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Regional Basic Professional Training Course in Korea

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❙ 47 ❙<br />

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

Iod<strong>in</strong>e concentration decreases exponentially (simple decay). As the Xenon’s half-life is<br />

longer than the Iod<strong>in</strong>e’s one, Xenon concentration first <strong>in</strong>creases, reaches a maximum<br />

(the Xenon poison<strong>in</strong>g peak) and then starts to decrease s<strong>in</strong>ce Iod<strong>in</strong>e is not renewed. This<br />

poison<strong>in</strong>g peak <strong>in</strong>creases with the flux level and, <strong>in</strong> some cases; the reactivity effect could<br />

be such that it is not possible to restart the reactor at the time when the peak occurs. Then,<br />

the operator has either to restart before the peak or wait for the Xenon decay.<br />

Now, the same reason<strong>in</strong>g is applied to 149<br />

Sm. The follow<strong>in</strong>g diagram (all data were taken<br />

from JEF-PC-version 2) gives its production and destruction schemes with fission yield<br />

correspond<strong>in</strong>g to thermal fission on 235<br />

U.<br />

The first five beta decays have relatively short periods. Thus, one could simplify the<br />

above scheme, thus keep<strong>in</strong>g only the sequence after 149<br />

Pm for which, the fission yield<br />

will be the summation of all previous yields and neglect<strong>in</strong>g the fission yields of 149<br />

Sm.<br />

149<br />

Pm → 149<br />

Sm<br />

The correspond<strong>in</strong>g equations are then simplified to:

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