A ride through Chernobyl

[SaraP]

That lowering the power output level wasn't the cause of the accident, I guess.

Yay.

Actually, it did. They shut down the safety overrides and powered down the reactor in order to test the backup power system for the coolant pumps, but the reactor became unstable when the power level was reduced and went into meltdown, which is why the power level spiked back up.

 

[SaraP]

Damn, I need to learn more about nuclear reactors... how would it be dangerous to LOWER a reactor's output level?

Due to its poor design, the RMBK-1000 reactor becomes unstable at low power output levels; xenon gas builds up in the reactor core, absorbing neutrons and choking the nuclear reaction. The Russians' usual response to this is to turn off the reactor's safety systems and retract almost all of the boron control rods from the reactor vessel, which crash-starts the failing reactor and brings it back up to full power. This procedure is extremely unsafe because the reactor is running completely out of control until you re-engage the control rods and safety systems, but it keeps the power flowing, which keeps you from loosing your head if you're a nuclear reactor tech in Soviet Russia.

 

[das_ben]

Thank you for repeating what the linked website said. Have a cookie.

 

[SaraP]

This particular site seems eager to tacitly exonerate the Russian reactor operators, whose actions were ultimately responsible for the meltdown (although it would not have been possible at all were it not for the poor design of the reactor).

This procedure did not go according to plan: for unknown reasons, the reactor power level fell to less than 1 per cent.

The reasons for the drop in power were hardly unknown; xenon gas formation in the reactor core at low power was a routine occurence in RBMK-1000 type reactors.

The power therefore had to be slowly increased.

The power was supposed to be slowly increased, but it was in fact very rapidly increased.

But 30 seconds after the start of the test, there was a sudden and unexpected power surge.

There was a sudden and unexpected power surge caused by the manually initiated shut-down of the coolant system, which happened because some moron decided to continue with a very dangerous test even though the reactor was still in the middle of recovering from a crisis situation.

The reactor’s emergency shutdown (which should have halted the chain reaction) failed.

The emergency shutdown did not fail; it was disabled.