[en] The equipment described was designed for measuring the power doubling time of the CABRI reactor at Cadarache during the exponential phase of the transient state produced by a stepwise change in reactivity. The doubling time must be known accurately since it yields the value of excess reactivity introduced and serves as a basis for intercomparison of experiments. For safety reasons the control room is located at a distance of 300 m from the reactor. The main characteristics of the apparatus are as follows. Detectors: Ionization chambers sensitive to neutrons or gamma radiation. Principle of measurement : The current from the ionization chamber is fed to the input of an amplifier. A fixed threshold at the amplifier output causes the negative feedback resistor R to be replaced by a resistor R/2. Between each passing of the threshold, the chamber current, and thus the power of the reactor, is doubled. A signal of 1 Mc/s from a time-base generator is fed to the counting input register of a high-speed memory made with thin ferromagnetic strips. With each change in range the contents of the register, i. e. the doubling time itself expressed in microseconds, are incorporated in the memory. Measurement ranges: Doubling times from 2 ms to 5 s. Dynamics: Eight doubling times for chamber currents from 10' to 10-5 A. Accuracy: Several times 10-3. Presentation of results: Three intermediate thresholds permit registration of the T/4 values. After each increase in reactor power the print-out unit presents 32 doubling-time measurements to four significant figures (four overlapping measurements per doubling time). Technology: The amplifier, the thresholds, the logical circuits, and most of the control circuits of the thin-strip memory are made with integrated circuits. Switching is carried out by means of field-effect transistors. Emphasis is placed on the problems posed by the use of advanced techniques such as integrated circuits and memories made with thin ferromagnetic strips, and the advantages derived from using them. (author)
[fr]
Cet appareil a été réalisé pour mesurer le temps de doublement de la puissance du réacteur CABRI de Cadarache pendant la partie exponentielle du régime transitoire provoqué par un échelon de réactivité. Le temps de doublement doit être connu avec précision, car il donne la valeur de l'excès de réactivité introduit et sert de base pour la comparaison des expériences entre elles. Pour des raisons de sécurité, la salle de contrôle est placée à 300 m du réacteur lui-même. Les caractéristiques principales de l'appareil sont les suivantes. Détecteurs utilisés: Chambres d'ionisation sensibles aux neutrons ou aux y . Principe de la mesure: Le courant de la chambre d'ionisation est envoyé sur l'entrée d'un amplificateur opérationnel. Un seuil fixe placé à la sortie de celui-ci provoque le remplacement de la résistance de contreréaction R par une résistance R/2. Entre chaque franchissement du seuil, le courant de chambre, donc la puissance du réacteur, passe du simple au double. Une base de temps 1 MHz est injectée dans le registre d'entrée comptant d'une mémoire rapide à lames minces ferromagnétiques. A chaque changement de gamme, le contenu du registre, c'est-à-dire le temps de doublement lui-même exprimé en microsecondes, est pris en mémoire. Gammes de mesure: Temps de doublement de 2 ms à 5 s. Dynamique: Huit temps de doublement pour des courants de chambre allant de 10-7 à 10-5 A. Précision de mesures: qq. 10-3. Présentation ¿es résultats: Trois seuils intermédiaires permettent d'enregistrer les T/4. Après chaque divergence, un programme permet de présenter sur imprimante 32 mesures du temps de doublement avec quatre chiffres significatifs Quatre mesures imbriquées par temps de doublement). Technologie: L'amplificateur opérationnel, les seuils, les circuits logiques, ainsi que la majorité des circuits de commande de la mémoire à lames minces sont réalisés en circuits intégrés. Les commutations sont réalisées à l'aide de transistors à effet de champ. On insistera sur les problèmes posés par l'utilisation des technologies avancées: circuits intégrés et mémoires à lames minces ferromagnétiques ainsi que sur les avantages qui découlent de leur utilisation. (author)Source
International Atomic Energy Agency, Vienna (Austria); 678 p; Jun 1966; p. 185-200; Conference on Nuclear Electronics; Bombay (India); 22-26 Nov 1965; IAEA-CN--22/24; ISSN 0074-1884; 
; 5 refs., 10 figs.
; 5 refs., 10 figs.
[en] In this work we examine the different aspects of catalyst ageing with effects ranging from the nano to the macro scale. Underlining the general importance of combining different characterisation techniques, like transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) for the nanoscale, we focus on the application of X-ray absorption micro-computed tomography (micro-CT) to capture macroscopic changes in the um to mm scale. Two series of tomographic measurements were carried out: (i) investigation of three differently treated samples by collecting one channel from a fresh, a conditioned and an aged monolith and (ii) examination of one single coated honeycomb channel with 4 wt% Pt/γ-Al2O3 and for comparison one with pure γ-Al2O3 washcoat, which have been measured in a non-destructive ex situ manner at the same position after each ageing treatment. Main observations of the tomographic study are: (1) coating inhomogeneities between different channels taken from the same honeycomb and between different honeycombs, (2) formation of cracks in the washcoat material and (3) formation of macroscopic Pt particles in the case of 4 wt% Pt/γ-Al2O3 washcoat. Particularly valuable is the non-destructive ex situ investigation after different ageing steps on the same channel using X-ray tomography.
Journal
Journal of Physics. Conference Series (Online); ISSN 1742-6596; ; v. 499(1); [11 p.]
; v. 499(1); [11 p.]
[en] We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies
Journal