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Regional Basic Professional Training Course in Korea

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<strong>Regional</strong> <strong>Basic</strong> <strong>Professional</strong> <strong>Tra<strong>in</strong><strong>in</strong>g</strong> <strong>Course</strong> (BPTC) on Nuclear Safety<br />

and 235<br />

U. The composition of fuel changes due to the transformation of nuclides<br />

(transmutation) after nuclear <strong>in</strong>teractions, the ma<strong>in</strong> projectile be<strong>in</strong>g neutrons. New nuclei<br />

are produced which may be unstable and would give other elements after radioactive<br />

decays (α and β). The follow<strong>in</strong>g simplified charts gives an idea of nuclear<br />

transformations. The most important neutron-nucleus <strong>in</strong>teractions, which play a role <strong>in</strong><br />

fuel evolution, are: fission, radioactive capture (n,γ) (represented by a vertical arrow ↓<br />

beta decay (represented as a horizontal arrow →. Only heavy nuclides transformations<br />

are represented, the fission process which produces <strong>in</strong>termediate-mass nuclei is omitted<br />

from this graph. Note that all heavy nuclei are also α emitters. However, this radioactivity<br />

mode is often characterized by long half-lives and could thus be neglected <strong>in</strong> the graphs.<br />

FIG. 1.24. Fissile nuclei are with<strong>in</strong> a bold frame.<br />

The <strong>in</strong>teraction of neutron with 235<br />

U may lead to fission, or to capture, produc<strong>in</strong>g a<br />

non-fissile nuclei 236<br />

U, which gives 237<br />

U after another neutron capture, and so on. This<br />

❙ 42 ❙

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