Semiempirical Formula for Removing the Higher Mode Components of Detector Responses in Subcriticality Measurements

Abstract

There are two main reasons generally suggested for the measurement of the subcriticalities of nuclear fuel systems, power reactors (during initial loading and refueling), fuel storage, and processing facilities: Knowledge of the subcriticality first provides a method to analyze and predict nuclear performance and second is helpful in obtaining the operational and safety aspects of the system. Here, a semiempirical formula for neutron detector responses, to be used to infer reactivities in subcriticality measurements, is presented. A formal theory for the multipoint approximation of the Boltzmann operators makes possible the description of a large variety of nuclear fuel systems by means of an equivalent two-point model that regards a whole system as the coupled system made up of an arbitrary number of nuclear fuels. Because the analytical formula includes the fitting parameter associated with the detector configuration and because the removal of spatial effects or higher mode contaminations in the detector responses is accomplished by devising the detector configurations, the conventional point approximation can be used to infer the reactivity of a far-subcritical system. For an example of an application to existing experiments, the current method is used to analyze subcriticality measurements by using the [sup 252]Cf source-driven neutron noisemore » analysis method.« less