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Gilberto Espinosa-Paredes,Ricardo I. Cazares-Ramirez,Vishwesh A. Vyawahare,Erick-G. Espinosa-Martinez Korean Nuclear Society 2024 Nuclear Engineering and Technology Vol.56 No.4
The aim of this work is to explore the effect of the double subdiffusion on the stability in BWRs. A BWR novel reduced order model with double subdiffusion effects: reduced order fractional model (DS-F-ROM) to describe the neutron and heat transfer processes was proposed for this study. The double subdiffusion was developed with a fractional-order two-equation model, and with different fractional-orders and relaxation times. The stability analysis was carried out using the root-locus method and change from the s to the W domain and were confirmed using the time-domain evolution of neutron flux for a unit step change in reactivity. The results obtained using the reduced fractional-order model are presented for different anomalous diffusion coefficient values. Results are compared with normal diffusion and P1 equations, which are obtained straightforwardly with DS-ROM when relaxation time tends to zero, and when the anomalous diffusion coefficient tends to one, respectively.
Energy optimization of a Sulfur-Iodine thermochemical nuclear hydrogen production cycle
Juarez-Martinez, L.C.,Espinosa-Paredes, G.,Vazquez-Rodriguez, A.,Romero-Paredes, H. Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.6
The use of nuclear reactors is a large studied possible solution for thermochemical water splitting cycles. Nevertheless, there are several problems that have to be solved. One of them is to increase the efficiency of the cycles. Hence, in this paper, a thermal energy optimization of a Sulfur-Iodine nuclear hydrogen production cycle was performed by means a heuristic method with the aim of minimizing the energy targets of the heat exchanger network at different minimum temperature differences. With this method, four different heat exchanger networks are proposed. A reduction of the energy requirements for cooling ranges between 58.9-59.8% and 52.6-53.3% heating, compared to the reference design with no heat exchanger network. With this reduction, the thermal efficiency of the cycle increased in about 10% in average compared to the reference efficiency. This improves the use of thermal energy of the cycle.
Using Largest Lyapunov Exponent to Confirm the Intrinsic Stability of Boiling Water Reactors
Gavilan-Moreno, Carlos J.,Espinosa-Paredes, Gilberto Korean Nuclear Society 2016 Nuclear Engineering and Technology Vol.48 No.2
The aim of this paper is the study of instability state of boiling water reactors with a method based in largest Lyapunov exponents (LLEs). Detecting the presence of chaos in a dynamical system is an important problem that is solved by measuring the LLE. Lyapunov exponents quantify the exponential divergence of initially close state-space trajectories and estimate the amount of chaos in a system. This method was applied to a set of signals from several nuclear power plant (NPP) reactors under commercial operating conditions that experienced instabilities events, apparently each of a different nature. Laguna Verde and Forsmark NPPs with in-phase instabilities, and Cofrentes NPP with out-of-phases instability. This study presents the results of intrinsic instability in the boiling water reactors of three NPPs. In the analyzed cases the limit cycle was not reached, which implies that the point of equilibrium exerts influence and attraction on system evolution.
On the numerical solution of the point reactor kinetics equations
Suescun-Diaz, D.,Espinosa-Paredes, G. Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.6
The aim of this paper is to explore the 8th-order Adams-Bashforth-Moulton (ABM8) method in the solution of the point reactor kinetics equations. The numerical experiment considers feedback reactivity by Doppler effects, and insertions of reactivity. The Doppler effects is approximated with an adiabatic nuclear reactor that is a typical approximation. The numerical results were compared and discussed with several solution methods. The CATS method was used as a benchmark method. According with the numerical experiments results, the ABM8 method can be considered as one of the main solution method for changes reactivity relatively large.
Suescun-Diaz, Daniel,Espinosa-Paredes, Gilberto,Escobar, Freddy Humberto Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2
The aim of this work considers a second order point reactor kinetics model based on the P1 approximation of transport theory, called in this work as P1 point reactor model. The P1 point reactor model implicitly considers the time derivative of the neutron source which has not been thus considered previously. The inverse method to calculate the reactivity in nuclear reactors -chosen because its high accuracy- Matrix Formulation. The numerical results shown that the Matrix Formulation for the reactivity estimation constitutes a method with insignificant calculation errors.
Fractional Radioactive Decay Law and Bateman equations
C.-A. Cruz-Lopez,G. Espinosa-Paredes 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.1
The aim of this work is to develop the fractional Bateman equations, which can model memory effects insuccessive isotopes transformations. Such memory effects have been previously reported in the alpha decay,which exhibits a non-Markovian behavior. Since there are radioactive decay series with consecutive alphadecays, it is convenient to include the mentioned memory effects, developing the fractional Bateman Equations,which can reproduce the standard ones when the fractional order is equal to one. The proposed fractionalmodel preserves the mathematical shape and the symmetry of the standard equations, being the onlydifference the presence of the Mittag-Leffler function, instead of the exponential one. This last is a veryimportant result, because allows the implementation of the proposed fractional model in burnup and activationcodes in a straightforwardway.Numerical experiments showthat the proposed equations predict highdecay rates for small timevalues, in comparisonwith the standard equations,which have high decay rates forlarge times. This work represents a novelty approach to the theory of successive transformations, and opensthe possibility to study properties of the Bateman equation from a fractional approach
Vyawahare, Vishwesh A.,Datkhile, G.,Kadam, P.,Espinosa-Paredes, G. Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2
The aim of this work is the analysis, design and hardware implementation of the fractional-order point kinetics (FNPK) model along with its closed-loop controller. The stability and closed-loop control of FNPK models are critical issues. The closed-loop stability of the controller-plant structure is established. Further, the designed PI/PD controllers are implemented in real-time on a DSP processor. The simulation and real-time hardware studies confirm that the designed PI/PD controllers result in a damped stable closed-loop response.