432540]It's not [I]that[/I] drastically serious. I've seen jokes on way worse.[/QUOTE]
I was not criticizing anyone, just sharing my perspective.
I've been doing a lot of reading into the accident. Particularly the mechanics behind the accident itself, as in what happened in the reactor itself.
A common misconception is that Chernobyl was a meltdown. It actually wasn't. A meltdown (like Three Mile Island and Fukushima) is where the fuel overheats due to improper cooling and eventually melts. This type of accident can take place over hours or days. Chernobyl was a [B]uncontrolled runaway[/B], which means that the reaction accelerated out of control until the resulting energy tore the core apart and stopped itself. This type of accident plays out over a matter of seconds.
You see, most power-generating reactors need something called a [B]moderator[/B], this material slows down neutrons to make the reaction easier to sustain. There are several materials one can use for this role.
In the west, we use plain water (most of the time) as a moderator, which works well enough. Water serves double duty as the coolant as well (simplifying things) and water is cheap. Thing is, as a moderator, water's okay, not great, but okay.
In the RBMK reactor (Chernobyl's type) they used graphite (Like what's in pencils). Graphite is a great moderator, so much so that the fuel in an RBMK reactor doesn't need enriching first, which saves a lot of money. Problem is, graphite is solid, and can't be used as coolant. RBMK uses plain water as a coolant, but only as a coolant.
Now that was a lot of rambling to say that water moderated reactors cannot runaway like Chernobyl. You see, if such a drastic increase in power were to occur, the heat would vaporize the water. That means the moderator is gone, and the chain reaction will come to a halt.
Well in Chernobyl, the graphite doesn't go anywhere, so even if the reactor is bone dry, it can still react. Matter of fact, it can react moreso without water in it than with. In Chernobyl, because it has graphite as a moderator, the water is just in the way. If it vaporizes in the core, it means there will be [U]more[/U] power. Not less. Which means more vaporization. More power. You can see where this is going.
[QUOTE=michaeldim;40433951]I've been doing a lot of reading into the accident. Particularly the mechanics behind the accident itself, as in what happened in the reactor itself.
A common misconception is that Chernobyl was a meltdown. It actually wasn't. A meltdown (like Three Mile Island and Fukushima) is where the fuel overheats due to improper cooling and eventually melts. This type of accident can take place over hours or days. Chernobyl was a [B]uncontrolled runaway[/B], which means that the reaction accelerated out of control until the resulting energy tore the core apart and stopped itself. This type of accident plays out over a matter of seconds.
You see, most power-generating reactors need something called a [B]moderator[/B], this material slows down neutrons to make the reaction easier to sustain. There are several materials one can use for this role.
In the west, we use plain water (most of the time) as a moderator, which works well enough. Water serves double duty as the coolant as well (simplifying things) and water is cheap. Thing is, as a moderator, water's okay, not great, but okay.
In the RBMK reactor (Chernobyl's type) they used graphite (Like what's in pencils). Graphite is a great moderator, so much so that the fuel in an RBMK reactor doesn't need enriching first, which saves a lot of money. Problem is, graphite is solid, and can't be used as coolant. RBMK uses plain water as a coolant, but only as a coolant.
Now that was a lot of rambling to say that water moderated reactors cannot runaway like Chernobyl. You see, if such a drastic increase in power were to occur, the heat would vaporize the water. That means the moderator is gone, and the chain reaction will come to a halt.
Well in Chernobyl, the graphite doesn't go anywhere, so even if the reactor is bone dry, it can still react. Matter of fact, it can react moreso without water in it than with. In Chernobyl, because it has graphite as a moderator, the water is just in the way. If it vaporizes in the core, it means there will be [U]more[/U] power. Not less. Which means more vaporization. More power. You can see where this is going.[/QUOTE]
Can that be definitively labeled as a bad design though? Or is it more of a trade off?
[QUOTE=genkaz92;40434862]Can that be definitively labeled as a bad design though? Or is it more of a trade off?[/QUOTE]
The graphite core isn't necessarily bad. The UK used and continues to use graphite moderated power reactors. ([url=http://en.wikipedia.org/wiki/Magnox]Magnox[/url] and [url=http://en.wikipedia.org/wiki/Advanced_gas-cooled_reactor]The AGR[/url]) One big difference is, they use CO2 cooling, not water, which can't evaporate.
Additionally the RBMK is bad in a dozen other ways:
The RBMK uses limited containment. The reactor is so large, that containing it was seen as too pricey. The Soviets decided instead to build the reactor in a compartmentalized system, which is nowhere near appropriate.
The RBMK uses what are called [B]pressure tubes[/B] which means instead of one giant vessel with everything in it, there are 1600 tubes running through the core with the fuel in and the water running around it. This provides one of the biggest advantages the RBMK has, the ability to be refuelled without shutting down. This also is a huge weakness; the tubes can burst and the piping to make the RBMK work is a maze of insanely complex and intricate pipes.
The biggest failure is the control rods, which absorb neutrons to regulate the reaction. You see, when the rods are pulled out of the core, water fills in the channels behind them. Water acts as a slight neutron absorber, so the control rods are less effective. The decision was made to add graphite "runners" to the end of the rods. This means that when the rods are pulled up, the runner keeps water from filling in, which makes the difference between the rods being in and being out greater. Most of the time, this actually makes the system more safe.
The problem is that these runners [U]are not[/U] as long as the core is. When a control rod is pulled completely from the core, the runner is a little more than 1 meter from the bottom of the core, which fills with water. At the time of the disaster, a large number, more than was safely allowable, of control rods were removed from the core. This meant that there were a large number of these graphite runners positioned about a meter from the bottom of the core. When the experiment started to go south, the decision was made to execute an emergency shutdown. The operators pressed the emergency shutdown button, which began an insertion of all of the control rods into the core.
Now, the control rods began moving down, at the same time pushing the graphite runners ahead of them. These runners pushed the water underneath them out of the way, and for the same reason I listed above, the absence of this water led to an increase in power. The number of rods being inserted at one time combined with the unique and extremely unstable state the reactor was in caused a massive increase in power.
There is one great way I can remember the Chernobyl accident.
My birthday is on the 26th of April.
[QUOTE=tratzzz;40435301]There is one great way I can remember the Chernobyl accident.
My birthday is on the 26th of April.[/QUOTE]
Happy Birthday, tratzzz! Have a good one ;)
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