There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Recent advances in nuclear power: A review

Applications of ANNs in flow and heat transfer problems in nuclear engineering: A review work

CORE SIM: A multi-purpose neutronic tool for research and education

This chapter deals with neutron fluctuations in nuclear systems. Such neutron fluctuations, or neutron noise, fall into two categories: neutron noise in zero power systems and neutron noise in power reactors. The concepts, the theory, and the methodology of these fluctuations as well as their various applications for extracting information in a nonintrusive way about the system in question are described. A number of specific applications are described, where detection and analysis of zero power and power reactor noise make it possible to extract diagnostic information about the system by determining some parameters of the system during normal operation, or by detecting, identifying, and quantifying developing anomalies at an early stage and determining their severity. This chapter ends with an outline of future developments and actual issues in the field.

Noise Techniques in Nuclear Systems

Classification of two-phase flow regimes via image analysis and a neuro-wavelet approach

This report gives an account of the work performed by the Department of Nuclear Engineering (formerly Reactor Physics), Chalmers, in the frame of a research contract with Ringhals, Vattenfall AB, contract No. 578254-003. The contract constitutes Stage 12 of a long-term co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in Stage 12 has been performed between March 1st, 2007 and May 31st, 2008. In Stage 12 we have worked with four items as follows:

Development of the beam mode core barrel vibration diagnostics;

Investigation of the axial in-core neutron noise by measurements;

Calculation of the conversion factor between core barrel displacement and the relative change in the ex-core detector signal;

Evaluation of detector impacting.

This work was performed at the Department of Nuclear Engineering, Chalmers University of Technology by Imre Pazsit (project leader), Christophe Demaziere, Carl Sunde, Petty Bernitt and Augusto Hernandez-Solis. Contact persons at Ringhals were Tell Andersson (project leader) and Henrik Nylen.

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Final Report on the Research Project Ringhals Diagnostics and Monitoring, Stage 12

Calculation of the eigenfunctions of the two-group neutron diffusion equation and application to modal decomposition of BWR instabilities

The subject of this paper is the calculation of the in-core neutron noise induced by the shell-mode vibrations of the core barrel. The original motivation was to investigate whether an out-of-phase behavior can exist between the in-core and ex-core (ex-vessel) detectors lying at the same azimuthal position. To this end, a two-region two-group diffusion model was used in one dimension. The noise was calculated by representing the vibrations of the core barrel by a model developed earlier to describe control rod vibrations. It was found that such an out-of-phase behavior indeed exists, although only for in-core detector positions close to the core boundary. This behavior is due to the local component of the noise, which is accounted for in a two-group treatment. The finding is in accordance with the experiment whose result prompted the present work. In addition to its effect on the phase, the local component also manifests itself by a large amplitude of the noise around the vibrating core boundary, i.e., in both the core and the reflector. The appearance and the properties of the local component of the neutron noise for core-barrel vibrations is the main finding of this paper. The results suggest that the efficiency of core-barrel vibrations can be enhanced if in addition to the ex-core detectors, the in-core detectors in the outermost fuel assemblies are used.

Calculation of the Neutron Noise Induced by Shell-Mode Core-Barrel Vibrations in a 1-D, Two-Group, Two-Region Slab Reactor Model

The usefulness of wavelet transform and wavelet filtering techniques for the improvement of the estimation of the decay ratio (DR), characterising the stability of BWRs, is discussed. There are two distinct areas investigated. The first concerns the improvement of the quality of the traditionally used auto-correlation function (ACF) for the estimation of the DR, by trend elimination and denoising. The subsequent estimation of the DR itself is made by traditional methods such as the peak-topeak method or curve fitting. The second area is the estimation of the DR by the use of continuous wavelet transform. The possibility of estimating two different DRs in case of dual oscillations, and in particular the finding of the higher DR, is also investigated. It was found that wavelet pre-processing does not always improve the estimation of the ACF of a non-ideal signal, compared to other methods; but for signals containing various trends and data scatter in the ACF, is brings a noticeable improvement. As an extension of the discrete wavelet methods, the continuous wavelet transform appears to be a promising candidate to determine the critical DR even in the case of two oscillations being co existent with different stability properties. The methods investigated or developed here were also tested on measured data from Swedish BWRs.

Carl Sunde

Papers

Classification of two-phase flow regimes via image analysis and a neuro-wavelet approach

Final Report on the Research Project Ringhals Diagnostics and Monitoring, Stage 12

Calculation of the eigenfunctions of the two-group neutron diffusion equation and application to modal decomposition of BWR instabilities

Calculation of the Neutron Noise Induced by Shell-Mode Core-Barrel Vibrations in a 1-D, Two-Group, Two-Region Slab Reactor Model

Wavelet techniques for the determination of the decay ratio in boiling water reactors