In the last years KWU-PWR plants have shown an increase in the neutron noise normalized root mean... more In the last years KWU-PWR plants have shown an increase in the neutron noise normalized root mean square. The frequency region of interest is below 1 Hz, so that thermohydraulic fluctuations seem to be one of the main reasons behind. In order to advance in understanding this phenomenon, the code S3K has been used to simulate temperature, flow and combined fluctuations at the core inlet. The S3K model used corresponds to Trillo Nuclear Power Plant which has a Flow Distribution Device, whose effect on the neutron noise levels has also been investigated. The results are compared with an analytical model and real plant data.
Journal of Nuclear Engineering and Radiation Science, Feb 29, 2016
The low frequency noise is a phenomenon observed in some PWR reactors causing an influence on the... more The low frequency noise is a phenomenon observed in some PWR reactors causing an influence on the normal operational behavior of the power plant. Fluctuations in the neutron flux density, in the low frequency range up to 4Hz, generate noise in the neutron instrumentation (in-core and ex-core neutron detectors) that could affect to the limitation and protection system of the reactor core, even it can activate a scram signal due to high neutron flux. This activity is included as a complementary study of our ongoing efforts in the study of the neutronic noise in the PWR reactor cores and their associated instrumentation. In this project, a deep analysis of the behaviour of a PWR reactor core has been carried out when a set of inlet thermal-hydraulic perturbations are applied. A set of inlet mass flow perturbations have been simulated with the CTF/PARCSv2.7 coupled code, which provides 3D results in both termal-hydraulics and neutronics. The cross sections have been obtained using the SIMTAB methodology and the signal of incore and excore neutron detectors are directly extracted from PARCS through modifications incorporated in the code. The power and outlet temperature fluctuations obtained with CTF/PARCSv2.7 have been analyzed for providing an overview of the global results supporting the phenomenology observed in the real PWR reactor cores.
Resumen-En este trabajo se presenta el análisis del comportamiento del núcleo de un reactor PWR f... more Resumen-En este trabajo se presenta el análisis del comportamiento del núcleo de un reactor PWR frente a distintas perturbaciones de los parámetros termohidráulicos a la entrada de éste. Este trabajo forma parte de los esfuerzos conjuntos de CNAT e ISIRYM en el estudio del fenómeno de ruido neutrónico. Para ello se simulan una serie de perturbaciones del caudal de entrada al núcleo mediante el código 3D acoplado neutrónico-termohidráulico RELAP5/PARCSv2.7. In this work, an analysis of the behavior of a PWR facing different perturbations on the thermalhydraulic parameters at the inlet is presented. This work is part of the joint efforts between CNAT and ISIRYM for the neutronic noise study. A set of perturbations on the inlet core mass flow are performed with the 3D coupled neutronic-thermalhydraulic code RELAP5/PARCSv2.7.
In order to reduce the response time when simulating large reactors in detail, a parallel version... more In order to reduce the response time when simulating large reactors in detail, a parallel version of the thermal-hydraulic subchannel code COBRA-TF (CTF) has been developed using the standard Message Passing Interface (MPI). The parallelization is oriented to reactor cells, so it is best suited for models consisting of many cells. The generation of the Jacobian matrix is parallelized, in such a way that each processor is in charge of generating the data associated with a subset of cells. Also, the solution of the linear system of equations is done in parallel, using the PETSc toolkit. With the goal of
It is a known fact that noise analysis is a suitable method for sensor performance surveillance. ... more It is a known fact that noise analysis is a suitable method for sensor performance surveillance. In particular, controlling the response time of a sensor is an efficient way to anticipate failures and to have the opportunity to prevent them. In this work the response times of several sensors of Trillo NPP are estimated by means of noise analysis. The procedure applied consists of modeling each sensor with autoregressive methods and getting the searched parameter by analyzing the response of the model when a ramp is simulated as the input signal. Core exit thermocouples and in core self-powered neutron detectors are the main sensors analyzed but other plant sensors are studied as well. Since several measurement campaigns have been carried out, it has been also possible to analyze the evolution of the estimated parameters during more than one fuel cycle. Some sensitivity studies for the sample frequency of the signals and its influence on the response time are also included. Calculati...
The dynamic response of several RTDs located at the cold leg of a PWR has been studied. A theoret... more The dynamic response of several RTDs located at the cold leg of a PWR has been studied. A theoretical model for the heat transfer between the RTDs and the surrounding fluid is derived. It proposes a two real poles transfer function. By means of noise analysis techniques in the time domain (autoregressive models) and the Dynamic Data System methodology, the two time constants of the system can be found. A Monte Carlo simulation is performed in order to choose the proper sampling time to obtain both constants. The two poles are found and they permit an advance in situ surveillance of the sensor response time and the sensor dynamics performance. One of the poles is related to the inner dynamics whereas the other one is linked to the process and the inner dynamics. So surveillance on the process and on the inner dynamics can be distinguished.
In the last years KWU-PWR plants have shown an increase in the neutron noise normalized root mean... more In the last years KWU-PWR plants have shown an increase in the neutron noise normalized root mean square. The frequency region of interest is below 1 Hz, so that thermohydraulic fluctuations seem to be one of the main reasons behind. In order to advance in understanding this phenomenon, the code S3K has been used to simulate temperature, flow and combined fluctuations at the core inlet. The S3K model used corresponds to Trillo Nuclear Power Plant which has a Flow Distribution Device, whose effect on the neutron noise levels has also been investigated. The results are compared with an analytical model and real plant data.
Journal of Nuclear Engineering and Radiation Science, Feb 29, 2016
The low frequency noise is a phenomenon observed in some PWR reactors causing an influence on the... more The low frequency noise is a phenomenon observed in some PWR reactors causing an influence on the normal operational behavior of the power plant. Fluctuations in the neutron flux density, in the low frequency range up to 4Hz, generate noise in the neutron instrumentation (in-core and ex-core neutron detectors) that could affect to the limitation and protection system of the reactor core, even it can activate a scram signal due to high neutron flux. This activity is included as a complementary study of our ongoing efforts in the study of the neutronic noise in the PWR reactor cores and their associated instrumentation. In this project, a deep analysis of the behaviour of a PWR reactor core has been carried out when a set of inlet thermal-hydraulic perturbations are applied. A set of inlet mass flow perturbations have been simulated with the CTF/PARCSv2.7 coupled code, which provides 3D results in both termal-hydraulics and neutronics. The cross sections have been obtained using the SIMTAB methodology and the signal of incore and excore neutron detectors are directly extracted from PARCS through modifications incorporated in the code. The power and outlet temperature fluctuations obtained with CTF/PARCSv2.7 have been analyzed for providing an overview of the global results supporting the phenomenology observed in the real PWR reactor cores.
Resumen-En este trabajo se presenta el análisis del comportamiento del núcleo de un reactor PWR f... more Resumen-En este trabajo se presenta el análisis del comportamiento del núcleo de un reactor PWR frente a distintas perturbaciones de los parámetros termohidráulicos a la entrada de éste. Este trabajo forma parte de los esfuerzos conjuntos de CNAT e ISIRYM en el estudio del fenómeno de ruido neutrónico. Para ello se simulan una serie de perturbaciones del caudal de entrada al núcleo mediante el código 3D acoplado neutrónico-termohidráulico RELAP5/PARCSv2.7. In this work, an analysis of the behavior of a PWR facing different perturbations on the thermalhydraulic parameters at the inlet is presented. This work is part of the joint efforts between CNAT and ISIRYM for the neutronic noise study. A set of perturbations on the inlet core mass flow are performed with the 3D coupled neutronic-thermalhydraulic code RELAP5/PARCSv2.7.
In order to reduce the response time when simulating large reactors in detail, a parallel version... more In order to reduce the response time when simulating large reactors in detail, a parallel version of the thermal-hydraulic subchannel code COBRA-TF (CTF) has been developed using the standard Message Passing Interface (MPI). The parallelization is oriented to reactor cells, so it is best suited for models consisting of many cells. The generation of the Jacobian matrix is parallelized, in such a way that each processor is in charge of generating the data associated with a subset of cells. Also, the solution of the linear system of equations is done in parallel, using the PETSc toolkit. With the goal of
It is a known fact that noise analysis is a suitable method for sensor performance surveillance. ... more It is a known fact that noise analysis is a suitable method for sensor performance surveillance. In particular, controlling the response time of a sensor is an efficient way to anticipate failures and to have the opportunity to prevent them. In this work the response times of several sensors of Trillo NPP are estimated by means of noise analysis. The procedure applied consists of modeling each sensor with autoregressive methods and getting the searched parameter by analyzing the response of the model when a ramp is simulated as the input signal. Core exit thermocouples and in core self-powered neutron detectors are the main sensors analyzed but other plant sensors are studied as well. Since several measurement campaigns have been carried out, it has been also possible to analyze the evolution of the estimated parameters during more than one fuel cycle. Some sensitivity studies for the sample frequency of the signals and its influence on the response time are also included. Calculati...
The dynamic response of several RTDs located at the cold leg of a PWR has been studied. A theoret... more The dynamic response of several RTDs located at the cold leg of a PWR has been studied. A theoretical model for the heat transfer between the RTDs and the surrounding fluid is derived. It proposes a two real poles transfer function. By means of noise analysis techniques in the time domain (autoregressive models) and the Dynamic Data System methodology, the two time constants of the system can be found. A Monte Carlo simulation is performed in order to choose the proper sampling time to obtain both constants. The two poles are found and they permit an advance in situ surveillance of the sensor response time and the sensor dynamics performance. One of the poles is related to the inner dynamics whereas the other one is linked to the process and the inner dynamics. So surveillance on the process and on the inner dynamics can be distinguished.
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Papers by Juan Bermejo