A Layman’s Guide To What Happened In Chernobyl

Here at 5MN, we don’t “sugar coat” anything! Here is what you need to know about the incident at Chernobyl…

 

Chernobyl is perhaps the most famous nuclear disaster in the history of nuclear power, though Fukushima Daiichi is a strong contender.

Many point to Chernobyl as a warning of nuclear power and the dangers it holds.

However, the disaster at Chernobyl was not due to the inherent danger of nuclear power; RATHER, it was due to humans actively disabling the safety systems and going against operating doctrine. (READ:  being both arrogant and negligent.)

I won’t get into the uber-technical details, but if you had to point to a single reason the disaster happened, it is because the operators ignored the operating instructions and forcibly removed all control rods from the reactor. (Control rods absorb excess energy and stop bad things from happening.)

These rods were never meant to be fully removed…and the operators knew that.

The reason they were removed is due to a phenomenon called Xenon Poisoning.

======================== A word on Xenon Poisioning======================== 

Xenon-135, a common noble gas,  is an isotope produced by fission that actually inhibits fission by absorbing neutrons that could otherwise cause fission.

It is referred to as a “poison” only because it stops Neutrons from causing a fission event in a reactor. In fact, Xe-135 is the most powerful neutron poison known.

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When a reactor starts producing power and has lots of fission interactions, Xenon is produced as a byproduct. Generally, this is not even a small problem because, in an operating reactor, the Xenon reaches an equilibrium value and has a steady concentration-we simply do the math and it is completely taken care of! No issues! 

However, RESTARTING A REACTOR IS A COMPLETELY DIFFERENT STORY and an analogy is formed:

Think of Xenon poisoning like water on a campfire. Water doesn’t burn; however, a fire could continue if its already burning and then a little water was introduced.

Here is the problem with Chernobyl. When a reactor shuts down, it doesn’t stop producing Xenon. Some fission fragments decay into Xenon and without the reactor running, causes the amount of Xenon in the system to grow and reach a maximum value. Akin to a cold firepit in a storm; it gets wetter and wetter, and harder and harder to start a fire.

The operators at Chernobyl tried to restart the reactor when the Xenon concentration was at a maximum.

If Xenon is water, and a reactor is like a campfire, removing the control rods is like gasoline. It helps things get started, and if you want to increase the fire, we all know that the addition of more gasoline is sure to make it bigger!

In Chernobyl, the operators couldn’t get the fire(reactor) to start because they had a lot of water (Xenon poisoning), so they added gasoline (removed control rods) to help light the fire.

However, they added EVERY BIT OF GASOLINE THEY HAD (removed control rods all the way) and subsequently started a forest fire (uncontrollable reactor).

 

The sad thing is, Xenon poisoning is based on Xe-135 which is radioactive- and all radioactive things go away eventually. It so happens that if you wait only about 10 hours, the Xenon goes away and you can start the reactor in a safe manner-just as it was designed. 

To keep the analogy alive, had the operators just waited 10 hours for their firewood to dry out, they wouldn’t have started a forest fire. Additionally, if they used less gasoline they wouldn’t have started a forest fire. Chernobyl did not have to happen. It was not due to an unsafe nuclear process.

If those operating the reactor simply followed the directions as described by those that designed the reactor, such a disaster would not have occurred. this fact is validated by the many disaster free models of the same reactor still used throughout the world.(Model is RMBK)

So now you know! Chernobyl just is not a product of an inherently unsafe physics process but one where humans had to go well out of their way to create- which simply wouldn’t happen within the United States and many other nuclear states. (Consider removing everything after the dash, i think flow and impact is better without-Joseph)

 

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Have a great day and we here at 5MN will talk to you soon!

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