The Nuclear Reactor

Types of Nuclear Reactor

The nuclear reactors in use today work in the same basic way and are known as "burners" (possible alternatives are discussed in the Other Forms page). The radioactivity from the uranium generates heat which is transferred to a substance such as water known as the coolant. For safety's sake, the heat is then transferred from this "primary coolant" to a "secondary coolant" which spins turbines to generate electricity. The process of radioactive breakdown is controlled by a substance called a "moderator" and it is generally the different forms of coolant and moderator that classify reactor types. This is summarised in the table below [Storm].

88% of the world's reactors are LWRs as is shown in the chart below.

In the reactors common today, only about 0.6% of the uranium delivered from the mine is actually used (fissioned). So, for every kilogram of natural uranium, 994 grams is left over as depleted uranium and highly radioactive spent fuel [Storm]. (This is shown in the image right where the used fuel is blue and the waste is red. When the fissile content of the fuel in the reactor falls below a given value (about 0.8%), the fuel has to be replaced by fresh fuel.

Experience shows that most reactors last about 40 years. About 45% of all reactors worldwide are older than 25 years, 90% are now operating for more than 15 years [EWG].

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