Nuclear Reactors

The ultimate would be to cause melting of the fuel. It must be shown (theoretically) that this would be contained in the bottom of the reactor vessel. The fission chain reaction would have stopped but there is after heat from radioactive decay and this must be absorbed by emergency cooling to avoid damage to the vessel. This is an extreme case and might be caused by a severe loss of cooling accident, but is very unlikely in most reactors.

Short answer: Chernobyl. Physics answer: That heat has to go somewhere and it's not inclined to have a discussion about where. The heat in a fission reactor is generated by the interaction between the fuel (uranium) and the neutrons that are produced by the interaction itself. Basically, the neutrons cause the uranium atoms to break (fission). When the uranium atoms break, they release heat (nice, because we need that for things like generating electricity) and more neutrons (sort of nice, because it feeds itself). But if you don't get the heat out of there, you've got a major problem on your hands. In order to control the heat released by uranium/neutron interactions, to slow them down, nuclear reactors have "control rods" that can absorb neutrons. They're usually made of carbon. If you screw this part up, and there is no coolant, your reactor turns into the scariest heat factory you ever dreamed of. Flooding it with coolant now will result in two things: Steam explosions and radioactive coolant. If a coolant leak is all you get in this scenario, then count yourself lucky. You just avoided a complete reactor melt-down, the equivalent of an atom bomb detonating in your neighborhood.

The average temperature of a nuclear reactor can vary depending on the type and design of the reactor. In general, most nuclear reactors operate at temperatures ranging from 500 to 700 degrees Celsius (932 to 1292 degrees Fahrenheit).

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I guess because it is the one with the fewest operational problems and the longest operational life. BWR's introduce the problems of a contaminated turbine. Gas cooled graphite reactors are efficient but there are life limitations on the graphite. Heavy water reactors have the benefit of using natural uranium but the heavy water is very expensive to produce. So the choice is between enriching uranium as for the PWR, or producing heavy water as for the CANDU. Most countries are now opting the PWR way as enriching uranium by centrifuge has become much less expensive than the old gaseous diffusion method.

A fusion reactor is a type of nuclear reactor, one which fuses hydrogen atoms into helium atoms, as opposed to a fission reactor (by far the dominant source, and the only one used to commericaly generate power), which spilts uranium or plutonium atoms (mostly these two). Both use these reactions to generate heat, turning water to steam which then drives and turbine, which in turn drives a generator, creating electricity.

The Chicago Pile-1 was the nuclear reactor where the first controlled fission chain reaction occurred. The United States constructed it as part of the Manhattan Project during World War 2, and the Italian physicist Enrico Fermisupervised the project with help from his associates Martin Whittaker and Walter Zinn. The atomic pile was set up at the University of Chicago. Note that the term nuclear reactor came along quite a bit later, but this was a nuclear reactor, and the first one of these machines. A link can be found below to the story behnd this historic project. It's a good read. Why not surf on over and check it out?

Overheating inside a nuclear reactor can lead to a meltdown, where the nuclear fuel overheats to the point of damaging the reactor core. This can result in the release of harmful radioactive materials into the environment, posing serious health and safety risks to people and the environment. Emergency response measures, such as cooling systems and containment strategies, are in place to prevent and mitigate the effects of overheating in a nuclear reactor.

Normaly, a reactor is shut down by gradualy lowering the control rods into the core of the reactor, which is the opposite of starting the reactor up. The control rods are made from a neutron absorbing material, and they will "soak up" neutrons to diminish the chain reaction and eventually stop it. There is also what is called a "reactor scram" where the control rods are released from their drive mechanisms and allowed to fall into the core. They bottom out in just a couple of seconds, and with the rods in, the chain reaction comes to a screeching halt. In another type of emergency shutdown, certain chemicals that are neutron absorbers and are called "poisons" can be pumped into a fluid moderator (liquid or gas) to break the nuclear chain and shut the reactor down. As a final note, consider that a reactor which has been operating at even a moderate power level continues to generate a lot of heat after shutdown. A lot of it. If some kind of loss of coolant accident (LOCA) occurs, a shutdown is the least of the worries of the operating staff. The core will have to be continuously cooled for days and even weeks afterward to keep the fuel from melting its way out of its cladding. And with a loss of coolant because of, say, a major leak, things will get hairy as the operators scramble to get coolant circulating through the core, or at leasted pumped over it to keep the fuel elements from failing and releasing fission products into the coolant. Ruptured fuel elements are a disaster as they contaminate the primary plant enormously. And if containment fails, these highly radioactive materials get out into the environment.

Heavy water (deuterium) functions as a moderator. It slows down fast neutrons released by fission reactions in order to allow the reaction to be sustained. Fast neutrons pass through the reactor before initiating another fission reaction.

A fuel rod is a metal tube (zirconium alloy) that contains fuel pellets in bundles (stacks). Fuel pellets vary in composition, but most consist of uranium and/or plutonium in some form. One type is uranium dioxide powder that has been compressed and heated to form a ceramic. Zirconium is used as a container because it has low neutron absorption, and allows the neutron radiation being produced by the fuel to escape into the surrounding reactor core so it can do its work of heating water to make steam that drives the power plant turbines.

The size of a fuel rod depends on the type of fuel and the application. A CANDU fuel rod, for example, may be 50 cm long and 10 cm in diameter.

I don't know the total installed capacity in Australia, but with a population of about 20 million, if we assume 1 kw per person, this gives 20,000 Mw. The largest power reactors are now about 1,500 Mw, so this would need about 13 to 14 reactors. In an all nuclear system though you would need extra plants to cover refuelling outages and unexpected down time due to faults, so I should think about 18 in total. If the installed capacity is different to what I have assumed, adjust accordingly.

It's a complicated story, there are many different elements in the fission products, and they have widely different half lives and radioactive characteristics. Some decay quickly and turn into other isotopes which may have much longer half lives. I recommend you read the first part of the linked article, if you want to go further there is much more detail available in the rest of the article. Note that nuclear reactors and nuclear weapons produce differing actual quantities and types of fission products because in the reactor they are retained in the spent fuel whereas in a nuclear explosion they are scattered widely and so have a more immediate effect.

Chemical disasters can be caused by human error, equipment failure, improper handling or storage of hazardous materials, natural disasters (such as earthquakes or floods), or deliberate acts of sabotage or terrorism. Any of these factors can lead to releases of toxic substances, fires, explosions, or other hazardous incidents with potentially devastating consequences.

Under nuclear fission with thermal neutrons uranium release an enormous quantity of energy (202,5 MeV per one atom of 235U); the obtained heat is converted in electricity.

And we need electricity and heat. also uranium is an alternative to fossil fuels; nuclear reactors don't contribute to global warming and don't release carbon dioxide.

It can produce low grade plutonium that need be extracted from the used nuclear fuel through used fuel reprocessing. However, power reactors are subject to the international nuclear safeguards to prevent its misuse.

The most commonly used fuel for nuclear reactors is enriched uranium, typically in the form of uranium-235. This fuel undergoes nuclear fission to produce heat energy, which is used to generate electricity. Different types of reactors and fuel cycles may also use other materials like plutonium or thorium.

A nuclear reactor produces electricity through a process called nuclear fission. The reactor uses uranium fuel to generate heat, which then boils water to produce steam. The steam drives turbines that are connected to generators, producing electricity.

No, the RBMK design was evolved in the Soviet Union, and has not been used anywhere except Russia and former Soviet Bloc countries like the Ukraine. Russia has now moved to PWR reactors, but I think some RBMK's are still operating there. Existing ones had some mods made after Chernobyl to improve safety. All the Chernobyl reactors are shutdown permanently. this was a condition of EU assistance.

Neutron absorption, or neutron capture, converts fertile materials, which cannot be used directly for fuel in a nuclear reactor, into fissile or fissionable fuels, which can.

Current nuclear reactors use fission to provide heat. Fission requires one of three kinds of fuel, fissile, fissionable, or fertile. Fissile fuel undergoes fission spontaneously and provides sufficient neutrons in the process to produce a chain reaction, if there is a enough such fuel around, or a critical mass. Fissionable fuel will undergo fission if it is hit hard by a neutron with the proper energy. Fertile material can be converted into fissile or fissionable fuel through neutron capture.

Neutron capture happens when a neutron collides with the nucleus of an atom. becoming part of it. This changes the isotope of the atom, increasing the number by one. Thus n + 232Th -> 233Th. The half life of 232Th is 14 billion years, but he half life of 233Th is a little less than 22 minutes. So the 233Th quickly decays, producing 233Pa. 233Pa has a half life of a little less than 27 days, so it also quickly decays, and it produces 233U. 233U is fissile, so it undergoes fission spontaneously and is a useful fuel for the nuclear reactor. Thus, the neutron capture has converted material that cannot be used directly for fission into something that can.

In a conventional reactor, the neutrons needed are produced by the decay of fissile fuel. There are other kinds of reactors, however, such as an accelerator driven system, in which the neutrons are produced from outside the reactor. This means that a critical mass is not really necessary to produce the reaction. The accelerator driven system, also called an energy amplifier or subcritical reactor, is now in the development stage.

Please bear in mind that this description of things is quite simplistic. Things usually happen this way in a neutron flux, but there are a lot of other outcomes. An atom of 233U is likely to capture another neutron and become 234U, for example. Also, collisions with neutrons cause atoms to decay or divide, and so the half lives do not represent what is actually going on in the reactor; an atom with a 27 day half life is very unlikely to last that long in a neutron flux.

Transport number is a measure of the efficiency of an ion transport process in a solution. It is defined as the ratio of the flux of a particular ion to the total flux of all ions in the solution. Transport number helps to quantify the contribution of individual ions to the overall transport process.

In light water reactors the new fuel has about 4 to 5 percent U-235, which is the fissionable part, the rest being U-238. In some countries mixed oxide fuel is used (MOX) which contains some Plutonium as well as U-235, but the fissionable content is much the same. Heavy water or graphite reactors can use natural uranium, which contains 0.7 percent U-235.

Control rods are a key component in a Pressurized Water Reactor (PWR) that help regulate the nuclear reaction by absorbing neutrons and controlling the rate of fission. They are made of neutron-absorbing materials such as boron or cadmium. Drive mechanisms are used to move the control rods in and out of the reactor core to adjust the reactivity levels of the reactor.