What Technically Happened at Chernobyl

A public lecture on the history, physics, and lessons to be learned from the Chernobyl disaster given by a real-life nuclear engineer, me (Ethan Chaleff).

[Corristo]

Props to whoever put that 3D model of the RBMK reactor's piping together, only to be relegated to complete obscurity on the internet. That must be like filming the most brilliant movie in human history, only to end up in a dark shelf on DVD at an abandoned video rental store.

[firewalker]

“When the truth offends, we lie and lie until we can no longer remember it is even there, but it is, still there. Every lie we tell incurs a debt to the truth. Sooner or later that debt is paid”. Brilliant lecture on how this happened.

[clarkrivers]

As a nuclear safety engineer, this is hands down one of the best presentations I’ve seen. Enough technical while simplifying it down. Well done!

[tetchuma]

My stepmother was 6yo, and lived in Pripyat in 1986. Her father, Anatoly (not Dyatlov) has worked at the Chernobyl plant since 1982. Today, he’s part of the maintenance crew.
They were evacuated to Kozyn, just south of Kiev.
She still has health problems. She had a hysterectomy at 15 because of tumors. Because of this, she had to take hormone replacements at a young age. (That probably why she still looks 19) Her mother had to have a double mastectomy and hysterectomy by 1988.

She told stories of Soviet officials waiving Geiger counters over food shipments in the open markets, to make sure they were safe to eat; All the while saying the radiation wasn’t as bad as “the West” was saying.

She told me in 2007, that the Soviet Union is still alive.

Only in the last 3 months, she was able to migrate her sister and niece to Toronto, due to the Russian invasion.

[johnedwards]

I went through Navy Nuclear Power School as a reactor operator 52 years ago.
Decades later, I worked with a young PhD Mechanical Engineer (from Ireland) who lent me a copy of the official Soviet account of the Chernobyl disaster.
To understand what happened, it helps to bear in mind that there are two types of reality: political and physical.
Joseph Stalin represented the former; reactor physics represented the latter.
Although Stalin died long before Chernobyl, his influence was still felt by the minds of many.
That influence (fear of being shot) accounts for the several-day denial, and why Moscow didn't know what was happening until neighboring countries complained. That's why it's response was so slow.

The fatal flaw was that there were two career paths to the top job in the nuclear power plant administration.
One path was through the nuclear-physics side,
The other path was through the electrical power generating side.
[Think Power source vs. Power load]
Chernobyl was caused by a person who rose from the electrical power side.

Another flaw was ego -- the pursuit of bragging rights.
Reactor plants seem simple when everything is running well -- as when tending a fire.
But a nuclear fire is caused by energetic neutrons rather than energetic electrons.
It occurs much more rapidly as neutrons instantaneously erupt from a variety of fission chains.
The key to controlling a plant is to fully understand the influence of those fission chains while staying within narrow limits because the secondary neutrons from intermediate fission reactions introduce enough delay to make a reactor plant controllable.
But, the rate of change of neutrons, during adjustments, also affects reactivity which requires things to be done slowly.
In other words, you can't simply react without understanding some very abstract processes.
There is a narrow range between controllable and uncontrollable conditions.

One way plant supervisors can test the safety of a plant is by disabling some safeguards to make sure the control sequences are "fail-safe". Chernobyl was caused by someone from the electrical side who didn't understand reactor physics yet pursued an ultimate bragging right by disabling all backup systems. He believed this would lead to a reactor shutdown. His bragging rights would come when he performed a reactor startup by using the inertia of the huge electrical generators to do a reactor restart. It failed.
Reactivity rate changes, due to cooling as well as Xenon poisoning & decay, put the system outside of its controllable range. The reactor, responding to its internal processes produced far more power than the system could handle.
The excess power quickly destroyed Chernobyl and shut down the once vibrant city.

A mindless "Religion" of bureaucracy is never an alternative to the constant need for observation & respect of behavior
-- whether neutrons -- or people.
Chernobyl is an important lesson that helped end the cold war.
In this increasingly complex world, unrecognized ignorance can cause major problems that can threaten humanity and the Earth, itself.

[jamesspash]

I work in hydro electric production. What is happening now, happened over the years, and it's happened before, is there is no one from, design, engineering or operations to for us old guys at all the mentioned levels, to train. I work with folks from all ends who do not have a clue what they are doing. Direct out of school engineers, don't get me wrong, smart folks, but no experience. We are going to do this... We in opps people say NO, that will not work and will cause problems!!. Were told "there are smarter people than you working on this" Shut up. Then when It fails and or doesn't work, we the opps folks get blamed for the failure or hear crickets chirping from the engineering group, while we fix it. My motto is, " I didn't engineer it, my job is to make it work."

[akio]

I'm glad you went into detail about Xe poisoning. A *lot* of "explanations" leave out the Xe, and it's really important for how the nosedive in power came to be to begin with, and why they had to pull out so many control rods to get the reactor back to what they managed.

[visnjamusa]

8:50 There is NOT one turbine on each side of the reactor and there is NOT just one turbine. There are exactly TWO turbines mounted on one side of the reactor, specifically SOUTHERN side at Chernobyl. Steam from left side of the reactor usually drives one turbine, steam from the right side usually drives the other turbine. Steam lines of the far side are routed around the reactor to the turbine room. I said "usually", because there are valves that can route steam from all drums to run just one turbine - ANY turbine of two available. At the night of accident, as the reactor power dropped, the operators did exactly that: they shut down one turbine and left the other to run alone up until the accident.

[WhiteSkyMage]

I think you made literally the best technical presentation of what happened at Chernobyl that i managed to find on the net. Good job!

[fanBladeOne]

Literally THE most comprehensive and complete explanation I have found so far on YouTube. Thank you!

[ivanskunov]

It was very strange to hear from such a specialist that there were no enrichment plants in the USSR. In fact, the cascade centrifuge allowed the USSR to enrich uranium much more efficiently than the method used in the United States.

[johnspence]

Im sort of amazed how much conflict there is AMONGST NUCLEAR ENGINEERS about what exactly happened.

[VintageTechFan]

Finally someone who makes the control rod change understandable! The popular opinion is that they were totally retracted out of the core and then they inserted graphite first, which sounds totally crazy. And it is, that's why the didn't do it that way. It's just that the very bottom of the core already was on the verge of power excursion which was triggered by the redistribution of power because of the graphite absorbers. By making them flush with the bottom of the stack, that couldn't happen anymore.

[monkeyboy]

I didn't see it mentioned specifically in the comments, but I have read that the reason for the graphite tipped control rods was because they originally were not able to achieve criticality when the reactor was first started up. They added the graphite to increase neutron moderation and thus were able to get the reactor to go critical. When the control rods were lowered into the core, at first they actually increased the power output because of the increased moderation. Since the reactor core was so large, power was increasing in the part of the core where the graphite tips were traveling.

[cyclingnerddelux]

Thank you for not forgetting the human element this story. As a historian, I'm often saddened by the cavalier manner these tragedies are discussed.

[almondjoy]

Ethan: 1+1 = 2
Audience: laugh excitedly

[retrocompaq]

im a car mechanic and it, not even close to be a nuclear physician but i really wanted to understand what happened like 2 years ago, i watched tons of videos and i barely get everything you mentionned in the video, i wish i would have seen this before, 50min is only what i needed lol thanks alot great work!!!

[Serafimxxxx]

I've watched dozens of Chernobyl explanation videos.

This is, by far, the best I've seen.

Even as a layperson, I feel like I really understand exactly what went wrong and why.

Still, it boggles the mind to think that so many disparate designers and teams tickled the dragons tail like this... that nobody recognized the lack if understanding or danger.

[rcsontag]

Mr. Chaleff's refusal to address reality - the NUCLEAR EXPLOSION is astonishing, even after admitting the reactor was "Prompt Critical". Prompt critical is a supercritical condition that is exactly the chain reaction in an atomic bomb. Thankfully it was very localized and self-limiting.

[benphartine]

2:54 Gets Started
6:00 The good and bad aspects of the Chornobyl reactor.
9:46 The fundamental challenges of reactor design.
12:47 The basics