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Fast breeder

From Academic Kids

The fast breeder or fast breeder reactor (FBR) is a type of fast neutron reactor that produces more fissile material than it consumes.

A fast neutron reactor, commonly called simply fast reactor, is a nuclear reactor design that uses no moderator but instead relies on fast neutrons to sustain its chain reaction. Achieving this requires high-grade fuel such as enriched uranium or plutonium, but once this has been provided for the initial startup the reactor produces its own fuel and a surplus that can then be used to start other FBRs, hence the concept of a breeder.

Contents

Technical

FBRs usually use a mixed oxide fuel of up to 20% Plutonium dioxide (PuO2) and at least 80% Uranium dioxide (UO2). The plutonium used can be from reprocessed civil or dismantled nuclear weapons sources. Surrounding the reactor core are tubes containing non-fissile Uranium-238 which, by capturing neutrons from the reaction in the core, is partially converted to fissile Plutonium 239 (as is some of the Uranium in the core), which can then be reprocessed for use as nuclear fuel. Early FBRs used metallic fuel, either highly enriched uranium or plutonium.

Fast reactors typically use liquid metal as the primary coolant, to cool the core and heat the water used to power the electricity generating turbines. Sodium is the normal coolant for large power stations, but lead and NaK have both been used successfully for smaller generating rigs. Some early FBRs used mercury. One advantage of mercury and NaK is that they are both liquids at room temperature, which is convenient for experimental rigs but less important for pilot or full scale power stations.

Water primary coolant cannot be used since it would act as a moderator, and also absorb sufficient neutrons to make breeding impossible with uranium fuel. However a heavy water moderated thermal breeder reactor using thorium to produce Uranium-233 is theoretically possible, see below.

FBR generating plants

FBRs have been built and operated in the USA, the UK, France, the former USSR, India and Japan. One of the plants in the USSR was also previously used for desalination in addition to power generation. As of 2004, a prototype FBR was under construction in China, while another experimental FBR in Germany was built but never operated.

On December 20, 1951, the fast reactor EBR-I (Experimental Breeder Reactor-1) at the Idaho National Engineering and Environmental Laboratory in Idaho Falls, Idaho produced enough electricity to power four light bulbs, and the next day produced enough power to run the entire EBR-I building. This was a milestone in the development of nuclear power reactors.

The next generation experimental breeder was EBR-II (Experimental Breeder Reactor-2), which went into service at the INEEL in 1964 and operated until 1994. It was designed to be an "integral" nuclear plant, equipped to handle fuel recycling onsite. It typically operated at 20 megawatts out of its 62.5 megawatt maximum design power, and provided the bulk of heat and electricity to the surrounding facilities.

Another early FBR was the experimental Dounreay Fast Reactor (DFR) which started operating in 1959 at Dounreay, Scotland, using a sodium-potassium coolant, and producing 14MW of electricity. This was followed by a larger 250MW Prototype Fast Reactor (PFR) on the same site in the 1970s until it was closed down in 1994 as the British government withdrew major financial support for nuclear energy development (DFR having previously been closed).

The world's first commercial liquid-metal-cooled FBR, and the only such plant in the US, was the 200 megawatt Enrico Fermi Atomic Power Plant, commonly known as "Fermi 1." Designed in a joint effort between Dow Chemical and Detroit Edison as part of the Atomic Power Development Association consortium, groundbreaking in Lagoona Beach, Michigan (near Monroe, Michigan) took place in 1956. The plant went into operation in 1963. It shut down on October 5, 1966 due to high temperatures caused by a loose piece of zirconium which was blocking the molten sodium coolant nozzles. Partial melting damage to six subassemblies within the core was eventually found. The zirconium blockage was removed in April of 1968, and the plant was ready to resume operation by May of 1970, but a sodium fire delayed its restart until July. It subsequently ran until August of 1972 when its operating license renewal was denied.

The largest fast breeder reactor to date, Superphénix, entered service in France in 1984, producing 1,200MW of electricity, and used a liquid sodium heat transfer medium. Its predecessor, Phénix is currently the centre of work on destruction of nuclear waste by transmutation. However, Superphénix was shut down in 1997 due to high costs of operation, and various incidents; the liquid sodium cooling system proved largely unwieldy. Superphénix was also the focus point of various groups hostile to nuclear energy.

The Soviet Union constructed a series of fast reactors, the first being mercury cooled and fueled with plutonium metal, and the later plants sodium cooled and fueled with plutonium oxide. BN-350 on the Caspian Sea produced 130MWe plus 80,000 tons of fresh water per day. BN-600 commenced operation in 1980 and produced 600MWe. Plans for larger plants were cancelled by the breakup of the Soviet Union. The BN-600 (Beloyarsk NNP in the town of Zarechny, Sverdlovsk Oblast) is still operational. A second reactor (BN-800) is scheduled to be constructed before 2015 [1] (http://www.bellona.no/en/international/russia/npps/beloyarsk/35835.html).

Dec 8 1995 the 300MWe Monju reactor in Japan was put out of service after a sodium accident.

Future plants

As of 2003 one FBR was planned for India, and another for China using Soviet technology.

South Korea is developing a design for a standardised modular FBR for export, to complement the standardised PWR and CANDU designs they have already developed and built, but has not yet committed to building a prototype.

The FBR program of India includes the concept of using fertile thorium-232 to breed fissile uranium-233. India is also pursuing the thermal breeder reactor again using thorium. A thermal breeder is not possible with purely uranium/plutonium based technology. Thorium fuel is the strategic direction of the power program of India, owing to their large reserves of thorium, but worldwide known reserves of thorium are also some three times those of uranium.

Economics

The breeding of plutonium fuel in FBRs, known as the plutonium economy, was for a time believed to be the future of nuclear power. It remains the strategic direction of the power program of Japan. However cheap supplies of uranium and especially of enriched uranium have made current FBR technology uncompetitive with PWR and other thermal reactor designs. PWR designs remain the most common existing power reactor type and also represent most current proposals for new nuclear power stations.

Proliferation

It is generally agreed that - if designed incorrectly - the FBR poses a greater risk of proliferation of nuclear weapons than the PWR. Unlike a PWR, an FBR can in theory produce weapons grade material. However, to date all known weapons programs have used far more easily built thermal reactors to produce plutonium, and there are some designs such as the SSTAR which avoid proliferation risks by both producing low amounts of plutonium at any given time from the U-238, and by producing three different isotopes of plutonium (Pu-239, Pu-240, and Pu-242) making the plutonium used infeasible for atomic bomb use (dirty bomb use still being a possibility though).

Associated reactor types

One design of fast neutron reactor, specifically designed to address the waste disposal and plutonium issues, was the Integral Fast Reactor (a.k.a. Integral Fast Breeder Reactor, although the original reactor was designed to not breed a net surplus of fissile material) [2] (http://www.nuc.berkeley.edu/designs/ifr/) [3] (http://www.nationalcenter.org/NPA378.html).

To solve the waste disposal problem, the IFR had an on-site electrorefining fuel reprocessing unit that recycled the uranium and all the transuranics (not just plutonium) via electroplating, leaving just short half-life fission products in the waste. Some of these fission products could later be separated for industrial or medical uses and the rest sent to a waste repository (where they would not have to be stored for anywhere near as long as wastes containing long half-life transuranics). It is thought that it would not be possible to divert fuel from this reactor to make bombs, as several of the transuranics spontaneously fission so rapidly that any assembly would melt before it could be completed. The project was canceled in 1994, at the behest of then-Secretary of Energy Hazel O'Leary.

External links

fr:Surgénération nl:Broedreactor ja:高速増殖炉 fi:Hyötöreaktori sv:Bridreaktor

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