Ghostwriting Sample: Nuclear Meltdown
The term nuclear meltdown is a term used to describe the process of melting of the core of a nuclear reactor by accident, implying a total or partial collapse of the core, technically called "core melt accident" or "partial core melt" respectively. The purpose of a nuclear reactor is to initiate and control a continuous nuclear chain reaction in order to generate electrical energy. During this process the reactor core generates heat in a number of ways. This heat is then carried away from the reactor by some cooling system - generally water - which is circulated past the reactor core to absorb the generated heat. This heat can then be used to generate steam.
A meltdown refers to a very serious collapse of a power plant's system and its ability to manage temperatures. What one means by meltdown is that at some point the core isn't covered by water, or any other cooling system used. If the heat generated by the reactor cannot be removed, for some reason, by the cooling system adequately, it might happen that at least one nuclear fuel element goes past its melting point. A meltdown is an extremly critical issue because it can lead to release of radioactive material into the environment. One of the factors that may cause a meltdown is the "Loss-of-Pressure-Control Accident" which may occur in the pressurized water type of reactor using a pressure vessel to maintain pressure in the plant and prevent boiling in the core. The critical point is reached when the pressure of the confined coolant falls below specification without the means to restore it. There is also a mode of nuclear plant failure called "Loss-of-Coolant Accident" or LOCA which may occur when the flow of the coolant system used is reduced, or lost completely, and the plant's Emergncy Core Cooling System (ECCS) fails to operate as designed causing heat to increase the fuel temperature to the meltdown point. Other factors responsible for nuclear meltdown could be an accidental increase of nuclear chain reactions in a fissile material, like enriched uranium or plutonium, also known as 'power excursion' or, in some types of reactors, fire within the reactor core. In order to make such accidents as described above unlikely, contemporary nuclear plants have multiple layers of safety systems which are designed both to make a meltdown unlikely, and, should it occur, to contain it inside the containment structure of the reactor. However, the meltdown will severely damage the reactor itself. The whole structure will possibly be contaminated with highly radioactive material, but a significant radiation release outside the plant or any danger to the public will be contained. One must in this context keep in mind that a complete meltdown would release uranium and dangerous byproducts into the environment posing serious health risks.
The gravity of a nuclear accident is rated using the International Nuclear and Radiological Event Scale (INES) introduced in 1990 by the International Atomic Energy Agency (IAEA). It is a logarithmic scale comparable to the earthquake measurement scale. Each increasing level of INES represents an accident approximately ten times more severe than the previous level. However, in contrast to earthquakes, whose intensities are evaluable quantitatively, a nuclear accident is a man-made disaster whose level of severity has to be interpreted. For this reason, the INES level of an incident cannot be evaluated shortly after the incident, and is therefore of limited assistance as far as disaster-aid activities are concerned. The INES scale has 7 levels above the zero level (no incident level), out of which the levels 1, 2 and 3 are called the incident-levels, and the levels 4,5,6 and 7 are called the accident-levels.
A level 7 accident is a Major Accident causing major release of radioactive material with far-reaching effects on health and environment. Such an accident requires implementation of extended countermeasures. There have been 2 level 7 nuclear accidents to date:
- Chernobyl disaster
During a test procedure on 26 April 1986 at the nuclear plant in Chernobyl, Ukraine, a power output surge led to a strong steam explosion and fire releasing a big chunk of core material into the environment causing spread of radioacrive contamination over much of Western Russia and Europe. Among people exposed to the increased doses of radiation, 56 died within a span of few months and an estimated 4000 cancer deaths have been registered since then. Over 500,000 workers were involved to fight the disaster, and from 1986 to 2000 350,000 people had to be evacuated and resettled. Even 25 years after the catastriphe, substantial levels of Caesium have been detected in some wild plants thousands of kilometers away from Chernobyl, in Southern Bavaria in Germany.
- Fukushima I nuclear accidents
An earthquake of magnitude 9.0 occured on Friday, 11 March 2011 in East Japan with the epicentre of the quake at approx. 72 km east of the Oshika Peninsula of Tohoku, hence known as the Tohoku Earthquake or the Great East Japan Earthquake. This quake triggered tsunami waves of up to 37.9 metres. These natural disasters severly damaged the 6 light water reactors of the Fukushima I Nuclear Power Plant. Although the reactors were automatically shut down after the earthquake, and emergency generators began running the control electronics and water pumps, the entire plant was flooded by tsunami water because a seawall designed to protect the plant from tsunami waves up to 5.7 metres could not withstand the 14 metre wave that arrived 15 minutes after the earthquake. As a result, the generators went dysfunctional and all power for cooling was lost, overheating the reactors and producing explosions in at least 3 of them. Radiation leakages caused a permanent evacuation of residents within a 20 km radius of the nuclear plant.
Besides the two level 7 accidents, a handful of nuclear meltdowns of lesser degrees of severity have occurred since the 1950s, when researchers began building and testing nuclear reactors, the most serious of them being:
- Khystym Disaster
A level 6 accident occured on 29 September 1957 at Mayak, a nuclear fuel reprocessing plant near the town of Khystym in the Soviet Union. A cooling system had failed releasing a radioactive cloud that reached around 350 kilometers from the origin of the accident. An area of more than 800 square kilometers, usually referred to as the East-Ural Radioactive Trace (EURT), suffered a long-term contamination, primarily with caesium-137 and strontium-90.
- Three Mile Island Accident
A level 5 accident began on 28 March 1979 at the Three Mile Island Nuclear Generating Station near Harrisburgh in Philadelphia, USA. There was a core meltdown in one of the reactor units.