Theory of neutron noise induced by source fluctuations in accelerator-driven subcritical reactors

ÐThe space-dependent neutron noise in a source-driven subcritical system is investigated. The noise is induced by thefluctuations of the source (intensity or position). Besides of investigating the linearly exact solutions in a 1-D system the validity of the point kinetic and adiabatic approximations is also investigated. These reactor physical approximations have actually not been defined in a consistent manner before for non-critical systems thus the present study also supplies the theory of such approximations in source-driven subcritical systems. It is found that the applicability of these approximations depends in addition to frequency of the perturbation and system size also on the space-time structure of the perturbation. Depending on whether or not the source can be factorized what regards dependence on space and time (frequency) the domain of applicability of the reactor physics approximations can be either wider or more restricted than in the traditional case. A general trend is however that for a given perturbation type the applicability of reactor kinetic approximations increases with increasing system subcriticality. This is shown through both developing the general theory and also through quantitative evaluation of concrete cases