Would Not Pressing AZ-5 SAVE Chernobyl?

The final chain of events that ultimately led to the explosion of Chernobyl Unit Four in 1986 were set in motion when Leonid Toptunov pressed the AZ-5 button. However, let’s envision a scenario where Akimov doesn’t order Toptunov to shut down the reactor, and instead tells him to wait for some unknown reason. That doesn’t matter. Let’s instead look at this scenario, because there are actually two diverging opinions here.

Sources

INSAG-7
The Chornobyl Accident Revisited
Multidimensional Analysis of the Chernobyl Accident
INSAG-1
Turbine Rundown Programme

[honestinsincerity]

You're delirious, RBMK reactors can't explode. Someone take this man to the infirmary

[AiOinc]

So what you're saying is that the only way unit 4 wouldn't have blown up is if they weren't goofing off with their nuclear reactor at 2am

[abloogywoogywoo]

Don't press AZ-5: explosion happens later
Press AZ-5: explosion happens sooner

[johnharris]

Imagine you are fighting a fire, the fire is getting out of control and you hit a button to turn on the sprinkler system to stop the fire. Except the first thing out of the Sprinklers is gasoline, then water. That is exactly how those graphite tipped control rods reacted.

[adamw.]

In my opinion, the reactor was lost when the control rods were raised too high to break the xenon poisoning in the core. The use of AZ-5 only made the situation worse. Failure was already inevitable. Interesting and good video.

[anatolydyatlov]

It doesn't need saving, IT'S FINE. Just get that water flowing, for the love of god, how many more years will I have to wait? The reactor NEEDS WATER

[robertgaines-tulsa]

Hindsight is 20/20, but without having such knowledge, the operators might have been in big trouble if they didn't press the AZ-5 button. It's like Titanic would have been saved if they had crashed the ship head first into the iceberg, but it would have looked like incompetent operation, and the crew probably would never sail a ship ever again. Society is funny like that. Instead of doing the safe thing and crash the ship head first into the iceberg, we do all we can to not cause any damage to the ship gambling that it will pay off even if the odds are stacked against you.

[swokatsamsiyu]

Thank you for another well-done video. There may be one (little known) reason why the guys in Canada did their own report quite quickly after the accident; their own CANDU reactors. The CANDU, like the RBMK, is a pressure tube reactor. It even shares a special characteristic with the RBMK, the positive void coefficient. After the accident, they may have wanted to find out if they would run the risk of a possible similar accident in certain scenarios. However, the CANDU is very well-built, with full containment, a lot of redundancy and two separate safety systems that can independently, _and_ without power or operator intervention, shut the reactor down within 2 seconds flat.

[krashd]

"Leonid Topyunov, who was all of 25 years old, and his mustache of just 18 years old."

[SittingOnEdgeman]

So to summarize - essentially, to "save" Chernobyl at that point, they would have had to undertake a dedicated series of very rapid, very unintuitive actions - they would have to disable the automatic scram system altogether, they would have to inject cold water to bring reactivity down, and start inserting control rods "slowly" (compared to the scram at least) one bank at a time.

In other words, do exactly the set of actions that would destroy literally any other reactor in the world other than an RBMK.

That's exactly the kind of thing that they COULD have been TRAINED to do, but nobody in their right mind would ever do unless they were trained. If lessons had been learned from the Leningrad accident, and crews had been trained on an emergency procedure to manage positive scram reactivity, it might have been possible to minimize the damage at Chernobyl, but yeah... that would have required the Soviet Union to admit a flaw in its design and that was never going to happen.

[mr.pilgrim]

I've heard it said that in order for a modern nuclear reactor to blow up like Chernobyl's did, someone would have to be in the control room *actively trying* to make it explode. It sounds to me like, in the case of Chernobyl, to have kept the reactor from exploding, someone would have had to have been in the control room actively trying to make it *not* explode.

[andyb]

The best way to prevent the Chernobyl disaster would be to go all the way back to the late 60s and design a better/safer reactor

[dez]

Thank you again for doing our homework for us! This is a great channel. It amazes me how many people are so fascinated with the Chernobyl accident. It amazes me more that we have a few people who are covering it today. 3 channels that cover different aspects of the accident. All are fantastic in their own way. You are the one who covers all of the technical aspects of what happened that night. Personally, I am very thankful for you and your work. I stand amazed at your understanding of the accident and how you help some of us to understand that night a little better. The "what if's" are even more important here. Knowing that the explosion would have most likely happened anyway no matter what. Thank you for your work! You are appreciated.

[noahbarton]

If they hadn’t pressed AZ-5 then likely the worst that would’ve happened would’ve been a reactor meltdown, not an explosion.
The main reason the reactor exploded was the immense pressure created by the steam, so if they had kept the valves closed then the reactor likely wouldn’t have exploded.. at least not in a nuclear explosion because the Chernobyl reactor had a positive coefficient.

[adamc]

Can you do a video about them not having chefs run the nuclear reactors

[joez.]

My understanding is if the control rods were designed to "slam home" when AZ-5 was pressed (vs. operating at "servo speed"), an explosion _might_ have been averted. As far as the explosion being caused by the graphite tips (which is what you're asking), I think they passed the point of no return a while back.

[killman]

After learning everything i could about this disaster over 10 years. I think there was only one possible way to save the reactor. They would've had to resist the urge to press AZ-5 and instead slowly start reintroducing control rods a dozen or so at a time. Because at that point in the evening the reactor was at its limit. You can't make huge changes to a system under that much strain, it will fail. You have to slowly and carefully walk it back from the edge of disaster first.

[SamwiseOutdoors]

This is actually a really interesting topic to explore. I've often wondered whether the die was cast long before the SCRAM function was initiated, or if there could have been a way to gradually reduce reactivity and slow down to a safe stop.

[oscarr.g.]

And once more, another great video. Thank you Sir !

[testplmnb]

I read Dyatlov book about what has happenned over there, but the most important thing is AZ-5 portrayal. AZ-5 was not "Oh shit button", but normal turn off switch that was not plumbed and that you use to shut down reactor at normal condition too. In the series they show that there was dense atmosphere, but Dyatlov as a proof kept mails from the people that worked with him that day. Those mails opposed what was being shown in the HBO series. The amosphere was calm and in control. The only reason why the reactor blew was that the government has HIDDEN THE REASON why the crew had to keep more control rods in the reactor despite of what operation manuals stated after the reactors were turned hot. Also, there is a reason why Dyatlov was released after being just 3 years in the prison. He knew, that they knew that he knew and that's why, despide deaths of thousands or hundreds of thousands of people he was free not long after. The party would not want to create a precendence within nuclear engineering society in which operators are being to blame for what was beyond their control, because not much people would like risk it all.
Also he described Legasov as government dog that in fact had no competence to judge him (he had bad general knowledge that was not focused in nuclear engineering- he was a chemist) and also Legasov followed the general narrative presented by the party members.

Dyatlov was sentenced even before the trial started. Designers of the reactors did not bare the consequences. The best example of that happened in viena where Legasov presented UPDATED manuals, which were released AFTER the accident occured! They kept old manuals hidden.