Fate of Chernobyl's vehicle graveyard

[mister mishka]

Radiophobia has real, documented impacts - alcoholism, depression - so please don't add to it via hyperbole, especially in the nuclear engineering forum. The commonly found emissions rates for sites all over the Chernobyl area in recent years are available here, and are in the uSv per hour range, aside from equipment and materials used during immediate aftermath of the accident:
http://chernobylgallery.com/chernobyl-disaster/radiation-levels/

Yeah I should ellaborate better, the black forest is an area the guide showed us (by pointing to it from a distance) where there were still high levels of radiation. How he found that out was during winter he went over there wanting to measure amount of radiation of the black trees and say it was quite high and quickly left (and also left his boots). Though I don't know enough on this topic to give any good details or information worthy of this physics forum, I merely wanted to just share an experience.

Thanks for that link though, lots of good information in there!

 

[a.ua.]

johnnyrevCs-137 at Chernobyl has about hit its half-life by now, if I'm not mistaken. However, Cs-137 is most dangerous due to its water solubility, and what do trees drink?
-------------------------------------------------------
but
dangerous strontium 90 and americium 241
easily dissolved and a long half-life. ( half-lives of 432.2 for americium)

 

[Salvador]

All things are somewhat dangerous if one misuses them.I stayed rather long in the sun today , It's June here and this is the time sun has it's highest radiation levels in my location so after a few hours I got pretty burnt.
Chernobyl is actually getting better faster than most people , even experts thought and the wildlife has definitely been doing much much better than at any time in the history of that area simply due to the lack of humans.

I think the really nasty side of radiation is that most of the radioactive dust and particles get into dirt and trees and water faster than anyone can clean up so then they get stuck there and so cause contamination since it's impossible to clean up every square inch of landmass and trees.

 

[Darknoiz]

The vehicles have all been cut up for scrap. In the satellite shot in the third post, top centre. All those dots are the vehicles that once were in the field below. This has been done officially (well, with the knowledge of those who man the checkpoints). Metal reclamation is rife in the Zone. There are teams at work stripping the remains of reactor 5 (there are far fewer cranes around it than there once were), the ships in the dockyard and there are rumours work has even started on the druga 3 array (although I haven't witnessed that myself). Small scale theft, window frames and radiators etc has been going on for years but is periodically clamped down on.

http://chernobylgallery.com/galleries/chernobyl-reactor-5/reactor-5-exterior/

 

[nikkkom]

But yeah, I don't really feel the security / safety systems for the exlusion zone are that well enforced. So I wouldn't be surpised if some deal was made regarding the scrap, but I find it unlikely since moving all material would be too difficult for it not to get noticed (unless the corruption / "deal" happened at a level higher up in the chain).

Yes, that's exactly how it happens: the "deal" happens high enough and material is moved with the knowledge of the guards and their superiors.

 

[nikkkom]

It would be interesting to review the remediation efforts made at Hiroshima and Nagasaki, now 70 years old, and determine how effective they were, and what impact remediation has had on the million or so people living in those contaminated areas.

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.

 

[mheslep]

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.

In totaling the radioactive material from the WWII bombs, add to the fission products the couple of moles of MeV neutrons which activate materials immediately adjacent the bomb before dispersal.

The fire and steam explosion from the Chernobyl accident ejected both radioactive and non-radioactive material. 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.

http://large.stanford.edu/courses/2012/ph241/wessells1/
http://nuclearweaponarchive.org/Nwfaq/Nfaq2.html
http://www.world-nuclear.org/inform...rity/safety-of-plants/chernobyl-accident.aspx

 

[nikkkom]

In totaling the radioactive material from the WWII bombs, add to the fission products the couple of moles of MeV neutrons which activate materials immediately adjacent the bomb before dispersal.

The fire and steam explosion from the Chernobyl accident ejected both radioactive and non-radioactive material. Tons of graphite was ejected (not vaporized).

Reactor had about 200 tons of uranium, and hundreds of tons of graphite. Reactor jumped to estimated 30+ GWt power just before explosion. After explosion, it burned for *days* (there are numerous eyewitness accounts that the flame was very large, comparable to smokestack's height). It means a lot of graphite and fuel turned into microscopic ash-like particles.

 

[Salvador]

Well the army helicopters started flying over very soon after the accident , and from the tapes it can be seen the fire wasn't to the height of the smoke stack because the smoke stack in the RBMK is very high if the flames were that high the helicopter's wouldn't have been anywhere near but we have the tapes from the aftermath showing us the flame size.Ofcourse what happened there the night of the accident is left only in the memories of the ones who were there because no cameras were there to catch any of that.

I think the fire more resembled a cloud of smoke rising from a steel melting furnace than an ordinary fire were something actually chemically combusts and goes up in flames since there isn't much burning material in the reactor hall or anywhere in the active zone its all pretty much steel and concrete but i guess the enormous heat caused by the still ongoing chain reaction and decay is what caused the materials to simply melt and turn themselves into a sparkling soup.
It can actually be seen from the tapes later released that the hot spot is not so much fire as it's a lava like soup that sits in the middle of the reactor like an egg.

 

[mheslep]

Reactor had about 200 tons of uranium, and hundreds of tons of graphite. Reactor jumped to estimated 30+ GWt power just before explosion. After explosion, it burned for *days* (there are numerous eyewitness accounts that the flame was very large, comparable to smokestack's height). It means a lot of graphite and fuel turned into microscopic ash-like particles.

We are discussing the comparison of remediation between WWII atomic attacks and Chernobyl. That is, *nuclear* remediation. What does graphite have to do with this? Or Uranium, how is it significant?

 

[Salvador]

I'm not fully sure of this I hope people with more knowledge will correct me but it seems that a fully loaded and fully working nuclear reactor undergoing meltdown causes much more contamination and after effects than a detonated nuclear bomb, especially the new age ones were the bombs are made more precise and more of the fissile material undergoes chain reaction before the blast rips it apart and the chain reaction ceases.

Also to bear in mind is that in the case of Chernobyl there was very little standing in the way between the reactor fuel and atmosphere , and even with a strong containment structure I think such a blast would have made the structure to collapse and result in what already happened.
after all Fukushima reactors had the safety vessel and yet they too failed to contain the pressure the only blessing that they weren't operating at 100x times their maximum when they went off like Chernobyl was.

 

[nikkkom]

We are discussing the comparison of remediation between WWII atomic attacks and Chernobyl. That is, *nuclear* remediation. What does graphite have to do with this? Or Uranium, how is it significant?

Reactor graphite has significant amounts of C14.

Uranium per se is not too dangerous (it has no intermediate-lived isotopes except U232), but reactor's uranium oxide ceramic pellets, of course, have all sorts of fission products in them. When they melt (or even "merely" strongly heated in an open air fire), those fission products are released.

I don't understand why you are even asking the question, since you for sure know this already.

 

[mheslep]

Reactor graphite has significant amounts of C14.

Uranium per se is not too dangerous (it has no intermediate-lived isotopes except U232), but reactor's uranium oxide ceramic pellets, of course, have all sorts of fission products in them. When they melt (or even "merely" strongly heated in an open air fire), those fission products are released.

I don't understand why you are even asking the question, since you for sure know this already.

Curies from the generated C14 in the entire graphite stack (N content ~30 ppm with 100% conversion) is trivial compared to the Curies from the reactor Cs 137 alone.

The fission product mass from the accident is indeed the health problem. All of it, as I addressed earlier, was calculated and tallied in the dozens of kg range. Whether or not fission product happens to be inclosed in ceramic or buried separately in the dirt, the amount of dangerous radioisotope is not "tons". As you say, you know this from earlier, so it's unclear why you insist on "tons".

 

[nikkkom]

Curies from the generated C14 in the entire graphite stack (N content ~30 ppm with 100% conversion) is trivial compared to the Curies from the reactor Cs 137 alone.

C14 is generated from C13 too, via neutron capture. C13 content in graphite is 1.1%. That's why reactor graphite emits thousands of R/h.

The fission product mass from the accident is indeed the health problem. All of it, as I addressed earlier, was calculated and tallied in the dozens of kg range. Whether or not fission product happens to be inclosed in ceramic or buried separately in the dirt, the amount of dangerous radioisotope is not "tons".

Yes, they are measured in tons. To be more precise, it's about 1-2 tons. RBMK reactors use natural or lightly enriched Uranium. Let's say it's 1% U235. Typical power reactor fissions about the same amount of atoms as fuel enrichment. (Some U235 remains not fissioned; but some U238 gets converted to Pu239 and then fissioned, so it roughly balances out).

RBMK reactor contained a bit less than 200 tons of fuel. 1% of 200 tons is 2 tons. That, very roughly, is how much fission products should have been in that fuel. Definitely not "dozens of kg". Chernobyl reactor was not freshly loaded at the time, the opposite: it was planned to shut down for refueling.

(Edit: googled for it and it seems RBMKs used to use 2% enriched fuel back then, today they use 2.4%. So make that "2-4 tons of fission products")

 

[nikkkom]

Finally found the amount of graphite in RBMK: 1850 tons.

 

[Salvador]

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.

 

[nikkkom]

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]

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 ), 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

 

[jim hardy]

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]

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.

 

[nikkkom]

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 ), 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:

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.

 

[nikkkom]

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]

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 ), 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.

 

[mheslep]

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.

 

[nikkkom]

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.

 

[nikkkom]

From Medvedev's book, a testimony of one of Unit-4 operators:

...

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

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.

 

[Salvador]

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.

 

[nikkkom]

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]

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.

 

[Salvador]

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.

 

[nikkkom]

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]

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.

 

[Salvador]

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/inform...l-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.

 

[nikkkom]

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.

 

[Salvador]

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.