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The time is Midnight, a warm evening in Prypiat, April 25th. In 48h, the city will be empty. Unit 4, believe it or not, is stable, producing around 97% (3100)  of its total thermal capacity (3200MW). A test is to be conducted, on the unit. And at 0:34 The order is given to begin the power reduction in small steps, from 3100, to 2400, to 1900, to 1600 {mw}. However, Toptunov let it drop a little too low, to around 1500MW. So he pumps it back up, raising more rods to compensate. This is where the xenon Concentration starts to increase, but it will be slowly burnt away by nuclear fission or decay away. At 5:34, sunlight hits the Chernobyl nuclear powerplant, and work picks back up. The most important part, turbine bearing vibration measurements are being conducted on TG-7 and 8 (TG - Turbo Generator). Measurements could not be conducted on turbine 8, as sensors are supposed to be connected to brackets welded onto the turbine, were just simply not there. At this moment, fate struck, the south Ukrainian Nuclear Plant had unexpectedly encountered an issue, and scrammed, taking 1000MW from the grid. Chernobyl Unit 4, with one Turbine running (TG8) pumping out roughly 500MW into the grid, is now a vital life line to prevent a shortage in the Soviet MIR grid. The grid dispatcher called the Chief shit supervisor, begging them not to shutdown. The order had been given, Do not shut down till further notice. Yuri Tregub, Once a senior reactor Control engineer, had been brought to control a reactor he thought had shut down 2 hours before. Instead of lowering the power further, he does the opposite raising the power back up, to 1600MW. This is the first official protocol violation. As the emergency core cooling system had been permitted to be turned off, by Nikolai Fomin via his signature on the run down experiment protocol, bringing it out of operation was allowed, leaving it off was out of regulation, as the delay was not included in this scenario. Tregub calls the New Shift Supervisor, Gennedy Dick, if they have permission to lower the power. They did not. 2 Hours later, Tregub calls Dick, worried U4 had been forgetten about. They still had no permission for the run down, as the grid dispatcher had still not found alternative power sources to combat the Energy demand. However, Dick did inform Tregub they need to call Dyatolov in his Prypiat Apartment to proceed with the run down. So, Yuri Tregub makes another phone call to Dystovs apartament. First time he does not answer, so he called again. Dyatolv informs Tregub not to shut down before he was in the control room. Yuri tried to push him for some answers to his questions about the Rundown Program, as he was confused. Dyatlovs Response was quote: "This is Not a question for the telephone, do not start without me in the control room" and proceeded to hang up. 
10:00PM
Right after this, he receives another phone call from Nikolai Fomin, he tells him they had not shut down the reactor. And Nikolai informed him again not to shut down before Dyatolov had arrive. Tregub Call Dyatlov for the 3rd time, this time his Wife answers, she says Duatlov had already left, and should be there soon. 
Dick Has called Tregub, to inform them that they have permission to lower the power, but Dyatlov had not arrived in over an hour. They called U3, and got their answer. Dyatlov was there, Barrating someone for underperformance. They finally could lower the power, tregub gave the order, and his SIUR Konstantine Irmukov did just that. At this point in time, the peak xenon Concentration in the reactor had long since decayed away. The Operating reactivity margain was around 26, a safe level. Akimov has arrived back in the control room to talk to Tregub about the experiment. Power was 1200MW and dropping.

It is Midnight, reactor power is finally 760MW. The reactor will explode in 105 Minutes.

It is Now midnight. This is an extremely important part. Toptunov is lowering the power further, down to 700MW, and disables the local Automatic Control. Then a spontaneous power drop occurs. This was caused by so called "Self propelled" rods that withdraw or insert themselves fully out or into the reactor. And the only thing Toptunov can do, is watch as power drops to 30MW and emergency signals flash and he can do nothing about it. Tregub knows that if they are quick enough, they can prevent them selves from falling into a xenon pit that would lead to the abandonment of the experiment. They desperately try to increase power, and end up at 50Mw for now. This drop in power, causes significant problems for the MCP and steam drum operator, to prevent and automatic shutdown, he lower the minimum pressure, and waited for Toptunov to regain control. At the Turbine desk, Igor Kirshenbaum only watched as the steam flow to TG-8 plummented, and the vibration measurements and spin down experiment would be doomed. The Turbine workshop cheif, Razim Davletbaev had to help Igor in maintaining the turbine and keeping it from shutting down. And then, Dyatlov Walks into the room, Akimov walks up and informs him the power had fallen to 30MW. Dyatlov didn't seem to care that much, as there were no raised voices, no screaming and when he told Antaloy that they want to raise the power to just 200MW, he agreed. TG-8 is disconnected from the reactor, for vibration measurements, and would not be reconnected until 35 minutes later. Toptunov finally reached 160MW and switches on the Automatic Regulators again. Power was now steadily climbing, and too fast at times as the positive void co efficiencent gave it self away. To record the Parameters from the rundown, the dreg program had to be turned on and off again in the skala computer, as new magnetic tape was inserted. The operators were controling the reactor 5 minutes delayed, with up-to-date readings for around 20 minutes or so. At 1:00 AM the thermal power is around 200MW. And at this point, the job of the AR (Automatic Regulators) was switched from rasing the power, to keeping it stable at that level.

24 Minutes to destruction.
Boris Stolyarchuk can now do his Job, correct water levels and turn on all MCP's. However, to do that you require more water in the steam separators. So he let loose on the feed water flow for around 2 minutes. One problem comes to light, the reactivity. As colder masses of water enter the core suddenly, the steam bubbles (voids) collapse. Since the RBMK takes most moderation from groahite, the water acts as an absorber. So if more voids are created, the less absorption and more power. If there are less voids, less Power. And this can go like this; More boiling, less absorption, more boiling, less absorption, more boiling. This is not inheritly dangerous, and can be combated by control rod insertion. Most reactors take moderation from water. More reactivity; less moderation; less activity, Self regulating.

To keep the reactor from Stalling, Toptunov had to withdraw AR control rods first, and after than, he had no choice but to withdraw more manual rods. The Operating Margain was still on a safe level, and reactivity kept stable at 200MW. This is where a fatal mistake it made. Seemingly by choice, Toptunov withdraws USP rods, that insert from the bottom. This means that neutron absorption at the bottom of the core is not regulated. Toptunov is unaware that 150 out of 178 manual rods are in position to cause such a spiral mentioned earlier, and since the xenon Concentration had been increasing due to the low power level, more are to join them. Stolyarchuk again increase feed water flow, collapsing voids, Toptunov has to withdraw rods to keep the thing running. This time the SKALA Computer records the ORM, it is around 7-8. Way below the safe limit. As the feed water surge ends, power starts to climb as voids form. This is handled by the Automatic Control rods. The water at the bottom of the core is now less than a degree lower of that at the which is basically boiling. And increase in reactivity will be extremely magnified by the positive void coefficient. At 1:23:04, Metlenko issues the order to start the test. Many paramaters are being recorded, such as TG revolutions, voltage, MCP flows and revolutions. Kirshenbaum shuts off the emergency stop valve to TG-8, causing it to spin down. Meanwhile, MCP's 13,14,23,24 all begin to run down as well, reducing flow from these pumps. Metlenko looks at Lisuk, the guy that was supposed to press a button simulating a design basis accident. He does, and Turbine 8 is connected to U4, powering the pumps. The Diesel Generators start up, and the question begs how long the TG will last until it won't be producing enough Power. In the reactor, a different story is unfolding. The decrease in feed water causes more voids to form, increasing the positive void coefficient. AR rods that were already accounting for most Cr insertion, were approaching their end caps. And yet power was rising 1MW/s. And the order to shut down the reactor was missing, Toptunov turned to Akimov, and he makes a tapping motion to indicate a shutdown. At 1:23:39, Toptunov Presses the A3-5 button
A few things will happen, one of which is the insertion of all rods into the core. 
The control rods insert, and their graphite Displacers are replace water in their respective channels, replacing it with moderation. Water at the bottom of the core, already 1 degree below boiling, flashes into steam. This lock the graphite in place, infinitely accelerating the reaction. The pressure closes the backflow Valves, removing any flow of water into the core. All remaining water flashes into steam, the pressure can no longer be held back. Explosion, the 3600 Tonne lid of the reactor is blasted a few meters into the air, like a coin. Then, built up hydrogen gas explodes on contact with oxygen and molten fuel. Explosion, the lid is blasted again, sending it 15 meters into to air, and it lands back onto the reactor sideways.