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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 />

multiplication factor for each second is 1.0020 compared to 55 <strong>in</strong> the case without<br />

delayed neutrons.<br />

FIG 1.25. A graphical resolution of Nordheim’s equation<br />

When the reactivity excess is close to β the k<strong>in</strong>etic behaviour changes dramatically. In<br />

fact, the reactor becomes critical with only prompt neutrons and we end to a situation,<br />

which is similar to the one without delayed neutrons. Reactivity is sometimes expressed<br />

<strong>in</strong> terms of<br />

β and the unit used then is $; a 1 $ reactivity corresponds to ρ = β.<br />

❙ 52 ❙

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