Analytical investigation of the properties of the neutron noise induced by vibrating absorber and fuel rods

A. Jonsson; H. N. Tran; V. Dykin; I. Pázsit

doi:10.3139/124.110258

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Article

Analytical investigation of the properties of the neutron noise induced by vibrating absorber and fuel rods

A. Jonsson , H. N. Tran , V. Dykin and I. Pázsit

Published/Copyright: May 18, 2013

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From the journal Kerntechnik Volume 77 Issue 5

Abstract

Analytical solution methods for the neutron noise in a one-dimensional multi-region system in two-group theory, which have so far been based on the adjoint function technique, are extended here to using the forward Green's function technique. The forward Green's functions were calculated analytically for a noise source in a core surrounded by reflector regions at both sides. It is shown that with symbolic computation methods, the forward Green's function can be used for the calculation of the space- and frequency-dependent noise in the first order approximation for arbitrary noise sources which have an analytical representation. The properties of the induced neutron noise were investigated for vibrations of both absorbers and fuel assemblies, with two representations of the noise sources: a point-like source which corresponds to the vibrations of a fuel rod, and a finite width source which corresponds to vibrations of a fuel assembly. The contributions of the components induced by the fluctuations of the various types of macroscopic cross sections in the total noise are also discussed and the information content of the noise in the fast group is explored for the identification of fuel assembly vibrations.

Kurzfassung

Analytische Lösungsmethoden für das Neutronenrauschen in eindimensionalen multi-regionalen Systemen in der Zwei-Gruppentheorie, die bisher auf der Methode der adjungierten Funktionen basierten, werden hier erweitert durch Anwendung vorwärts gerichteter Greenfunktionen. Diese wurden analytisch berechnet für eine Rauschquelle in einem Kern umgeben von Reflektorregionen. Es wird gezeigt, dass mit symbolischen Rechenmethoden, die vorwärts gerichtete Greenfunktion zur Berechnung des orts- und frequenzabhängigen Rauschens in erster Näherung für willkürliche Rauschquellen verwendet werden können. Die Eigenschaften des induzierten Neutronenrauschens wurden untersucht auf Vibrationen sowohl der Absorber wie auch der Brennelementanordnungen mit zwei verschiedenen Darstellungen der Rauschquellen: einer punktförmigen Quelle, die den Vibrationen eines Brennstabs entspricht, und einer Quelle endlicher Weite, die Vibrationen einer Brennelementanordnung entspricht. Die Beiträge der Komponenten, die durch Fluktuationen verschiedener Arten von makroskopischen Wirkungsquerschnitten im Gesamtrauschen induziert wurden werden ebenfalls diskutiert. Der Informationsgehalt des Rauschens in der schnellen Gruppe wird untersucht zur Identifizierung der Vibrationen der Brennelementanordnung.

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Received: 2012-04-16

Published Online: 2013-05-18

Published in Print: 2012-11-01

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https://doi.org/10.3139/124.110258