Nuclear Reactors

When we talk about the reactor cooling system, the meaning is usually the system for removing the reactor thermal output and transferring it to the steam raising units. This is obviously the way the reactor power is utilised. There are other cooling systems though, the most important being the emergency cooling system which can remove the reactor after heat, after it has been shutdown. This system can be powered by back up diesel generators if the connection to the grid has been lost. There will also be an emergency cooling system for the secondary containment, should there be a large loss of coolant accident, though this is very unlikely to happen.

Question incomplete. Pu-241 is formed from Pu-240, the longer the fuel is irradiated in the reactor the more of the higher mass Pu isotopes are formed. This is why to produce weapons grade Pu, which must be mostly Pu-239, the fuel has to be irradiated only for a limited period. Pu-241 is fissile, so could be used in a weapon, but I believe the disadvantage is that it fissions spontaneously which can lower the weapons efficiency. I suggest you (a) complete the question, and (b) put it in the Nuclear Weapons category, possibly also Nuclear Physics, rather than Nuclear Energy which I take to be about civil use of nuclear power.

It is called a nuclear meltdown when fuel rods in a nuclear power plant generate so much heat that they start to melt. This can lead to the release of radioactive material and poses a serious threat to both human health and the environment.

Nuclear reactors can be harmful if not managed properly, such as in the case of accidents or leaks. However, when operated safely and within regulatory guidelines, nuclear reactors provide clean energy and help reduce greenhouse gas emissions. Strict safety measures and regulations are in place to minimize risks associated with nuclear power generation.

1. meltdown
2. generation of hydrogen gas when water contacts overheated zirconium alloy on fuel pellets, possible hydrogen explosion (chemical not nuclear)
3. warping of fuel rods
4. warping of control rods making it impossible to move them to regulate the reactor
5. structural failures
6. etc.

About 70% of France's electricity is generated from nuclear power, making it one of the largest users of nuclear energy in the world. France has 56 nuclear reactors in operation across 19 nuclear power plants.

control rods

There are 100 nuclear power reactors operating in USA besides five under construction as of July 2014.

There were no operational nuclear reactors in 1934 as the first functioning nuclear reactor, the Chicago Pile-1, was not built until 1942 as part of the Manhattan Project.

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).

See www.world-nuclear.org for country by country information:

INFORMATION PAPERS
NUCLEAR BASICS
Outline History of Nuclear Energy The Nuclear Debate Glossary
FACTS AND FIGURES
World Nuclear Power Reactors 2008-09 and Uranium Requirements Nuclear share figures, 1998-2008 - May 2009 Uranium production figures, 1998-2008 - June 2009
COUNTRY AND REGIONAL BRIEFINGS
Uranium in Africa Nuclear Power in Argentina Nuclear Power in Armenia Australia's Uranium Nuclear Energy Prospects in Australia Nuclear Power in Belgium Nuclear Power in Brazil Nuclear Power in Bulgaria California's Electricity Nuclear Power in Canada Nuclear Power in Canada Appendix 1: Ontario Energy Policy Nuclear Power in Canada Appendix 2: Alberta Tar Sands Uranium in Canada Uranium in Canada Appendix 1: Brief History of Uranium Mining in Canada Uranium in Central Asia Nuclear Power in China Nuclear Power in China Appendix 1: Government Structure and Ownership China's Nuclear Fuel Cycle Nuclear Power in Czech Republic Nuclear Energy in Denmark Nuclear Power in Finland Nuclear Power in France Nuclear Power in Germany Nuclear Power in Hungary Nuclear Power in India Nuclear Energy in Iran Nuclear Power in Italy Nuclear Power in Japan Uranium and Nuclear Power in Kazakhstan Nuclear Power in Korea Nuclear Power in Lithuania Nuclear Power in Mexico Uranium in Namibia Nuclear Energy Prospects in New Zealand Nuclear Power in the Netherlands Uranium in Niger Nuclear Power in Pakistan Nuclear Power in Romania Nuclear Power in Russia Nuclear Power in Slovakia Nuclear Power in Slovenia Nuclear Power in South Africa Nuclear Power in Spain Nuclear Power in Sweden Nuclear Power in Sweden Appendix 1: Barsebäck Closure Nuclear Power in Switzerland Nuclear Power in Taiwan Nuclear Power in the United Kingdom Nuclear Power in Ukraine Nuclear Power in United Arab Emirates Nuclear Power in the USA Nuclear Power in the USA Appendix 1: US Operating Nuclear Reactors Nuclear Power in the USA Appendix 2 Power Plant Purchases: Nuclear Power in the USA Appendix 3: COL Applications US Nuclear Fuel Cycle US Nuclear Fuel Cycle Appendix 1: US Uranium Mining and Exploration US Nuclear Power Policy Emerging Nuclear Energy Countries

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.