Why the Chernobyl Nuclear Reactor Exploded
https://www.vice.com/en_us/article/597k9x/why-the-chernobyl-nuclear-reactor-exploded.Jun 4 2019
On April 26, 1986 a nuclear reactor exploded in the Soviet Union. You might already know this, either because you’re a history buff or just a fan of HBO’s hit miniseries Chernobyl, which ended with Monday night’s dramatic finale.
In the wake of the show’s popularity, some viewers expressed on social media that nuclear power is too dangerous to use. Craig Mazin, writer-producer of Chernobyl, weighed in on Twitter in April, writing, “The lesson of Chernobyl isn't that modern nuclear power is dangerous.
The lesson is that lying, arrogance and suppression of criticism is dangerous.â€...
...The Chernobyl plant was a High Power Channel-type Reactor (RBMK) that used water to both cool the core and generate steam for its reactions Crucially, most of Chernobyl’s control rods were made of boron tipped with graphite. The control rods slipped into the reactor to slow reactivity. The boron slowed the reactions down, but the graphite tips initially increased the rate of fission. This was a design flaw, was one of the main factors that caused the explosion....
...ronically, on April 25, Chernobyl staff were conducting an experiment to make the power plant safer.
In the event of a power failure, fission would continue but the reactor would still need power to run the water pumps. The backup diesel generators used by the Soviets took a full minute to spin up. Soviet scientists felt that minute-long gap was a disaster waiting to happen and wanted to use some of the residual spin from the powered-down nuclear turbine to bridge the gap.
The night of the experiment, the workers disabled the emergency core cooling system, local automatic control system, and the emergency power reduction system. In the event of a nuclear meltdown, the plant’s computers were designed to sink the control rods into the reactor to completely shutdown fission. Chernobyl’s workers bypassed this system, took manual control over the rods, and had pulled most of the 211 control rods out of the reactor.
Safety standards at the time required a minimum of 28 rods in the core. The workers only left 18....
...At 1:23 AM, forty seconds after the experiment began, someone pressed the emergency shutdown button. To this day, no one is sure why the emergency shutdown button was pressed or who pressed it. The emergency shutdown was supposed to plunge the control rods into the overheating reactor and cool everything down. Tragically, it had the opposite effect....
...At the press of the button, the graphite-tipped control rods plunged into the coolant water. Though the boron in the rods was meant to slow the reaction down, the graphite tips briefly increased fission in the core. The initial reaction was so powerful that it cracked the control rods, jamming them a third of the way into their journey, burying the reactive graphite tips into the coolant water.
The reactor created more steam than it could vent, the fission reactions churned on, and the pressure from the steam exploded, rupturing fuel lines and exploding out the roof of the reactor. Second later, a second explosion spewed hunks of graphite into the surrounding area and began to spread radiation....
