Journal article Open Access

Analysis of the neutron noise induced by fuel assembly vibrations

Andrea Zoia; Amélie Rouchon; Baptiste Gasse; Christophe Demazière; Paolo Vinai

The investigation of neutron noise is key to several applications in nuclear reactor
physics, such as the detection of control rod or assembly vibrations and
the diagnostic of coolant speed and void fraction. In this paper we will elucidate
some aspects of the noise equations in the Fourier domain, for the case of
periodic fuel rod vibrations with frequency ω0 in a small symmetrical system
in which the perturbation is centrally located. We will in particular focus on
the double frequency effect, i.e., the emergence of a noise component at 2ω0
(possibly stronger than the one at the fundamental frequency ω0). Our analysis
will be carried out without truncating the noise source at the first order and in
the context of a non-perturbative approach (i.e., without resorting to linearization).
For this purpose, we will select a simple benchmark configuration that
is amenable to accurate reference solutions obtained by solving the exact timedependent
transport equations. The analysis carried out in this work suggests
that the non-perturbative noise equations are mandatory in order to properly discriminate
the possible emergence of double frequency effects in neutron noise,
especially in view of comparing simulation results to experimental data

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