MovieChat Forums > Chernobyl (2019) Discussion > 3-4 megatons what?

3-4 megatons what?

posted 5 years ago by Induspavo (4)
21 replies | jump to latest

Ok toward the end of episode two it’s stated if the storage tanks under the core are full of water an explosion will occur when the melting core contacts the cold moderator. I heard a 3-4 megaton explosion stated which is impossible. The Chernobyl accident was the result of a steam explosion when the water in the graphite cooling channels immediately turned to steam due to the prompt supercritical condition caused by the testing the night crew was doing.
The worst thing a melting core can contact is water, which may allow the core to go critical again, causing another steam explosion. There is no way a melting core can explode like an atomic bomb, and especially a hydrogen bomb which is needed for a 3-4 Megaton yield.
I’m a nuclear engineer and so far have been impressed by the scientific accuracy of the accident and the radiation exposure consequences. Why overstate the science for dramatic affect now, when the writers are doing so good? I can’t figure it out. Maybe someone knows.

[–] MovieManCin2 (26342) 5 years ago

Because it was made by Hollyweird, and they exaggerate to be more dramatic, and make more money.

😎

[–] jimmyzimms (72) 5 years ago

Huh turns out it wasn't hollywood drama. It really could have produced a set of explosions in the multimegaton range.
https://www.youtube.com/watch?v=AZ4qOMN527s&t=14m30s
Above video at 14:30 interviewing soviet sr scientist involved in the crisis.

[–] MovieManCin2 (26342) 5 years ago

Wow! Thanks. I will watch this NatGeo documentary.

😎

[–] MovieManCin2 (26342) 5 years ago

I just watched the documentary, and also one on Fukushima. They were fascinating. Thanks.

😎

[–] Induspavo (4) 5 years ago

I’m watching the video and this Vassili Nesterenko physicist that’s being interviewed has to have been misquoted or something. Anything in the 2-4 megaton range has to be a fusion (hydrogen) bomb which is impossible to do with any nuclear reactor. A molten mass of core material hitting a pool of water would cause an explosion, but only a steam explosion, which is still really bad. Most people don’t realize how exquisitely difficult it is to assemble a critical mass long enough to get any kind of yield. Even if the molten core went critical again, the released energy would make the whole mass fly apart. Once you lose the geometry, the fissioning stops, and the yield is limited to an explosion of maybe 4-400 tons (guessing). All this is really bad, but there would not be a megaton sized mushroom cloud like the video is suggesting.

[–] MoviesSuck (964) 5 years ago

You’re a nuclear engineer and yet you come to this website for answers to your nuclear engineering questions? That’s frightening.

[–] Alex (1489) 5 years ago

For God's sake! Don't press the AZ-5 button!

[–] mineofilms (37) 5 years ago

Would it be "inappropriate" to call my band "The AZ-5 Band" - "The AZ-5 Button" or just "AZ-5" lol????

[–] dmac8 (5050) 5 years ago

That might be a valid question/statement if he actually asked nuclear engineering questions instead of asking why the writers exaggerated this one aspect.

[–] MoviesSuck (964) 5 years ago

Hang on...I’ll get the writers in here so that we can ask them.

[–] dmac8 (5050) 5 years ago

Is that reply supposed to increase the validity of your first statement? On moviechat website, nuclear engineering questions vs why film/tv writers do what they do. Six or half a dozen, huh? Yet it seems no one else saw any nuclear engineering questions and they managed to reply without snide. You have an odd way of admitting that you didnt really read what he wrote the first time.

[–] MoviesSuck (964) 5 years ago

I haven’t heard the word “snide” in years. Love that word.

[–] dmac8 (5050) 5 years ago

How bout "gaffe" and "evasion"?

[–] [deleted] 5 years ago

Did you see the last episode? When Legasov explains how the core exploded and lays out the conditions which led up to that event, including the Soviet’s use of graphite tips on boron rods which accelerated the reaction? The core casing did explode, exposing the core. The damage was widespread. The entire region is contaminated to this day. I don’t see any overstatements.

[–] Induspavo (4) 5 years ago

A steam explosion is not a nuclear explosion. A subsequent hydrogen/graphite/O2 explosion is not a nuclear explosion, but a chemical reaction. The power spike caused the core to lose its geometry and the fissioning stopped. There was no nuclear explosion. The exposed core stays hot for a long time because of decay heat, from radioactive fission products, which can be high as 8% of the thermal output before the core disassembled, which was quite high (>30GW). Decay heat is the major problem with nuclear reactors and why the core needs cooling even after it shuts down, especially the first few hours.
My question was with the writers, they did not need to dramatize so far as to threaten a nuclear explosion. The situation was bad enough already. All the other historical facts are quite accurate.

[–] chefao (398) 5 years ago

I've seen someone calculate earlier that it should be something like a 140-150ton explosion. Then again the math kind of went over my head there and we don't know if they're factoring in some other reactions. It's possible that they just like to say the word "megaton" to easily emphasize that it's a big deal to layman like me.

Found it: https://physics.stackexchange.com/questions/480113/how-large-would-the-steam-explosion-at-chernobyl-have-been

[–] Nosduj (144) 5 years ago

Megaton is a unit of measurment to describe blast energy in tons (1000) of TNT. So to answer your specific question 3-4 megatons of TNT. That is what they were saying.

Stating the blast could be on a magnitude of 3-4 megatons no way implies a nuclear explosion.

Nuclear yields are measured in tons (1000) of TNT. Just like many explosions. Not the other way around. Some are measured in the metric UoM Joules of course.

Honeslty, a nuclear engineer would know this.

[–] Induspavo (4) 5 years ago

I re-read my post and I might know where the disconnect could be. Stating an explosion would occur, with a 3-4 megaton yield, doesn’t specifically imply that it’s nuclear generated, I agree and you’re right. What does imply that it’s a nuclear explosion is the size of the yield itself. In my opinion this kind of yield can only come from a fusion bomb. Unless I suppose you had a mountain of TNT that weighed 3-4 million tons, it’s just not conceivable to get that size explosion from non-nuclear fission/fusion means.

[–] Nosduj (144) 5 years ago

Yeah it would take quite a unique situation to yield a 1 megaton not to mention 3-4 times that. Did they say kiloton and we just heard megaton? I did not go back to check.

Chalk it up to the typical hair-on-fire hyperbole that so many people employ to get attention.

"The world is going to end in 12 years" type thing.

[–] Martoto (4301) 5 years ago

They never said there would be a nuclear explosion. They said the instant vaporisation of 20,000 metric tons of water under the core would create a thermal explosion the equivalent of 2-4 megatons.

[–] LukewarmCereal (88) 4 years ago

I read it like this:

They're talking to politicians, trying to put scientific concepts into terms they understand. A steam explosion underneath a nuclear reactor would be bad. Like, really really bad. Not a nuclear explosion, and the explosion itself wouldn't be anything like as large as 3 megatons. But it would scatter radiactive fuel into the atmosphere in a way that would make the previous explosion look trivial. Effectively, it would be a huge dirty bomb.

Calling it a 3 megaton bomb is just a shorthand way of saying it would be bad, in a way those politicians would understand. Also a way the audience would understand.