Name: Chu Mnh Tun ID: ILI12118

Explain how a nuclear power plant works and what are the risks of accident areAuthors nameAbstract: This article discuss several fundamental principles of a modern nuclear power plants mechanism. Also this paper will cover the risks of accidents caused by nuclear power plant

1. IntroductionRising expectations best characterize the current prospects of nuclear power in a world that is confronted with a burgeoning demand for energy, higher energy prices, energy supply security concerns and growing environmental pressures. It appears that the inherent economic and environmental benefits of the technology and its excellent performance record over the last twenty years are beginning to tilt the balance of political opinion and public acceptance in favor of nuclear power. Nuclear power is a cost-effective supply-side technology for mitigating climate change and can make a substantial contribution to climate protection. 2. Definition A nuclear power plant is a facility that converts atomic energy into usable power. In a nuclear electric power plant, heat produced by a reactor is generally used to drive a turbine which in turn drives an electric generator. Nuclear power plants are usually considered to be base load stations, since fuel is a small part of the cost of production. The fuel is usually a fissile material (plutonium, uranium, palladium...)3. How do Nuclear power plant workNuclear plants, like plants that burn coal, oil and natural gas, produce electricity by boiling water into steam. This steam then turns turbines to produce electricity. The difference is that nuclear plants do not burn anything. Instead, they use uranium fuel, consisting of solid ceramic pellets, to produce electricity through a process called fission.Nuclear power plants obtain the heat needed to produce steam through a physical process. This process, called fission, entails the splitting of atoms of uranium in a nuclear reactor. The uranium fuel consists of small, hard ceramic pellets that are packaged into long, vertical tubes. Bundles of this fuel are inserted into the reactor.4. Chain reaction detail

A nuclear chain reaction occurs when one single nuclear reaction causes an average of one or more subsequent nuclear reactions, thus leading to the possibility of a self-propagating series of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g. 235U). The nuclear chain reaction releases several million times more energy per reaction than any chemical reaction. The chain reaction is as followed:92 235+ 0 (1 3) 0 + Nuclear power plants operate by precisely controlling the rate at which nuclear reactions occur, and that control is maintained through the use of several redundant layers of safety measures. Moreover, the materials in a nuclear reactor core and the uranium enrichment level make a nuclear explosion impossible, even if all safety measures failed. On the other hand, nuclear weapons are specifically engineered to produce a reaction that is so fast and intense it cannot be controlled after it has started. When properly designed, this uncontrolled reaction can lead to an explosive energy release.

5. Control the chain reactionChain reactions naturally give rise to reaction rates that grow (or shrink) exponentially, whereas a nuclear power reactor needs to be able to hold the reaction rate reasonably constant. To maintain this control, the chain reaction criticality must have a slow enough time-scale to permit intervention by additional effects (e.g., mechanical control rods or thermal expansion). Consequently, all nuclear power reactors (even fast-neutron reactors) rely on delayed neutrons for their criticality. An operating nuclear power reactor fluctuates between being slightly subcritical and slightly delayed-supercritical, but must always remain below prompt-critical.6. Water inside the reactionInside the core of a typical pressurized water reactor or boiling water reactor are nuclear fuel rods equivalent to the diameter of a large gel type ink-pen, each about 4 m long, which are grouped by the hundreds in bundles called "fuel assemblies". Inside each fuel rod, pellets of uranium, or more commonly uranium oxide, are stacked end to end. Also inside the core are control rods, filled with pellets of substances like boron or hafnium or cadmium that readily capture neutrons. When the control rods are lowered into the core, they absorb neutrons, which thus cannot take part in the chain reaction. The heat of the fission reaction is removed by the water, which also acts to moderate the neutron reactions. An alternative form of nuclear fuel would be fissile uranium-233 (U-233) made by the neutron-bombardment of the common thorium-232.

7. TurbinesAll power plants - gas, coal, nuclear, hydro use turbines to drive the generator. In many parts of the world, a plant will have 2 turbines of 1/2 full load, rather than a single unit as is common in the United States.The Turbine has one major function: Convert the energy from the high pressure steam to mechanical energy in the form of shaft rotation so that the generator will turn. This conversion is done in two (2) stages - first in a smaller High Pressure Turbine, and after passing through the moisture separator, then in 2 or more large Low Pressure Turbines.The Turbine Support Systems have the following functions: Control the amount of steam admitted to the turbine, lubricate the generator, keep the steam inside the turbine, protect the turbine in the case of a fault (electrical or mechanical)

8. Risks from any nuclear power plant in Vietnam First of all, disasters such as tsunami, hurricanes, typhoons... can cause dangerous affect to the nuclear reactor and release radioactive materials to the natural environment and human life surrounding that area. In addition, errors caused by human such as errors of operators can cause a disaster, just like in Chernobyl. Another factor that nuclear power plants in Vietnam are not safe is the substandard construction. Also, thieves can steal materials for scrap metals. Last but not least, terrorists can sabotage these power plants, causing leaks of dangerous radioactive elements into the environment. These radioactive elements remain there for a long time.9. Conclusion

Nuclear power plant, is very popular electricity generator in the world but it also cause a lot of terrible disasters. No safety guarantee yet for nuclear power plants in Vietnam because of many reason we mention above. Instead of spending money developing that system we should use that money to invest in other green power plants like wind farms or solar arrays.

References[1]. Wikipedia, Nuclear power plant, Wikipedia Foundation http://en.wikipedia.org/wiki/Nuclear_power_plant#Safety_valves, March 13th 2008, April 22th 2015.[2]. Wikipedia, Nuclear reactor , Wikipedia Foundation http://en.wikipedia.org/wiki/Nuclear_reactor, July 16th 2015.