Chernobyl Fate of Chernobyl's vehicle graveyard

  • Thread starter nikkkom
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I don't have time to check the other facts you mentioned nikkkom but I know one thing , RBMK reactor isn't shut down when refueling , it continues to operate and the refueling goes on with some 2 to 5 fuel rods changed per day.
They don't shut it down typically they just change the most burnt out fuel assemblies.
 
I don't have time to check the other facts you mentioned nikkkom but I know one thing , RBMK reactor isn't shut down when refueling , it continues to operate and the refueling goes on with some 2 to 5 fuel rods changed per day.
They don't shut it down typically they just change the most burnt out fuel assemblies.
The reactor was first brought online 2 years before the accident. Consequently, all fuel bundles were new fuel at the beginning, and now all of them were nearing end-of-life, fully burnt.

Chernobyl Unit-4 shutdown being a planned shutdown is a well-established historical fact. In particular, Medvedev in his book writes: "That day, 25 April 1986, they were preparing to shut down the fourth power-generating unit for regular preventive maintenance".

You are likely correct that it was not planned to be a purely "refueling" outage, I assume there was a plan to transition from initial "uniformly aged" fuel load to the online refueling regime, where different fuel bundles have different ages.
 

mheslep

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C14 is generated from C13 too, via neutron capture. C13 content in graphite is 1.1%. ..
Trivial compared to the Cs 137, even if all 1200 tons of graphite were ejected, which it was not. About 1/4 of the graphite was ejected. C-14 production in graphite reactors, from all sources (such as C13 n capture) is 200 Ci/GW-yr (http://web.ornl.gov/info/reports/1977/3445605743782.pdf [Broken]), or 600 Ci/yr for the Chernobyl reactor, of weak beta radiation with no gamma. By contrast, the Cs-137 released had total activity of 2.2 million Ci (27 kg at 83 Ci/gm) with beta and strong gamma.

...(Some U235 remains not fissioned...)...Definitely not "dozens of kg".
I provided references earlier on the Cs-137 quantity (27 kg) and circling back is tedious. Not all of the radioisotopes were expelled from the reactor in the accident. Half of the radioactivity that was released was in the form of the noble gases, highly radioactive at the time of release, but which decay quickly, disperse, are inert, and not an issue for subsequent remediation, the topic at hand.

Stanford:
...During the Chernobyl explosion, about 27 kg of cesium-137 were expelled into the atmosphere. [2] After the rapid decay of iodine-131, cesium-137 was the predominant source of radiation in fallout from the Chernobyl explosion.
WNA:
It is estimated that all of the xenon gas, about half of the iodine and cesium, and at least 5% of the remaining radioactive material in the Chernobyl 4 reactor core (which had 192 tonnes of fuel) was released in the accident.
A total of about 14 EBq (14 x 1018 Bq) of radioactivity was released, over half of it being from biologically-inert noble gases.*
Most of that gas would have been Xenon-135 with half life 9.2 hrs.

Also see WNA wrt fuel cycles; the spent fuel composition of a typical LWR, for all fission products at the time of removal, including the gases, the very short half-life and lower radioactivity material is 1.1 mt:
Used fuel 25.5 tonnes containing 240 kg transuranics (mainly plutonium), 24 t uranium (<1.0% U-235), 1100 kg fission products.
The total fission product in an RBMK per ton of initial fuel is going to be substantially less because RBMK burn-up is maybe a 1/3 of a modern LWR (Table 1)

References:
Stanford: The Legacy of Cesium-137 After Nuclear Accidents

WNA: Chernobyl Accident 1986
WNA: Nuclear Fuel Cycle
 
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jim hardy

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Carbon's being such a basic component of DNA is the reason we quit atmospheric weapons testing. See Asimov's "At Closest Range" .
Was the amount of C14 from Chernobyl (and Windscale) significant compared to that from 1950's weapons testing ?

www.alzforum.org/news/research-news/dating-birth-human-cells-carbon-14-runs-rings-around-competition
Analysis of growth rings from pine trees in Sweden shows that the proliferation of atomic tests in the 1950s and 1960s led to an explosion in levels of atmospheric carbon 14. Now, Jonas Frisen and colleagues at the Karolinska Institute in Stockholm have taken advantage of this spike in C14 to devise a method to date the birth of human cells. Because this test can be used retrospectively, unlike many of the current methods used to detect cell proliferation, and because it does not require the ingestion of a radioactive or chemical tracer, the method can be readily applied to both in vivo and postmortem samples of human tissues. In today’s Cell, Frisen and colleagues report how they used the dating method to dismiss the possibility that neurogenesis takes place in the adult human cortex.
 

mheslep

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Was the amount of C14 from Chernobyl (and Windscale) significant compared to that from 1950's weapons testing ?
600 Curies of C14 from Chernobyl vs the atmosphere? No.
 
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Trivial compared to the Cs 137, even if all 1200 tons of graphite were ejected, which it was not. About 1/4 of the graphite was ejected. C-14 production in graphite reactors, from all sources (such as C13 n capture) is 200 Ci/GW-yr (http://web.ornl.gov/info/reports/1977/3445605743782.pdf [Broken]), or 600 Ci/yr for the Chernobyl reactor, of weak beta radiation with no gamma. By contrast, the Cs-137 released had total activity of 2.2 million Ci (27 kg at 83 Ci/gm) with beta and strong gamma.
From the document you linked with "table 9", from page 11:

Untitled.png


So, they measured emissions of 8 and 6 Curies of C14 *from non-exploding, normally operating plants which have no 1800 tons of graphite in them* (they are BWRs/PWRs).
And you want me to believe that blowing up a plant which was online at ~3GWt for 2 years, and then burning up its exposed melted core, will release only 200 Curies of C14? That's impossibly low.

BTW, table 9 is not about C14 generation in graphite, it lists N and O data, not C13.

C14 indeed is a weak beta emitter. Its danger is not coming from its beta; it's coming from the fact that it bioaccumulates, and decay of C14 inside an organic molecule destroys said molecule, no matter how weak the emitted beta.
 
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Also see WNA wrt fuel cycles; the spent fuel composition of a typical LWR, for all fission products at the time of removal, including the gases, the very short half-life and lower radioactivity material is 1.1 mt:

|Used fuel 25.5 tonnes containing 240 kg transuranics (mainly plutonium), 24 t uranium (<1.0% U-235),
|1100 kg fission products.

The total fission product in an RBMK per ton of initial fuel is going to be substantially less because RBMK burn-up is maybe a 1/3 of a modern LWR (Table 1)
Thus, you are saying that 25.5 tonnes of LWR spent fuel contains 1100 kg fission products. And you are saying that RBMK will be ~1/3 of that. Thus, 25.5 tonnes of RBMK fuel contains ~350 kg fission products. 190 tons of RBMK fuel, then, contains ~2600 kg of fission products. Sounds right in my range of estimates.
 

mheslep

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Trivial compared to the Cs 137, even if all 1200 tons of graphite were ejected, which it was not. About 1/4 of the graphite was ejected. C-14 production in graphite reactors, from all sources (such as C13 n capture) is 200 Ci/GW-yr (http://web.ornl.gov/info/reports/1977/3445605743782.pdf [Broken]), or 600 Ci/yr for the Chernobyl reactor, of weak beta radiation with no gamma. By contrast, the Cs-137 released had total activity of 2.2 million Ci (27 kg at 83 Ci/gm) with beta and strong gamma.


I provided references earlier on the Cs-137 quantity (27 kg) and circling back is tedious. Not all of the radioisotopes were expelled from the reactor in the accident. Half of the radioactivity that was released was in the form of the noble gases, highly radioactive at the time of release, but which decay quickly, disperse, are inert, and not an issue for subsequent remediation, the topic at hand.

Stanford:


WNA:



Most of that gas would have been Xenon-135 with half life 9.2 hrs.

Also see WNA wrt fuel cycles; the spent fuel composition of a typical LWR, for all fission products at the time of removal, including the gases, the very short half-life and lower radioactivity material is 1.1 mt:

The total fission product in an RBMK per ton of initial fuel is going to be substantially less because RBMK burn-up is maybe a 1/3 of a modern LWR (Table 1)

References:
Stanford: The Legacy of Cesium-137 After Nuclear Accidents

WNA: Chernobyl Accident 1986
WNA: Nuclear Fuel Cycle
Sorry, that's Table 5 in the reference, not 9, showing total C 14 from all sources at 200 Ci per GW yr.
From the document you linked with "table 9", from page 11:

View attachment 101883

So, they measured emissions of 8 and 6 Curies of C14 *from non-exploding, normally operating plants which have no 1800 tons of graphite in them* (they are BWRs/PWRs).
And you want me to believe that blowing up a plant which was online at ~3GWt for 2 years, and then burning up its exposed melted core, will release only 200 Curies of C14? That's impossibly low.

BTW, table 9 is not about C14 generation in graphite, it lists N and O data, not C13.

C14 indeed is a weak beta emitter. Its danger is not coming from its beta; it's coming from the fact that it bioaccumulates, and decay of C14 inside an organic molecule destroys said molecule, no matter how weak the emitted beta.
 
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mheslep

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Thus, you are saying that 25.5 tonnes of LWR spent fuel contains 1100 kg fission products. And you are saying that RBMK will be ~1/3 of that. Thus, 25.5 tonnes of RBMK fuel contains ~350 kg fission products. 190 tons of RBMK fuel, then, contains ~2600 kg of fission products. Sounds right in my range of estimates.
As you know, I am not "saying"; the reference WNA and not me, which I took the trouble to quote, gives typical LWR fission product mass. You also now know, from the other references, for purposes of remediation around Chernobyl, that 27 kg of Cs 137 is the relevant figure, not the total mass of the fission products generated inside the reactor, much of which never left the reactor, or that which existed in the form of noble gases which decayed and dispersed within hours or days of the accident.
 
As you know, I am not "saying"; the reference WNA and not me, which I took the trouble to quote, gives typical LWR fission product mass. You also now know, from the other references, for purposes of remediation around Chernobyl, that 27 kg of Cs 137 is the relevant figure, not the total mass of the fission products generated inside the reactor, much of which never left the reactor, or that which existed in the form of noble gases which decayed and dispersed within hours or days of the accident.
I will remind you where your exchange started.
I said:

me>>> Those bombs had only a few kilograms of fissile material, and IIRC less than half of it fissioned in the explosion. Chernobyl blast is estimated to vaporize several TONS of reactor core.

You responded:

you>> Tons of graphite was ejected (not vaporized). Of the radioisotopes released, 50% were inert noble gases, which though dangerous at the time like the prompt radiation from a weapon, the gases also decayed quickly away. Some *27 kg* of long lasting Cs-137 was released.


As I see it, you were objecting to my statement, seeing it as exaggeration of Chernobyl. Note that neither my statement nor your response contained any statements limiting discussion to todays' remediation concerns. In any case, both nuclear explosions and reactor accidents are EQUALLY affected by such facts as "some fission products are noble gases and thus much less dangerous".

Now after our exchange, when we both dug out and refreshed data, it is clear that my statement was in fact UNDERstating Chernobyl releases. There were not some "tons" of graphite and reactor core. There was 1850 tons of graphite. And not known exactly, but large fraction of it burned up and ended up outside. There were also 190 tons of spent fuel, which included more than 2 tons of fission products (not all of them Cs-137, true). It also burned after the explosion; and a part of it definitely melted (and possibly even vaporized) during the power excursion. Tons, and likely tens of tons of this fuel ended up outside the reactor. For one, liquidators SAW THE FUEL lying outside of the building, hundreds of meters from the reactor.

My phrase that "Chernobyl blast is estimated to vaporize several TONS of reactor core" did not adequately describe the magnitude of this release.
 
From Medvedev's book, a testimony of one of Unit-4 operators:

Untitled1.png

....
Untitled2.png



Now, some numbers.
The roof of Unit-4 is 71 meters above ground level. Vent stack is additional ~80 meters:
smokestack.jpg


If "gigantic flame curled around the ventilation stack", then the flame was AT LEAST 100 meters high. The reactor and surrounding rooms have no materials which would classify as flammable (oil, wood, etc). This flame could only be generated by the burning core and graphite.
 
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In order to vaporize something you need a huge amount of energy , a nuclear bomb has this energy capacity so it vaporizes itself and stuff around it upon explosion , a nuclear reactor core doesn't have such a level of enrichment nor critical mass to achieve these conditions.

The blast at Chernobyl was huge no doubt , thick reinforced concrete walls and structures collapsed.
To me it seems most of what got out was either solid objects (fuel pellets, control rods, graphite core elements , some piping and everything else that got along the blast shockwave) then everything else was mostly smoke from the fire and dust.

Take for example the 9/11 when the twin towers fell there were large dust clouds created , also whenever a building falls even small few story ones much dust goes up, would you also say that the building vaporized itself? Or can we simply conclude that dry cement (the wtc towers had thin cement floor slabs to finish off each floors surface area) creates dust even when simply being drilled or scratched with a sandpaper not to mention total destruction upon a complete vertical collapse.


All in all I doubt the core vaporized itself , it exploded yes maybe some tiny bits got vaporized but then after the explosion it lost it's critical mass and all that happened from then was a rather slow melting of the leftover steel and concrete due to a heat source creating huge temperatures.

Although I think it's hard to say the exact amounts of C14 or other releases simply because at the moment nobody really gave much attention to it as everyone was too busy trying to contain as much as they can and save what can be saved.Also I don't get why you talk so much about core vaporization , any radioactivity release is just as bad , what would it matter , the smoke too contain particles as dust etc.


P.S. Since you posted while I was writing , well you are right , since i was in such a unit myself I can say there really isn't anything that can burn with such a flame , everything is either metal or reinforced concrete.
I'm not an expert I don't know whether graphite can burn so much , maybe it can if it's surrounded by a large heat source that happens to be radioactive at the same time.
The few people who saw it that night also described bright flames and sparks shooting out.

Well maybe check out the "Windscale accident" which happened in 1957 in UK. They too had a graphite core reactor, a very simple design , it's only purpose was plutonium production.They too had the core "on fire" because some fuel rods overheated and melted themselves although If I recall the core itself didin;t catch fire.Well the total power also wasn't so high but well who knows.

I don't want to dismiss the eyewitness account but remember also that eyewitness account is the most contradictionary evidence there is especially when the eyewitness himself has gone through something as severe and traumatizing both mentally and physically as a nuclear reactor explosion when you are it's operating crew.
the firefighters also said back then that they picked up the glowing graphite and fuel elements ejected and throw them to one another because they didin't know what it was but they were attracted to it because of it's strange glow, now after 30 years those who survived which are few , tell a different story , they now say they actually knew that it was half molten uranium rods they were holding in their hands.
Now which case you believe more? From my experience and knowledge I definitely can say that they knew nothing of how dangerous the things were that night nor that they handpicked live uranium for fun, because if they would have known they would have never went anywhere near that place.
So much for eyewitness accounts.
 
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In order to vaporize something you need a huge amount of energy , a nuclear bomb has this energy capacity so it vaporizes itself and stuff around it upon explosion , a nuclear reactor core doesn't have such a level of enrichment nor critical mass to achieve these conditions.
Any functioning reactor most definitely can go critical. It _does_ go critical in order to work. In order to increase its power, it even goes (very slightly) supercritical.

Chernobyl reactor went supercritical and way beyond its design power - estimated power during excursion in above 30GWt.

Now, what is a typical power density in a power reactor? My google-fu says it's up to 50kW per kilogram of fuel. Higher power is desirable, but with power densities higher than this it's difficult to remove heat fast enough to keep fuel rods from melting.

Chernobyl core briefly, for 10-20 seconds, jumped to about half a megawatt of generated power (heat) per kilogram of fuel. You sure this is not enough to melt and vaporize stuff? (Half a megawatt is about 250 electric kitchen kettles.)
 

jim hardy

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since i was in such a unit myself I can say there really isn't anything that can burn with such a flame , everything is either metal or reinforced concrete.
I'm not an expert I don't know whether graphite can burn so much , maybe it can if it's surrounded by a large heat source that happens to be radioactive at the same time.
Graphite is carbon, basically purified coal. Wikipedia says it's difficult to ignite .

www.theenergycollective.com/charlesbarton/55702/did-graphite-chernobyl-reactor-burn
The Chernobyl release must be viewed as resulting from both very high temperatures in the core rubble, extensive mechanical disruption and dispersal of core material and the large draft “chimney effect” that followed the total disruption of that particular reactor configuration.
in other words, fuel plus oxygen plus heat = fire
The design configuration excludes the oxygen and removes the heat. Destroy that configuration and Mother Nature takes over.
 
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nice sum up Jim. I have always wondered is the graphite used for early reactors and also RBMK designs the very same graphite used in pencils? Sounds a bit funny but the words are the same and seems to me the material should also.



@nikkkom are you sure your given time scale of the super output power at unit 4 is correct? 10-20 seconds is quite some time for a 30GWt output, even from a 3000MW thermal reactor design....
The reactors super critical state was very short because upon the first explosion which was steam rupturing pipes the whole reactor just fell apart and with that the whole power surge was gone.
 
The reactors super critical state was very short because upon the first explosion which was steam rupturing pipes the whole reactor just fell apart and with that the whole power surge was gone.
Flash boiling and steam rupture of the piping did not stop the excursion - rather, power could start to climb even faster. RBMK had negative void coefficient, remember? - neutrons were moderated primarily by graphite, not by water. Water was absorbing some neutrons.

When flash boiling started, pipes ruptured and disconnected above and below the reactor and steam escaped above and below, core was left in a hot, dry and still supercritical state.
 

jim hardy

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I have always wondered is the graphite used for early reactors
One book i read about Manhattan Project's Chicago pile describes Enrico Fermi sawing up commercial graphite blocks on a Sears table saw..


https://en.wikipedia.org/wiki/Chicago_Pile-1
Fermi and Szilard met with representatives of National Carbon Company, who manufactured the graphite, and Szilard made another important discovery. By quizzing them about impurities in their graphite, he found that it contained boron, a neutron absorber. He then had graphite manufacturers produce boron-free graphite.[27] Had he not done so, they might have concluded, as the Germans did, that graphite was unsuitable for use as a neutron moderator.[28]
Sounds like a practical guy.
 
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interesting stuff thanks Jim for pointing out.
So I guess the answer to my pencil question is almost yes.I could gather a gazillion pencils and use them as a moderator.


As for what you said @nikkkom , first of all RBMK had POSITIVE void coefficient , not negative.The less dense the coolant the higher the chain reaction.
Secondly from what i remember after the steam explosion the reactor lid and much of the structure just went completely bananas , it disintegrated with a very brute force so no further power excursion was possible since the fuel elements now were thrown around the reactor hall , many were even outside the building and most were thrown into a pile that formed the central lava which then melted the core leftovers and slowly sank down into the basement levels until cooled down and stayed there, and lies there till this day.

As for the fire being as high as the smoke stack , well I don't know
read the text in the lowermost part of the paper under "further information"

http://www.world-nuclear.org/information-library/safety-and-security/safety-of-plants/appendices/chernobyl-accident-appendix-1-sequence-of-events.aspx
the smoke stack together with the reactor building would be some 50 stories high in terms of typical office buildings so what your saying is that there was something there which burned with a flame as high as a average skyscraper.Maybe the eyewtiness saw the devastation and upon the lethal doses he was receiving couldn't see everything clearly , also it was night outside.
 
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As for what you said @nikkkom , first of all RBMK had POSITIVE void coefficient , not negative.The less dense the coolant the higher the chain reaction.
Correct.

Secondly from what i remember after the steam explosion the reactor lid and much of the structure just went completely bananas, it disintegrated with a very brute force so no further power excursion was possible since the fuel elements now were thrown around the reactor hall
There is a way to know more: *read about it more*, do not simply invent a scenario which looks plausible to you.

Unit-4 explosion was investigated. Perevozchenko saw the moment when reactor power excursion started - he saw how reactor channel top assemblies (the circular ring of small squares in the reactor hall) started vibrating and "jumping" (moving vertically up and down a bit).

Then, several witnesses reported hearing SRVs triggering (it is a quite loud bang) - this indicates steam overpressure in the reactor.

Then, analysis of the ruins indicates that a large explosion happened in the reactor hall, i.e. in a large room above the reactor. From this it is inferred that top piping was torn off by rising steam pressure, and steam with steam/zircon reaction products, hydrogen and oxygen, filled the hall.

It is not known whether there were two hydrogen explosions (one in the hall and one in the reactor) or one. Witnesses' accounts on the numbers of explosions differ. (Additional complication is that most inexperienced people can classify SRV triggering sound as an "explosion").

Last, and largest explosion is assumed to be a hydrogen explosion, not steam explosion. Flash boiling is assumed to not destroy the reactor.
 
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well it is hard to tell , yes nikkkom I know how the reactor hall looks like and also I stood myself on the very cube shaped metal tops beneath which lies the various detectors and ends of the control rods, fuel assemblies etc.
One of the reasons I wanted to have an in depth visit inside an RBMK was because of Chernobyl , the other reason was pure fascination by science.

Frankly does every small detail matter here ? The general idea is that the chain reaction got out of hand which produces heat , heat increased so rapidly that some parts of the core could not withstand the heat/pressure so they broke as they did everything got even worse and more out of hand and the end is well we know the reactor disintegrated with a huge blast and also took much of it;s building with it.Surely there were many more steps by the seconds inbetween the final destruction and the tops shaking moment but i'm talking generally here , yet the question about the huge fire is still open.

I don't doubt the many facts you have presented as I know them myself and everyone can read them but I think with some information you are overreacting or speculating.
 

mheslep

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Baffling as to why someone would approach a reactor accident within a 100 meters unless they were emergency response.
 
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Not sure about the eyewitness from nikkkoms post but the emergency teams were just as unprotected as he was.If I'm correct all of the firefighters from that night died within weeks.And I bet their death was slow and painful.No one actually knew what the heck just had happened.maybe just the reactor crew and even they were probably in a state of shock.But from the other side the firefighters had no time to prepare anyways even if someone told them that this is a kamikaze mission.
the fire was raging and they had no time , it might have easily burnt up unit 3 which was separated by a thick wall from unit 4, imagine the fallout then if both RBMK units went up in smoke.
It's somehow a miracle that only unit 4 got obliterated , I wonder would the blast have been any stronger or the reactor lid thrown sideways instead of right up things could have went differently.



But I assume the fire and the flames must have been gigantic in size because many people came out in the night and watched towards the reactor as it burned through the night , after all the city was only 3km away so the scenery was probably worth a million action movies, sadly most of the watchers got quite lethal doses of radiation.
 
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mheslep

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...
If the flame really was that high it deserves to be in the guiness world records as the highest man made flame ever or even highest natural flame ever , ...
170 M a record? Forest fires throw up flames 200M. And then there are the man made fires n chemical explosions.
http://www.tandfonline.com/doi/abs/10.1080/00049158.1984.10676001?journalCode=tfor20
http://www.bbc.com/news/world-asia-china-33924501

The two explosions, seconds apart, caused a fireball visible from space and a shockwave that damaged buildings within a 2km radius (1.5 miles). The second of the blasts was the equivalent of 21 tonnes of TNT.
 
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I guess I had a weak idea of height comparisons in my head but 170m seemed rather huge , well i haven't seen a large fire in my life so it's hard to imagine a forest fire being 60 stories above the actual forest because 200m is about a 50/60 story building, and that's pretty damn high for a flame originating from a pile of loosely packed wood.

I remember reading about the China chemical explosions , although never though about the flame height but seems they were massive.
Well thanks for pointing out.
 

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