Атомные электростанции

Атомные электростанции - современные установки. Они состоят из нескольких основных узлов и большого количества вспомогательных единиц.

В ядерном реакторе в качестве топлива используется уран. В процессе работы высвобождается огромное количество тепла и радиоактивное излучение. Ядерный реактор охлаждается за счет циркуляции воды. Водяное охлаждение циркулирует через систему труб, в которых вода нагревается до температуры 250 ~ 300 ° C. Для предотвращения закипания воды, она поступает в реактор под давлением до 150 атмосфер.

Парогенератор содержит ряд теплообменников, содержащихся в трубах. Вода нагревается в реакторе, затем поступает в систему теплообменных труб. Потоки воды во внешнем цикле испаряются, проходя с внешней стороны этих труб. Произведенный пар подается в турбогенератор.

Кроме того, атомная электростанция содержит обычный турбогенератор, паровой конденсор с циркулирующей водой и распределительный щит.

Атомные электростанции имеют как преимущества, так и недостатки. Реакторы и парогенераторы работают в них беззвучно; атмосфера не загрязняется пылью и дымом. Что касается расхода топлива, это не имеет особого значения, нет никаких проблем транспортировки топлива.

Недостатком электростанций, использующих ядерное топливо, является их излучение. Радиоактивное излучение, возникающее в реакторах опасно для обслуживающего персонала. Таким образом, реакторы и парогенераторы установлены под землей. Они также экранированы толстыми бетонными стенами (до 1,5 м). Весь процесс управления осуществляется при помощи автоматических устройств. Это служит мерой защиты людей от радиоактивного излучения.

SUPPLEMENTARY TEXTS

ATOMIC ENERGY

A man trying to see a single atom is like a man trying to see a single drop of water in the sea while he is flying high above it. He will see the sea made up of a great many drops of water but he certainly will not be able to see a single drop. By the way, there are so many atoms in the drop of water that if one could count one atom a second, day and night, it would take one hundred milliard years. But that is certainly impossible.

Man has, however, learned the secret of the atom. He has learned to split atoms in order to get great quantities of energy. At present, coal is one of the most important fuel and our basic source of energy. It is quite possible that some day coal and other fuel may be replaced by atomic energy. Atomic energy replacing the present sources of energy, the latter will find various new applications.

The nuclear reactor is one of the most reliable "furnaces" producing atomic energy. Being used to produce energy, the reactor produces it in the form of heat. In other words, atoms splitting in the reactor, heat is developed. Gas, water, melted metals, and some other liquids circulating through the reactor carry that heat away. The heat may be carried to pipes of the steam generator containing water. The resulting steam drives a turbine, the turbine in its turn driving an electric generator. So we see that a nuclear power-station is like any other power-station but the familiar coal-burning furnace is replaced by a nuclear one, that is the reactor supplies energy to the turbines. By the way, a ton of uranium (nuclear fuel) can give us as much energy as 2.5 to 3 million tons of coal.

The first industrial nuclear power-station in the world was constructed in Obninsk not far from Moscow in 1954. It is of high capacity and has already been working for many years. One may mention here that the station in question was put into operation two years earlier than the British one and three and a half years earlier than the American nuclear power-stations.

A number of nuclear power-stations have been put into operation since 1954. The Beloyarskaya nuclear power-station named after academician Kurchatov may serve as an example of the peaceful use of atomic energy in the USSR.

Soviet scientists and engineers achieved a nuclear superheating of steam directly in the reactor itself before steam is carried into the turbine. It is certainly an important contribution to nuclear engineering achieved for the first time in the world.

We might mention here another important achievement, that is, the first nuclear installation where thermal energy generated in the reactor is transformed directly into electrical energy.

Speaking of the peaceful use of atomic energy it is also necessary to mention our nuclear ice-breakers. "Lenin" is the world's first ice-breaker with a nuclear installation. Its machine installation is of a steam turbine type, the steam being produced by three reactors and six steam generators. This ice-breaker was followed by many others.

The importance of atomic energy will grow still more when fast neutron reactors are used on a large scale. These reactors can produce much more secondary nuclear fuel than the fuel they consume.

Chernobyl Accident

The accident which was of global concern was the accident in Ukraine in the Chernobyl power plant located in Polesye on the River Pripyat.

On 26 April, 1986, Unit 4 of the Chernobyl nuclear plant suffered a major accident. The Chernobyl 4 reactor was a graphite-moderated, light water-cooled system. The installed electrical generating capacity was 1 GW. The accident followed some engineering tests of a generator.

During the tests, basic operating safety rules were being violated. Most control rods were withdrawn from the core and the safety systems were switched off. Two explosions and a fire that followed them damaged the reactor and the containment building. The graphite started to burn. Explosive energy was released, which resulted in the 1000 ton cover plate of the reactor being lifted up.

A prolonged release of large quantities of radioactive products transported by the cloud from Chernobyl was detected not only in northern and southern Europe but also in Canada, Japan, and the US.

The major part of the release took place over the period of about ten days. There were two peaks in release rate (26th April and 5th May). Later on, the release continued for many weeks at a lower rate before the destroyed reactor was finally sealed, which took place some five months later.

Initially the cloud of radioactive material was carried over the Baltic Sea into Scandinavia. After a few days the wind direction rotated clockwise and the cloud travelled eastwards across the USSR and southwards to Turkey.

The total mass of the radioactive particles released in the accident was about 6000-8000 Kg. More than half of it was deposited near the plant but the rest travelled thousands of kilometres (see Fig, 26).

There is no doubt that the nuclear plant accidents offer a number of lessons to be learnt.

At present, over 200 nuclear power reactors for commercial electricity production operate in Europe,

The accident at the Chernobyl nuclear plant has shown that large-scale accidents in nuclear power plants can lead to contam.