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Montrama t1_jc1elu5 wrote

I think tipped with graphite is kinda misleading. When we say it like this it feels like a small portion of the control rod is made from graphite at the tip. In reality there is a slightly smaller graphite rod which is connected to the boron rod. So when you raise the boron rod it gets replaced by graphite rod which is also called "Displacer".

Why they have graphite rod than? Two main reasons. One is to increase the efficiency of control rods. When you raise the control rod it gets replaced by displacer graphite rod which accelerates the reaction. When you push the boron rod back, displacer got removed from the reactor and boron rod takes it place and slows down the reaction. So your delta power is much higher between two states and this gives you better control ability over the reaction. Second reason is to increase capacity of the reactor. Graphite accelerates the reaction so increases the maximum power that the reactor can create with same footprint.

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radioactive_dude t1_jc1usah wrote

This is probably a decent representation of the ratio of the boron part of the rod to the graphite "tips".

https://i.stack.imgur.com/Ai7Yp.jpg

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Hiddencamper t1_jc2nqpi wrote

That’s a great picture.

And just so people are thinking about this the right way. From a safety perspective We don’t care about the graphite as long as it is in the fuel region or below the fuel region, because during a scram they go down which means graphite will be exiting the fuel region and control rods will be coming in.

It’s only a problem when those followers are all the way up and partially out. They will raise power below them as they drive down, right into the power peak.

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jobblejosh t1_jc4z2bf wrote

Also gives a great look into why it's named RBMK. Reaktor Bolshoy Moshknosti Kanalnyy; High-power Channel-type reactor; since the cooling water is sent through individual channels as opposed to being in one large pressure vessel.

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CleverNameTheSecond t1_jc2oogs wrote

To me this looks like the equivalent of having a car with just one pedal that handles both the acceleration and the braking depending on how hard you push down on it.

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The_Real_RM t1_jc5vpcw wrote

You just described one-pedal driving in electric cars. We in fact have exactly this

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