Nuclear power reactors

The first 30 years of nuclear power have seen considerable developments in reactor design. The early stations in Britain, the Magnox type were improved versions of Calder Hall. The Magnox design has been superseded by the Advanced Gas-cooled Reactor (AGR) which, with higher steam temperature and pressure, operates at much higher efficiency.

Parallel development of water-cooled reactors, mainly in the United States, produced the Pressurized Water Reactor (PWR). Much research and development has gone into the fast reactor, which can use uranium far more effectively. A commercial demonstration fast reactor, featuring a common European design, is expected to be built by the turn of the century.

In electrical power production, there is no fundamental difference between fossil fuel and nuclear systems. Heat generated from splitting atoms or burning coal, oil or gas is used to boil water, make steam, drive turbines and generate electricity. This book is basically concentrated on the nuclear power reactor

The reactors considered here are the pressurized-water reactor, the boiling water reactor, the heavy water reactor and the gas-cooled reactor. All the types considered are thermal reactors, that is, the neutrons are moderated to make use of the higher fission cross-sections at low neutron energy.

The predominant commercial reactor is the light-water reactor (LWR). The light-water reactor is found in two types, the pressurized water reactor (PWR) and the boiling water reactor (BWR). These reactors use ordinary water as the moderator and coolant. Natural uranium cannot be used as the fuel in a LWR. All the fuel is, indeed, uranium. But the concentration of the fissile U235 has to be increased from its natural 0.7 % to almost 3 % in order for such a reactor to operate. The 24 life-time uranium requirement of a LWR is 4000 to 6000 tons of natural U3O8.

Schematic Pressurized -Water Reactor

The primary reactor system is enclosed in a steel-lined concrete containment building. Steam generated within the building flows to the turbine-generator system (outside the building), after which it is condensed and returned to the steam generator.

The primary interest in nuclear reactors arises from their potential for serving as heat sources for plants that generate electrical power. Electricity can be generated in a number of ways, but the conventional method by which it is generated is to use thermal energy (heat), to produce steam, which drives a turbine-generator system. This technique may be thought of as employing two basic systems: a steam supply system, which uses heat from the combustion of fossil fuels or from nuclear reactions to boil water, and an electrical generating system, which uses the resulting steam to produce electricity. In principle, even the sun may serve as the heat source for the steam supply system, but for the near future fossil-fueled boilers and nuclear reactors will be the central components in large electrical generating plants. In recent years, a growing portion of such generating capacity has been provided by nuclear power plants.

The nuclear power plants of this century depend on a particular type of nuclear reaction, fission, for the generation of heat. Fission is the splitting of a heavy nucleus, the center of an atom such as uranium, into two or more principal fragments, as well as lighter pieces, such as neutrons. Neutrons are, in fact, one of the two basic components of nuclei (the other is the proton), and, as noted, they are released during fission, thereby becoming available to induce subsequent fission events. Under suitable conditions, a "chain" reaction of fission events may be sustained.The energy released from the fission reactions provides the heat,part of which is ultimately converted into electricity.

However, dependence on a fission chain reaction does introducesome special aspects to the reactor. The first arises from the fact that anuclear reactor depends on a chain reaction. Maintaining a constantpower level requires that the chain reaction be controlled so that, on theaverage, each fission causes only one subsequent fission. The secondfeature of a nuclear reactor is that the products of reactor operation arehighly radioactive. As a result, reactor design is aimed at limiting theprobability of release of these products.

2. Задайте пять вопросов по содержанию текста.

3. Составьте аннотацию к тексту (2-3 предложения).

4. Составьте реферат текста (10-15 предложений).

5. Выскажите свое мнение по проблемам, изложенным в тексте:

Обозначение проблемы

Анализ различных мнений по проблеме (С одной стороны…, с другой стороны….)

Выводы (ваше отношение и решение проблемы)

Заключение.

Вариант 3

1. Прочитайте и переведите текст: