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Because some of the fission products are neutron poisonsthat as they build up reduce the reactivity. Without the excess reactivity available to overcome this the reactor would shut itself down until the neutron poisons decayed away. This effect was observed in the first production reactor at Hanford (B reactor) when it was first started.

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Q: Why excess reactivity is built in nuclear reactor?
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What chemical reactions are involved in a nuclear reactor?

Chemical reactions are undesirable and are not a feature of the intended reactor behaviour. The water quality in the primary circuit in a PWR or BWR must be well controlled both to avoid chemical reactions with the reactor materials (steel and zircaloy) and to avoid picking up radioactivity as far as possible. What is wanted is a reactor assembly that undergoes as little chemical reaction as possible, in order to prolong the reactor life up to 60 years. In gas cooled (that is carbon dioxide cooled) reactors as built in the UK, corrosion of steel components was a problem in the magnox type and resulted in maximum gas temperature being limited with loss of output. In the AGR all the hot end of the reactor had to be made of stainless steel to avoid corrosion.


What Nuclear material is used in nuclear power plant?

The reactor is usually initially fueled with uranium (for water moderated reactors this is enriched to 3% uranium-235, but other designs may be enriched more or less than that). A few reactors (e.g. reactors in France) are initially fueled with plutonium or a mixture of both uranium and plutonium.After a reactor has operated for a period of time significant levels of transuranic elements have built up in the reactor core, these will also fission and the reactor uses them also as fuel (but unless it is a fast breeder reactor it neither produces nor burns these transuranic fuels very efficiently.Note: a fast breeder reactor contains no moderator to slow neutrons and therefor if fueled with uranium usually requires it to be enriched to 93.5% uranium-235, commonly referred to as weapons grade uranium). The advantage of a fast breeder is that it efficiently converts the normally unusable uranium-238 to plutonium and other transuranics. The plutonium it produces would have far too much plutonium-240 and plutonium-241 in it (due to long fuel burn cycles) for use in weapons and could be used to fuel nuclear reactors of other types. It is also able to efficiently burn all the transuranics it produces, meaning the waste it produces would contain little more than the fission products which all have short halflives; therefor this waste would only have to be stored a few hundred years (not the tens of thousands of years that the wastes of current reactors must be stored, because they still contain unburned plutonium and other transuranics).


How many fuel channels does an advanced gas-cooled reactor have?

I don't believe that the design is fixed at this time. General Atomics and others have been working on designs and one has been built in South Africa, but the companies are still working out the final design. A link is provided to an interesting read on the latest evelopments. The advanced gas-cooled reactors, at least the ones I know, have been built in the UK but not elsewhere. The last ones built were at Heysham Stage 2 and Torness, in Scotland. As far as I can remember the number of channels was 332. I think the first answer may have been on the pebble bed reactor, which is gas cooled and advanced, but not the same as the AGR in UK.


How is using nuclear energy less harmful to the environment than using fossil fuels?

Neither fossil fuels nor nuclear energy can be considered completely clean energy like hydroelectric. The recent nuclear accident in Japan shows that accidents from nuclear power plants can be devastating. The environmental impact of fossil fuels results when we use them in our cars and power plants. The primary pollutant is carbon dioxide, which is responsible for global warming and acid rain. Some question the conclusions of global warming as related to carbon dioxide but it is a fact that burning fossil fuels causes pollution. The principal problem with nuclear energy, under normal operations, is the safe disposal of the spent fuel. As more nuclear power plants are built, this becomes a very large and complex problem, as the spent fuel stays radioactive for many years. Transporting it to a safe location, and insuring that it will never leak radioactivity is difficult. I have attached links on the environmental problems with nuclear energy. A nuclear power plant that is not operating properly with the cooling of the core, runs the risk of radiation leaks, and ultimately if not controlled, a melt-down. You may find extensive discussion on the nuclear power plant accidents in the links I have provided. There is little environmental impact of nuclear power under normal operations of generating electricity. There are occasional releases of low level radioactivity, and the impact of this radiation in the surrounding areas is generally considered minor. The cooling water does become radioactive, but is contained in a closed loop so it is not under normal operating conditions released to the atmosphere. I have tried to find links in the internet that are not biased and present the facts about nuclear energy and fossil fuels. See related links.


What was one of the labs where the atomic bombs were made?

There are 2 main nuclear weapons labs. 1 at Los Alamos, NM (established 1943) and 1 at Livermore, CA (established 1952). Each weapons lab eventually had a nearby branch of Sandia Labs (Los Alamos in Kirkland AFB in Albquequeque, NM and Livermore nearby in Livermore, CA) that designed the non-nuclear parts of the weapons. Once designed and prototypes built and tested production was moved to a factory like PANTEX outside Amarillo, TX. Dozens of facilities across the country supplied these labs and factories with nuclear and non-nuclear components; including Hanford, WA (plutonium metal), Oakridge, TN (enriched uranium metal), Fernald, OH (plutonium and uranium extrusions and machined parts), etc.

Related questions

When and where was last nuclear reactor built?

The last nuclear reactor has not been built yet.


When was the first nuclear reactor built?

The first demonstration nuclear reactor was built in USA by Enrico Fermi in Chicago Stadium. Fermi was an Italian Physicist, best known for his work on Chicago Pile-1 (the first nuclear reactor). on 26 June 1954, in the town of Obninsk, near Moscow in the former USSR, the first nuclear power plant was connected to an electricity grid to provide power to residences and businesses. Nuclear energy had crossed the divide from military uses to civilian applications.


Where was the first South African nuclear reactor built?

Koeburg


What were some of the uses for the first nuclear reactor?

The very first nuclear reactor was Chicago Pile 1. It was built for research and scientific use. The first nuclear reactor outside of a university was built (at Hanford, Washington) primarily to yield plutonium for the atomic bomb destined for Nagasaki, Japan. Nuclear reactors were built primarily for electrical generation beginning in about 1951.


In 1950 where was the first nuclear reactor?

The first nuclear reactor was in former Soviet Union that operated in year 1954 at obninisk.


Who was the inventor of first nuclear plant?

Leo Szilard invented the nuclear reactor in 1933, but did not build it.Enrico Fermi built first nuclear reactor, CP-1 in 1942.Walter Zinn built the first nuclear power plant, EBR-1 in 1951.


What are the release dates for TEDTalks - 2006 Taylor Wilson Yup I Built a Nuclear Fusion Reactor?

TEDTalks - 2006 Taylor Wilson Yup I Built a Nuclear Fusion Reactor was released on: USA: March 2012


Could a reactor be fueled with americium?

The Russians are working on the problem of creating a nuclear reactor fuel out of americium, but they're still working the problem. In addition, they haven't built a reactor that uses americium as a nuclear fuel yet, either.


Does nuclear reactors contain uranium-235?

It really depends on the nuclear reactor, but many are built to work specifically with that isotope.


Under what NFL team's stadium was a nuclear reactor built?

The Chicago Bears, Soldier Field


Who built the first nuclear fission reactor?

Enrico Fermi at the U of Chicago squash court


Who first invented nuclear reactors?

The nuclear reactor was invented in 1933 by Leo Szilard, in London, but he did not try to build one. The first functioning nuclear reactor, CP-1, was designed and built in 1942 by Enrico Fermi, in Chicago, IL.