Neutron monitoring based on the higher order statistics of fission chamber signals
Doktorsavhandling, 2016

The work in this thesis corresponds to the safety aspect of Generation IV nuclear systems. One of the safety aspects concerns the enhancement of the performance of the in-vessel on-line core monitoring with neutron flux measurements. It was concluded earlier that fission chambers are the best candidate to provide in-vessel measurements in sodium cooled fast reactors. This thesis focuses on the performance of signal processing methods in order to unfold the count rate of fission chambers. The main goal is to investigate the possible application of processing methods based on the higher order statistics of the signal in order to provide accurate count rate estimation over a wide range both for stationary and transient signals. The work also consists of the study of self-monitoring capabilities in order to detect fission chamber malfunctions at an early stage. The investigation is based on analytic assessments, on simulation of fission chamber responses and signals, and on experimental application of processing methods. The thesis covers five main studies. The first part presents the theoretical description of fission chamber signals. The second part investigates the performance of the traditionally applied methods (pulse and Campbelling mode) through simulations. It is shown that these methods are not capable to cover the whole count rate range of the chamber. Therefore, the third part studies the possible application of methods based on higher order statistics of the signal through simulations and experiments. It is shown that these methods can provide accurate estimations over a wide count rate range. The fourth part covers the theoretical background of self-monitoring capabilities based on the spectral properties of the signal. Finally, the fifth part presents the implementation of the methods in a real-time neutron monitoring system based on a System on a Chip, which embeds a field-programmable gate array. By the methods elaborated in this thesis, a faster, more effective and more accurate monitoring of the reactor power is possible than with the methods used so far, even when the normal operating state is changing.

Campbelling mode

Filtered Poisson process

High order

Simulation

Neutron flux monitoring

Experiment

Fission chamber

PJ lecture hall, Origo, Kemigården 1, Göteborg
Opponent: Professor Sara Pozzi, Department of Nuclear Engineering and Radiation Sciences, University of Michigan, USA

Författare

Zsolt Elter

Chalmers, Fysik, Subatomär fysik och plasmafysik

Nuclear energy remains the only zero-carbon generating source that we can operate around-the-clock with very high reliability. (...) If our objective is lower carbon emissions, then nuclear should be part of the solution.'' - Lynn Good (CEO of Duke Energy): Solving the Lower-Carbon Puzzle.

Although there are debates about the role of nuclear power in the energy resource mix, it is undoubtedly carbon-free and part of the solution to the sustainability dilemma. The recent R\&D of Generation IV nuclear reactors aims to improve the nuclear technology further by addressing the enhancement of sustainability, economics, safety and reliability, proliferation resistance and physical protection.

One aspect of the safe operation concerns the monitoring of the proper functioning of nuclear reactors. This thesis focuses on the possible enhancements of neutron monitoring. Namely, the goal of this work is to investigate the applicability of detector signal processing methods, which could result in less complex and more reliable measurement systems, and incorporate self-monitoring capabilities in order to detect the possible malfunctions of the monitoring system itself at an early stage.

Neutron detector signals contain a stochastic fluctuation around its mean value, whose interpretation is challenging. It is shown in this thesis that unfolding important information about the reactor power level is possible by investigating the statistical properties (variance-like quantities of a measured sample) of the signal. The accuracy of such methods was investigated and verified through simulations and experimental applications. By the methods elaborated in this thesis, a faster, more effective and more accurate monitoring of the reactor power is possible than with the methods used so far, even when the normal operating state is changing.

Zsolt Elter obtained his MSc degree in Physics at the Budapest University of Technology and Economics in 2011. He was working for one year at the Hungarian Atomic Energy Research Institute on the reactor physics aspects of Gas cooled Fast Reactor systems. He has started his PhD studies in 2012. This thesis contains the work that the author has performed during the last four years, from which 2.5 years were spent at CEA Cadarache (France) in the frame of an agreement between the Swedish Research Council and CEA.

Ämneskategorier

Övrig annan teknik

Signalbehandling

ISBN

978-91-7597-460-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: Ny serie nr 4141

Utgivare

Chalmers tekniska högskola

PJ lecture hall, Origo, Kemigården 1, Göteborg

Opponent: Professor Sara Pozzi, Department of Nuclear Engineering and Radiation Sciences, University of Michigan, USA