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Regional Basic Professional Training Course in Korea

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energy of the fuel nuclei.<br />

❙ 9 ❙<br />

1. Nuclear Reactor Pr<strong>in</strong>ciples<br />

A vast amount of <strong>in</strong>formation has been collected regard<strong>in</strong>g the behaviour of stable and<br />

unstable nuclei. This compilation is known as the chart of the nuclides, and a small<br />

portion of it is reproduced <strong>in</strong> Figure 1.2.<br />

FIG. 1.2. The portion of nuclides chart<br />

As shown <strong>in</strong> Figure 1.2, the atomic number Z, is plotted along the y-axis aga<strong>in</strong>st the<br />

number of neutrons, N, along the x-axis. All the nuclides on the same horizontal l<strong>in</strong>e<br />

have the same atomic number, while all the nuclides with the same mass number lie along<br />

a 45° diagonal l<strong>in</strong>e, runn<strong>in</strong>g from the upper left to the lower right. When an element has<br />

various mass numbers for a given number of protons these are called isotopes (differ<strong>in</strong>g<br />

atoms of the same element). Although they may behave similarly <strong>in</strong> chemical reactions,<br />

their nuclear characteristics are very different. A good example of this is found <strong>in</strong> natural<br />

uranium, whose three isotopes are listed below with their abundance <strong>in</strong> parenthesis (an<br />

abundance is the atom percentage of an isotope present <strong>in</strong> natural uranium ore):

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