Individual involvement in the Chernobyl disaster
The individual involvement in the Chernobyl disaster refers to the roles and experiences of the personnel present at the Chernobyl Nuclear Power Plant during the catastrophic nuclear accident on April 26, 1986. The disaster, rated a level 7 on the International Nuclear Event Scale, was caused by a combination of operator error and reactor design flaws during a safety test.
At 01:23 MSD on April 26, 1986, an explosion at Reactor Number 4 spread debris and radioactive material across the surrounding area. Of 600 workers present on the site during the early morning of 26 April 1986, 134 received high doses of radiation and suffered from radiation sickness. This article details the specific actions and experiences of these individuals and others who responded in the immediate aftermath.
Individuals present on 26 April
Anatoly Stepanovich Dyatlov
Dyatlov, the deputy chief engineer, supervised the test. At the moment the reactor power slipped to 30 MW, Dyatlov reported that he was out of the control room and inspecting equipment elsewhere in the plant. Dyatlov stated that Akimov and Toptunov were already raising power upon his return, and that if they had not done so, he would have ordered them to. In testimony at the trial, several witnesses recalled Dyatlov remaining in the room but did not report any disagreements or "serious discussions" related to the increase in power or at any other point during the test. When the reactor power had decreased to approximately 500 MW, the reactor power control was switched from local automatic regulator to the automatic regulators, manually to maintain the required power level.: 11 AR-1 then activated, removing all four of AR-1's control rods automatically, but AR-2 failed to activate due to an imbalance in its ionization chambers. Toptunov reduced the power set-point to stabilize the automatic regulators' ionization sensors. The result was a sudden power drop to an unintended near-shutdown state, with a power output of 30 MW thermal or less. The circumstances that caused the power drop are unknown. Most reports attribute the power drop to Toptunov's error, but Dyatlov reported that it was due to a fault in the AR-2 system.: 11The power was stabilized at 200 MW at around 1:00 a.m., and the turbine rundown test was begun. A little under a minute after the beginning of the test, Dyatlov reports that Toptunov pressed the AZ-5 button to shut down the reactor upon completion of the test, and in accordance with maintenance which had already been scheduled for the weekend of April 26–27. Approximately three seconds after the initiation of the scram, the reactor underwent a power excursion, rising to 520 MW. As the control rods dropped into the core, the graphite displacers that made up the last few meters of the rods introduced additional moderation and hence reactivity into the reactor system. The first shocks occurred as the control rods were falling, and the subsequent damage prevented their further insertion into the reactor. Dyatlov's first concern after the explosion was that an accident in the deaerators immediately above the control room could result in boiling water raining down from the ceiling. He ordered everyone to evacuate to the backup control room, but no other operators left the room and Dyatlov soon countermanded his instructions. Other plant workers arrived in the control room, reporting damage.
Dyatlov went to the backup control room, pressing the AZ-5 button there and disconnecting power to the control rod servodrives. He ordered Kudryavtsev and Proskuryakov to lower the jammed control rods by hand, which Dyatlov recalls as his only mistaken command from that night. After witnessing the fallen roof, fires and spilling oil in the Turbine Hall, Dyatlov ordered Akimov to call the fire brigade. In the corridor, he met Genrikh and Kurguz and sent them to the medical station. Realizing the magnitude of the disaster, Dyatlov suspended coolant supply to the reactor, although pumping of water would be resumed by order of Chief Engineer Nikolai Fomin around dawn. Dosimetrist Samoilenko reported that radiation levels in the left hand and central sections of the control room were 500–800 μR/s, while readings were off the charts on the right hand side of the control room. Dyatlov ordered Akimov to send Toptunov and Kirschenbaum to the Unit 3 control room because they were of no further use, but Toptunov ultimately returned to the control room to retrieve the operator's log and remained on duty at Unit 4. Around 3:00a.m., Dyatlov instructed Babishev to relieve Akimov on duty, but Akimov also remained at his post.
Dyatlov ran to the control room of Block 3 and instructed Rogozhkin to shut down reactor 3, overriding the latter's objections that Bryukhanov's permission was needed. Dyatlov then returned to control room 4 and ordered Akimov to call the daytime shift and get people to the affected unit; namely Lelechenko, whose crew had to remove hydrogen from the generator 8 electrolyzer. Dyatlov then received the report of Perevozchenko that pump operator Khodemchuk was still unaccounted for. Perevozchenko led Dyatlov and Aleksandr Yuvchenko on a brief and unsuccessful search for Khodemchuk, in corridors where the 1000 μR/s dosimeters reached their maximum. During the night, Dyatlov and Yuri Tregub went to survey the plant from the outside. Tregub recalled telling him "this is Hiroshima" to which Dyatlov replied, "Not in my nightmares have I seen anything like this". Around 5:00a.m., already feeling ill, Dyatlov made a brief report to Bryukhanov in the Civil Defense Bunker, showing him the final printouts of reactor parameters leading up to the explosion. Dyatlov did not report the destruction of the reactor, but speculated that the accident was due to some malfunction of the Control and Protection System. Dyatlov was overcome by weakness and nausea in the bunker and went to the medical unit with Gorbachenko. Fomin replaced him at his post with Anatoly Sitnikov.
Aleksandr Fyodorovich Akimov
Akimov, the unit shift chief, was in charge of the test. He took over the shift at midnight from Tregub, who stayed on the site. At 1:23:04 a.m., the test began, and the main circulation pumps started cavitating due to the extremely high temperature of inlet water. The coolant started boiling in the reactor, and because of a combination of a positive void coefficient and , the power began to increase dramatically. At ~1:23:30 a.m., Toptunov asked Akimov whether he should shutdown the reactor for the planned maintenance. Akimov showed a gesture to Toptunov to press AZ-5. Toptunov pressed the button at 1:23:39. A second later, at 1:23:40 the SKALA computer registered the command. Akimov and many others heard a sound described as a Volga car failing to start up followed by two explosions. The room went black.When the explosions occurred, the air filled with dust, there was a power cut and only battery-powered emergency lights stayed on. Perevozchenko ran into the control room, reporting the collapse of the reactor top. Brazhnik ran in from the turbine hall, reporting fire there. Brazhnik, Akimov, Davletbayev, and Palamarchuk ran into the turbine hall, having seen scattered debris and fires on levels 0 and +12. Akimov called the fire station and the chiefs of electrical and other departments, asking for electrical power for coolant pumps, removal of hydrogen from the generators, and other emergency procedures to stabilize the plant and contain the damage.
Internal telephone lines were disabled; Akimov sent Palamarchuk to contact Gorbachenko. Kudryavtsev and Proskuryakov returned from the reactor and reported its state to Akimov and Dyatlov. Insisting the reactor was intact, Akimov ordered Stolyarchuk and Busygin to turn on the emergency feed-water pumps. Davletbayev reported loss of electrical power, torn cables, and electric arcs. Akimov sent Metlenko to help in the turbine hall with manual opening of the cooling system valves, which was expected to take at least four hours per valve. At 3:30 a.m., Telyatnikov contacted Akimov, asking what was happening to his firemen; Akimov sent him a dosimetrist. Akimov, already nauseated, was replaced at 6 a.m., by the unit chief Vladimir Alekseyevich Babychev. Despite this, Akimov, together with Toptunov, stayed in the plant. Believing the water flow to the reactor to be blocked by a closed valve somewhere, they went to the half-destroyed feed-water room on level +27.
Together with Nekhayev, Orlov, and Uskov, they opened the valves on the two feed-water lines, then climbed over to level +27 and, almost knee-deep in a mixture of fuel and water, opened two valves on the 300 line. Due to advancing radiation poisoning caused by a dose of over 15 grays, they did not have the strength to open the valves on the sides. Akimov and Toptunov spent half an hour turning the valves; the radioactive water in room 714/2 was half submerging the pipeline. Viktor Smagin went in to open the third valves, spent 20 minutes in the room, and received 3 grays. By 7:45 the group made their way back to the control room of unit 4, here Akimov apologised exclaiming that they were unable to fully restart feed-water flow; before running to vomit into a bin. Though he tried his best to explain the work to the next shift, he was unable to stop vomiting and so was ordered along with Toptunov and Nekhaev to make their way to the infirmary; they were still wearing their soaking wet clothes. Akimov was evacuated to the hospital in Pripyat where he was put on an intravenous drip, his skin now a greyish brown. He along with Toptunov were selected as part of the first 28 people to be evacuated to Moscow for specialised treatment at the 6th clinic there. By 28 April, the effects of his exposure had largely subsided and he was able to talk and smoke with his colleagues. His condition quickly worsened, his gastrointestinal system and bone marrow ravaged by the radiation, his skin now swollen and charcoal black. Interrogations proved difficult as he was unable to talk. He was selected for receiving a fetal liver cell transplant. He died on the 10th May, two weeks after the accident due to skin and intestinal injuries. Until his death, he insisted he had done everything correctly and had made no mistakes.