Journal article Open Access

Understanding the neutron noise induced by fuel assembly vibrations in linear theory

Demazière C; Rouchon A; Zoia A

This paper investigates the effects of stationary vibrations of fuel assemblies in nuclear
reactors. The incentive of this work is to understand the spatial pattern of the induced stationary
fluctuations of the neutron flux. For that purpose, an as simple as possible system was
considered: a one-dimensional three-region system, for which the boundaries between the
regions are vibrating. Using one-group diffusion theory, it is demonstrated that in the
frequency domain and in linear theory the amplitude and phase of the fluctuations in neutron
flux exhibit different patterns, stemming from competing contributions between the pointkinetic
and the space-dependent responses associated to each moving boundary. The results of
this work can be used for interpreting the results of more sophisticated tools used for modelling
the effect of fuel assembly vibrations onto the neutron flux, as well as measurements in reactors
where vibrations of fuel assemblies occur.

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