The Operation of a Nuclear Reactor and its Effect on the Environment

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Nuclear reactors are machines designed to produce energy by splitting uranium atoms in a controlled chain reaction. They are most often used to generate electricity, but they also can be used for plutonium production and for scientific experimentation. In the core of a reactor, which may be about 12 to 15 feet in diameter and 12 to 14 feet high, are thousands of the steel or zirconium tubes containing enriched uranium. (Although uranium is now commonly used for fuel, in the future many reactors will be fueled with plutonium.) The uranium in the fuel tubes of the reactor is constantly being bombarded by neutron bullets and undergoing fission.

The amount of energy generated by a reactor has to be carefully controlled. Otherwise the heat produced might melt the reactor core, causing the release of radiation and radioactive elements. Thus the reactor core contains many control rods. These absorb neutrons very easily but are not changed by them. When the rods are withdrawn from the core, the chain reaction is speeded up, because there are more neutrons available to split the uranium atoms. When the control rods are thrust back in, they slow the reaction down, because they absorb neutrons.

The splitting of the uranium atoms produces great amounts of energy, including intense heat. In most reactors, this heat is used to make steam for driving turbines. The turbines then generate electricity or propel ships and submarines. A reactor is constantly cooled by many gallons of water. This water, which has been highly purified, circulates around the reactor core in a closed system. In one kind of reactor, the cooling water itself is changed directly into steam by the heat of the reactor. The steam first drives the turbines, then is condensed back into liquid, and then is recirculated around the reactor core. This kind of reactor is known as a boiling water reactor. A more complicated reactor is the pressurized water reactor. In this kind, the water that circulates around the reactor core is kept under pressure, so that it never boils. The heat it carries away from the reactor goes through a heat exchanger, where the heat is transferred to a second water system. This water turns into steam, drives the turbines, undergoes condensation, and turns into steam again.

In both kinds of reactors, radioactive fission products escape into the reactor cooling water. They get out through the metal pipes and casings of the system. The steel used for the reactor and the pipes is subjected to intensive radiation bombardment, in the form of heat and penetrating gamma rays. This radiation weakens even the highest grades of steel. Some of the radioactive materials escape into the cooling water through tiny holes that develop in the rods; some diffuse through the metal casing.

The reactor cooling water, therefore, is contaminated with radioactive materials. In addition, any impurities already present in the water become radioactive themselves. After this water has become too contaminated, it must be replaced with new, chemically pure water. The old water goes through a filtering process to take out some of the radioactive wastes. Then it is stored for a while in hold-up tanks to allow some of its radioactivity to decay. Later this water is diluted and then released into rivers, lakes, or the ocean.

In this sinister way small quantities of radioactivity are being leaked continuously into the environment from every nuclear reactor in operation all over the country. The radioactive substances include cesium 137, which finds its way into the human muscle system and all living cells: tritium, which also invades the whole body; strontium 90, which works its way into the bones; and iodine 131, which gets into the thyroid gland. Hundreds of other radioactive isotopes are produced in a reactor, and some are probably being released into the environment. It is even possible that some of these radio-isotopes have not yet been identified. And the effects of some of the elements that have been identified are quite unknown. They have half-lives varying from a fraction of a second to millions of years. However, as is true of all radioactive substances, they accumulate in the body and can cause irreversible damage.

In addition to the radioactivity that does so much damage to the environment, the water around a nuclear power plant holds another menace – heat. Whenever steam is used to run turbines, vast amounts of water are necessary to condense the steam back into water after it has been used. Because this substantial supply of cooling water is so essential, nuclear reactors are built beside rivers, lakes, or the ocean. They take their cooling water out of the natural supply and then return it to the environment at a very much higher temperature.

Adding heat to a body of water is called thermal pollution. The heated water has a disturbing effect on aquatic life. It causes green algae in the water to grow too fast and poisonous blue green algae to bloom. When these increased amounts of vegetation die and decompose, they use up oxygen from the water. When the oxygen level falls, the plankton and fish cannot live. The whole life of the water is damaged. In the still water of a lake, thermal pollution is more disastrous than it is in a fast running river or in the ocean, where its effects are more quickly dispersed. But merely raising the temperature of the water can kill fish. Trout, for example, are especially sensitive to changes in water temperature. Also, the heat acts on any wastes that have been poured into the water upstream, converting some of them into toxic poisons.

Task I. Match the words in column A with the words in column B and translate the word combinations.

A

B

a

to split

electricity

b

chain

core

c

to generate

fission

d

enriched

poison

e

reactor

turbines

f

to drive

reaction

g

radioactive

damage

h

irreversible

atoms

i

toxic

uranium

Task II. Fill in the correct word from the list:

to speed ……, to slow ……, to be changed ……, to carry ……, to be subjected ……, to be contaminated ……, to be withdrawn ……, to do damage ……, to be known ……, to be replaced ……     

|away from, into, to, to, with, up, with, from, down, as.

Task III. Answer the following questions:

1. What is the main principle of work of a nuclear reactor?

2. What else can nuclear reactors be used for?

3. What substance will future reactors be fuelled with?

4. In what way is the amount of energy controlled?

5. What types of nuclear reactors do you know?

6. What are the essential principles of action of a boiling water reactor?

7. How does a pressurized water reactor operate?

8. What changes does the reactor cooling water undergo?

9. What radioactive isotopes can leak into the environment?

10. What is their effect on the human body?

11. What half-lives do radioactive isotopes have?

12. What is called thermal pollution?

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