Nuclear safety and a nuclear power station

Kategorie: Angličtina (celkem: 879 referátů a seminárek)

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  • Přidal/a: anonymous
  • Datum přidání: 21. ledna 2007
  • Zobrazeno: 1999×

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Nuclear safety and a nuclear power station

Good morning, ladies and gentlemen. First, let me introduce myself. My name is Peter Micenko and I’m student of The Department of Power Engineering at Faculty of Electrical Engineering and Informatics of Technical University in Košice. I’m going to talk today about nuclear power plants and their signification in the world. I would like to divide my presentation into three parts. Firstly, I`ll talk about how we produce electricity and what is its effect on environment. Secondly, I`ll define why are the nuclear power stations needed and finally I`ll describe the safety of the nuclear power plants. If you don’t mind, we’ll leave the questions until the end.
As you know, an electricity is a thing without which we can’t realize, we can’t image our usual day. Everybody of us uses it, but we don’t know how difficult, how hard is to produce it.So, if we want to produce the electricity, we must burn a quantity of coal, gas and oil. The exploiting, the burning of it cause the pollution of the atmosphere, and finaly it cause water pollution.
Unfortunately, the using of technologies often harms the environment. For example, the air pollution is a serious problem in many countries. Its negative results are a lung cancer and other health problems. In addition, the burning of oil, gas and coal gives rise to carbon dioxide in the atmosphere. To realize a harmful activity of it in the Earth atmosphere we can image a greenhouse. The carbon dioxide works like glass and when quantity of it increase in the atmosphere, the Earth becomes warmer, because less heat can escape.
If we want to change the Earth climate, we must stop the greenhouse effect. We should burn less gas, oil and coal in the future. We should build more power stations, which would be not so harmful to the Earth. However, not only carbon dioxide is produced by the thermal power plants. They produce additional chemical compositions, which are harmful to the environment and our health. We can change it by using of power plants that don’t burn the coal, oil and gas. You can see the emission of the thermal power stations in Slovak republic on the Graph No.1. Yes, we must do something! I think it is obvious, that energy consumption will grow in the future, but the raw material basis of the Earth is only for a few decades.
So, what to do? We have two alternatives.

At first, we will burn less of oil, gas and coal, and we will build more untraditional power stations like a wind-power station, a solar-power station or a hydro-power station. The second alternative is to build more nuclear power houses. Both have specific advantages and disadvantages, but we must produce electricity and we must decide. I think, it will be the best to use it together, but I prefer the second variant, because the untraditional solar or wind power plants don’t work effectively. I don’t want to manipulate your mind, but I present you the safety of a nuclear power station, because it’s usually rated as a dangerous.
Do you ask why people are afraid of it? The accident, that happened in the world, especially the one in the Chernobyl Nuclear Power Plant, Ukraine, was a warning for the mankind. This accident mobilized the specialists as well as the public. All nuclear power plants undergone inspections and numerous measures were implemented to improve their reliability.
Unfortunately, also the other nuclear power plants in the former Soviet Union were thought of as alike "dangerous". Understanding the safety of nuclear power plants resides in understanding the construction of nuclear reactors.
But look here carefully, now! The safety of nuclear power plants is one of the few human activities, to which is paid the highest attention. This results from the nature of physical process, which takes place inside the reactor core - nuclear fission. To utilize it, this process has to be always kept under the control. The nuclear fission produces thermal energy that shall be removed. The control of the nuclear fission and preventing the radioactivity release are the basic principles of safety.
As I promised as I will tell you something about safety of the nuclear power plants now. The constructions of nuclear reactors prevent any explosion similar to an atomic bomb. Any uncontrolled release of radioactivity is unacceptable. That's why there are set up measures to prevent such events. Here belong the equipment and systems designed to prevent accidents or mitigate their consequences, to trap radioactivity in special tanks and to prevent its release into the environment
The fundamental principle of safety in operation of nuclear power plants resides in a system of barriers separating the nuclear material from the environment.

The objective of these safety barriers is to prevent any release of radioactivity into the environment and protection against the ionising radiation in all operating modes, so during failures too.
A ceramic form of nuclear fuel assures the first barrier - pellets, which are capable to bind the irradiation products. The second barrier is represented by a sealed metal tube creating an envelope for the nuclear fuel. The next third barrier is created by a closed primary cooling system including the reactor pressure vessel, preventing to the release of primary coolant containing radioactive products into the environment at all design temperatures and pressures. And the last, fourth barrier is created by a hermetic box - containment, which collects the radioactivity leaked out through eventual breaks in the first or second barrier
Hence, there is an additional steel-concrete envelope surrounding the reactor vessel to protect the personnel against direct irradiation.
The individual safety barriers at nuclear power plant are completed by an extensive safety system. The function of safety systems is to shut down the reactor. Next, to stop the chain reaction, assure the residual heat removal from the rector core, keep the integrity of primary circuit and reduce the pressure in the containment to assure the function of the individual safety barriers in all operating conditions, even at maximum designed accident, i.e. primary loop break. Finally, reactor power is controlled by reducing, respectively increasing number of thermal neutrons in the reactor core. In practice it is done by inserting, respectively withdrawing control rods into and from reactor core. Reactor trip means rapid interruption of fission reaction, what is the basic requirement of nuclear safety. Reactor is for this reason equipped with safety system, which comprises control rods, arranged into a few groups. Actuation of this system is realised by interrupting power supply for electric drives, which otherwise maintain control rod groups in their working position, and all control rods fall into reactor core, interrupting fission process within period of 10 to 12 seconds and thus shutting reactor down. That brings me to the end of my presentation. Thank you for your attention and if you have any questions, I`ll be glad to answer them. .

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