Results 1 - 10 of 49
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[en] Highlights: • Fractional-space neutron point kinetics (F-SNPK) is developed. • F-SNPK has a new term called anomalous diffusion source. • The anomalous diffusion source is a function of fractional geometric buckling. • F-SNPK considers neutron leakage. • The neutron leakage is greater with decreasing anomalous diffusion exponent. - Abstract: The aim of this paper is the mathematical derivation, and numerical analysis of the fractional-space neutron point kinetics (F-SNPK) equations for nuclear reactor dynamics. The classic neutron point kinetics (CNPK) equations are one of the most important models of reduced order in nuclear engineering, that been the subject of countless studies and applications to understand the reactor dynamics and its effects. The F-SNPK derived in this work is an extended model respect to CNPK. The F-SNPK model was derived considering a fractional-space law for the neutron density current where the differential operator is the fractional order (FO), also known as anomalous diffusion exponent. The physical meaning is related with non-Fickian effects (anomalous diffusion), which in F-SNPK gives rise to a new term called in this work anomalous diffusion source that considers neutron leakage, and it depends on the geometric buckling and anomalous diffusion exponent. The numerical analysis shows that the neutron leakage is greater with decreasing anomalous diffusion exponent.
[en] The aim of this Letter is to show that the injection of small damping signals can suffice to regulate the motion of a chaotic system around less complex attractors, such as equilibrium points and periodic orbits. The proposed feedback controller is composed by a high-pass filter and a saturator, so its implementation is quite simple and can be made on the basis of measured signals. The Duffing and the Chua systems are used to illustrate the performance of the controller
[en] This paper describes a comparative study of the thermal behaviour of drilling fluids and the surrounding rock when air-water mixtures and conventional muds are used as drilling fluids in geothermal wells. The computations were performed with two numerical simulators: TEMLOPI/V.2, which is used to compute the transient temperature disturbance when mud is employed, and GEOMIST, which is used when air-water mixtures are employed as drilling fluid. Data from a well from the Las Tres Virgenes Mexican geothermal field are used in this analysis. The results of simulation include temperatures computed during circulation and shut-in, and the latter results are compared with temperatures logged during drilling stoppages. It was found that the thermal disturbance caused by circulation of an air-water mixture has a smaller thermal effect than the thermal disturbance caused by drilling muds
[en] Two different methods to determine the effective thermal conductivity of six Mexican cementing systems used in geothermal well completion were compared in the temperature range from 28 to 200 deg. C. Measurements were taken using the classical line-source method and the Jaeger method. The experimental thermal conductivity uncertainties were 4% and 11.8% for the line source and Jaeger's methods, respectively
[en] A methodology to obtain a mathematically reliable process model is presented and analyzed in this paper. The method is based on the structural and dynamic analysis of the numerical solution of the model. As an example, the thermal-hydraulic dynamic model to describe the behavior of the nuclear reactor is presented, emphasizing the procedure for numerical scrutiny of the results to assure proper model
[en] Highlights: • Bivariate empirical mode decomposition (BEMD) in BWR’s instabilities is studied. • The phase determines out-of-phase oscillations in the BWR instability. • The method based in BEMD does not represent a high computational complexity. • The methodology was validated with Nuclear Power Plants stability benchmarks. • The results show that the method contributes to detect out-of-phase oscillations. - Abstract: In this paper a new method based on the bivariate empirical mode decomposition to estimate the phase of regional (out-of-phase) or global (in-phase) modes associated with instabilities in boiling water reactors (BWR), is explored. The proposed method allows decomposing the analyzed signal (constructed from two different Local Power Range Monitors, LPRMs) in different levels or intrinsic mode functions (IMF). The estimation of the phase between these LPRM signals can be achieved by tracking the modes associated to the instability of the BWR and obtaining the cross-correlation function of their corresponding IMF. This phase determines possible out-of-phase oscillations, which play an important role in the BWR instability. The method is relatively simple to implement and it does not represent a high computational complexity. The methodology was tested with simulated signals and validated with two events reported in the Forsmark and Ringhals stability benchmarks. The results of the cases studied show that the proposed method clearly contributes on the fact to detect possible cases of out-of-phase oscillations
[en] This paper was concerned with a theoretical closure relationships derivation to describe the hydrodynamic interaction in a dilute dispersion of gas bubbles in a continuos liquid phase with bubble radius variation due to expansion effects. The starting point in the present study was the three-dimensional transient averaged transport equations. The closure relationships were formulated as an associated problem for the deviation around averaging values of the local variables. The derivations were based on the concentric cell approach and taking in account compressibility of the gas phase. The closure relationships for the dyad product of velocity spatial deviations, virtual mass and the difference between the intrinsic and interface averages of the pressure on the continuous phase side were developed. In this work a new term, which is a function of the squared radial velocity, into the closure for the dyad product of velocity spatial deviation was founded
[en] A comparison between the HELIOS computer code and a pin cell burnup benchmark is presented in this paper. The benchmark is based on a thorium fuel pin cell moderated with light water. The burn-up dependent eigenvalue and isotopes concentrations obtained with HELIOS were compared with those obtained with state-of-the-art transport codes (MOCUP, INEEL-MOCUP and CASMO4). The pin cell model considers eight azimuthal regions in the moderator zone and two radial regions in the fuel. The analysis with HELIOS was carried out with cross section libraries of 35 and 190 energy groups. The HELIOS results showed that the average absolute difference as a function of burnup were less than 1% δk/k in the eigenvalue and an average absolute difference of around 5% in the isotopes concentration, with respect to CASMO4 code
[en] This paper introduces a wavelet-based method to analyze instability events in a boiling water reactor (BWR) during transient phenomena. The methodology to analyze BWR signals includes the following: (a) the short-time Fourier transform (STFT) analysis, (b) decomposition using the continuous wavelet transform (CWT), and (c) application of multiresolution analysis (MRA) using discrete wavelet transform (DWT). STFT analysis permits the study, in time, of the spectral content of analyzed signals. The CWT provides information about ruptures, discontinuities, and fractal behavior. To detect these important features in the signal, a mother wavelet has to be chosen and applied at several scales to obtain optimum results. MRA allows fast implementation of the DWT. Features like important frequencies, discontinuities, and transients can be detected with analysis at different levels of detail coefficients. The STFT was used to provide a comparison between a classic method and the wavelet-based method. The damping ratio, which is an important stability parameter, was calculated as a function of time. The transient behavior can be detected by analyzing the maximum contained in detail coefficients at different levels in the signal decomposition. This method allows analysis of both stationary signals and highly nonstationary signals in the timescale plane. This methodology has been tested with the benchmark power instability event of Laguna Verde nuclear power plant (NPP) Unit 1, which is a BWR-5 NPP
[en] Highlights: • The empirical mode decomposition (EMD) is applied in this work. • EMD performs signal analysis of non-stationary signals that stem non-linear systems. • EMD may produce oscillations with disparate scales; such issue is known as mode mixing. • “Mode Mixing” may spoil signal decomposition through EMD. • An EMD variant is applied to mitigate mode mixing effects improving signal analysis. - Abstract: In this paper a new method based on the improved complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN), was developed to estimate the Decay Ratio (DR) in boiling water reactors (BWR). The proposed method mitigates the so-called mode mixing phenomenon, a common problem that may appear when neutronic signals are analyzed through the standard empirical decomposition (EMD), a data driven method to decompose non-stationary signals that may stem from non-linear systems. The EMD decomposes the signals of interest in different levels called intrinsic mode functions (IMFs). When applying the EMD to real data, the mode mixing problem often appears, this means that the EMD method has a very high sensitivity towards noise fluctuations that might lead to a biased IMF extraction. In our case, the presence of mode mixing in the IMFs extracted through EMD decomposition of BWR real signals might hinder the estimation of the proposed DR. The methodology was validated with an artificial signal, and was applied to a specific case from the Forsmark stability benchmark.