Accidents meltdown

By the 1970s, nuclear power was in widespread use, in the U S. and abroad, as a source of electricity. As of 2007, nuclear power provided about 19.3% of the electricity generated in the U.S., created by 104 licensed nuclear reactors. Nonetheless, the potential for accidents, meltdowns and other disasters has never been far from the minds of many consumers (after all, for many of us the first image that comes to mind upon hearing the word nuclear is a nuclear bomb). The 1979 Three Mile Island nuclear power plant accident in the U.S. led to the cancellation of scores of nuclear projects across the nation. This trend was later reinforced by the disaster at... 

Of these phenomena, the first three in particular, involve thermal hydraulics beginning with the pre-accident conditions. Items 4 through 7 address the meltdown of the core and its influence on (1) hydrogen production, which affects containment loads, (2) fuel temperatures, which affect in-vessel fission product releases, (3) thermal-... 

L Wooton, R. O. and H. I. Avci, MARCH (Meltdown Accident Response Characteristics) Code Description and User s Manual, BCL, October 1980. 

Tlie advances of modern teclmology have brought about new problems. Perliaps tlie most serious of these is tlie tlireat of a nuclear power plant accident known as a meltdown. In tliis section several of tliis era s most infamous accidents are examined some possible explanations are also offered. 

As described in Chapter 1, the three largest radiological accidents of the last twenty years tire tlie explosion at Chernobyl, the partial core meltdown at Three Mile Island Unit 2, tuid the mishandling of a radioactive source in Brazil. The least publicized, but perhaps tlie most appropriate of tliese accidents, witli respect to waste management, was tlie situation in Brazil. 

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. 

A much more serious nuclear accident occurred at Chernobyl in the USSR on April 26, 1986, when one of the Chernobyl units experienced a full-core meltdown. The Chernobyl accident has been called the worse disaster of the industrial age. An area comprising more than 60,000 square miles in the Ukraine and Belarus was contaminated, and more than 160,000 people were evacuated. However, wind and water have spread the contamination, and many radiation-related illnesses, birth defects, and miscarriages have been attributed to the Chernobyl disaster. 

Nuclear power plants in the United States are supposed to be designed well enough to prevent accidents as serious as the one at Chernobyl. Nevertheless, the Three Mile Island plant in Pennsylvania, an aerial view of which is shown in Figure 22-14Z). experienced a partial meltdown in 1979. This accident was caused by a malfunctioning coolant system. A small amount of radioactivity was released into the environment, but because there was no explosion, the extent of contamination was minimal. 

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 battle over nuclear power waxed hot and heavy for several years, swaying back and forth as incidents unfolded. The publication of the government-sponsored Reactor Safety Study in 1975, which showed that there would be very modest consequences from nearly all reactor accidents, was a positive event. The report concluded that the average number of fatalities from a meltdown would be about 400 and that there might be one meltdown in every 20,000 years of plant operation, or 0.02 deaths per year versus about 25 deaths per year due to air pollution from a coal-burning plant.8 It received little notice outside the scientific community. The movie The China Syndrome (released in 1979), which implied that a reactor meltdown accident would have— not possibly might have—very horrible consequences, was an important negative event. 

Nuclear power plants are designed to prevent accidents such as meltdown by careful control of fuel-rod placement and positioning of control rods made of boron or other materials that have high affinity for neutrons. If the core of the reactor should become overheated, the fuel rods are... 

In the past only two nuclear accidents (Three Mile Island and Chernobyl) were widely reported, while over 100 went unreported. These other accident were not caused by only earthquakes, design errors or terrorist acts, but more recently also by software virus attacks through the Internet. For example, on January 25, 2003 a Slammer worm penetrated the private computer network of Ohio s Davis-Besse nuclear power plant, and stopped its control computer. The only reason a meltdown did not result is because the plant was not in operation. 

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... 

The important accidents involving commercial plants were the Three Mile Island Reactor partial meltdown accident, which did not breach the outer containment but totally ruined the plant, and the Chernobyl meltdown accident, which caused major releases of radioactivity to the atmosphere and global fallout. 

The primary source of radionuclides produced in the fission process and found in the environment is atmospheric testing of nuclear weapons. The public has been exposed to these and other radionuclides for five decades, but there has been a substantial decline in atmospheric testing in the past two decades. Therefore the major source of fission product radionuclides in recent years has been from nuclear accidents. A nuclear reactor meltdown could release a spectrum of radionuclides similar to that of a nuclear bomb explosion, but the ratios of nuclides would greatly differ for the two cases. The reason for the differences in ratios of radionuclides is that during the reactor operation the long-lived radionuclides tend to build up progressively, whereas the... 

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) ... 

Three historical events have been recognized as significant radiological accidents. These events include the meltdown at Chernobyl, the partial meltdown at Three Mile Island, and an incident of radioactive waste mishandling in Brazil. Elaborate on the events that occurred in Brazil. What were the impacts on the public health of the local community ... 

Since the nuclear accidents at the Three Mile Island power plant in the U.S. in 1979, and the near meltdown at Chernobyl, Ukraine in 1986 (cf. Stone 1996 Bradley et al. 1996), the value of uranium... 

A part of the US Nuclear Regulatory Commission s (NRC) severe accident research program was dedicated to hydrogen issues in LWR containment designs under core meltdown conditions. The analysis included the in-vessel and ex-vessel hydrogen generation as well as its mixing and distribution in the containment. 

The Sandia code CONTAIN is a lumped parameter code with mechanistical models for simulating the physical and chemical conditions in the nuclear containment to predict hydrogen and steam concentration distribution as well as the consumption of H2 by respective combustion. Assuming a core meltdown accident and no vessel breach, i.e., no corrosion/concrete interaction, the code has predicted a thermally stratified containment atmosphere with relatively low temperatures in the central and lower regions which would permit steam condensation. Concerning H2 deflagration, CONTAIN predicts respective bums, if sprays are used for steam removal [56],... 

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