Analysis methods for the determination of possible unseated fuel assemblies in BWRs
Journal article, 2006

This paper describes noise-based methods, the purpose of which is to determine whether the core of a Boiling Water Reactor (BWR) contains unseated fuel assembly(ies) or not. The characteristic feature of an unseated fuel assembly is to render the corresponding fuel channel thermal-hydraulically unstable since some of the coolant bypasses the fuel channel. The induced neutron noise has a strong space-dependence due to the localized character of the perturbation. Several techniques relying on the analysis of the spatial structure of the in-core neutron noise can thus be used to determine whether the induced neutron noise might correspond to unseated fuel assembly(ies). These techniques rely on time-domain and frequency-domain analysis. This paper presents in all cases expected spatial signatures determined from calculations, and compares these theoretical findings to two practical examples, where noise measurements were carried out: a local instability event, and a global oscillation coexisting with a regional oscillation.

Decay Ratio (DR)

Boiling Water Reactor (BWR)


noise measurement

core calculations


neutron noise analysis


Christophe Demaziere

Chalmers, Applied Physics, Nuclear Engineering

International Journal of Nuclear Energy Science and Technology

1741-6361 (ISSN) 1741-637X (eISSN)

Vol. 2 3 167-188

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