Chernobyl 2nd explosion

[AskWazzup]

Ok, so i wanted to watch a documentary about chernobyl (the first one that comes out in the search, at 2+ million views), but the part where they started to talk about the second explosion going nuclear, had me scratching my head:



It's at 32:55

The guy in the video is Vassili Nesterenko, supposedly a physicist. He claims that if the melted core would have reached the water bellow, it could have caused an explosion in magnitude of 3 to 5 megatons, and then says that this would level Minsk, a city 300 km away....

So i tried out the second claim here:

http://www.nuclearsecrecy.com/nukem...lng=30.2008924&airburst=0&hob_ft=0&ff=55&zm=7

I have no idea if something was lost in the translation, as i can't hear what he is saying because of the english translation overlay, but this seems pretty stupid.

Now my physics knowledge is pretty miniscule, but the first claim about molten uranium of lower than 20% concentration (which should not be fissile?) causing a nuclear explosion, if contacting the water, seems pretty dubious, and more so because a nuclear weapon has to have explosives detonated around it in very precise manner to make it happen. So am i missing something here, or is this total crock of shit?

 

[Hassknecht]

Doesn't make any sense. You can't trigger an actual nuclear explosion in a nuclear reactor. What can happen is that the molten core creates a steam explosion in contact with the water, and the graphite used as a moderator creates flammable gases at high temperatures, too.
3-5 MT from just a little bit of unconfined uranium? Bollocks. Sure, if a significant part of the molten core material were to be used in a chainreaction, but guess what, the steam explosion would scatter all the fissile material around, stopping the nuclear reaction.
And, as you noticed, 3-5 MT doesn't do shit 300 km away, and it certainly won't render Europe uninhabitable. That documentary is typical fearmongering.

 

[AskWazzup]

Wonder how many people binge watch these kind of documentaries thinking they are actually getting some quality time (as in learning something useful, or interesting). It seems like you can't trust any documentaries or news websites these days when it comes to science, they just can't resist the urge to color everything (or just don't have a competent enough bullshit detector when communicating with their sources). And then you have successful kickstarters to boot:



)

 

[valcik]

What can happen is that the molten core creates a steam explosion in contact with the water, and the graphite used as a moderator creates flammable gases at high temperatures, too.

Plus, you can have conventional explosion caused by highly explosive mixture of hydrogen and oxygen, thanks to high concentrations of hydrogen produced as a result of chemical reaction between zirconium casing on fuel rods and hot water.

edit:
This is pretty good documentary in form of drama, based on facts and filmed at Chernobyl power plant site, which makes it very accurate:

 

[AskWazzup]

Plus, you can have conventional explosion caused by highly explosive mixture of hydrogen and oxygen, thanks to high concentrations of hydrgogen produced as a result of chemical reaction between zirconium casing on fuel rods and hot water.

edit:
This is pretty good documentary in form of drama, based on facts and filmed at Chernobyl power plant site, which makes it very accurate:

Thanks for the link.

 

[valcik]

Whops, had to replace the link actually, now it's the correct documentary I had in my mind. Previous footage was more than two hours, probably screwed upload.

edit:
I'm just watching that video in first post and to be fair, he doesn't mention nuclear explosion anywhere. He clearly says that melted fuel touching water reservoir would cause conventional explosion with effect comparable to huge nuclear blast in terms of area levelling. So yes, he's right.

 

[Hassknecht]

Whops, had to replace the link actually, now it's the correct documentary I had in my mind. Previous footage was more than two hours, probably screwed upload.

edit:
I'm just watching that video in first post and to be fair, he doesn't mention nuclear explosion anywhere. He clearly says that melted fuel touching water reservoir would cause conventional explosion with effect comparable to huge nuclear blast in terms of area levelling. So yes, he's right.

Yeah, an equivalent 5 megaton explosion. Sorry, but I don't believe it.
And even then, destruction of Minsk and total contamination of Europe is just ridiculous.

 

[AskWazzup]

edit:
I'm just watching that video in first post and to be fair, he doesn't mention nuclear explosion anywhere. He clearly says that melted fuel touching water reservoir would cause conventional explosion with effect comparable to huge nuclear blast in terms of area levelling. So yes, he's right.

But that doesn't seem right, can you even have a non-nuclear explosion of that magnitude with the elements involved? Plus his claim of Minsk being raised.

 

[valcik]

Yup, I can hardly believe that whole Minsk would have been destructed, sounds a little over the top. The second thing, I don't know. There's more than 40 tons of uranium fuel rods in one reactor, so if all of it would have been lifted up by second explosion, who knows how big part of Europe would have been contaminated?

 

[AskWazzup]

Well, for what it's worth, the largest non-nuclear human caused explosions i could find, all vary between 2-4 kilotons:

https://en.wikipedia.org/wiki/Largest_artificial_non-nuclear_explosions

So nothing human caused (excluding nuclear explosions) has ever came close to even a megaton. Other than that it seems you would need a 40 meter diameter rock coming from space at 20km/s to get a blast at around 4 megatons (the tunguska event is estimated at around 10 megatons).

 

[valcik]

Okay, but consider this:
How many tons of cooling water were stored below the reactor? Hundreds I guess? The melted fuel, corium, could reach almost 3000 degrees Celsius, which is enough to cause thermolysis in 50% of overheated water molecules. Another thing is radiolysis, high levels of radiation would split water molecules too, creating another hydrogen and oxygen. This is probably what Nesterenko in your video call chain reaction - all the tons of water would have been turned into highly explosive mixture of hydrogen and oxygen in a very short time span. This sounds much more dangerous than any gunpowder explosion witnessed by men.

 

[AskWazzup]

Ok, at 33:42 he is saying "kritichiskaja masa" as in critical mass, but can't hear what he said before that.

Also tried to search the web for research on "corium contact with water", but none of the papers i found have reffered to any large scale explosions (from what i understood), like the one mentioned in the video. They state (from my very limited understanding) that if the corium melt temperature is high enough, it can lead to a steam explosion when in contact with the water, but nothing about the yield (it does refer to pressure in megapascals generated, but i'm too dumb to understand those charts):

https://www.researchgate.net/public...n_experiments_using_partially_oxidized_corium

http://www.kns.org/jknsfile/v41/JK0410603.pdf

http://www.sciencedirect.com/science/article/pii/S0029549300003198

The last one states: "Visual observations showed that the corium jet penetrated deep into the water while maintaining its shape. The tests did not produce spontaneous explosions. However, the second test with an external trigger produced an explosion with a relatively low efficiency of 0.15%"

 

[valcik]

Test conditions - water: 367 kg, corium: 6.3 kg.
Another thing what's Nesterenko saying is that estimated amount of corium needed to start chain reaction is 1400 kilograms, such a small amount used in test was probably cooled down before thermolysis started.

edit: There are some really cheap tricks in this documentary though. That atomic mushroom cloud at 34:46 used as illustration.. Holy shit.

 

[AskWazzup]

Damn it, now i just can't seem to get rid of this urge - the urge to find out if corium can lead to a conventional explotion as powerful as a hydrogen bomb. Are there really no nuclear physicist in nma? What a sad day...

 

[valcik]

Same here.
We won't find out, I'm afraid. The nuclear reactors are constructed differently nowadays, without any flaws observed in Chernobyl, so it's highly unlikely something like that would ever repeat.

Also, small update! According to World Nuclear Association, there's 192 tons of uranium fuel rods in Chernobyl reactor 4 and the amount of cooling water was 300 tons per hour injected in the damaged core. Much bigger proportions than I had assumed before:
http://www.world-nuclear.org/inform...rity/safety-of-plants/chernobyl-accident.aspx

 

[peadar87]

Damn it, now i just can't seem to get rid of this urge - the urge to find out if corium can lead to a conventional explotion as powerful as a hydrogen bomb. Are there really no nuclear physicist in nma? What a sad day...

Not a nuclear physicist, but I have worked as an engineer in a nuclear power plant. Hope that's good enough!

Hydrogen has an energy density of 142 MJ/kg. 11% of the mass of water is hydrogen.

From adding up the volumes of the reactor vessel and the steam separators of an RBMK reactor like Chernobyl, I get an upper limit of about 3500 m^3 of cooling water in the primary circuit, which will have a mass of 3,500,000kg.

Splitting all of that will liberate 385,000kg of hydrogen. If all of that reacts with oxygen, it will liberate 55 Petajoules of energy. According to this handy conversion site that's only 13 kilotons, even when you make gross assumptions like the entire charge of coolant is split.

I can categorically state that the Corium won't cause a nuclear chain reaction. Nuclear warheads are highly engineered pieces of kit that have to use focused shockwaves and incredibly highly-enriched fuel. If even the slightest thing goes wrong with that, the warhead fizzles, and you don't get a nuclear explosion. That's not the sort of thing that will ever happen by accident with reactor-grade uranium.

 

[valcik]

13 kilotons? Well, that's almost as powerful as Little Boy detonated over Hiroshima. Probably not strong enough to destroy whole Minsk, still dangerous enough in terms of contamination with 192 tons of uranium fuel stored above.

I can categorically state that the Corium won't cause a nuclear chain reaction.

Yup, that's what we all agreed upon.

 

[Hassknecht]

13 kilotons? Well, that's almost as powerful as Little Boy detonated over Hiroshima. Probably not strong enough to destroy whole Minsk, still dangerous enough in terms of contamination with 192 tons of uranium fuel stored above.


Yup, that's what we all agreed upon.

Especially not destroy Minsk over a distance of 320 km. Not even the original design for the Tsar Bomba with a yield of a 100MT could do that. The fallout of such a surface-explosion could reach Minsk, sure, but that's it.

 

[Sn1p3r187]

I don't think this would'v happened. Plutonium and uranium would have to be weaponized to actually do that I think.

 

[valcik]

From adding up the volumes of the reactor vessel and the steam separators of an RBMK reactor like Chernobyl, I get an upper limit of about 3500 m^3 of cooling water in the primary circuit, which will have a mass of 3,500,000kg.

According to many sources there was 20000 metric tons of water pumped out of the basement under reactor core, instead of 3500 assumed by you. Seems that not only water from primary circuit was pooled here, but also water from external sources injected into damaged reactor:
http://chernobylgallery.com/chernobyl-disaster/timeline/

Fire brigade pumps drain the basement under the core of water. The operation was not completed until 8 May, after 20,000 metric tons of highly radioactive water were pumped out.

As a reward, the fire fighters receive 1000 rubles each (approximately 2000 US dollars).

I've found the same amount of water in wikipedia, and some books from Russian authors too, after googling for names of three divers who've entered the pool voluntarily.