Leonid Toptunov

Leonid Fedorovych Toptunov (, ; 16 August 1960 – 14 May 1986) was a Soviet nuclear engineer who was the senior reactor control chief engineer at the Chernobyl Nuclear Power Plant Reactor Unit 4 on the night of the Chernobyl disaster, 26 April 1986.

Early life Leonid Toptunov was born on 16 August 1960 in Mykolaivka, Buryn Raion, Sumy Oblast, Ukraine. His father was involved in the Soviet space program and during his childhood, he was surrounded by scientists and engineers.

In 1983, he graduated from the Obninsk Institute for Nuclear Power Engineering with a specialist degree in nuclear power plant engineering.

Chernobyl

In March 1983, Toptunov began his career at the Chernobyl Nuclear Power Plant. During his studies of the reactor documentation, he mentioned to his friend, Sasha Korol, that control rods may, in certain circumstances, accelerate rather than slow the reaction.

On the night of 26 April 1986, Toptunov worked in the control room at the reactor control panel with Akimov. Toptunov only had two months' experience in operating the reactor, and this was his first shutdown as operator. The operators attempted to perform a rundown test before scheduled routine maintenance. In preparation, Anatoly Dyatlov ordered the power to be reduced to 700 MW, as the test plan stipulated. However, the reactor stalled unexpectedly during test preparations, dropping to a low 30 MW, due to a failure in the automatic regulators. Some theories have suggested that xenon poisoning was the cause of this power drop, however it has been determined that xenon alone could not have caused such a rapid power drop.

He was initially admitted to Pripyat Hospital, but quickly transferred to Moscow Hospital 6. By 28 April, the symptoms of radiation sickness had mostly subsided. His parents visited him in the hospital; although he could walk, his parents could see he had severe skin damage. During his stay, he discussed possible causes of the accident with Akimov and Dyatlov, but they were mystified. Toptunov received a bone marrow transplant in an attempt to restore his immune system, while Akimov did not get a transplant as it would have seemed insufficient due to the severity of his ARS. Toptunov died from acute radiation poisoning on 14 May 1986 and was laid to rest at the Mitinskoe Cemetery in Moscow. His family was informed that his death was the only reason he was not prosecuted for the accident. However, the operators were found to have deviated from operational procedures, changing test protocols on the fly, and having made "ill judged" actions, making human factors a major contributing factor.

He was portrayed by actor Volodya Stepanenko in the 2004 Zero Hour TV series. He was portrayed by Michael Colgan in the 2006 BBC production Surviving Disaster: Chernobyl Nuclear Disaster and by Robert Emms in the 2019 HBO miniseries Chernobyl.