In this paper, we present the model experiments in order to study the magnetic flux distortion of a two-phase liquid metal flow excited by an AC magnetic field in a range of pulsation where Faraday induction and Lorentz force effects are significant. These experiments realized with solid aluminum rods allow to characterize the effects of flow velocity ($0\hspace{0.17em}\lesssim \hspace{0.17em}U\le 1\hspace{0.17em}{\text{ms}}^{-1}$ ), void fraction ($0\le \alpha \le 6.9\hspace{0.17em}\%$ ), pulsation of the AC magnetic field ($1.5\times {10}^3\le \omega \le 12.5\times {10}^3\hspace{0.17em}\text{rad}\hspace{0.17em}{\mathrm{s}}^{-1}$ ), and of two different void geometries. The results are analyzed on the basis of a first order expansion of magnetic flux in U and α. Despite the strong coupling between Faraday induction and Lorentz force effects, the results show that the contributions of U and α on a magnetic flux distortion can be well separated at both low magnetic Reynolds number and α values. These results are independent of void geometry.

This paper presents the design, manufacture, and testing of a gas composition sensor for measuring the composition of fission gases inside experimental rods coming from an experimental reactor such as the future Jules Horowitz Nuclear Reactor (JHR). The piezoelectric element is a cerium-modified bismuth niobate titanate (NBT) ceramic screen-printed onto an alumina substrate. These types of piezoelectric elements have been shown in the past to be capable of operating in environments subject to particular thermal and radiative stresses [1]. Thus, three NBT (Na _0.5 Bi _(4.5-x) Ce _(x) Ti ₄ 0 ₁₅ ) ceramics with different dopants of elemental cerium (Ce) were fabricated, characterized and compared to the state of the art, especially with respect to piezoelectric (d ₃₃ ) and dielectric (ε _r and tan (δ)) performance. A study of the electrical impedance at different temperatures concluded that cerium-modified NBT with a Ce dopant of x=0.04 and x=0.06 was suitable for temperatures up to 340°C. These two NBT variants were then integrated into an acoustic cavity to form the sensor. The performance of these sensors was tested with two gas mixtures: pure helium and a mixture of 80% helium and 20% xenon. These laboratory sensors have shown the possibility of characterizing the composition of the gas mixtures for limited lower pressures of 40 bar for a Helium - Xenon mixture. Finally, the sensor is tested in various ternary gas mixtures containing helium, xenon and krypton, with accuracy on the composition estimation of 5%.

A model has been developed to predict the response of an eddy current flow meter (ECFM) to the passage of a non-conductive inclusion moving in a cylindrical tube filled with a liquid metal. The model can be solved analytically for small inclusion diameters and moderate AC frequencies of the excitation signal. This condition is expressed as vbSω≪1, where vb is the dimensionless inclusion volume and Sω is a function of the ratio between the characteristic length of the system and the penetration depth of the magnetic field. The magnetic induction equation for this problem has also been solved numerically. A very good agreement between the analytical model and numerical solutions has been found for vbSω≪1. Two experimental setups have been designed. First, the ECFM model has been validated by comparing the response due to the passage of traveling beads of known diameters in a low melting point alloy. In a second experiment, the diameters of ascending argon bubbles have been estimated with the ECFM model. The numerical model predicts the gas volume with very good accuracy in the range of bubble diameters studied, between 1.5 and 6 mm, while the analytical model only deviates significantly from the experimental data when vbSω≳0.1. Moreover, we establish that the ECFM can also measure the radial deviation of the bubble trajectory, and the results are consistent with the theoretical limit for isolated bubbles between the regimes of oscillating/zigzag motion of ellipsoidal bubbles and non-oscillating motion of spherical bubbles. Another observation is that the dependence of the ECFM response on the shape of the bubble is negligible; indeed, the ECFM response is well approximated by a linear relation with the bubble volume as is assumed in the analytical model. Finally, an estimation of the terminal rising velocity of bubbles was also carried out.

In this article, we present an analytical model to calculate the perturbation of the magnetic vector potential due to a non-conducting inclusion in a liquid metal translated at constant velocity. The model is valid for a low magnetic Reynolds number, $R{e}_m$ , and a low shielding parameter, $S_{\omega }$ . We establish that the first order perturbation of the vector potential can be directly obtained from the value of the unperturbed eddy-current calculated at the location of the inclusion. An ECFM (Eddy-Current FlowMeter) device has been designed to validate the model and to study the frequency effects of the eddy-current and the volume of one inclusion and its location. We observe a good agreement between the model predictions and experimental data within the limit of the validity of the model. Based on scaling analysis, we show that a unique relation exists between the perturbation of the emf (electromotive force) measured with the ECFM and the volume of the inclusion and its location, which reflects the self-similarity of the model solution.

In support of the French ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) reactor program, which aims to demonstrate the industrial applicability of sodium fast reactors with an increased level of safety demonstration and availability compared to the past French sodium fast reactors, emphasis is placed on reactor instrumentation. It is in this framework that CEA studies continuous core monitoring to detect as early as possible the onset of sodium boiling. Such a detection system is of particular interest due to the rapid progress and the consequences of a Total Instantaneous Blockage (TIB) at a subassembly inlet, where sodium boiling intervenes in an early phase. In this paper, the authors describe all the particularities which intervene during the different boiling stages and explore possibilities for their detection.

Since the Fukushima-Daiichi accident, severe accident research has been reconsidered from another perspective. In the case of a severe accident in a nuclear reactor, the core can melt to form corium, a complex mixture of molten fuel and structural materials. In order to improve reactor safety and mitigate the accident on site, it is important to understand the behaviour of corium in the configurations. In the context of in-vessel retention (IVR) studies, the scientific community has limited knowledge of immiscible phase stratification phenomenon. This knowledge could be further developed thanks to experiments with dedicated online instrumentation to follow the metal relocation transient occurring below the oxide phase and the stratification inversion kinetics. This instrumentation has to resist an aggressive liquid and high temperatures (1700–3000°C). The study of an ultrasonic technique, based on time-of-flight measurements, using a refractory material waveguide is in progress. This paper describes the feasibility approach used and the resulting choice of waveguide (able to withstand high temperatures, no interaction with steel, and transmission of the acoustic wave in the waveguide and at the waveguide/ steel interface), the choice of ultrasonic transducer, the numerical simulations, and the results of preliminary experiments performed at high temperature (>1500°C).