Chernobyl (HBO Mini Series)
Discussion
Trying to answer the chernobyl 'big bang' question simply (and please note I haven't been in the Nuclear industry for a very long time);
A runaway fission nuclear reaction such as a nuclear bomb actually takes a lot of effort and design to get it exactly right, and there are lots of recorded examples of 'fizzles' which are failed, or smaller nuclear reactions than expected.
The (very) basic principle of a nuclear bomb is to impact two radioactive sources together with sufficient energy and fissile material to set off a uncontrolled chain reaction.
Most nuclear reactors in simple terms contain enough radioactive material to make a bomb but due to the way they are designed to use that material it is spread a lot further about than in a bomb.
The theoretical threat of a nuclear reactor becoming a bomb is therefore very, very small but it is still there. It would be dependant upon a sufficiently large thermal (conventional) explosion being able to force sufficient levels of the radioactive material together to start the reaction - prompt criticality.
To simply explode a normal nuclear reactor core would be extremely (almost impossibly) unlikely to achieve this, as the radioactive material is too far apart and has too much other reactor core construction elements in the way.
The problem identified at Chernobyl was that the reactor core had already exploded meaning that lots of elements of the core that were designed to keep the highly radioactive elements apart had either been ejected from the core or destroyed in the thermal explosions that occurred when the core overheated.
Now you have a damaged, molten, indeterminable mass of radioactive material, and as identified by the team, the threat of another thermal explosion should the molten mass find its way through to a pond of cold water. Whether this next thermal explosion would definitely have resulted in a prompt critical chain reaction such as nuclear explosion is incredibly difficult to assess now, let alone then, but what could be said with a good amount of confidence then is that the risk of that happening had increased quite considerably now that it was known that the reactor core had been severely compromised and that there was absolutely no control of the original core.
I hope that explains it reasonably simply.
I lived in Ukraine for a year and more some years after the incident, in Kiev in fact, and the human damage of the accident was as palpable then as it perhaps is now. A generation of people for whom radiation would affect their lives from cradle to grave whether indirectly though the loss of loved ones or the limits on their lives, travel and diet, or directly through their cancers, their risk of abnormal births, and the other sort and long term effects of radiation poisoning.
It is also very important to remember than by populus I believe Belarus was more adversly affected due to the prevailing weather patterns following the incident; I remember once or twice meeting and talking to some young Belorussians about the incident and the effect on their lives and country.
A runaway fission nuclear reaction such as a nuclear bomb actually takes a lot of effort and design to get it exactly right, and there are lots of recorded examples of 'fizzles' which are failed, or smaller nuclear reactions than expected.
The (very) basic principle of a nuclear bomb is to impact two radioactive sources together with sufficient energy and fissile material to set off a uncontrolled chain reaction.
Most nuclear reactors in simple terms contain enough radioactive material to make a bomb but due to the way they are designed to use that material it is spread a lot further about than in a bomb.
The theoretical threat of a nuclear reactor becoming a bomb is therefore very, very small but it is still there. It would be dependant upon a sufficiently large thermal (conventional) explosion being able to force sufficient levels of the radioactive material together to start the reaction - prompt criticality.
To simply explode a normal nuclear reactor core would be extremely (almost impossibly) unlikely to achieve this, as the radioactive material is too far apart and has too much other reactor core construction elements in the way.
The problem identified at Chernobyl was that the reactor core had already exploded meaning that lots of elements of the core that were designed to keep the highly radioactive elements apart had either been ejected from the core or destroyed in the thermal explosions that occurred when the core overheated.
Now you have a damaged, molten, indeterminable mass of radioactive material, and as identified by the team, the threat of another thermal explosion should the molten mass find its way through to a pond of cold water. Whether this next thermal explosion would definitely have resulted in a prompt critical chain reaction such as nuclear explosion is incredibly difficult to assess now, let alone then, but what could be said with a good amount of confidence then is that the risk of that happening had increased quite considerably now that it was known that the reactor core had been severely compromised and that there was absolutely no control of the original core.
I hope that explains it reasonably simply.
I lived in Ukraine for a year and more some years after the incident, in Kiev in fact, and the human damage of the accident was as palpable then as it perhaps is now. A generation of people for whom radiation would affect their lives from cradle to grave whether indirectly though the loss of loved ones or the limits on their lives, travel and diet, or directly through their cancers, their risk of abnormal births, and the other sort and long term effects of radiation poisoning.
It is also very important to remember than by populus I believe Belarus was more adversly affected due to the prevailing weather patterns following the incident; I remember once or twice meeting and talking to some young Belorussians about the incident and the effect on their lives and country.
Pesty said:
Did a woman really save the world or is that but made up?
Watch each episode to the end. There is a piece at the very end where the producers, director, actors etc give some insight on that particular episode. Your question is answered by the piece at the very end of episode 2.
If you can't watch it again, I'll post it here once some more people have seen ep. 2.
Edited by Corso Marche on Wednesday 15th May 04:58
On top of McGee's excellent layman's description, I just wanted to add that there's different levels/types of Uranium (isotope 235 in this case).
The higher the enrichment, the higher the chance of criticality and the more energy stored. Power plants generally have something around the 3-8% mark.
As GaryC alludes to above, there was stuff other than fuel rods in the reactor core and lots of speculation as to what they were.
Chernobyl was also the reason that graphite was no longer used as a moderator anywhere else and we moved to both heavy and light water.
I'm glad they've included the diver story. those 3 men are real unsung heros, and it looks like they're following the events that actually happened. Such as swimming 500m in the dark/feeling by hand as all the electronics failed due to the radiation level.
ETA - Link of diver story
The higher the enrichment, the higher the chance of criticality and the more energy stored. Power plants generally have something around the 3-8% mark.
As GaryC alludes to above, there was stuff other than fuel rods in the reactor core and lots of speculation as to what they were.
Chernobyl was also the reason that graphite was no longer used as a moderator anywhere else and we moved to both heavy and light water.
I'm glad they've included the diver story. those 3 men are real unsung heros, and it looks like they're following the events that actually happened. Such as swimming 500m in the dark/feeling by hand as all the electronics failed due to the radiation level.
ETA - Link of diver story
Edited by Lazadude on Wednesday 15th May 07:56
daddy cool said:
Ep2 was good. I might need to rewatch it, but the first chopper that flew over the reactor to drop sand seemed to just fall apart and then crash - did the radiation affect machinery, or did the pilot clip the rotors on something structural?
Radiation would have fried/melted stuff.They put an armoured bomb disposal robot on the roof of the reactor to help clear debris and that instantly failed.
(EDIT) Just rewatched it - YT Link to real life one - and it looks like it loses control (radiation kills pilot) and hits a crane. So both.
Edited by Lazadude on Wednesday 15th May 08:35
Really enjoying this!
I do have a question for anyone that can answer it, a did google it last night after I watched the episode but didn't really find much information.
How did they continue to operate the remaining reactors for the years after before they were switched off? Did the plant not need physically manning or was it a case of if you had to go in you donned a radiation suit?
I do have a question for anyone that can answer it, a did google it last night after I watched the episode but didn't really find much information.
How did they continue to operate the remaining reactors for the years after before they were switched off? Did the plant not need physically manning or was it a case of if you had to go in you donned a radiation suit?
Lazadude said:
Radiation would have fried/melted stuff.
They put an armoured bomb disposal robot on the roof of the reactor to help clear debris and that instantly failed.
(EDIT) Just rewatched it - YT Link to real life one - and it looks like it loses control (radiation kills pilot) and hits a crane. So both.
I seem to remember reading that the actual cause was the pilot flying too close to various guide/crane cables which got sucked into the main rotor and smashed the blades. I don't think there was a loss of control/malfunction involved.They put an armoured bomb disposal robot on the roof of the reactor to help clear debris and that instantly failed.
(EDIT) Just rewatched it - YT Link to real life one - and it looks like it loses control (radiation kills pilot) and hits a crane. So both.
Edited by Lazadude on Wednesday 15th May 08:35
McGee_22 said:
Most nuclear reactors in simple terms contain enough radioactive material to make a bomb but due to the way they are designed to use that material it is spread a lot further about than in a bomb.
The theoretical threat of a nuclear reactor becoming a bomb is therefore very, very small but it is still there. It would be dependant upon a sufficiently large thermal (conventional) explosion being able to force sufficient levels of the radioactive material together to start the reaction - prompt criticality.
At the fuel enrichment level found at Chernobyl, and all other power reactors, it can't explode like a fission bomb regardless of what happens. Simply going briefly prompt critical is not enough - the initial thermal explosion was caused as the reactor went prompt critical. The theoretical threat of a nuclear reactor becoming a bomb is therefore very, very small but it is still there. It would be dependant upon a sufficiently large thermal (conventional) explosion being able to force sufficient levels of the radioactive material together to start the reaction - prompt criticality.
hairykrishna said:
McGee_22 said:
Most nuclear reactors in simple terms contain enough radioactive material to make a bomb but due to the way they are designed to use that material it is spread a lot further about than in a bomb.
The theoretical threat of a nuclear reactor becoming a bomb is therefore very, very small but it is still there. It would be dependant upon a sufficiently large thermal (conventional) explosion being able to force sufficient levels of the radioactive material together to start the reaction - prompt criticality.
At the fuel enrichment level found at Chernobyl, and all other power reactors, it can't explode like a fission bomb regardless of what happens. Simply going briefly prompt critical is not enough - the initial thermal explosion was caused as the reactor went prompt critical. The theoretical threat of a nuclear reactor becoming a bomb is therefore very, very small but it is still there. It would be dependant upon a sufficiently large thermal (conventional) explosion being able to force sufficient levels of the radioactive material together to start the reaction - prompt criticality.
I know from my own personal experience that operating a Nuclear Reactor under Emergency Operating Procedures is vastly different from operating under Standard Operating Procedures, and it's not simply a different set of guidelines and parameters, it is the way and speed with which the Reactor responds and reacts, and the vastly different response that secondary plant can ellicit, as well as some interesting readings that can be a little unexpected and more tricky to anticipate, understand and explain.
Getting back to the materials question, one of the reasons RBMK's were so widespread and common throughout the Soviet Union was that they used normal Uranium 235 and not enriched Uranium 235 which is vastly more expensive to prepare for use- put simply, they were a lot cheaper.
Another latterly identified point regarding the Chernobyl incident was the fact that the graphite tipped control rods locally increased reactivity as they were inserted, which whilst not being a sole contributor to the size of the accident was one of a number of contributory factors; it turns out this localised increase in reactivity had been identified but not fully understood, almost by accident, during a different test on a different Soviet RBMK reactor some time before but once again, due to the secrecy and heavy-handed information control exerted by the Communist regime had not been communicated to other RBMK reactor operators or Atomic Energy Authorities worldwide.
The human element of initial disbelief at what had happened cannot be overlooked either; these were normal men and women, experienced and knowledgable in their fields and roles, going to work and being asked to conduct a test which they had been assured was within the safe limits of the reactor. The fact that they could not initially comprehend what had gone wrong goes a long way to explain why there is now so much openess and facility to spread information in the Nuclear industry. One of the lessons from Chernobyl was, if you have made a mistake or believe something is going wrong for heavens sake stand up, be heard and say so.
Again my own experience was of one incident where I was initially deemed at fault for a reactor shutting down rather unexpectedly in the middle of the night during what should have been a fairly routine procedure - I was suspended from operating for a very short time then supervised for a period before component testing revealed an age related fault that required Fleet wide testing, and limitations placed upon other Operators carrying out the same procedure before extensive component testing and replacement had been undertaken.
I was convinced I had done nothing wrong but the intial reactions of some of my colleagues was that I had quite royally f
ked up; my immediate superior and the Head Engineer however were aware of my ability as an operator and honesty as a person and withheld judgement until testing had been carried out. Needless to say, once it was proven I was not at fault the naysayers were shut up and in one case forced to apologise and undergo further training as he was overly vocal in his personal criticism of me and this was taken as a sign that he was not open-minded enough to appreciate that a material fault could have taken place instead of a human error.It was a small element that went to prove that no one person knows everthing within the Nuclear Industry and that making sweeping statements and assumptions can, and will, lead down a path that veers quite clearly away from truth and understanding.
Edited by McGee_22 on Wednesday 15th May 10:01
The Hypno-Toad said:
Bloody hell, episode 2 was even more scary! 
Agreed, sent a shiver down my spine. If not for the actions of a few unsung heroes it sounds like the World could have been a very different place! If true incredible that Russia tried to cover it up and went so far as not to evacuate people from right nearby the place until forced to do so.TX.
Lazadude said:
daddy cool said:
Ep2 was good. I might need to rewatch it, but the first chopper that flew over the reactor to drop sand seemed to just fall apart and then crash - did the radiation affect machinery, or did the pilot clip the rotors on something structural?
Radiation would have fried/melted stuff.They put an armoured bomb disposal robot on the roof of the reactor to help clear debris and that instantly failed.
(EDIT) Just rewatched it - YT Link to real life one - and it looks like it loses control (radiation kills pilot) and hits a crane. So both.
Edited by Lazadude on Wednesday 15th May 08:35
McGee_22 said:
Like most industries and technologies, times move quickly and knowledge dissemination has improved exponentially since the advent of the internet, but I'm fairly sure that you wouldn't have been quite so certain and self-assured back in 1986, just North of Pripyat, with a test that had just gone quite horribly wrong.
I was 6 in 1986 so you're probably right about my confidence. Basic reactor physics hasn't changed since then; my copy of Glasstone was published in the 70's. The realities of how fission works mean that a reactor can't possibly explode like a fission bomb. No set of circumstances, no matter how unfortunate or contrived can cause it to. This is not misplaced confidence in or ignorance of engineering. It would be impossible to make it happen even if you wanted it to.
Emmapuma said:
Really enjoying this!
I do have a question for anyone that can answer it, a did google it last night after I watched the episode but didn't really find much information.
How did they continue to operate the remaining reactors for the years after before they were switched off? Did the plant not need physically manning or was it a case of if you had to go in you donned a radiation suit?
Each reactor has its own control room, so the control etc for reactor 1 is about 1/2 km away from unit 4. Even for unit 3 which is 'twinned' with unit 4 most of the functionality could be approached from the other end of the building. Probably even just after the accident radiation levels in that direction (especially inside the building) were not terrible - the majority of the material ejected and initial plume went the other way: towards the infamous red forest. Block B, the link between 3 and 4 that has the stack on it served both, so some realignment of things needed to be done internally afterwards. They only replaced the stack a few years ago as they had to move it out of the way to slide the NSC over the top.I do have a question for anyone that can answer it, a did google it last night after I watched the episode but didn't really find much information.
How did they continue to operate the remaining reactors for the years after before they were switched off? Did the plant not need physically manning or was it a case of if you had to go in you donned a radiation suit?
About the time of building the sarcophagus they also repaired the damaged parts of the turbine hall (which ran the length of the building supporting all 4 reactors) and put in dividing walls so they could continue to use the turbines etc for 1 - 3.
Terminator X said:
The Hypno-Toad said:
Bloody hell, episode 2 was even more scary!
Agreed, sent a shiver down my spine. If not for the actions of a few unsung heroes it sounds like the World could have been a very different place! If true incredible that Russia tried to cover it up and went so far as not to evacuate people from right nearby the place until forced to do so.TX.
In early 1991 I was on an overnight train with fellow students between Kiev and Moscow, in a compartment with a very poorly looking bloke, one of us mentioned Chernobyl as we passed by it at the closest point the railway gets (still a fair distance away, but the accident laid heavily on minds in those days). The poorly chap pipes up that he's in the state he is as he was a fireman on site the day it went up. Told us he probably had a few months left to live at best estimates. Up to that point we'd been the usual pissed-up noisy student pains in the arse, that shut us all up pretty promptly. Was thinking about the poor b
d as I watched this programme. Pretty lumpy on the old throat.Lazadude said:
They show the evacuation, what they don't show is the parade and fair etc that they put on.
In order to reassure the populace of Pripyat, they had effectively a street party with all the kids parading...
I never knew about the family dogs left behind and there are stories of them desperately trying to get on the buses or running after them as we saw in episode 2. They sent in squads after to shoot all animals but some escaped and their descendants are still there.In order to reassure the populace of Pripyat, they had effectively a street party with all the kids parading...
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