What /Actually/ Happened at Chernobyl

This video was so dang fun to research, which, of course, I feel super guilty about because, like, real people died. But, after watching the HBO miniseries, I knew there was more to the science of this. I've also heard a lot of stuff from both credible and non-credible sources that just doesn't hold up to scrutiny. The idea of the "graphite tipped rods" for example is just a simplification for broad audiences. But I've also heard smart folks talk about how RBMK reactors have a positive /fuel/ temperature coefficient, which is not true. No nuclear reactors do, since fuel that reacted more as it got hot would be the kind of thing that would explode every time.

However, for a moment, because water had become such a vital part of the neutron absorption in the reactor, it did have a positive temperature coefficient...meaning that getting hotter made it hotter which made it hotter which made it hotter. That's a coefficient for the entire reactor, and it's due to the "positive void coefficient" where, as the water got hotter, it got less good at absorbing neutrons.

Usually that would be more than counter-acted by the negative fuel temperature coefficient, which is why they thought it couldn't explode...but it was not in this particular circumstance.

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[vlogbrothers]

Corrections!
1. Not all of the uranium in a nuclear bomb...fizzes...actually only pretty small amount does before the core blows up and the atoms get too far apart. And yet...it's still a pretty big deal.

2. It's not "fizzes." Fission is both a noun and verb, so uranium "fissions"

3. I imply in this video a little bit that you can't have a light (regular) water reactor with a negative void coefficient...you can, you just need a different fuel / moderator realtionship. There are lots of light water reactors that are much safer than RBMK designs....they tend to require more fuel enrichment.


4. An earlier version of this video got the date wrong and said October 26th instead of April 26. I just removed that line, which is something YouTube lets you do now.


Let me know if you've got anything else I should add here!!

[ShyamSharma-gstt]

After watching Chernobyl.
You know I am something of Nuclear Physicist myself.

[feynstein]

Dyatlov: Hank is clearly in shock. Get him to the infirmary.

[MR_GPU]

"Graphite tipped rods"
Pencils?

[BKnight_]

Wait, did you just explain how an RBMK reactor explodes? This man is in shock, take him to the infirmary.

[thewiirocks]

Hank, this is a great explanation! I can clarify the moderator confusion though. It's not as complex as you think. All you need to understand is that *no atom "smashing" occurs during nuclear fission*. Quite the opposite. The actual reaction is that atoms absorb the slow moving neutrons like magnets snapping into each other. The additional atomic weight makes the atom too heavy to maintain its cohesiveness, resulting in the atom falling apart. That's what we mean by "splitting the atom".

Once you understand this, it's easy to understand why fast-moving neutrons are a problem. They have too much energy to get captured by nearby atoms. It's like the difference between hand-tossing a magnet past another magnet versus firing the magnet out of a high-powered rifle. In the former case the magnetic field pulls the magnets together and halts the throw. In the second case the magnet moves out of the magnetic field too fast for the bond to be established.

Now replace magnetic fields with strong nuclear forces and you've got it. :)

[DrYeet]

0:03 : no it didn't. This man is in shock. Toptunov, take him to the infirmary.

[recklesflamngo]

*Reactor explodes*
Dylatov: “Not great, not terrible”

[KarlKarpfen]

Well the "thing that broke" during the SCRAM of the reactor was actually two things: The control rods did move very slowly in an RBMK reactor because of tight fits between control rods and their channels and the reactor is very huge, so it has to travel very long distances, while even a very slight inbalance in neutron generation per fission is a rapid increase of power: 1.01 neutrons per fission on average are a doubling of power every 7 milliseconds. That lead to a thing, the reactor was never designed for: A rupture of more than one fuel channel. This resulted in the reactor vessel turning into a giant steam piston and shooting out it's upper lid through the Ceiling of it's hot box, while pulling out all control rods and evaporating all the coolant at once because of the pressure release, it creates.
For the following burning of the core: Graphite basically is the highest grade hard coal.

[onytay]

Hank saying why does anything exist is how I like to get pumped up for my day.

[ViolentaShadow]

John: Good! I know how a nuclear reactor works. Now I don't need you.

[jamesricker]

In defense of the Soviets regulations for running the reactor stated the exact amount of control rods that were to be in the reactor at all times. Dyatlov broke that rule the computer suggested they shut down the reactor, Dyatlov didn't listen.
The biggest mistake is they did not make the reactor idiot proof.

[KG]

I majored in Physics at university, and you've done a really good job of explaining each term and each process step in a coherent way for the general audience - well done Hank :)

[sebastjansslavitis]

Correction, there was no graphite, BECAUSE IT'S NOT THERE!

[sergioferrero]

I missed explanation videos! These are the best! +4 minutes of good content right here!

[shivam_k]

I don't know much about nuclear physics and reactors, but I think the words "CHEAP" and "NUCLEAR REACTOR" in a sentence is not the best idea in most cases


Edit: I cant believe that i need to to mention it explicitly, but here we go... THIS IS A JOKE!

[shunkela]

Had to listen at .75 speed to make my brain work faster. Much like slowing down neutrons to speed up the reactor :-o

[Alvarin_IL]

Thank you, this was the first time I learned to understand what has happened. My dad was on the medical team at cleanup. Luckily, got no lasting ill effects.

[joshuagreen]

Today's XKCD alt-text gives a pretty clever analogy to explain Chernobyl: "You know when you can't hear your speakers, and you keep turning various volume controls up higher and higher in confusion, and then someone hits the mute button and there's a deafening blast of sound? That's basically what happened at Chernobyl."

[mad__crafter]

You're wrong with your definition of Neutrons.





It's *B U L L E T S*