A nuclear explosion cannot occur because the fuel is not compact enough to allow an uncontrolled chain reaction. The MIT reactor has a large amount of water and core structural materials that slow down neutrons before they reach other fissile atoms. Even an uncontrolled reaction would occur too slowly to cause an explosion. A thermal explosion cannot occur because our reactor is designed to want to shut down on its own as the temperature increases (i.e.
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At every turn, Chernobyl referred to the ineptitude of Russian governance, the inflexible courage of the liquidators tasked with cleaning the site, the weight that weighed on the shoulders of all scientists investigating the disaster, and the harsh reality of atomic energy. Moments after the reactor explosion, Chernobyl burns. Valery Legasov, the head of the commission charged with investigating the disaster, participates in the trial of three power plant officials responsible for the explosion and its immediate consequences. Together with politician Boris Shcherbina and physicist Ulana Khomyuk, the trio details the key reasons behind the disaster and directly points to the failures of those officials, including chief engineer Anatoly Dyatlov, as the cause of the plant's explosion.
But here we are talking about nuclear physics. The term positive vacuum coefficient is used and that is not a term you hear every day. Even Chernobyl engineers could not fully understand the consequences of their actions. So we dug into the radioactive quagmire to show you the science behind the Chernobyl RBMK reactor explosion, and the reasons why it's not likely to happen again.
The RBMK reactor that exploded in Chernobyl, No. The most important segment of the reactor is the core, a huge piece of graphite, sandwiched between two biological shields like the meat of a hamburger. You can see this design below. A schematic of the plant used in HBO's Chernobyl showing the graphite core and biological shields.
The core is where the fission reaction takes place. It has thousands of channels that contain fuel rods, composed of uranium, which has atoms that are easy to split. The core also has channels for control rods, boron compounds and graphite tips, designed to neutralize the reaction. Water flows through the channels of the fuel rods, and the entire structure is lined with steel and sand.
Fuel rods are the energy source of the core and are composed of uranium atoms. Uranium atoms project a lattice into the nucleus and, as rogue neutrons ping inside, pass through the solid graphite that surrounds them. Graphite slows down these neutrons, as does water, making them more likely to be captured by the network of uranium atoms. Colliding with this network can cause more neutrons to be released.
If the process occurs over and over again in a chain reaction, it generates a lot of heat. Therefore, the water in the channel boils, turns into steam and is used to create energy. If left unchecked, this reaction would flare up and cause a melt, but control rods are used to equilibrate the reaction. Simply put, if the reactor generates too much energy, the control rods are placed in the core, preventing neutrons from colliding with the same regularity and slowing down the reaction.
In a perfect world, the systems, and the men who control the systems, ensure that the scale never tilts too much one way or the other. Control rods enter and exit the reactor, water is constantly pumped to keep everything cool, and the power plant produces energy. But if the plant itself loses energy, what happens? That is one of the shortcomings of the RBMK reactor. A lack of power means that water is no longer pumped to cool the reactor, and that can quickly lead to disaster.
In the early morning of April 26, 1986, the reactor was undergoing a safety test with the aim of solving this problem. Valery Legasov testifies before the commission, in front of the three power plant officials responsible for the disaster. The safety test is the starting point in a chain of errors that ultimately resulted in the explosion of reactor 4. The low power state in the RBMK reactor is not like putting the computer in sleep mode.
You can't quickly return to your usual power state. However, the Chernobyl control room team tried to do just that and ignored existing safety protocols. To try to bring the energy back to an acceptable level, the workers removed the control rods from the core, hoping to reactivate the reaction and raise the energy again. During the 10-hour delay, the low-power state of the nucleus caused an accumulation of xenon, another type of atom that essentially blocks the process of nuclear fission.
The core temperature also dropped so much that it stopped boiling water and producing steam. We heard the term “positive vacuum coefficient” shouted by Legasov from Jared Harris in the final episode of Chernobyl and it's key to the explosion, but it's not exactly explained. Remember how water cools the core and slows down the reaction. However, when water becomes steam, it lacks the ability to do both effectively, because it evaporates and becomes bubbles or voids.
The ratio of water to steam is known as the vacuum coefficient. In other nuclear reactors, the vacuum coefficient is negative: more steam, less reactivity. Emily Watson is fascinating as a nuclear physicist who represents all the real-life scientists who worked to unravel how Chernobyl exploded. The safety test shuts down the reactor and the remaining water evaporates.
Steam Makes Nuclear Fission More Efficient, Accelerating It. More heat makes water boil faster. If we freeze the frame here, the scenario is bleak. The core generates steam and heat rapidly in a runaway reaction.
All but six of the 211 control rods have been removed from the core and the water no longer provides any cooling effect. The core is now a giant ball pool for children in an earthquake, with neutrons bouncing around the chamber and constantly colliding with each other. All plant workers could do was press the emergency stop button. Control rods should slow down the reaction, but because they have graphite tips, they actually cause the power to increase even more.
Over the next five seconds, the power increases dramatically to levels that the reactor cannot withstand. The caps at the top of the reactor core, which weigh more than 750 pounds, literally begin to bounce off the reactor room. The 700-pound steel blocks resting on top of the reactor core began to rumble and rise into the air in the moments leading up to the explosion. After Chernobyl, a series of changes were implemented in RBMK reactors across Russia.
Today, 10 of these reactors are still operating across the country, the only place where they currently operate. These sites were modernized with safety devices in order to prevent a second Chernobyl accident. Control rods became more abundant and can be inserted into the core faster. Fuel rods contain slightly more enriched uranium, which helps to control nuclear reactions a little better.
And the positive vacuum coefficient, although it still exists in the design, has been drastically reduced to avoid the possibility of a repeat fusion at low power. Of course, the only thing that hasn't changed is us. Chernobyl was a failure on a human scale, long before it was a failure in the atomic. There will always be risks when trying to control nuclear fission reactions and those risks can only be mitigated, not reduced to zero.
Chernobyl and other nuclear reactors are not nuclear bombs waiting to detonate. The HBO series teaches us that they can become dangerous if we don't understand the potential of atomic science. So can this type of nuclear catastrophe happen again? Yes. As long as we try to harness the power of the atom, the odds will fall in favor of disaster.
But should we stop trying to do it? Not. Harnessing the power of the atom and mitigating the risks of nuclear energy to the best of our ability is one of the ways to achieve a cleaner energy future. So we will continue to harness the power of the atom and improve. While a nuclear reactor can never explode like an atomic bomb, an explosion can still occur.
All power plants are a potential site for an explosion, because the fuel used, whether coal, uranium or natural gas, must be energy dense. In coal plants, sparks can ignite coal dust and cause an explosion. Gas leaks can cause explosions in natural gas plants. Usually, in a nuclear reactor, the type of explosion seen would be a steam explosion.
A steam explosion could only occur if the reactor were to melt. A melt means that, due to lack of coolant or excessive fission, the core becomes so hot that it melts. Due to the intense heat produced, water turns into steam. In addition, fuel rods melt, turning them into a liquid.
This allows the metal to react with the steam, causing an explosion. On April 26, 1986, RBMK reactor number four at the Chernobyl nuclear power plant, Ukraine, went out of control during a low-power test, causing an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere. Despite all the help from public and private organizations, the cleaning and decommissioning of the Fukushima Daiichi nuclear power plant is subject to considerable delays and uncertainties. It is not a nuclear explosion, but a steam explosion, caused by the enormous build-up of pressure inside the core.
The other accelerator concept proposed some time ago (Rubbia, 1994; Rubbia and Rubio, 199) integrates the accelerator and the reactor-like device in what is called an energy amplifier. RBMK reactors do not have what is known as a containment structure, a concrete and steel dome over the reactor itself designed to keep radiation inside the plant in the event of such an accident. Radioactive decay is the process by which some atoms revert to a more stable nuclear configuration by emitting energy (e). Grossi also clearly stated that there is no current threat of nuclear melt at that facility.
Although this concept is not supported by the existing reactor industry, it will be used here as a template for the scenario presented below, due to its unique promise to reduce all three objections to the current variety of nuclear reactors. In modern nuclear reactors, the nuclear power plant design adopts redundancy and diversity in its safety features designed with multiple layers of independent defense in depth. The United States does not currently have a final tank or reprocessing program for nuclear fuel. To understand these differences, it is first important to understand the concept of nuclear fission and criticality.
Some of the risks present at the Zaporizhzhia nuclear power plant would be that the fighting disconnects the power grid installation or that the damage causes the cooling tanks to empty, according to James Acton, co-director of the Nuclear Policy Program at the Carnegie Foundation for International Peace, in his speech at the Rachel Maddow show. Safety measures ignored, uranium fuel in reactor overheated and melted through barriers. . .