Medición de reactividades

Abstract

The measurement of reactivities is made by studying the immediate neutronic answer to a perturbation of the critical parameters of a reactor originally at the critical state. The method used is applicable to perturbations whose magnitude is out of the experimental range of Nordheim's relation ( 1 ) , due to the fact that reactivities over 0.170 $ are hardly measurables since the asymptotic period is reached at a high power. Therefore, it is necessary to arrive to criticality working 011 a power scale extremely low, with much noise and uncertain criticality. Another limitation of the method of stable period is its inapplicability to the measurement of negative reactivities. In a critical facility like the one used by us * there are other limitations which oblige to abandon the method of stable period. These limitations are for example the maximal neutrón flux, consistent with the permissible dose and the activation of the fuel elements.In this work, we show how it is possible to measure negative and positive reactivities, with an appreciable accuracy, by means of the study of the immediate neutronic answer.