Determination Error of Reactor Subcriticality from Sensor Indications

Abstract

The simplest approximations (1D and 2D reactor, one-group diffusion model of neutron transport) are used to study the insensitivity, due to undetermined local perturbations of the multiplication power, of neutron-flux sensor indications to reactor subcriticality. The analysis is based on the conservative assumption that such perturbations can combine with one another in an adverse manner. A 1D model is used to establish the quantitative dependence of the error resulting from this phenomenon in the subcriticality recorded on a determining complex formed by the geometric characteristics and material parameter of the reactor. It is shown for a commercial uranium–graphite reactor that this error can be substantial in physically large reactors.