ALBERT

Description: Presents the table of contents for this issue of the publication.

Description: Safe, stable, and efficient operation of nuclear reactors is very necessary for the development of nuclear power industry. During the course of its operation, a nuclear reactor is subjected to many intentional or unintentional perturbations which tend to change the rector power from its steady operating value. Power-level regulation is a significant technique for guaranteeing both operation stability and efficiency of nuclear reactors. Therefore, thorough stability analysis of power control loop is necessary to demonstrate its ability to withstand the reactivity perturbations. In this paper, the stability of the total power control loop of a large pressurised heavy water reactor is investigated in discrete-time domain by linearizing the system around its equilibrium points and identifying eigenvalues of the closed-loop system. The dynamics of the system vary widely depending on factors such as operating power levels, core–fuelling states and cycle time of reactor regulating system. Hence, the input to the stability analysis are these system parameters and the output is a stability characterization in terms of the stability regions shown in $G_{P}$ (total power control gain)– $G_{H}$ (level tilt gain) plane. The results quantify the influence of these system parameters on the stability of the total power control loop.

Description: A parity space approach to monitoring and fault detection and identification of systems in nuclear power plants (NPPs) can be beneficial. However, if the number of fault classes exceeds the total independent residual signatures, the parity space method needs to be further enhanced to achieve the optimal fault classification. This situation happens frequently in NPP applications, where the safety and reliability are paramount. A possible enhancement proposed in this paper is to combine Fisher discriminant analysis with the parity space method to maximize the scatter among different fault classes, while minimizing the scatter within each class. Under identical conditions, the proposed technique can achieve optimal separation among different fault classes. Design, real-time implementation, and experimental evaluation of the proposed method are detailed in this paper. The implemented system has been validated on the Nuclear Power Control Test Facility to demonstrate the feasibility. The test results have revealed many salient features of the proposed method with potential applications in NPPs.

Description: In this paper, a compendium of InGaAs photodiode irradiation test results is presented. These photodiodes were irradiated either with $gamma $ -rays, protons, neutrons, electrons, pions, alpha particles, or carbon ions of various energies. The displacement damage dose formalism was found to be effective in describing the radiation-induced dark current increase of any of the studied InGaAs photodiodes. The exploitation of capacitance-bias voltage and current-bias voltage measurements also allows us to deduce a damage factor that can be used to assess the radiation-induced dark current in a great number of radiation environments.

Description: A physics-based compact model of the parasitic bipolar current induced by an energetic particle is presented for single-event transients in FinFETs. The terminal charges are modeled to predict the body voltage of the FinFET in the transient correctly. The models are implemented using Verilog-A and are verified through 3-D technology computer-aided design (TCAD) simulations. The results of the modeling show good agreement with the TCAD data, for both structural variations and energy variations of the energetic particles.

Description: An in situ detection method for beta-ray distribution was developed. The method uses the gamma-ray sensitivity difference between two scintillators: a cadmium–tungstate (CdWO 4 ) scintillator and a plastic scintillator. The gamma-ray sensitivity ratios for several gamma-ray sources such as 137 Cs, 60 Co, 22 Na, and 54 Mn were experimentally characterized. The sensitivity ratio for 137 Cs between the CdWO 4 and plastic scintillators was 8 ± 0.32, while the sensitivity ratio for beta rays from 90 Sr was 1.03 ± 0.006. The beta-ray contributions to the total counts can be evaluated using this characteristic. A combined beta-ray and gamma-ray source was prepared, and its beta-ray distribution was successfully obtained using the proposed method.

Description: Environmentally friendly 99.998%-pure indium iodide (InI), one candidate materials for the room-temperature operating radiation detector, was purified more than 250 times using the zone-refining method to reduce the impurities. Segregation coefficient of major positive and negative impurities of the purified InI ingot was analyzed using time-of-flight secondary ion mass spectroscopy. Electrical and spectroscopic properties of the purified Pd/InI/Pd detector were also determined. Planar Pd/InI/Pd detector showed the 59.5-keV gamma peak of Am-241 clearly. However, low-energy gamma peaks were buried in the noise. Mechanical or electrical degradation under an ambient condition was not observed for six months. Electrical resistivity and electron mobility-lifetime product of the multiple-refined InI were $4times 10^{11},,Omega cdot textrm {cm}$ and $1.3times 10^{-3},,textrm {cm}^{2}/textrm {V}$ , respectively.

Description: Optically read out time projection chambers (TPCs) based on gaseous electron multipliers (GEMs) combine 3-D event reconstruction capabilities with high spatial resolution and charge amplification factors. The approach of reconstructing particle tracks from 2-D projections obtained with imaging sensors and depth information from photomultiplier tubes is limited to specific cases such as straight particle trajectories. A combination of optical and electronic readout realized by a semitransparent anode placed between a triple-GEM stack and a camera in an optically read out TPC has been realized and used to reconstruct more complex particle tracks. High spatial resolution 2-D projections combined with a low number of charge readout channels enable accurate 3-D event topology reconstruction. Straight alpha tracks as well as more complex cosmic events have been reconstructed with the presented readout concept. Relative depth information from electronically read out charge signals has been combined with drift time information between primary and secondary scintillation pulses to absolute alpha track reconstructions.

Description: AREVA Mines and the Nuclear Measurement Laboratory of CEA Cadarache are collaborating to improve the sensitivity and precision of uranium concentration measurement by means of gamma-ray logging. The determination of uranium concentration in boreholes is performed with the Natural Gamma Ray Sonde (NGRS) based on a NaI(Tl) scintillation detector. The total gamma count rate is converted into uranium concentration using a calibration coefficient measured in concrete blocks with known uranium concentration in the AREVA Mines calibration facility located in Bessines, France. Until now, to take into account gamma attenuation in a variety of boreholes diameters, tubing materials, diameters and thicknesses, filling fluid densities, and compositions, a semiempirical formula was used to correct the calibration coefficient measured in Bessines facility. In this paper, we propose to use Monte Carlo simulations to improve gamma attenuation corrections. To this purpose, the NGRS probe and the calibration measurements in the standard concrete blocks have been modeled with Monte Carlo N-Particles (MCNP) computer code. The calibration coefficient determined by simulation 5.3 $text{s}^{-1}cdot text {ppm}_{U}^{-1}$ with 10% accuracy is in good agreement with the one measured in Bessines (and for which no uncertainty was provided), 5.2 $text{s}^{-1}cdot text {ppm}_{U}^{-1}$ . The calculations indicate that the concrete blocks used for measuring the calibration coefficients measured in Bessines are underestimated by about 10%. Based on the validated MCNP model, several parametric studies have been performed. For instance, the rock density and chemical composition proved to have a limited impact on the calibration coefficient. However, gamma self-absorption in uranium leads to a nonlinear relationship - etween count rate and uranium concentration beyond approximately 1% of uranium weight fraction, the underestimation of the uranium content reaching more than a factor 2.5 for a 50% uranium weight fraction. Parametric studies have also been performed with different tubing materials, diameters, and thicknesses, as well as different borehole filling fluids representative of real measurement conditions, in view to validate gamma attenuation corrections based on the semiempirical formula. In addition, a multilinear analysis approach has been tested to further improve accuracy on uranium concentration determination, leading to only a few percent uncertainties on a large range of configurations.

Description: Radiation measurements and monitoring are very important for particle physics accelerators, hadron therapy institutes, and nuclear facilities. An Application Specific Integrated Circuit (ASIC) able to digitize current generated from ionization chambers was designed and characterized in order to be used as the front-end of the new radiation monitoring system at CERN. The design of the Utopia 2 ASIC was motivated by the need to measure input currents as low as 2 fA and over a wide dynamic range of 9 decades. This paper presents the challenges, the design procedure, the architecture, and the measurement results of the front-end that was fabricated in AMS 0.35- $mu text{m}$ technology. The main limitation was related to the leakage currents that are injected into the input of the ASIC from various sources and are added to the signal of the detector. By active leakage current compensation, the ASIC can measure current down to 1 fA, and by introducing a multiple range architecture, the ASIC can digitize current up to $5~mu text{A}$ .