I ended up learning about nuclear disasters in Chernobyl and Fukushima. I know that they used totally different reactors but there's one thing that i can't wrap my head around. In Fukushima they used BWR reactors which were using light water as a moderator and coolant which makes sense to me. In RBMK reactor that were operating in Chernobyl uses graphite as moderator and water as a coolant. From what i was able to learn they have to use graphite endings on the control rods to compensate for waters neutron absorption ability which doesn't make sense to me because water is used as a moderator. Can anyone explain to me what i'm understanding wrongly about this thing?