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Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

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658 CHAPTER 12<br />

Figure 12-4. Activity–time relationship of certain fission products after removal from a reac<strong>to</strong>r that had<br />

been operating at a power level of 1 MW for 1 year. (Reproduced from Radiological <strong>Health</strong> Handbook.<br />

Rev ed. Washing<strong>to</strong>n, DC: US Dept <strong>Health</strong> Education & Welfare; 1970.)<br />

CRITICALITY CONTROL<br />

The occurrence of an accidental criticality depends on the following fac<strong>to</strong>rs:<br />

1. Quantity of fissile material.<br />

2. Geometry of the fissile assembly.<br />

3. Presence or absence of a modera<strong>to</strong>r.<br />

4. Presence or absence of a neutron reflec<strong>to</strong>r.<br />

5. Presence or absence of a strong neutron absorber (poison).<br />

6. Concentration of fissile material, if the fissile material is in solution.<br />

7. Interaction between two or more assemblies or arrays of fissile materials, each<br />

one of which is subcritical by itself. Consideration of this possibility is important<br />

in the transport and s<strong>to</strong>rage of fissile materials.

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