The Effect of Different Perturbations on the Stability Analysis of Light Water Reactors
Licentiatavhandling, 2010

Neutron noise analysis techniques are studied and developed, with primary use of determining the stability of Boiling Water Reactors (BWRs). In particular, the role of a specific perturbation prevailing in Light Water Reactors, the propagating density perturbation, in the stability of BWRs and on the noise field of LWRs in general, is investigated by considering three topics. In the first topics, we investigate how the neutronic response of the reactor, usually described as a second order system driven by a white noise driving force, is affected by a non-white driving force. This latter arises from the reactivity effect of the propagating density perturbations. The investigation is performed by using spectral and correlation analysis. Propagating perturbations with different velocities are analyzed. We investigate how the accuracy of the determination of the so-called decay ratio (DR) of the system, based on the assumption of white noise driving force, deteriorates with deviations from the white noise character of the driving force. In the second topics, the space dependence of the neutron noise, induced by propagating density perturbations, represented through the perturbation of the absorption, is determined and discussed. A full analytical solution was obtained by the use of the Green's function technique. The solution was analyzed for different frequencies and different system sizes. An interesting new interference effect between the point-kinetic and space-dependent components of the induced noise was discovered and interpreted in physical terms. In the last topics, a non-linear stability analysis of a BWR is performed, using so called Reduced Order Model (ROM) techniques. A ROM is usually constructed by reducing the full set of 3D space-time dependent neutron-kinetics, thermal-hydraulics and heat transfer equations to time-dependent ones, by considering space dependence in a lumped parameter model (one or two discrete channels). The main novelty of our work is to treat the space dependence by four heated channels. This extension makes it possible to account for the effect of three neutronic modes: fundamental, first and second azimuthal ones. The Forsmark-1 instability event in 1996/1997 was chosen to be investigated by the ROM developed in this work. The reactor response was determined for various operational points to identify the stable/unstable reactor behavior. The suitability of using the DR as the stability parameter in case of non-linear oscillations is also being investigated.

BWR and PWR stability

stability indicators

propagating density perturbation

autocorrelation function

density wave oscillations

decay ratio

non-white driving force

damped harmonic oscillator

reduced order models

Green's function technique

Opponent: Vasily Arzhanov


Victor Dykin

Chalmers, Teknisk fysik, Nukleär teknik

Investigation of the space-dependent noise induced by propagating perturbations

Annals of Nuclear Energy,; Vol. 37(2010)p. 1329-1340

Artikel i vetenskaplig tidskrift

Remark on the role of the driving force in BWR instability

Annals of Nuclear Energy,; Vol. 36(2009)p. 1544-1552

Artikel i vetenskaplig tidskrift


Subatomär fysik

Övrig annan teknik

Annan fysik

CTH-NT - Chalmers University of Technology, Nuclear Engineering: 235




Opponent: Vasily Arzhanov

Mer information

Senast uppdaterat