| 1. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Calculation of the eigenfunctions and corresponding eigenvalues of the two-group diffusion equation in heterogeneous systems
- 2007
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Ingår i: Proc. Joint Int. Topl. Mtg. Mathematics & Computation and Supercomputing in Nuclear Applications (M & C + SNA 2007). - 0894480596
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the extension of an existing code developed at the Department of Nuclear Engineering, Chalmers University of Technology, to the calculation of the higher order eigenfunctions and corresponding eigenvalues of the two-group diffusion equations. More specifically, this code, originally meant for calculating the two-group static neutron flux and its adjoint for any two-dimensional heterogeneous system, is modified in order to calculate any higher mode of both the neutron flux and its adjoint. A one-dimensional two-region system is first considered for benchmark purposes, where the reference solution can be determined semi-analytically. The numerical solution is computed using a modified power iteration method. The agreement between the numerical solution and the reference solution is found to be excellent, both regarding the eigenfunctions and the eigenvalues, and both for the forward and adjoint problems. The modified power iteration method is then applied to the calculation of the different modes of the neutron flux and its adjoint in a two-dimensional heterogeneous representation of the Swedish Forsmark-1 BWR core corresponding to the 1996/1997 channel instability event.
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| 2. |
- Sunde, Carl, 1976, et al.
(författare)
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Final Report on the Research Project Ringhals Diagnostics and Monitoring Stage 11
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Department of NuclearEngineering (formerly Reactor Physics), Chalmers, in the frame of a research contract withRinghals, Vattenfall AB, contract No. 566379-003. The contract constitutes Stage 11 of along-term co-operative research work concerning diagnostics and monitoring of the BWRand PWR units. The work in Stage 11 has been performed between October 1st, 2005 andOctober 1st, 2006. In Stage 11 we have worked with three items as follows:1. Beam mode core barrel vibration diagnostics;2. A literature study of the methodology of the calculation of the conversion factor betweencore barrel displacement and the relative change in the ex-core detector signal;3. Evaluation of detector impacting and local and regional stability in R-1.This work was performed at the Department of Nuclear Engineering, ChalmersUniversity of Technology by Imre Pázsit (project leader), Carl Sunde and ChristopheDemazière. Contact person at Ringhals was Tell Andersson (project leader).
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| 3. |
- Sunde, Carl, 1976, et al.
(författare)
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Investigation of the validity of the point-kinetic approximation and of the break-frequency method in 2-D subcritical systems
- 2007
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Ingår i: Proc. Joint Int. Topl. Mtg. Mathematics & Computation and Supercomputing in Nuclear Applications (M & C + SNA 2007). - 0894480596
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Konferensbidrag (refereegranskat)abstract
- The accuracy and applicability of the break-frequency method for estimating the reactivity in a subcritical 2-D, 2-group reflected system with a distributed source is investigated for two different system sizes. The source is distributed according to the static thermal flux. This method could be useful in power reactor cores during loading conditions for determining the subcriticality. The validity of the point-kinetic approximation in the same systems is also tested. A neutron noise simulator is used to calculate the actual neutron noise induced by fluctuations of the source which is compared with the analytically calculated point-kinetic term. The break-frequency method is used to estimate the reactivity from the neutron noise calculated by the simulator. The conclusion of this work is that the point-kinetic approximation in general is not valid in 2-D, 2-group reflected systems and hence the break-frequency method is not valid either.
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| 4. |
- Sunde, Carl, 1976
(författare)
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Noise diagnostics of Stationary and Non-Stationary Reactor Processes
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the application of noise diagnostics on different problems in the area of reactor physics involving both stationary and non-stationary core processes. Five different problems are treated, divided into three different parts.The first problem treated in the first part is the classification of two-phase flow regimes from neutron radiographic and visible light images with a neuro-wavelet algorithm. The algorithm consists of wavelet pre-processing and of an artificial neural network. The result indicates that the wavelet pre-processing is improving the training of the neural network. Next, detector tubes which are suspected of impacting on nearby fuel-assemblies in a boiling water reactor (BWR) are identified by both a classical spectral method and wavelet-based methods. It was found that there is good agreement between the different methods as well as with visual inspections of detector tube and fuel assembly damage made during the outage at the plant. The third problem addresses the determination of the decay ratio of a BWR from the auto-correlation function (ACF). Here wavelets are used, with some success, both for de-trending and de-nosing of the ACF and also for direct estimation of the decay ratio from the ACF.The second part deals with the analysis of beam-mode and shell-mode core-barrel vibrations in pressurised water reactors (PWRs). The beam-mode vibrations are analysed by using parameters of the vibration peaks, in spectra from ex core detectors. A trend analysis of the peak amplitude shows that the peak amplitude is changing during the fuel cycle. When it comes to the analysis of the shell-mode vibration, 1-D analytical and numerical calculations are performed in order to calculate the neutron noise induced in the core. The two calculations are in agreement and show that a large local noise component is present in the core which could be used to classify the shell-mode vibrations. However, a measurement made in the PWR Ringhals-3 shows that it is impossible to use this local component due to practical reasons, i.e. due to the limitations of the possible detector positions.In the third and final part the validity of the break frequency method for the estimation of the reactivity in a subcritical system is investigated. A numerical calculation of the neutron noise in a 2-D subcritical system corresponding to a power reactor during loading conditions is performed. From the auto power spectral density of the numerically calculated neutron noise, the reactivity is estimated by the break-frequency method. The result indicates that the break-frequency method yields only a rough, although conservative, 64estimate of the reactivity.
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| 5. |
- Sunde, Carl, 1976, et al.
(författare)
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Wavelet techniques for the determination of the decay ratio in boiling water reactors
- 2007
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Ingår i: Kerntechnik. ; 72:1-2, s. 7-19
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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