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Published February 1, 2023 | Version v1
Journal article Open

On the simulation of neutron noise induced by vibrations of fuel pins in a fuel assembly

Description

Vibrations of fuel assemblies are an important issue in the safe operation of nuclear reactors, because they can
challenge the integrity of the fuel with potential for radioactive releases. Reactor neutron noise-based techniques
for monitoring vibrations are valuable for core diagnostic since they are not intrusive and make use of ordinary
neutron flux measurements from ex-core and in-core detectors. The application of these techniques involves the
solution of inverse problems that require numerical simulations capable of estimating the reactor neutron noise,
given a model of the vibrations. For this purpose, several novel reactor neutron noise solvers have been
developed in the CORTEX project using either Monte Carlo or deterministic methods, such as the discrete ordinates
method, the method of characteristics, and the diffusion approximation. In the current work, these
solvers have been scrutinized by computing the neutron noise induced by vibrations of one or multiple fuel pins
in a simplified UOX fuel assembly benchmark, via proper variations of macroscopic neutron cross sections. The
comparison of these neutron noise solutions obtained from the different methods shows novel insights into the
simulation of neutron noise induced by mechanical vibrations, such as the challenges posed by the Monte Carlo
method, the impact of the angular discretization on the application of the discrete ordinates method, and the
accuracy of the diffusion approximation assessed via the higher-order neutron transport methods.

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Funding

CORTEX – Core monitoring techniques and experimental validation and demonstration 754316
European Commission