Interpretation of Flux Shape Transient with Concepts of "Region of Unity" and "Region of Influence"
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概要
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Concepts of " region of unity " and " region of influence " are introduced to interprete space-time flux behavior in general. The normalized fractional power change <I>U</I> is first defined by <I>U</I>(<I>r</I>, <I>t</I>)≡<I>f</I>/max<I>f</I>, where <I>f</I>≡δψ(<I>r</I>, <I>t</I>)/ψ<SUB>0</SUB>(<I>r</I>) is the fractional power change. Thefactor of unity is then defined by <I>u</I>(<I>t</I>) =min<I>U</I>(<I>r</I>, <I>t</I>). The fractional power change through-out the core is therefore estimated within the limits of [<I>u</I>, 1]. If the flux shape does not change, u is always equal to unity in a reactor core ; u can be a measure of coupling strength or " degree of unity " of the transient flux distribution inside a core. The region of unity is finally defined to be a region in which the normalized fractional power change <I>U</I> is larger than a predetermined number close to 1 (0.8 for example). Within the region of unity, approximations relevent to a point reactor are applicable, and the power change proceeds at the same pace throughout this region. Thus, one detector for each region of unity is sufficient for keeping track of the core power distribution. <BR>The region of influence is similarly defined to be a region in which the normalized fractional power change <I>U</I> is larger than a predetermined number which is close to 0 (0.1 for example). Beyond the region of influence around a point, a change in power taking place at the point is no longer felt to any appreciable extent, and one detector per region of influence is necessary for discerning a disturbance in any part of the core. <BR>Analysis on a model aimed at simplification leads to the conclusion that the factor of unity depends on two parameters-size of the core and that of the inserted dis-turbance. The former element has already been recognized as an essential factor in space dependent kinetics, but now the latter element is shown to be the more important parameter. In most cases, the radii of the regions of unity and of influence are of the same order as the radius of disturbance.
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