[en] In this paper, we mix two approaches, the standard methodology and the dynamics reconstruction theory to calculate the stability characteristics of BWR neutronic signals. We review the singular system analysis (SSA) methodology considering the continuous and discrete case, focusing our attention on oscillating signals. We analyze analytic and real neutronic signals, showing that the use of SSA methodology improves the decay ratio calculations

[en] This paper proposes different iterative methods to combined blocks with acceleration techniques for solving liner systems resulting from the neutron diffusion equation dependent on time in hexagonal geometries. Also it is proposed a low cost pre-conditioner for the complete matrix.

[en] Most of the simulation codes of a nuclear power reactor use the multigroup neutron diffusion equation to describe the neutron distribution inside the reactor core. to study the stationary state of a reactor, the reactor criticality is forced in artificial way leading to a generalized different eigenvalue problem, known as the Lambda modes equation, which is solved to obtain the dominant eigenvalues of the reactor and their corresponding eigenfunctions. (Author)

[en] Adaptive methods are system identification methods which are commonly used to analyze nonlinear and nonstationary signals. The use of three of these methods to study the time dependence evolution of the linear stability parameters of a Boiling Water Reactor using neutronic noise signals has been analyzed. Both simulated and real neutronic signals have been considered to perform the analysis

[en] It has been implemented in the attached code a new method of inducing instabilities in NPP with BWR reactor, through disturbances in the moderator density based on the shape and amplitude of the power modes. This method has been tested and verified with the simulations presented here. The results of the simulations under the conditions of the Record 9' of Ringhals-1 nuclear power plant with the coupled codes show that the type of stability depends on the perturbed mode and amplitudes of these disturbances, that is, the stability of the reactor not only depends on the conditions thermohydraulics previous to the swing, but also the disturbance that starts the swing.

[en] The objective of this study is qualify this coupled code against this type of accidents complex three-dimensional that may occur in the reactor core.

[en] The steady-state simplified spherical harmonics equations (SP_N equations) are a higher order approximation to the neutron transport equations than the neutron diffusion equation that also have reasonable computational demands. This work extends these results for the analysis of transients by comparing of two formulations of time-dependent SP_N equations considering different treatments for the time derivatives of the field moments. The first is the full system of equations and the second is a diffusive approximation of these equations that neglects the time derivatives of the odd moments. The spatial discretization of these methodologies is made by using a high order finite element method. For the time discretization, a semi-implicit Euler method is used. Numerical results show that the diffusive formulation for the time-dependent simplified spherical harmonics equations does not present a relevant loss of accuracy while being more computationally efficient than the full system

[en] This paper reviews different techniques to analyze BWR's stability regime from neutronic power signals, and alternative methodologies based on the singular value decomposition (SVD) of a given matrix are proposed. The results obtained from experimental signals using two different constructions of the embedding space of the system have been compared. SVD-based AR models have been studied and the results obtained with these methods have been compared with those of a standard AR model for short neutronic power signals

[en] The paper deals with the calculation of the 3D harmonic lambda modes in a B.W.R. reactor. An algorithm to calculate the harmonic lambda modes corresponding to the steady state two-group 3D neutron-diffusion equation is presented. The algorithm uses subspace iteration method techniques combined with convergence acceleration based on variational principles. The methodology has been tested on two benchmark problems, and applied to obtain the 3D modes of the Cofrentes Nuclear Power Plant. (Author)

[en] The development of a procedure to calibrate the LEACHM and EU-Rotate_N models for simulating water and nitrogen dynamics in cauliflower crops. Calibration was performed using experimental data obtained from measurements in a cauliflower crop sited in Valencia (Spain) region. A procedure based on generalized sensitivity indices for time-dependent outputs was used to determine the most influencing model parameters, in order to reduce the number of parameters to be calibrated and to avoid overparameterization. The most influencing parameters were introduced in an optimization process that uses the experimental measurements of soil water and nitrate content to determine its optimal value and obtain calibrated models.After this analysis, the most important hydraulic parameters found were the coefficients of Campbell’s equation for the LEACHM model and the soil water content at field capacity and drainage coefficient for the EU-Rotate_N model. For the N cycle, the most influencing parameters were those related with the nitrification, humus mineralization rate and residue decomposition for both models. Both calibrated models provided good simulation of soil water content with an error between 5-7%. However, larger errors in soil-nitrate content simulation were found, mainly in the period corresponding to the crop residues incorporation. The prediction of the calibrated models in a different plot gave error values of about 7-9% for soil water content, but for soil nitrate content errors computed were 34% and 58%. After calibration, both models can be used to optimize the farmer water management and fertilization practices in horticultural crops, although in the N case further studies should be performed.