What Exactly Happened at Chernobyl?

On April 26, 1986, in modern day Ukraine, the Soviet Union’s Chernobyl Power Complex nuclear reactor 4 exploded. This week on Reactions, we talk about the chemistry behind this catastrophic event.

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Credits:
Producer: Andrew Sobey
Writer: Samantha Jones, PhD
Scientific Consultants: Roger N. Blomquist, Ph.D. Michael P. Short, Ph.D., Najmedin Meshkati, Ph.D., Harry Elston, Ph.D.
Executive Producer: George Zaidan

Music:
Deep Space Dissolves
By Si Phelps, Neologist

Sources:

Ever wonder why dogs sniff each others' butts? Or how Adderall works? Or whether it's OK to pee in the pool? We've got you covered: Reactions a web series about the chemistry that surrounds you every day.

[harveysmith]

The clearest and simplest explanation about Chernobyl. Thank you.

[madalinpaull]

i watched so many vids on this reactor....and this is the only one that actually made any sense....thank you 😭

[BludgeonedDEATH]

“Every lie we tell incurs a debt to the truth. Sooner or later that debt is paid”
-Dr. Valery Legasov, **Chernobyl**

[andrewblewski]

This isn't an entirely accurate explanation, nor was the HBO series. The rods were not "graphite" tipped. Almost half of a rod was made of graphite, with almost another half being made of boron, with space in between. The rods would go in and out exposing either the graphite end, or the boron end. The problem with Chernobyl is that once the Xenon gas ran out, the reaction spun out of control damaging the rod movement system and locking the rods in a position where mostly graphite was exposed.

[Ms_Ink]

This is the 8th video that I’ve watched about Chernobyl and the first time I have understood what actually happened! I can’t thank you enough for explaining it so well!! Amazing! 👏👏👏

[r.daneel.]

Without exaggeration, this is the best explanation of the incident I have seen. It lacks some deeper technical details, but it manages to perfectly summarize what others cannot in less than 40--60 minutes.

[Shandchem]

A very clear concise explanation of what happened at Chernobyl causing a very sad and avoidable event.

The tips weren't made of graphjite, there were whole graphite rods attached to the control rods, so that when removed, there would be a moderator. When the control rods were lowered, the graphite rod at the bottom displaced water, that was inhibiting the reaction, which in turn accelerated it.

[puncheex]

The reactor is designed too continuously "burn off" the xenon (actually, to transmute it with neutrons into a less poisonous xenon isotope) created when it is running at 80-100% of rated capacity. When running at below 50% rated, the xenon starts building up faster than it is burned. When the reactor gets loaded with xenon, there are two things that can be done. The first is to simply stop the reactor. The xenon will decay away in about three days, and the reactor can then be started up normally. The other is to raise the power to burn the extra xenon. With the xenon present acting like control tods, that can only be done by withdrawing the control rods maximally. When the burn starts, the xenon is being converted and the reactor has to be closely watched, inserting rods to replace the xenon as the power rises, but not so many as to quench the reaction. They were on the slope of another positive feedback, which ran away and ultimately took them to 3, 000 times the full rated power of the reactor for a few milliseconds, long enough to wipe out all the rest of the xenon "control" and boil all the coolant water away.

[bhamacuk]

I've watched lots of videos attempting to explain the Chernobyl disaster. This is the only one that does so in an easy to follow fashion. It explains the physics of fission in a very clear way.

[davidmorse]

This was the best easy-to-understand explanation I've come across about Chernobyl and how reactors work. Thanks!

[rickyricardo]

I've watched dozens of vids on the exact steps of this disaster - even the movie. This one is by far and away the best layman's explanation!

[saintuk]

One thing that was missed, mentioning the lack of a containment structure. Fukushima had 3 meltdowns, compared to Chernobyl's 1, only releasing 10% of the amount of radiation into the surrounding area and atmosphere. The RBMK had no containment structure, hence its massive level of contamination.

[Weathership]

Really well written and the graphics are terrific...combined to create a great explanation.... Kudos to Sam and the team

[DyslexicMitochondria]

3.6 roentgen - not great, not terrible

[misceryyt]

7:27 They didn’t do that. They instead had a graphite rod attached to the control rod in order to make the control rods a better controller of the nuclear reactor's reactions. The graphite rod was also shorter at the top and at the bottom to balance neutron flux levels (neutron movement). So when that rod goes into the bottom half of water, the power went up and jammed the rods in the position.

[gdevelek]

The "graphite tip" she's referring to is a few meters long. It's the moderator rod, attached to the control rod. One goes in, the other is pushed (or pulled) out.

[LouisePriciliaPily]

Ah I finally get it, thanks for the explanation

[PiperTMTotalWar]

excellent explanation, very informative.

[Mirandorl]

Don't bother watching the video, it seems all the nuclear experts are in the comment section