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Chernobyl, 26th April, 1986

Wikipedia:

quote:

On April 25, 1986, the Unit 4 reactor was scheduled to be shut down for a test. It had been decided to use this occasion as an opportunity to test the ability of the reactor's turbine generator to generate sufficient electricity to power the reactor's safety systems (in particular, the water pumps) in the event of a loss of external electric power. Reactors such as Chernobyl have a pair of diesel generators available as standby, but these do not activate instantaneously�the reactor was, therefore, to be used to spin up the turbine, at which point the turbine would be disconnected from the reactor and allowed to spin under the force of its own rotational inertia, and the aim of the test was to determine whether the turbines in the rundown phase could sufficiently power the pumps while the generators were starting up. The test was successfully carried out previously on another unit (with all safety provisions active) and the outcome was negative (that is, the turbines generated insufficient power in the rundown phase to power the pumps), but additional improvements were made to the turbines which prompted the need for another test. The power output of the Chernobyl-4 reactor was to be reduced from its normal capacity of 3200 MW thermal to 1000 MW thermal in order to conduct the test at a safer, lower level of power. However, due to a delay in beginning the experiment the reactor operators reduced the power level too rapidly, and the actual power output fell to 30 MW thermal. As a result, the concentration of the nuclear poison product xenon-135 increased (this product is typically consumed in a reactor under higher power conditions). Though the scale of the power drop was close to the maximum allowed by safety regulations, the crew's management chose not to shut down the reactor and to continue the experiment. Further, it was decided to 'shortcut' the experiment and raise power output only to 200 MW. In order to overcome the neutron absorption of the excess xenon-135, the control rods were pulled out of the reactor somewhat farther than normally allowed under safety regulations. As part of the experiment, at 1:05 AM on April 26, the water pumps which were to be driven by the turbine generator were turned on; the water flow generated by this action exceeded that specified by safety regulations. The water flow increased at 1:19 A.M.�since water also absorbs neutrons, this further increase in the water flow necessitated the removal of the manual control rods, producing a very unstable and dangerous operating condition. At 1:23:04 A.M., the experiment began. The unstable state of the reactor was not reflected in any way on the control panel, and it does not appear that anyone in the reactor crew was fully aware of danger. Electricity to the water pumps was shut off, and as they were driven by the inertia of the turbine generator the water flow rate decreased. The turbine was disconnected from the reactor, increasing the level of steam in the reactor core. As the coolant heated, pockets of steam formed in the coolant lines. The particular design of the RBMK graphite moderated reactor at Chernobyl has a large positive void coefficient, which means that the power of the reactor increases rapidly in the absence of the neutron-absorbing effect of water, and in this case, the reactor operation becomes progressively less stable and more dangerous. At 1:23:40 A.M. the operators pressed the AZ-5 ("Rapid Emergency Defense 5") button that ordered a "SCRAM" � a shutdown of the nuclear reactor, fully inserting all control rods, including the manual control rods that had been incautiously withdrawn earlier, into the reactor. It is unclear whether it was done as an emergency measure, or simply as a routine method of shutting down the reactor upon the completion of an experiment (the reactor was scheduled to be shut down for routine maintenance). It is usually suggested that the SCRAM was ordered as a response to the unexpected rapid power increase. On the other hand, Anatoly Dyatlov, chief engineer on Chernobyl nuclear station at the time of the accident, writes in his book: "Prior to 01:23:40, systems of centralized control ... didn't register any parameter changes that could justify the SCRAM. Commission ... gathered and analyzed large amount of materials and, as stated in its report, failed to determine the reason why the SCRAM was ordered. There was no need to look for the reason. The reactor was simply being shut down upon the completion of the experiment." [6] Due to the slow speed of the control rod insertion mechanism (18�20 seconds to complete), the hollow tips of the rods and the temporary displacement of coolant, the SCRAM caused the reaction rate to increase. Increased energy output caused the deformation of control rod channels. The rods became stuck after being inserted only one-third of the way, and were therefore unable to stop the reaction. By 1:23:47 the reactor jumped to around 30 GW, ten times the normal operational output. The fuel rods began to melt and the steam pressure rapidly increased causing a large steam explosion, displacing and destroying the reactor lid, rupturing the coolant tubes and then blowing a hole in the roof. To reduce costs, and because of its large size, the reactor was constructed with only partial containment. This allowed the radioactive contaminants to escape into the atmosphere after the steam explosion burst the primary pressure vessel. After part of the roof blew off, the inrush of oxygen�combined with the extremely high temperature of the reactor fuel and graphite moderator�sparked a graphite fire. This fire greatly contributed to the spread of radioactive material and the ultimate contamination of outlying areas. There is some controversy surrounding the exact sequence of events after 1:22:30 local time due to the inconsistencies between eyewitness accounts and station records. The version that is most commonly agreed upon is described above. According to this theory, the first explosion happened at approximately 1:23:47, seven seconds after the operators ordered the "SCRAM". It is sometimes claimed that the explosion happened 'before' or immediately following the SCRAM (this was the working version of the Soviet committee studying the accident). This distinction is important, because, if the reactor went critical several seconds after the SCRAM, its failure would have to be attributed to the design of the control rods, whereas the explosion at the time of the SCRAM would place the blame on the operators. Indeed, a weak seismic event, similar to a magnitude-2.5 earthquake, was registered at 1:23:39 in the Chernobyl area. The situation is complicated by the fact that the "SCRAM" button was pressed more than once, and the person who actually pressed it died two weeks after the accident from radiation poisoning. In January 1993, the IAEA issued a revised analysis of the Chernobyl accident, attributing the main root cause to the reactor's design and not to operator error. The IAEA's 1986 analysis had cited the operators' actions as the principal cause of the accident.

this will break your heart

>>The Legacy<<

i'm waiting for one of you guys to blame this in George Bush.

quote:

Originally posted by tiesto14 i'm waiting for one of you guys to blame this in George Bush.

well, can you rule that out ?

quote:

Originally posted by tiesto14 i'm waiting for one of you guys to blame this in George Bush.

If anyone is interested in a good documentary about the effects of the chernobyl disaster, check out Chernobyl Heart. It's very hard to get through, but if you can, it will certainly educate you.

Well, yeah..safety regulations are there for a reason. When you save money on construction works, do an experiment that has already been known to have failed, turn off automatic safety regulations, and finally ignore all the system warnings, you might just as well expect something like this to happen. What really puzzles me is how the operators of the plant who should have been well versed in the plant operations didn't realize the risks of what they were doing.

do you think govts should be focussing on renewable energy as opposed to nuclear? did i read that china is looking to open a few new ones soon. seems like there might be better ways around the energy question that nuclear...but i dont know an awful lot about it.

quote:

Originally posted by svens_bath do you think govts should be focussing on renewable energy as opposed to nuclear? did i read that china is looking to open a few new ones soon. seems like there might be better ways around the energy question that nuclear...but i dont know an awful lot about it.

Definitely. Renewable energy is the direction we should be headed in. I looked at the Wikipedia article and noticed that we're at the 20th anniversary since the catastophe, though it will be centuries or millennia until that area can safe for humans to go to again.

quote:

Originally posted by svens_bath do you think govts should be focussing on renewable energy as opposed to nuclear? did i read that china is looking to open a few new ones soon. seems like there might be better ways around the energy question that nuclear...but i dont know an awful lot about it.

The problem is cost. Most renewable energy sources are not very cost efficient costing as much as two to three times more than nuclear power. Nuclear power is slightly cheaper than most coal and gas plants. Significantly cheaper if you factor in the cost of C02 emissions.

Click on linky and go to figure 1.1 on page 4

quote:

Originally posted by tiesto14 i'm waiting for one of you guys to blame this in George Bush.

Defently, Bush is to blaim for all of worlds problems

quote:

Originally posted by ali92 Definitely. Renewable energy is the direction we should be headed in. I looked at the Wikipedia article and noticed that we're at the 20th anniversary since the catastophe, though it will be centuries or millennia until that area can safe for humans to go to again.

It was a gash (that means bad) design too. 20 second SCRAM lol!!!!

And renewable is a good asperation but as yet out of reach.

ive visted chernobyl. Very wierd place quiet and dreary and most is still marked off. And no i dont have a 3rd arm or my balls fell off

quote:

Originally posted by DrUg_Tit0 Well, yeah..safety regulations are there for a reason. When you save money on construction works, do an experiment that has already been known to have failed, turn off automatic safety regulations, and finally ignore all the system warnings, you might just as well expect something like this to happen. What really puzzles me is how the operators of the plant who should have been well versed in the plant operations didn't realize the risks of what they were doing.

Hehe, exactly

quote:

Originally posted by occrider The problem is cost. Most renewable energy sources are not very cost efficient costing as much as two to three times more than nuclear power. Nuclear power is slightly cheaper than most coal and gas plants. Significantly cheaper if you factor in the cost of C02 emissions. Click on linky and go to figure 1.1 on page 4

ok but what is the source of these costs..surely there must be a way of cutting them down somewhere (sorry if its in the link..ive not got time to read it all). surely this would be worth it because nuclear just doesnt see like a very prudent option for me...our govt's plans to get rid of the waste?...dig a very large hole and bury it. that cant be right, can it?

quote:

Originally posted by svens_bath ok but what is the source of these costs..surely there must be a way of cutting them down somewhere (sorry if its in the link..ive not got time to read it all). surely this would be worth it because nuclear just doesnt see like a very prudent option for me...

At this moment you really can't do much to decrease those costs. A silicone solar panel pretty much costs a fixed amount of money to produce, and so does a big wind turbine, and there really isn't any way to reduce the price tags of those items. But the real issue with the renewable energy sources is that they can't work continuously. A solar power plant works only during daytime, and it works at full capacity only when there's no clouds. A wind turbine works, well, only when there's wind blowing. Hydroelectirc plants are a bit more stable in that aspect, but they can only be built on specific locations, and they still are suspectable to environmental issues (freezing of the water, floods, droughts..). So to have a continuous power supply, you simply have to have conventional or nuclear plants around. Generally you can't really get much more than about 25% of your power from such sources.

quote:

our govt's plans to get rid of the waste?...dig a very large hole and bury it. that cant be right, can it?

Well, all that radioactive material that's used to power up the plant did infact come from a big hole in the ground, so dropping the nuclear waste back into a big hole in the ground isn't really that inconcievable. The only other thing you could do with it is launching it into orbit or something, but when it's burried so deep it's not really that hazardous for such a costly operation to be considered.

quote:

Originally posted by DrUg_Tit0 At this moment you really can't do much to decrease those costs. A silicone solar panel pretty much costs a fixed amount of money to produce, and so does a big wind turbine, and there really isn't any way to reduce the price tags of those items. But the real issue with the renewable energy sources is that they can't work continuously. A solar power plant works only during daytime, and it works at full capacity only when there's no clouds. A wind turbine works, well, only when there's wind blowing. Hydroelectirc plants are a bit more stable in that aspect, but they can only be built on specific locations, and they still are suspectable to environmental issues (freezing of the water, floods, droughts..). So to have a continuous power supply, you simply have to have conventional or nuclear plants around. Generally you can't really get much more than about 25% of your power from such sources. Well, all that radioactive material that's used to power up the plant did infact come from a big hole in the ground, so dropping the nuclear waste back into a big hole in the ground isn't really that inconcievable. The only other thing you could do with it is launching it into orbit or something, but when it's burried so deep it's not really that hazardous for such a costly operation to be considered.

re. the price tags, couldnt companies cut the price of these things, because its a global common interest that we find a good solution.

i hear what youre saying about the unreliability..there must be areas where its constantly windy though? off the coasts and that..

isnt there a difference between the radioactive material before its processed, and the waste material, in terms of hazard? is there not a chance it could seep into the earths core or something? or even make its way back to the surface?

so is nuclear youre preferred option then i take it?

quote:

Originally posted by svens_bath re. the price tags, couldnt companies cut the price of these things, because its a global common interest that we find a good solution.

Well, companies are not charities. The only way you could do that would be if the government subsidizes them, but then you'd get increased taxes on some other product, so ultimately the end result would be the same. But as I've said, that's not the primary problem.

quote:

i hear what youre saying about the unreliability..there must be areas where its constantly windy though? off the coasts and that..

Well..yeah, but you can't really find an area where there's a constant wind of the right magnitude. There are areas where there's often windy, but the strength of the wind is important also. If it varies too much, your generators will either not provide enough power or burn out.

quote:

isnt there a difference between the radioactive material before its processed, and the waste material, in terms of hazard? is there not a chance it could seep into the earths core or something? or even make its way back to the surface?

The only difference is that the unprocessed material is not concentrated. So yeah, being close to a processed fuel lump is more dangerous than being around raw uranium ore. But I suppose if you'd take the waste fuel into an airplane and then sprinkle it evenly all over the globe, you'd effectively nullify the danger

quote:

so is nuclear youre preferred option then i take it?

Yes, at least until (and if) we manage to create a working fusion reactor.

good to get your views on this, cheers

Uranium ore in its native state is a solid that inhabits the earth just like all the other minerals on earth. The waste material is a liquid, and by burying that in barrels that can easily degrade over time, is a whole different ball game. You must understand the ability of a liquid to travels through what may seem as solid rock. It is in fact full of joints, cracks, and depending on the material has a certain porosity. Throw in all that the water table, another liquid that inhabits the same regions in the same manner, which most folks get their water from, and you have the makings of a dangerous situation.

quote:

Originally posted by InterMilan31 ive visted chernobyl. Very wierd place quiet and dreary and most is still marked off. And no i dont have a 3rd arm or my balls fell off

...but you never need a night light...

quote:

Originally posted by Fir3start3r ...but you never need a night light...

That was uncalled for.

quote:

Originally posted by metalgearsolid That was uncalled for.

Get a sense of humour...

It's not like we can do anything about the past; we can learn from it though...

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Originally posted by Nou LOL no. Uhm... unprocessed uranium is very very very non-radioactive because it exists in very very minute amounts. You have to refine it thousands of times over for it to become useful in a reactor, and many more times for it to be weapons grade.

Well..that's kind of what I said. That the unprocessed ore is not as harmful as processed ore or waste because it is less concentrated. It's not really that miniscule amounts that we're talking about though, since uranium ore is not that uncommon.

Essay on Chernobyl
http://www.magnuminmotion.com/essay_chernobyl/

quote:

Originally posted by ogvh5150 Essay on Chernobyl http://www.magnuminmotion.com/essay_chernobyl/

repost.

it was the second post of this thread.

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