CHERNOBYL AZ-5 why it exploded

Nuclear energy has become routine. A bright atomic future awaited us. The Soviet Union had five of these huge nuclear power plants, but there is only one that we all know about... Chernobyl. That night there was no idea of ​​the disaster that would have a profound effect on the USSR and nuclear energy around the world. At 01:23 a.m. m., during a safety test, the AZ-5 button was pressed. About 8 seconds later, reactor 4 saw its hole. Why did the emergency button blow up the reactor? This is the central question of Chernobyl. Blerrie communists!!! At the time of the disaster, Ukraine was one of the 15 Soviet republics.

Chernobyl was in northern Ukraine, near the border with Belarus. The centerpiece of these power plants was the RBMK reactor. Strong nut - - dangerous nut!! The RBMK was a graphite reactor that fueled Soviet growth since 1970. Chernobyl reactor 4 was only two and a half years old. These are the most important systems. The nuclear reactor produces large amounts of heat. Pumps circulate water through the reactor to capture heat. Steam accumulates in the steam drums. The steam spins turbines that generate electricity. The steam is cooled back into the water by a large lake and returned to the system. It works like this at maximum power for months.

The buildings that housed the systems were very large. The components were located in separate sections. The concrete vault surrounding the small reactor was 2.5 m thick. The small reactor is housed in a steel drum. A central component of this story is graphite. The core contains large amounts of graphite, which was essential for the nuclear reaction. When an atom splits, it releases neutrons at the speed of light. These neutrons go too fast to split the surrounding uranium. The neutrons must first lose speed as they bounce around within the graphite. Only when they move more slowly do more atoms split.

Graphite is called a moderator because it moderates the speed of neutrons. Each graphite block has a hole in the center that contains the tubes for the fuel channels and control levers. Water flows at high pressure inside these pipes. Uranium fuel is formed in these small granules. Each pellet is extremely fuel dense and contains the equivalent thermal energy of a truck full of coal pellets. A reactor must have an on and off switch and a way to set the power level. This is done with control levers. They are made of boron, which is a very good neutron absorber.

If the rods are in the core, they turn off the reaction. With about 80% of the rods drawn, the reactor is running by hitting the drawbar. When the control rods were removed, they left a space behind. The bottom half of the control rods were made of graphite which filled this gap. Otherwise, squatters were installed. Replacing boron with graphite was a brilliant design principle. The reactor was more efficient and made the control rods twice as effective. The explosion was the result of a design defect called the "point effect." This caused a brief power spike, just when the control levers were supposed to quell the reactivity.

The graphite displacers do not extend to the floor of the reactor because there was not enough space underneath. The lower 1.25 meters are shortened. The reactor floor was where things went horribly wrong, but we'll check that out a little later. The objective of the test was to simulate the loss of electrical energy. If only the US tried to cut power lines or EFF stole copper. And see if the flywheel effect of the turbines could drive the water pumps until the diesel generators started up. 3 previous attempts failed. The test had to be carried out during a reactor shutdown.

That day, the shutdown was delayed for most of the day and the reactor was running at 50% power. This led to two major contributors to the disaster. 1. the reactor suffered neutron poisoning and 2. the test was performed by the less experienced night shift who did not receive adequate information for the test. At 01:00 the shutdown began, but was interrupted because the electrical grid needed additional power and Chernobyl Unit 4 had to make up the shortfall. This is how the Soviets avoided load shedding, but blew it all up in the process. After a pause of 19 hours, the reactor shutdown could continue.

The new shift took over at midnight and put the reactor into automatic control to keep it at 22% power. Except the automatic control was not intended for a poisoned core and the power dropped to only 1% before the test was even performed. While the reactor was operating at half power, it was poisoned with xenon gas. Xenon is a powerful neutron poison. A basic rule in a reactor is to never restart a reactor that has been poisoned because it is terribly unstable. Xenon is formed 6 hours later and pursues the fine balance of the nuclear reaction. The engineer in charge, Anatoly Dyatlov, was under pressure to perform the test.

He made the fateful decision to remove almost all of the control levers so that the reactor would once again have enough power for the test. It was like stepping on more than the accelerator in a car to counteract a stuck handbrake. 1 hour later, the controllers managed to increase the power again to 6%. The test was carried out at 01:23 hours and lasted 40 seconds. The control staff agreed in advance at the end of the test that the az5 button should be pressed to complete the shutdown. According to the control personnel, everyone was calm at this time. You may know the valve cap and rotary switch, but that was the adjustment after the disaster.

The button that Leonid Toptunov pressed was probably this. The tie rods were in this configuration when the AZ-5 was printed. It's scary that there is only one bar completely inserted. The core was never intended to have less than the equivalent of 26 active rods. But tonight there was almost no top roll because of the stupid attempt to cancel the xenon poison. Communists!! The reactor was now full of holes. Too much communist nonsense. The AZ-5 pressed all the control levers at once. Reactor 4 teetered on the edge of the abyss and the immediate effect was that one communist was one too many.

Water is a weak neutron poison. As the graphite displaced the water, a temporary surge of energy occurred on the floor of the reactor. Boron would arrive too late. The sudden increase in energy caused steam bubbles. Less water meant less neutron poison: more heat and more reaction. It was the feedback loop towards destruction. 1000 times faster than Zuma or Malema!! Not even Mandela could now stop unbridled reactivity. The reactor underpants were overwhelmed and the water channels were turned off. The reactor pressure was lost and the cooling water turned to steam over the entire core. Reactor 4 currently produces energy equivalent to part of the Soviet electrical grid.

The power of the reactor was estimated to be 20 times greater than the maximum. We actually have no idea, because there was nothing left to do to measure. The reactor drum and building structure were unable to contain the sudden release of energy. The explosion tore through the roof of the 2,000-ton reactor shell and landed on its side in the reactor pit. The north side of the building collapsed in the explosion, exposing the steam tanks and main pumps. Firefighters told how they warmed their hands over the graphite that was scattered on the ground. They did not know that they were exposing themselves to lethal doses of radiation.

It was an explosion of heat and gas. It was not an atomic bomb and nuclear scientists are scared when it is said that Chernobyl is. This is the control room about 25 years later. The equipment was reused elsewhere, while the rest was removed by souvenir hunters and radiation hunters. Soviet nuclear scientists were aware of the spike effect problem. There were previous conduit ruptures due to the AZ-5 tip effect at Leningrad 1975 and Ignalina 1983. Design changes were recommended, but the RBMK was considered very robust and was widely believed to have not

exploded

. No changes are made and, most importantly, the hidden threat is kept secret from controllers.

If they knew, they could compensate for it in their decision making. Controllers take comfort in the fact that the AZ-5 kill switch button is always there in case they need to shut down the reactor quickly. But it was the lighter hidden in the wrong place. The IAEA Commission found that control instruments have incomplete feedback with less than 50%. Low power risks were not well described in operational documentation and procedures were sometimes inconsistent. The operators would have been quite blind to what was happening inside the reactor and would have had to rely more on experience and intuition for control.

To build safer reactors, later designs, including those from Russia, used water as a moderator. Water is a much better moderator. This added additional automatic reactivity control needed and the core could be much smaller. As the water turns to steam, the moderator decreases and the reactivity immediately drops. With higher quality uranium, water could be used as a moderator. Graphite was the favored moderator in previous reactors around the world with low-grade uranium. The switch to water could occur when uranium enrichment technology has advanced enough and large quantities can be produced. In retrospect, it is very easy to be critical of the time when science was earlier and computer modeling was minimal.

Humans can dream the most wonderful things, but they are also responsible and push shit. Especially communists, Malemas and Zuptas. We will never truly know what happened in the control room that night, and most of those who were there paid with their lives as they heroically fought to deal with various other dangers that could have endangered the other reactors through a " reactor meltdown" and cause a greater disaster. It's natural to focus on the recklessness of a few, but it's also a story about the epic bravery and personal sacrifice of many. Sometimes people fail, but most of the time we succeed.

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