Nuclear reactor, core meltdown

Nuclear reactor core meltdown would cause loss of power, and possibly radiation exposure. Surface operations must abort mission and evacuate. If abort is unsuccessful or unavailable at the time, the crew could be lost All surface equipment is lost No environmental Impact on Earth. 

FTA is a top-down, deductive analytical method. In FTA, initiating primary events, such as component failures, human errors, and external events are traced through Boolean logic gates to an undesired top event, such as an aircraft crash or nuclear reactor core meltdown. 

The most serious accident tliat Ciui occur in a nuclear plant is a reactor core meltdown. In a core meltdown, the enclosed gases physically melt through tlie reactor vessel, and once contacting with cooler liquids or vapors either in a cooling jacket or in the outer enviromnent, cause a physical e. plosion to occur. However, tlie hazard caused by the e. plosion itself is minimal and more localized compared with the release of radioactive material that accompanies such an accident. 

Even if terrorists succeeded in detonating an explosive at a reactor site, the health consequences would be limited. The reactor accident at the Three Mile Island, Pennsylvania nuclear power plant caused a small release of radiation, insufficient to cause any radiation injuries. Bypassing several safety systems caused the Chernobyl reactor incident, involving two explosions, fires and reactor core meltdown. This accident caused the following early phase health effects (1) ... 

Maschek, W., Munz, C.D., Meyer, L., 1992. Investigation of sloshing motions in pools related to recriticalities in liquid-metal fast breeder reactor core meltdown accidents. Nuclear Technology 98, 27. 

CHINA SYNDROME. A term referring to a catastrophic accident in which a nuclear reactor core melts through the containment of a nuclear power plant and metaphorically burns its way downward through the Earth from the United States to China. American physicist Roger S. Boyd claimed to have coined the phrase in the early 1960s while he was working for the U.S. Atomic Energy Commission (AEC). See also MELTDOWN NUCLEAR PILE. 

Besides the aluminum industry, the nuclear power industry has been interested in molten aluminum-water explosions due to the presence of aluminum metal in some boding water reactors. Certain accident scenarios lead to a meltdown of the reactor core with concomitant contact of molten aluminum and water. 

The anthropogenic radionuclides of most concern are those produced as fission products from nuclear weapons and nuclear reactors. The most devastating release from the latter source to date resulted from the April 26, 1986, explosion, partial meltdown of the reactor core, and breach of confinement structures by a power reactor at Chernobyl in the Ukraine. This disaster released 5 x 107 Ci of radionuclides from the site, which contaminated large areas of Soviet Ukraine and Byelorussia, as well as areas of Scandinavia, Italy, France, Poland, Turkey, and Greece. Radioactive fission products that are the same or similar to elements involved in life processes can be particularly hazardous. One of these is radioactive iodine, which tends to accumulate in the thyroid gland, which may develop cancer or otherwise be damaged as a result. Radioactive cesium exists as the Cs+ ion and is similar to sodium and potassium in its physiological behavior. Radioactive strontium forms the Sr2+ ion and substitutes for Ca2+, especially in bone. 

Gas explosion in transit caused 100 deaths and 150 injuries One of two reactors lost its coolant, which caused overheating and partial meltdown of its uranium core. Some radioactive water and gases were released. This was the worst nuclear-reactor accident in U.S. history... 

Background. Natural convection driven by internal heat sources is of interest in geophysics, and the heat transfer associated with such motion is important in the design of tanks in which fermentation or other chemical reactions occur and in the safety analysis of nuclear reactors where a core meltdown is postulated. The last of these applications has led to the intensive study of internally generating horizontal fluid layers. 

The partial meltdown of the reactor core at Three Mile Island nuclear power plant was mainly due to human error (Heppenheimer, 2002). On March 28, 1979, maintenance workers were cleaning sludge from a small pipe when they inadvertently blocked the flow of cooling water. Heat in the core flashed some water into steam and the resulting pressure surge popped a relief valve. Emergency pumps started up to restore water flow, but two valves to the reactor core had been left closed. The water poured, instead, out of the relief valve. Unaware of the open valve, and... 

What is a meltdown, and how can it occur Most nuclear reactors use water as the cooling liquid. Is there any danger of a steam explosion if the reactor core becomes overheated ... 

Result. Core meltdown and considerable release of radiation to containment. A small amount was released to the environment. Reactor written off—operation of TMI-1 suspended. Clean-up and investigations have cost billions of dollars. Since then, there has been extensive reappraisal of safety requirements and no further ordering of nuclear plant by utilities in the USA. Uncertainty of situation and media reaction led to large public concern. 

In a core meltdown of a nuclear reactor, the failure of cooling would allow temperatures to rise above the melting point of the metal rods containing the uranium fuel (about 1205°C). In the worst scenario, the resulting mass of highly radioactive molten metal would melt through the steel and concrete of the containment vessel beneath it. 

Certainly the most catastrophic nuclear accident occurred on April 26, 1986, at the Chernobyl unit 4 reactor near Kiev, Ukraine. The accident resulted in a core meltdown, explosion, and fire. 

Although nuclear power reactors really do have a good safety record, the distrust and fear associated with radiation make most people sensitive to safety issues and accidents. The most serious accident to occur in the United States happened in 1979 at the Three Mile Island Plant in Pennsylvania. A combination of operator error and equipment failure caused a loss of reactor core coolant. The loss of coolant led to a partial meltdown and the release of a small amount of radioactive gas. There was no loss of life or injury to plant personnel or the general population. 

The melting down of the reactor core does not only affect the nuclear fuel, but also the core internals, i. e. the core support structures, control rods, BWR fuel assembly shrouds etc. (see Chapters 1 and 2). At the very high temperatures which are experienced during the meltdown process, radionuclides as well as non-radioac-... 

The authors of WASH-1400 concluded that the risk of core meltdown was 1 in 20,000 per reactor per year a risk level that was considered to be acceptably small. Around the same time the report was issued, the largest nuclear plant in the United States, in Browns Ferry, Alabama, was set on fire and temporarily put out of commission by a worker using a candle to check for air leaks. Core meltdown was narrowly averted. Needless to say, such an event had not been considered in WASH-1400. 

One particularly topical application may be its use as a chemical and thermal safety barrier since, when placed beneath the core of a nuclear reactor it would serve as both a chemical and thermal shroud in the event of a meltdown (Birkby and Stevens, 1996). 

The second problem with nuclear power is the potential for an accident. Many people wrongly fear that a nuclear power plant might detonate in a nuclear explosion this is impossible. As we saw earlier, a nuclear explosion requires the deliberate compression of a critical mass of highly enriched uranium-235 or plutonium. The uranium used in nuclear power plants is only slightly enriched (3% U-235 for nuclear power versus 90% U-235 for nuclear weapons), and there is no mechanism for compressing the uranium. However, other kinds of accidents, the most dangerous of which is meltdown of the reactor core, are possible. 

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