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Under given temperature and bias voltage conditions, partial discharges can create pulses in fission chambers. Based on experimental results, this phenomenon is in-depth investigated and discussed. A pulse-shape-analysis technique is proposed to discriminate neutron-induced pulses from partial-discharge-induced ones. [ABSTRACT FROM AUTHOR]

The detectors of the neutron flux monitoring system of the foreseen French GEN-IV sodium-cooled fast reactor (SFR) will be high temperature fission chambers placed in the reactor vessel in the vicinity of the core. The operation of a fission chamber over a wide-range neutron flux will be feasible provided that the overlap of the applicability of its pulse and Campbelling operational modes is ensured. This paper addresses the question of the linearity of these two modes and it also presents our recent efforts to develop a specific code for the simulation of fission chamber pulse trains. Our developed simulation code is described and its overall verification is shown. An extensive quantitative investigation was performed to explore the applicability limits of these two standard modes. It was found that for short pulses the overlap between the pulse and Campbelling modes can be guaranteed if the standard deviation of the background noise is not higher than 5% of the pulse amplitude. It was also shown that the Campbelling mode is sensitive to parasitic noise, while the performance of the pulse mode is affected by the stochastic amplitude distributions. [ABSTRACT FROM AUTHOR]

This paper investigates, through numerical simulations, the performance of a signal analysis method by which a high temperature fission chamber can be used over a wide range of count rates. Results reported in a previous paper (Elter et al., 2015 [1] ) indicated that the traditional Campbell method and the pulse mode cannot provide a sufficient overlap at medium count rates. Hence the use of the so-called Higher Order Campbell (HOC) methods is proposed and their performance is investigated. It is shown that the HOC methods can guarantee the linearity (i.e. correctness) of the neutron flux estimation over a wide count rate, even during transient conditions. The capabilities of these methods for suppressing parasitic noise (originating from various sources) are verified. [ABSTRACT FROM AUTHOR]

The signals of fission chambers are traditionally evaluated with Campbelling methods at medium count rates. Lately there has been a growing interest in the extension of Campbelling methods to cover a wider range of count rates. These methods are applied to measure the neutron flux in the stationary state of the reactor. However, there has not been any attempt to generalize these techniques for transient reactor states. This short note is devoted to a discussion of this question. It is shown through analytic and numerical calculations that for practical reasons the traditional, stationary Campbelling methods can be applied for transient scenarios as well. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the frame of dependable neutron flux instrumentation development for Generation IV reactors, the French Atomic and Alternative Energies Commission (CEA) investigates an innovative technology based on optical signal produced within a fission chamber. In such gaseous detectors, neutrons interact with fissile material, releasing heavy ions in the MeV range, eventually leading to spontaneous photons emission in the ultraviolet to infrared range. We hereby present the space–time evolution of heavy-ion slowing-down tracks parameters in noble gases, as computed with the SCENA radiation-induced cold-plasma simulation tool. Preliminary results on excited-states noble-gas population dynamic are reported. Population of upper-lying gas levels is completed within picoseconds, only micrometres behind the projectile ionization trail. [ABSTRACT FROM AUTHOR]

To provide future dependable neutron flux monitoring instrumentation for sodium-cooled fast reactors (SFR) of Generation-IV, French Alternative Energies and Atomic Energy Commission (CEA) is investigating the applicability of an innovative technology based on the optical signal produced within any type of ionization chambers such as fission chambers for instance. A mock-up of that innovative neutron detector was tested on a cold-neutron beamline at the ORPHEE nuclear facility. Experimental results regarding recovery time and detection efficiency showed promising possibilities for neutron instrumentation. [ABSTRACT FROM AUTHOR]

In order to provide dependable neutron flux instrumentation for Generation IV Sodium-cooled Fast Reactors (SFR), the French Atomic and Alternative Energies Commission (CEA) is investigating the feasibility of an innovative technology based on the optical signal produced within a fission chamber. In such gaseous detectors, neutrons interact with fissile material releasing heavy ions in the MeV-range, eventually leading to spontaneous photon emission in the ultraviolet-to-infrared range thanks to gas excitation and ionization. In this paper, the process of light generation is analyzed through semi-empirical models and custom-developed codes. A specific instrumentation has been defined and manufactured to emulate optical fission chambers and collect basic spectroscopic data required for model-based development approach. That testing device was named PSEG, which stands for Prototype of Scintillator Electrodes-Gas. Experimental validations have been carried out: the ionized argon gas exhibited no local thermodynamic equilibrium. Furthermore, the broadening of selected argon emission lines due to pressure change offers a promising self-diagnosis capability for future optical fission chambers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The neutron flux monitoring system forms an integral part of the safety design of a Generation IV sodium-cooled fast reactor. During the initial design phase of the neutron flux monitoring system, one needs to explore various detector locations and configurations. Diverse possibilities of the detector system installation should be studied for different locations in the reactor vessel in order to detect any perturbations in the core. In this paper, we investigate the possibility of placing fission chambers beyond the lateral neutron shield, ex-core but in-vessel and study the detectability of an inadvertent control rod withdrawal with these fission chambers. A generic core design of a Generation IV 1500 MWth French sodium-cooled fast reactor is used for the study, and calculations are performed with the Monte Carlo code SERPENT2. We propose certain design changes that are needed to be incorporated, w.r.t. the facilitation of neutron transport to this ex-core location. We are able to show that there is a detectable signature in the fission chambers following an inadvertent control rod withdrawal in the core. The equally-spaced azimuthal detectors are able to follow changes in the neutron flux distribution in the core. This study helps us to analyze multiple detector locations and give the general trends for monitoring indications to detect any perturbations in the core. [ABSTRACT FROM AUTHOR]

In this paper, we present experimental saturation curves of a small gap miniature fission chamber obtained in the MINERVE reactor. The chamber is filled with argon at various pressures, and the fissile material can be coated on the anode, cathode, or both. For analyzing the recombination regime, we consider a model of columnar recombination and discuss its applicability to our chamber. By applying this model to the data, it is possible to estimate the ratio between the recombination coefficient k and an effective column radius b , appearing in the model, to be k / b = ( 2.5 ± 0.9 ) × 10 − 6 m 2 / s for argon. From these results, a routine measurement of the recombination regime is proposed in order to detect gas leakage. This online diagnosis would be beneficial in terms of lifetime and reliability of the neutron instrumentation of nuclear reactors. [ABSTRACT FROM AUTHOR]

Xenon high temperature fission chamber, designed for sodium-cooled fast reactors, unlike the argon filled fission chambers, can operate at temperatures greater than 500°C without partial-discharges and discriminate neutrons and partial-discharges at temperatures up to 650°C. [ABSTRACT FROM AUTHOR]