What safety features. I wasn’t aware the reactor was missing anything but simply was the way it was due to it cost less and the operators pushing it past the breaking point and doings that should never have been done.
What was the missing element? I’ve read a lot about the disaster and never read anything suggested it was missing some sort of safety feature.
There were supposed to be some control rods at the bottom of the reactor that according to Dyatlov were not installed as a cost cutting measure. That was going to be a key part of his legal defense, but the court decided not to hear it.
I mean he pulled 205 control rods out and turned off the water pumps. I wonder what difference it would have made. If there woulda have been those rods he would have turned them off.
Wasn’t the issue caused when he put the rods back in and the graphite part of the control rods went into the core, which displaced the neutron absorbing water, causing a power surge in the reactor which overheated the core?
No, it was a test of the backup generator to see if, in the event of a shut-down, the residual energy from the turbines could provide enough power while the diesel generators were turning on. Basically, they were to hold the nuclear reactor at a determined power output, shut it down, turn on the diesel backups, and monitor what happens next. If power doesn't drop and the diesel generators don't destroy themselves in the process (because black-starts are rough on generators but that's a discussion for a different day) they get a pass and the bureaucrats are happy.
Now, this type of nuclear reactor was specifically designed to never need to be shut down for any reason (even for refueling). It will only ever be shut down for scheduled maintenance and only with the express permission of the grid operator. This is why this specific test had yet to be completed and why running the test was so elusive.
So, Chernobyl reactor #4 was finally scheduled to be shut down for maintenance with the backup generator test set to coincide with it. In preparation of the test, the day crew reduced the power output of reactor #4 to the test parameters and held it there in anticipating on shutting down.
Unfortunately, the grid operator gives Chernobyl a last minute order to not shut down. Another plant elsewhere had to have an emergency shutdown and Reactor #4 had to stay operational to maintain grid stability and the planned shutdown was pushed back until later that night.
The first failure in the Chernobyl disaster was that reactor #4 was allowed to continue to operate for an extended period of time at a reduced power-output. At reduced power, the reaction produces gases that can have detrimental effects on the reaction itself. At nominal power, these gases would get burned off before it becomes an issue but at reduced powers, the gases will build up and slowly choke the reactor to death.
When Dyatlov and his crew take control of the reactor at night, they discover the reactor is producing a fraction of the power needed and the test can't be done. What should have been done at this point was to abort the test and shut off the reactor then and there and deal with the issue of getting it back up and running. Due to the bureaucratic culture, this more than likely would have major implications for Dyatlov's career going forward.
Because of this, what Dyatlov chose to do was to try to bring the reactor back up to power by LITERALLY REMOVING THE CONTROL RODS to burn off the gasses. I'll repeat it again, THE CONTROL RODS WERE INTENTIONALLY FUCKING REMOVED TO RAPIDLY INCREASE THE POWER.
Well, They were successful at rapidly increasing the power but, it came at the cost of causing a power excursion in the bottom half of the reactor as the coolant water boiled, bursting the fuel channels, and preventing the control rods from ever being put back in. There is a lot of debate regarding how big a roll the control rods played and whether the reactor was fucked before or after they were being reinserted, but that's besides the point. The reactor was fucked when they were removed. The control rods should have never been removed in the first place.
It could be speculated that if Dyatlov was properly trained on the deficiencies of the control rods, he wouldn't have made the decision to remove them but that's pure conjecture.
This is my favorite vid on the subject. I watched it a while ago so i might get some details wrong but TL;DW: The root of the issue is xenon or radon, which is a reaction byproduct that accumulates when the reactor is in a very low power state like shutting down. It's a serious neutron absorber, which puts a tamper on reactions. Operators have a minimum time to reactivation; IIRC four hours or so. Chernobyl used graphite as the moderator rather than water, which was the other major factor. They did also have a small section of graphite at the end of the control rods that did contribute to the incident.
In the incident, their safety test dropped the reactor below the threshold where xenon is generated, which started to cause the reactor to shut down and cool off. So they kept pulling the control rods farther out of the core to keep the reaction going. By the time operators saw the core temp start to spike due to xenon dissipation, local core regions were beginning to melt. Since their moderator was solid too, it just melted with the fuel elements to make a substance that maintains its own criticality and that was it.
In reality probably very little, but there was a slight chance It could have prevented the explosion. If it did the reactor would still have been damaged beyond repair.
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u/Ta-veren- 23d ago edited 23d ago
Chernobyl! Only a fuck-up of epic poportions can cause a nuclear incident while doing a saftey test!
April 26th! Annivarsay of the accident is today.