Using the Modified One-Group Model of Reactor Kinetics For Negative Perturbations of Reactivity

The modified one-group model of reactor kinetics is considered, in which the effective decay constant of delayed neutron nuclei-precursors is a function of reactivity perturbation in its negative value domain. The dependence of effective decay constant is determined in the perturbation interval -1≤p/ß<0, the marked decrease in λ with an increase of reactivity magnitude is shown, which corresponds to the increase in the average lifetime of nuclei-precursors. The determined dependence, unlike that in the positive perturbation domain, has a clearly pronounced nonlinearity, which makes it possible to satisfactorily approximate it only by a polynomial of degree three. The performed approximation allows the application of the modified one-group model in the indicated perturbation interval with a reasonable level of errors in contrast to the one-group models with the unchangeable decay constants of nuclei-precursors. Using the modified one-group kinetics model permits a reactor period to be calculated with a high accuracy unlike the application of typical one-group models yielding the fundamentally incorrect results at substantial perturbations.

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