This will be a part of a nuclear plant playset that i'm designing for children. Future things to come include a pressurizer, turbine/generator, condenser, cooling tower, pumps, and snap together piping. The ring on the top moves the control rods up and down when rotated. WARNING: The Mk 1 version does not include an inherent Scram feature. If you pretend to lose control of reactivity, lightly tap the top of the control rods with a 40lb sledge hammer until the rods hit the bottom. I am not responsible for any damage to health or property from pretend reactor meltdowns. Imaginary radioactive waste must be properly stored and monitored by the user.Print (1) of each except for: Fuel Rod (5), Rod Follower (5)