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Accelerator-driven System
A subcritical reactor is a nuclear fission reactor concept that produces fission without achieving criticality. Instead of sustaining a chain reaction, a subcritical reactor uses additional neutrons from an outside source. There are two general classes of such devices. One uses neutrons provided by a nuclear fusion machine, a concept known as a fusion–fission hybrid. The other uses neutrons created through spallation of heavy nuclei by charged particles such as protons accelerated by a particle accelerator, a concept known as an accelerator-driven system (ADS) or accelerator-driven sub-critical reactor. Motivation A subcritical reactor can be used to destroy heavy isotopes contained in the used fuel from a conventional nuclear reactor, while at the same time producing electricity. The long-lived transuranic elements in nuclear waste can in principle be fissioned, releasing energy in the process and leaving behind the fission products which are shorter-lived. This would sho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Fission
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay. Nuclear fission was discovered by chemists Otto Hahn and Fritz Strassmann and physicists Lise Meitner and Otto Robert Frisch. Hahn and Strassmann proved that a fission reaction had taken place on 19 December 1938, and Meitner and her nephew Frisch explained it theoretically in January 1939. Frisch named the process "fission" by analogy with biological fission of living cells. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction. For heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fast Reactor
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV, on average), as opposed to slow thermal neutrons used in thermal-neutron reactors. Such a fast reactor needs no neutron moderator, but requires fuel that is comparatively rich in fissile material. The fast spectrum is key to breeder reactors, which convert highly abundant uranium-238 into fissile plutonium-239, without requiring enrichment. It also leads to high burnup: many transuranic isotopes, such as of americium and curium, accumulate in thermal reactor spent fuel; in fast reactors they undergo fast fission, reducing total nuclear waste. As a strong fast-spectrum neutron source, they can also be used to transmute existing nuclear waste into manageable or non-radioactive isotopes. These characteristics also cause fast reactors to be judged a higher n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scram
A scram or SCRAM is an emergency shutdown of a nuclear reactor effected by immediately terminating the fission reaction. It is also the name that is given to the manually operated kill switch that initiates the shutdown. In commercial reactor operations, this type of shutdown is often referred to as a "scram" at boiling water reactors, a "reactor ''trip''" at pressurized water reactors and "EPIS" at a CANDU reactor. In many cases, a scram is part of the routine shutdown procedure which serves to test the emergency shutdown system. Etymology There is no definitive origin for the term. United States Nuclear Regulatory Commission historian Tom Wellock notes that '' scram'' is English-language slang for leaving quickly and urgently (as in scrambling to get away), and he cites this as the original and most likely accurate basis for the use of ''scram'' in the technical context. Scram is sometimes cited as being an acronym for safety control rod axe man or safety cut rope axe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Mass
In building design, thermal mass is a property of the matter of a building that requires a flow of heat in order for it to change temperature. Not all writers agree on what physical property of matter "thermal mass" describes. Most writers use it as a synonym for heat capacity, the ability of a body to store thermal energy. It is typically referred to by the symbol ''C''th, and its SI unit is J/K or J/°C (which are equivalent). However: * Christoph Reinhart at MIT describes thermal mass as its volume times its volumetric heat capacity. * Randa Ghattas, Franz-Joseph Ulm and Alison Ledwith, also at MIT, write that "It hermal massis dependent on the relationship between the specific heat capacity, density, thickness and conductivity of a material" although they don't provide a unit, describing materials only as "low" or "high" thermal mass. * Chris Reardon equates thermal mass with volumetric heat capacity . The lack of a consistent definition of what property of matter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Critical Mass
In nuclear engineering, critical mass is the minimum mass of the fissile material needed for a sustained nuclear chain reaction in a particular setup. The critical mass of a fissionable material depends upon its nuclear properties (specifically, its nuclear fission cross-section), density, shape, enrichment, purity, temperature, and surroundings. It is an important parameter of a nuclear reactor core or nuclear weapon. The concept is important in nuclear weapon design. Critical size is the minimum size of the fissile material needed for a sustained nuclear chain reaction in a particular setup. If the size of the reactor core is less than a certain minimum, too many fission neutrons escape through its surface and the chain reaction is not sustained. Criticality When a nuclear chain reaction in a mass of fissile material is self-sustaining but not growing, the mass is said to be in a critical state, in which there is no increase or decrease in power, temperature, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decay Heat
Decay heat is the heat released as a result of radioactive decay. This heat is produced as an effect of radiation on materials: the energy of the alpha particle, alpha, Beta particle, beta or gamma radiation is converted into the thermal movement of atoms. Decay heat occurs naturally from decay of long-lived radioisotopes that are primordially present from the Earth's formation. In nuclear reactor engineering, decay heat continues to be generated after the reactor has been shut down (see SCRAM and nuclear chain reactions) and power generation has been suspended. The decay of the short-lived radioisotopes such as iodine-131 created in fission continues at high power for a time after shutdown (nuclear reactor), shut down. The major source of heat production in a newly shut down reactor is due to the beta decay of new radioactive elements recently produced from fission fragments in the fission process. Quantitatively, at the moment of reactor shutdown, decay heat from these radioact ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chernobyl Disaster
On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian Soviet Socialist Republic, Ukrainian SSR, Soviet Union (now Ukraine), exploded. With dozens of direct casualties, it is one of only two nuclear energy accidents rated at the maximum severity on the International Nuclear Event Scale, the other being the 2011 Fukushima nuclear accident. The response involved more than Chernobyl liquidators, 500,000 personnel and cost an estimated 18billion Soviet ruble, rubles (about $84.5billion USD in 2025). It remains the worst nuclear disaster and the List of disasters by cost, most expensive disaster in history, with an estimated cost of US$700 billion. The disaster occurred while running a test to simulate cooling the reactor during an accident in blackout conditions. The operators carried out the test despite an accidental drop in reactor power, and due to a design issue, attempting to shut down the reactor in those conditio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SL-1
Stationary Low-Power Reactor Number One, also known as SL-1, initially the Argonne Low Power Reactor (ALPR), was a United States Army experimental nuclear reactor in the Western United States, western United States at the Idaho National Laboratory#History, National Reactor Testing Station (NRTS) in Idaho about west of Idaho Falls, Idaho, Idaho Falls, now the Idaho National Laboratory. On January 3, 1961, at 9:01 pm MST, an operator fully pulled out the reactor's central control rod, causing the reactor to go from fully shut down to prompt critical. The intense heat from the nuclear reaction expanded the water inside the reactor core, producing extreme water hammer and causing water, steam, reactor components, debris, and fuel to vent from the top of the reactor where the three operators were working. As the water struck the top of the reactor vessel, it propelled the entire reactor vessel to the ceiling of the reactor room where it struck the overhead crane. A supervisor who ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inherent Safety
In the chemical and process industries, a process has inherent safety if it has a low level of danger even if things go wrong. Inherent safety contrasts with other processes where a high degree of hazard is controlled by protective systems. As perfect safety cannot be achieved, common practice is to talk about ''inherently safer design''. “An inherently safer design is one that avoids hazards instead of controlling them, particularly by reducing the amount of hazardous material and the number of hazardous operations in the plant.” Origins The concept of reducing rather than controlling hazards stems from British chemical engineer Trevor Kletz in 1978 paper "What You Don’t Have, Can’t Leak" on lessons from the Flixborough disaster,Kletz, Trevor (1978). “What You Don’t Have, Can’t Leak”. ''Chemistry and Industry'' pp. 287–292. and the expression "inherent safety" from a book that was an expanded version of the article.Kletz, T. A. (1984). ''Cheaper, Safer Plants ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MOX Fuel
Mixed oxide fuel (MOX fuel) is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the light-water reactors that predominate nuclear power generation. For example, a mixture of 7% plutonium and 93% natural uranium reacts similarly, although not identically, to low-enriched uranium fuel (3 to 5% uranium-235). MOX usually consists of two phases, UO2 and PuO2, and/or a single phase solid solution (U,Pu)O2. The content of PuO2 may vary from 1.5 wt.% to 25–30 wt.% depending on the type of nuclear reactor. One attraction of MOX fuel is that it is a way of utilizing surplus weapons-grade plutonium, an alternative to storage of surplus plutonium, which would need to be secured against the risk of theft for use in nuclear weapons. On the other hand, some studies warned that normalizing the global com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plutonium-239
Plutonium-239 ( or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years. Nuclear properties The nuclear properties of plutonium-239, as well as the ability to produce large amounts of nearly pure 239Pu more cheaply than highly enriched weapons-grade uranium-235, led to its use in nuclear weapons and nuclear power plants. The fissioning of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be absorbed by uranium-238 to produce plutonium-239 and other isotopes. Plutonium-239 can also absorb neutrons and fission along with the uranium-235 in a reactor. Of all the common nuclear fuels, 2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. Nuclear bombs have had yields between 10 tons (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). Yields in the low kilotons can devastate cities. A thermonuclear weapon weighing as little as can release energy equal to more than 1.2 megatons of TNT (5.0 PJ). Apart from the blast, effects of nuclear weapons include firestorms, extreme heat and ionizing radiation, radioactive nuclear fallout, an electromagnetic pulse, and a radar blackout. The first nuclear weapons were developed by the Allied Manhattan Project during World War II. Their production continues to require a large scientific and industrial complex, pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
