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Notes and Reflections on Books and Media

by Hannah Leitheiser

Control Rod Diagram

#chernobyl #soviet #controlrod

Midnight in Chernobyl: The Untold Story of the World's Greatest Nuclear Disaster

Adam Higginbotham

2019

Link

2019-06-18

Sorting through several pretty bad diagrams, I found this one, which is good. I think to understand why insertion of the boron rod would increase reactivity, you have to think of the core as having some horizontal sections of reaction. This was, after all, a particularly large reactor. Designing the the graphite rods so they didn't extend to the bottom of the core meant in the bottom slice, there was normally water, not graphite. As a reminder water absorbs neutrons; graphite make neutrons more likely to cause fission. So for the bottom slice, when the rods were lowered, the reaction increased, and given the primed state of the reactor in the Chernobyl incident, the reaction increase so fast it caused an explosion that seized the rods in place.

Image Source (reddit)