This paper reviews a new real-time measurement instrument dedicated for online neutron monitoring with fission chambers in nuclear reactors. The instrument implements the higher order Campbelling ...methods and self-monitoring capabilities on an open source development board. The board includes an CPU/FPGA System on a Chip.
The feasibility of the measurement instrument was tested both in laboratory with a signal generator and in the Minerve reactor. It is shown that the instrument provides reliable and robust count rate estimation over a wide reactor power range based on the third order statistics of the fission chamber signal. In addition, the system is able to identify whether the measured count rate change is due to the malfunction of the detector or due to the change in the neutron flux. The applied self-monitoring method is based on the spectral properties of the fission chamber signal. During the experimental verification, the considered malfunction was the change of the polarization voltage.
•A new online High Order Campelling measurement system is proposed.•It includes a fission chamber failure detection system.•The complete architecture of the measurement system is given.•Test on reactor show its accuracy over a wide count rate range.
Neutron radiation detector for nuclear reactor applications plays an important role in getting information about the actual neutron flux. Such a detector must be able to operate at high neutron flux ...levels (>10 9 cm −2 s −1 ) and discriminate the neutron and gamma responses in the nuclear reactor's mixed neutron-gamma environment. Silicon carbide and diamond are the most attractive semiconductor materials for neutron detection, thanks to their outstanding properties, such as high displacement threshold energy and wide bandgap energy, which allow them to operate in high radiation levels and high temperature. The aim of this article is to compare the ability to detect thermal neutrons of these two semiconductors at the same irradiation conditions. For this purpose, the neutron irradiation tests of detectors were implemented at MINERVE research reactor at CEA Cadarache. The 4H-silicon carbide (SiC) p + n diode has demonstrated better neutron-gamma discrimination at 0-V bias voltage than at −200 V which is explained by its increased sensitivity to gamma photons at −200 V caused by a wider charge collection region than at 0 V. Therefore, it is preferable to use the 4H-SiC p + n diode without an external electric field for applications in the mixed neutron-gamma environment such as nuclear reactor environment. The results show that the single-crystal chemical vapor-deposited (sCVD) diamond-based detector has better neutron to gamma discrimination, thanks to the use of 6 Li as a neutron converter instead of 10 B. However, the study of the radiation stability of detectors showed that the sCVD diamond-based detector suffers from the "polarization effect" when it operates at a high neutron flux (~10 9 cm<inline-formula> <tex-math notation="LaTeX">^{-2}\,\,\cdot \,\,\text{s}^{-1} </tex-math></inline-formula>).
The transfer function of a zero-power thermal reactor was successfully measured thanks to neutron noise techniques from 1 mHz to 160 Hz. During a month-long experimental campaign, the fluctuations of ...the neutron population in critical and subcritical configurations of the core were acquired using excore fission chambers and analysed through Cross-Power Spectral Density (CPSD) methodology. Firstly, the reactor’s kinetic parameters, i.e. prompt decay constant, effective delayed neutron fraction and generation time, were obtained at critical state. It required calibrating the reactor’s power, which was done by metal foil activation and measurement of the
235
U fission rate. Secondly, these parameters were used to estimate the groups’ abundances of delayed neutrons from the CPSD measured in a sub-critical state. Fitting data with a point kinetic model was done with Bayesian inference - CONRAD and Stan programs were used. A very good agreement was found between experimental abundances and the ones computed with TRIPOLI-4 Monte-Carlo transport code and JEFF3.1.1 nuclear data library. Uncertainties on prior abundances between 6 % to 101 %, held mainly by nuclear data, were lowered down to 4 % to 54 %, depending on the delayed group.
Since a few years, simulation codes were built at CEA Cadarache to predict the signal of ionisation chambers and taylor detectors for specific applications. It is proposed here to present COSICAF, a ...tool developed for mainly academic purpose and rapid fission chamber prototyping. This numerical simulation, mostly based on semi-empirical models and Monte-Carlo method will help students to understand how ionisation chambers work. Through the paper, models and their numerical implementation will be discussed. A focus is made on recently implemented features like charge multiplication and correlated source which make the simulation of proportional counter possible. To demonstrate the interest of the code, simulations of a planar fission chamber is proposed.
Since many years, the Instrumentation, Sensors and Dosimetry laboratory at CEA Cadarache has been working to propose innovative and robust design of fission chambers. In this framework, few ...simulation tools like Chester or PyFc were developed to make detector prototyping and optimisation possible. Up to now, the code experimental validations are scarce mainly because of the lack of flexibility of regular fission chambers. In order to set up an experimental database for code validation, an innovative modular twin fission chamber, the CFTM, was designed. It allows to set with precision the inter-electrode gap, the filling gas pressure as well as the fissile deposit used. This detector was irradiated in Minerve zero power reactor in order to gather results for code validation. Thanks to a calibration procedure, a bank of experimental results is available for simulation validation.
Applying Higher Order Campbelling methods in neutron flux monitoring with fission chambers is advantageous due to their capabilities to suppress the impact of unwanted noises and signal contributions ...(such as gamma radiation). This work aims to verify through experimental results that the basic assumptions behind the Higher Order Campelling methods are valid in critical reactors.
The experiments, reported in this work, were performed at the MINERVE reactor in Cadarache. It is shown that the calibration of a fission chamber and the associated electronic system is possible in higher order mode. With the use of unbiased cumulant estimators and with digital processing, it is shown that over a wide count rate range, accurate count rate estimation can be achieved based on signal samples of a few ms, which is a significant progress compared to similar experimental results in the literature. The difference between the count rate estimated by pulse counting and by the Higher Order Campelling is less than 4%.
The work also investigates the possibility of monitoring transient events. For this purpose, a control rod drop event was followed in Higher Order Campbelling mode.
The CEA MONACO v2 a multichannel acquisition system dedicated to neutron and gamma measurements. It is unique as it integrates all the following features in one module: automatic generation of ...saturation curves, automatic generation of pulse discrimination curves, detector pulse characterization using the embedded oscilloscope module, pulse mode acquisitions in count rate or pulse height analysis, fluctuation mode and current mode acquisitions. Sensors are plugged to a single connector and the implemented operating modes run constantly in parallel.
Firsly designed for on line local neutron and gamma measurements with gaseous detectors in reactor experiments, the MONACO v2 system will also be available for self-powered detectors thanks to its wide current mode working range.
After two years of development, CEA teams tested two MONACO v2 prototypes in the Slovenian TRIGA Mark II research reactor in 2018, using CEA miniature ion chambers and SPNDs. The system is now ready for industrialization to be available on the nuclear instrumentation market.
To minimise uncertainty and strengthen estimation of energy deposited during power transients, we set up an online passive neutron flux measurement of a pulse reactor.
Optical fission chambers, are ...being developed in the framework of dependable neutron flux instrumentation for Sodium-cooled Fast Reactor (SFR) and Molten-Salt Reactor (MSR) of Generation IV by the French Atomic Energy and Alternative Energies Commission (CEA). Neutron interactions with a fissile layer coating release heavy-ions in the MeV-range, eventually leading to spontaneous photon emission in the ultraviolet to infrared range of the surrounding noble gas. Prototypes have previously been tested in an ideal pure neutron field. In this paper, linearity of optical signal versus reactor power is assessed during startups and high power transients up to 21.6 GW. Excellent linearity results are obtained over 5 reactor power decades and detection remain possible over 7 decades. Detection range is only restrained by photodetector properties. Such detector may be routinely employed for high-dynamic transients monitoring by the core caisson of pulse reactors.
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