In the safety analysis for the core of the 4th Generation Reactors, the Total Instantaneous Blockage (TIB) is a hypothetic accident scenario involving the melting of the blocked subassembly with a risk of propagation to the neighbouring subassemblies. To avoid this latter consequence a detection system has to scram the reactor. For Superphénix or EFR project a Delayed Neutron Detection Integrated (DND I) was considered as efficient to limit the melting to the first neighbouring subassemblies. Nonetheless for the CFV core the objective of improving the safety leads to limit the melting to the blocked subassembly. For this purpose, the CEA has launched a program development to find a new detection method. This paper provides a brief review of the feedback of R&D, progress and program on the various early non-nuclear detection methods investigated by the CEA:• Temperature measurement at the subassemblies outlet by thermocouples. The advantage of this method is that it will require no additional instrumentation to that already present for continuous monitoring. • Temperature measurement at the subassemblies outlet by Optical Fibers Bragg Grating (OFBG). This technology has the electromagnetic immunity, compactness and short response time. • Temperature measurement at the subassemblies outlet by ultrasound. The measuring point is located closer to the head subassembly and the response time could be shorter. • Acoustic detection of sodium boiling. Boiling occurs early in the accident progress and the area to be monitored may be covered by few sensors. • Subassemblies loss of flow detection by eddy-current flowmeters. This method seems logically the easiest and the most immediate method to detect a blockage. To date, none of these methods has been fully demonstrated to be feasible. It should be noted that temperature measurement methods will probably consist of the detection of a low increase rate using specific signal processing. These methods have been compared according to their performance that may be expected and their maturity level. The shorter time to qualifying is for eddy-current flowmeters and thermocouples. K. Paumel, J.P. Jeannot, M. Vanderhaegen and N. Massacret are with the CEA, DEN,

International audienceThe In Service Inspection of internal structures of future liquid sodium cooled fast reactors implies, among different options, the use of ultrasounds from the outside of sodium circuit. In these conditions, ultrasounds have to propagate through the metallic envelope of main vessel, then other immersed plates. Thus the study aims at mastering ultrasonic propagation in these multilayered structures in order to determine the best conditions allowing NDT of a plate behind some screens. The necessity of propagating a maximum of energy through bounded media orientated the study towards Lamb waves. Those are often employed for singles plates or solid layers but they are less usual for liquid/solid alternations. Theoretical results are obtained using transfer matrix method. They are compared to in water experimental measurements. Cases with one, two and three parallel plates without then with an artificial defect are presented for identical and different thicknesses of plates. Results show that an artificial crack defect is obviously detected in a plate located behind one and two screens. Measured attenuation is compatible with industrial NDT conditions. Thus a promising potential is shown for this inspection technique

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 Շ U 1 ms À1 ), void fraction (0 a 6:9 %), pulsation of the AC magnetic field (1:5 Â 10 3 x 12:5 Â 10 3 rad s À1 ), and of two different void geometries. The results are analyzed on the basis of a first order expansion of magnetic flux in U and a. Despite the strong coupling between Faraday induction and Lorentz force effects, the results show that the contributions of U and a on a magnetic flux distortion can be well separated at both low magnetic Reynolds number and a values. These results are independent of void geometry.

International audienceUltrasonic inspection of sodium-cooled fast reactor requires a good acoustic coupling between the transducer and the liquid sodium. Ultrasonic transmission through a solid surface in contact with liquid sodium can be complex due to the presence of microscopic gas pockets entrapped by the surface roughness. Experiments are run using substrates with controlled roughness consisting of a network of holes and a modeling approach is then developed. In this model, a gas pocket stiffness at a partially solid-liquid interface is defined. This stiffness is then used to calculate the transmission coefficient of ultrasound at the entire interface. The gas pocket stiffness has a static, as well as an inertial component, which depends on the ultrasonic frequency and the radiative mass