The 25-year-old senior reactor control engineer who pressed the AZ-5 button at Chernobyl's Unit 4
While studying control-rod documentation, Toptunov told his friend Sasha Korol that 'in certain circumstances, the rods could accelerate rather than slow the reaction': three months later, that insight became reality under his own finger on the AZ-5 button.
Leonid Toptunov was the Senior Reactor Control Engineer (SIUR) at Chernobyl's Unit 4, a 25-year-old technician at the control panel during the night of the 26 April 1986 disaster. Only three months into independent duty and facing his first shutdown, he pressed the AZ-5 emergency shutdown button under pressure from deputy chief engineer Anatoly Dyatlov, but a design flaw in the RBMK control rods caused a reactivity surge that triggered the explosion; he returned to the control room afterward to manually open water supply valves, absorbing a lethal 1,300 rem before dying in a Moscow hospital on 14 May.
Career Timeline
- 1960Born in Mykolaivka, Sumy Oblast, Ukrainian SSR
- 1983Graduated from Obninsk Institute for Nuclear Power Engineering
- 1983–1986Chernobyl Nuclear Power Plant: unit control engineer, then Senior Reactor Control Engineer (SIUR), Unit 4
- 1986.04.26Pressed AZ-5 scram button during Unit 4 safety test on night shift; received lethal radiation dose
- 1986.05.14Died of acute radiation syndrome at Moscow Hospital No. 6; buried at Mitinskoe Cemetery