Title: Analysis methods for the determination of possible unseated fuel assemblies in BWRs

Authors: Christophe Demaziere

Addresses: Department of Reactor Physics, Chalmers University of Technology, SE-412 96 Goteborg, Sweden

Abstract: 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 localised 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 analyses. 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.

Keywords: neutron noise analysis; boiling water reactors; BWR; stability; decay ratio; space-dependence; core calculations; noise measurement; unseated fuel assembly; global oscillation; in-phase oscillation; nuclear reactors; nuclear energy; nuclear power; nuclear technology.

DOI: 10.1504/IJNEST.2006.010713

International Journal of Nuclear Energy Science and Technology, 2006 Vol.2 No.3, pp.167 - 188

Published online: 20 Aug 2006 *

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