The determination of the subcriticality level constitutes an important issue in the assessment of the accelerator-driven system technology. For this purpose, the interpretation of flux measurements requires a lumped-parameter model employed in an inverse fashion. This papers addresses the drawbacks of point kinetics in performing such a task. In particular, the problem of the generation of integral parameters is considered, in connection with the use of a shape function and of a projection weight tailored to the neutron flux detector. Furthermore, the question of the generation of the effective source is analysed, and some proposals to modify the time dependence of such a function to account for the time delay at the flux detector are presented and discussed. 1. Introduction The assessment of the feasibility of subcritical accelerator-driven systems requires the performance of experiments to verify the kinetic response features and the determination of the integral parameters that characterize the physical multiplying structure. Typical experiments involve the measurements of flux signals during source or reactivity-induced transients, either in pulsed or oscillated modes. Several experimental campaigns have been conducted in the past years [1, 2], and new more ambitious and advanced experiments are programmed in the near future. An issue that is particularly important is the monitoring of the subcriticality level of the reactor. It is, therefore, required to establish efficient procedures to interpret flux measurements retrieved from detectors localized in various positions of the structure. This constitutes a basic and challenging inverse problem in reactor physics since the early times of nuclear energy and various approaches have been developed [3–5]. The interpretation of local measurements may be carried out only through suitable physico-mathematical models. The inverse procedure can be easily implemented if a lumped-parameter model, such as classic point kinetics, is adopted. However, usually only localized values of the neutron flux are available from the detectors. Hence, the flux interpretation scheme needs unavoidably to account for spectral and spatial effects. It has been shown [6] by numerical simulations that the point model with integral kinetic parameters may be inadequate when local flux signals are used in a point framework to reconstruct the global system reactivity in an inverse fashion, while it may perform rather well for the analysis of the full power evolution, which is, however, seldom available from the direct experimental
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