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.
Montrama t1_jc1elu5 wrote
Reply to Why were the control rods in the reactor featured in the HBO series 'Chernobyl' (2019) tipped with graphite? by Figorama
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.