On the possible effects contributing to neutron noise variations in KWU-PWR reactor: Modelling with S3K (original) (raw)
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1985
The fundamental features of thermohydraulic fluctuations characterising the subcooled boiling in the PWR core have been investigated with the aim of boiling detection via neutron noise analysis. The relationship between different formulations of the model for thermohydraulic fluctuations and the inportant contributing phenomena has been exanine6 along the time scale of interest. A quasi-adiabatic one-channel coolant nodel has been derived for the description of fluctuations of flow variables. ±he effects of thermal nonequilibriuF feature of the two-phase flow on the ther~nydraulic fluctuations and the relationship between their statistical characteristics and engineering parameters cf the flow have been analysed. KEYIqORDS PWR, subcooled boiling, neutron noise, nonequilibriun~ two-phase flow, therzohy~raulic fluctuations, one-channel n odel.
Neutron noise experiments in the AKR-2 and CROCUS reactors for the European project CORTEX
EPJ Web of Conferences, 2020
the inherent fluctuations in neutron flux recorded by in-core and ex-core instrumentation, from which the anomalies will be differentiated depending on their type, location and characteristics. The method is non-intrusive and does not require any external perturbation of the system. The project will result in a deepened understanding of the physical processes involved. This will allow utilities to detect operational problems at a very early stage, and to take proper actions before such problems have any adverse effect on plant safety and reliability. In this framework, computer methods and models are developed. The purpose of the experimental campaigns at the AKR-2 and CROCUS reactors is to produce high quality noisespecific experimental data for the validation of these neutron noise computational models. The AKR-2 reactor at Technische Universität Dresden (TUD) is a thermal, homogeneous, polyethylene moderated zero-power reactor with an allowed maximum continuous power of 2 W. The CROCUS reactor at the École Polytechnique Fédérale de Lausanne (EPFL) is a twozone, uranium-fueled, and light water-moderated facility. With a maximum power of 100 W, it is a zero-power reactor used for teaching and research purposes, currently with a focus on studies on intrinsic and induced neutron noise [2]-[4]. The first campaigns at both facilities consisted in measurements at reference static states, and with the addition of mechanical perturbations. In the AKR-2 reactor, perturbations were induced by two devices: a rotating absorber and a vibrating absorber, both sets in experimental channels close to the core. In CROCUS, the project benefited from the COLIBRI experimental program: up to 18 periphery fuel rods are oscillated at a maximum of ±2.5 mm around their central position in the Hz range. The present article documents the experimental setups and measurement campaign for each facility and perturbation type.
Annals of Nuclear Energy, 2013
The dependence of the amplitude of the neutron noise in PWRs on the radial correlation length of the noise source, that is the inlet temperature fluctuations, is investigated. The motivation for this work comes from the recent observation that the noise amplitude has increased significantly in certain Spanish PWRs. The reason of this increase has not yet been satisfactorily identified, although there are a few assumptions. One new hypothesis, put forward in this paper, is that a coolant flow with more coherent characteristics, which has actually been observed, could explain the increase of the noise amplitude. A more coherent flow leads to a longer spatial (radial) correlation length of the inlet temperature fluctuations, which in turn, in case the APSD of the temperature noise is unchanged, will lead to the increase of the neutron noise APSD. The mechanism behind this phenomenon is the same as the reason of the failure of the traditional noise based method for the determination of the Moderator Temperature Coefficient (MTC), and is related to the characteristics of the spatially randomly distributed noise sources. In this paper the relationship between the radial correlation length of the inlet temperature fluctuations and the neutron noise amplitude is investigated quantitatively and the increase of the noise amplitude with the increased spatial correlation of the inlet temperature fluctuations is demonstrated.
A Finite Element Method for Neutron Noise Analysis in Hexagonal Reactors
EPJ Web of Conferences, 2021
The early detection of anomalies through the analysis of the neutron noise recorded by incore and ex-core instrumentation gives the possibility to take proper actions before such problems lead to safety concerns or impact plant availability. The study of the neutron fluctuations permits to detect and differentiate anomalies depending on their type and possibly to characterize and localize such anomalies. This method is non-intrusive and does not require any external perturbation of the system. To effectively use the neutron noise for reactor diagnostics it is essential to accurately model the effects of the anomalies on the neutron field. This paper deals with the development and validation of a neutron noise simulator for reactors with different geometries. The neutron noise is obtained by solving the frequency-domain two-group neutron diffusion equation in the first order approximation. In order to solve this partial differential equation a code based on a high order finite elemen...
Annals of Nuclear Energy, 2011
In this study, the neutron noise, i.e. the stationary fluctuations of the neutron flux around its mean value, is calculated in 2-group diffusion theory using the Analytical Nodal Method. A brief description of the calculation of the static flux is also included. The static solution is benchmarked against a reference solution in the case of a homogeneous core. The same calculational scheme for the neutron noise as for the static flux is used. As a dynamical benchmark, the calculated neutron noise for a 2D fully homogeneous reactor is compared with the analytical solution of a centered noise source at different frequencies. The numerical solution is also benchmarked to an off-centered source where the analytical solution is determined using the power reactor approximation, extended to two energy groups. The results of the benchmarks are that the numerical calculations using ANM accurately match the analytical solutions.
Linear reactor kinetics and neutron noise in systems with fluctuating boundaries
Annals of Nuclear Energy, 2000
The general theory of linear reactor kinetics and that of the induced neutron noise is developed for systems with varying size, i.e. in which the position of the boundary fluctuates around a stationary value. The point kinetic and adiabatic approximations are defined by a generalisation of the flux factorisation, and the full solution of the general problem with an arbitrarily fluctuating boundary is given by the Green's function technique. The correctness of the general solution is proven both generally and also by considering the simple case of a 2-D cylindrical reactor with a fluctuating radius, in which case a direct compact solution is possible.