Shigeaki Tsunoyama

Caorso limit cycle oscillation analysis with three-dimensional transient code TOSDYN-2

The Caorso limit cycle data observed during the stability tests were analyzed by the three-dimensional transient code TOSDYN-2. The Caorso limit cycle oscillation was spatially out of phase, and both the amplitude and the extent of the large amplitude region were large. For this reason, it is very valuable for the qualification of the TOSDYN-2 code. TOSDYN-2 employs a three-dimensional neutronics model and a multichannel-type thermal-hydraulic model. The channel-type grouping is important for qualification analysis. It was determined by considering the test results and the more detailed three-dimensional steady-state code results. The analytical results imply that many unstable channels or unstable regions might exist separately in the core. To account for this, TOSDYN-2 could accurately simulate both the amplitude of the limit cycle oscillation and the spatial power change profile. Thus, TOSDYN-2 applicability to the spatial power change phenomenon has been well verified.

Analysis of Flows around a BWR Spacer by the Two-Fluid Particle Interaction Method

The Moving Particle Semi-implicit (MPS) method, a particle interaction method developed in recent years, is formulated by representing the differential operators in Navier-Stokes equations as the interaction between particles characterized with a kernel function and adopts a mesh-free algorithm. The MPS method is particularly suitable for treating liquid breakup. We extended the MPS method to a two-fluid system, introduced a potential-type surface tension, and developed a kernel function for the interface between liquid and gas to simulate two-phase flows. This extended MPS method, which we call Two-Fluid MPS (TF-MPS) method, has been verified through a number of analyses of two-phase flow experiments. The objectives of this study are to verify the applicability of TF-MPS method to a flow around a BWR spacer and to make up constitutive correlations for macroscopic methods. In this paper, we describe the formulation and the calculation algorithm of TF-MPS method, and present the results of the verification studies.

Development of advanced core noise monitoring system for BWRS

A BWR core noise monitoring system is developed for addressing core anomaly problems in future advanced core operation. In order to monitor in-core status from a limited number of signals, various up-to-date signal processing algorithms are introduced to compensate for a lack of information. These algorithms, such as independent component analysis, factor analysis and model based parameter estimation, are demonstrated to be effective through real plant data analysis to evaluate core and regional stability index, reactivity coefficients and core flow rate. Through these practices, we demonstrate that the core noise monitoring system is an effective general platform for providing a variety of monitoring tools to meet the requirements in future advanced core operation.

Noise source and reactor stability estimation in a boiling water reactor using a multivariate autoregressive model

A method for evaluating reactor stability in boiling water reactors has been developed. The method is based on multivariate autoregressive (M-AR) modeling of steady-state neutron and process noise signals. In this method, two kinds of power spectral densities (PSDs) for the measured neutron signal and the corresponding noise source signal are separately identified by the M-AR modeling. The closed- and open-loop stability parameters are evaluated from these PSDs. The method is applied to actual plant noise data that were measured together with artificial perturbation test data. Stability parameters identified from noise data are compared to those from perturbation test data, and it is shown that both results are in good agreement. In addition to these stability estimations, driving noise sources for the neutron signal are evaluated by the M-AR modeling. Contributions from void, core flow, and pressure noise sources are quantitatively evaluated, and the void noise source is shown to be the most dominant.

Application of autoregressive (AR) technique to BWR stability estimation

Abstract Multivariable autoregressive (A-R) model has been applied in the simulation study of the core stability test of the boiling water nuclear reactor (BWR). The core stability test, adding the external disturbance to power plant, can provide data with such characteristics as a large signal-to-noise ratio in a short testing time, apparent transfer directions. A-R model technique was used for data analysis of Peach Bottom-2 core stability test, and provided the results of the stability margin of each component and global system in the reactor core. In this simulation study, to clarify the effectiveness of A-R model, the process dynamics has been estimated by two methods, the statistical approach using A-R model technique and the transient response method. By comparing both results, it is verified that A-R model is very effective for the stability estimation of the reactor core.