[en] This paper reviews recent developments dealing with Optical Fiber Sensors (OFS) or Sensor Networks (OFSN) and particularly with Fiber Bragg Grating sensors in the nuclear industry. Several OFS concern improvement of monitoring, i.e. the monitoring of structures (concrete measurement for nuclear shield monitoring, steam pipe monitoring,...) and measurements devoted to increase safety in NPP (H₂ risk, ionizing radiation detection, ...) or long term waste disposal monitoring (pressure, temperature, strain, ...). (author)

[en] The effect of many parameters need to be studied to characterize the long term behavior of nuclear waste in a deep repository. These parameters concern the chemical effects, radiolytic effects, mechanical properties, water composition, and microbiological activity. To evaluate microbial activity in such an environment, work was focused on an inventory of key nutrients (C, H, 0, N, P, S) and energy sources required for bacterial growth. The production of hydrogen in the nuclear waste environment leads to the growth of hydrogen oxidizing bacteria, which modify the gas production balance. A deep repository containing bituminized waste drums implies several sources of hydrogen: - water radiolysis; -corrosion of metal containers; - radiolysis of the embedding matrix (bitumen). Two deep geological disposal conditions leading to H₂ production in a bituminized nuclear waste environment were simulated in the present study: - H₂ production by iron corrosion under anaerobic conditions was simulated by adding 10% of H₂ in the atmosphere; - H₂ production by radiolysis of bitumen matrix was approached by subjecting this material to external gamma irradiation with a dose rate near real conditions (6 Gy/h). The presence of dissolved H₂ in water allows the growth of hydrogen oxidizing bacteria leading to: - CO₂ and N₂ production; - H₂ consumption; - lower NO₃^- concentration caused by reduction to nitrogen. In the first case, hydrogen consumption is limited by the NO₃^- release rate from the bitumen matrix. In the second case, however, under gamma radiation at a low dose rate, hydrogen production is weak, and the hydrogen is completely consumed by microorganisms. Knowledge about these hydrogen oxidizing bacteria is just beginning to emerge. Heterotrophic denitrifying bacteria adapt well to hydrogen metabolism (autotrophic metabolism) by oxidizing H₂ instead of hydrocarbons. (authors)

[en] Since the out-of-pile semi-integral tests performed at Studsvik in 2011 for the NRC [1] and the Halden Loss-Of-Coolant Accident (LOCA) test series IFA-650 [2], a major safety interest has raised for Fuel Fragmentation, Relocation and Dispersal (FFRD) during a LOCA sequence. In addition to the characteristics of the fuel ejected from the rod after the clad failure, the fuel behaviour before the clad failure is still to be investigated, especially its fragmentation and its possible relocation within the rod during the clad ballooning phase. Furthermore, the chronology and the sequencing of these phenomena is of particular interest. For this purpose, the VINON-LOCA program, lying in the framework of a trilateral agreement between EDF, Framatome and CEA, is aimed at performing Out-Of-Pile heating tests on irradiated repressurized fuel rods, reproducing a typical Loss Of Coolant Accident thermal sequence. The VINON-LOCA experimental set-up is located in the so-called VERDON lab of the LECA-STAR hot cell complex. This lab was dedicated to the VERDON-ISTP program [3]. The VINON-LOCA set-up is thus largely instrumented for addressing not only these FFRD topics, but also Fission Gas Release (FGR), combining both online measurement (gamma stations, gamma camera, acoustic sensor, pressure, temperatures, flow meters, microGC…), and preand post-test characterization (gamma scanning, tomography, metrology, fuel fragments weighing and sieving, gas analyses…). An extensive and substantial qualification campaign has been performed to validate the furnace design regarding the desired test conditions, and to qualify the instrumentation. Following some preliminary modelling and calculations, it has included tests on an out-of-cell twin mockup and tests on dummy inactive rods in the hot cell. This allowed achieving successfully the first experimental qualification test of the program end of 2019 on an irradiated UO2 fuel rodlet. A second irradiated experiment is planned with increased instrumentation capabilities, notably a 2D gamma camera for online fuel motion detection. Key words: Nuclear fuel / experimentation / gamma imaging / FFRD / LOCA / Hot lab

[en] Supersonic molecular beam injection (SMBI) was successfully operated in JT-60U after improving the performance of the vacuum seal used inside the injector head. Frequent density jumps were clearly observed in the main plasma against the SMBI pulses with filling gas pressures (P_FG) of 0.2-0.6 MPa. The fuelling efficiency exhibited a weak dependence on P_FG and the injection direction (high- and low-field-side injections). The amount of fuelling necessary for achieving the same density level is much smaller for SMBI than for gas puffing. It is comparable for SMBI and pellet injection even with shallower penetration of SMBI as discussed. The SMBI ionization area was estimated based on emission measured using a fast TV camera with a time resolution of 0.167 ms. The estimations indicated a similar penetration position for P_FG = 0.6 and 0.2 MPa, although the ionization area was larger for 0.6 MPa. This result supports the weak P_FG dependence of the fuelling efficiency. The front of the ionization area moved between the first and second frames of the fast TV camera and it reached just inside the separatrix in the second frame. The ionization area was significantly expanded even in the first frame from the expected SMB size and the expansion was enhanced in the second frame. These relatively slow changes between the two frames suggest that the interaction between the SMB and the plasma significantly influences the fuelling characteristics.

[en] The characteristics of the internal transport barrier (ITB) have been investigated under reactor relevant conditions with edge fuelling and electron heating in JT-60U weak shear plasmas. In order to investigate the effects of edge fuelling and electron heating separately, two independent classes of experiments were performed, i.e. one with edge fuelling and ion dominant heating and the other with central beam fuelling and additional electron heating. High confinement was sustained at high density with edge fuelling by shallow pellet injection or supersonic molecular beam injection. The ion temperature (T_i) in the central region inside the ITB decreased due to cold pulse propagation even with edge fuelling. By optimizing the injection frequency and the penetration depth, the decreased central T_i recovered and a good ITB was sustained with enhanced pedestal pressure. The T_i-ITB also degraded significantly with electron cyclotron heating (ECH), when the stiffness feature was strong in the electron temperature (T_e) profile. The ion thermal diffusivity in the ITB region increased with the electron thermal diffusivity, indicating the existence of a clear relation between ion and electron thermal transport. On the other hand, the T_i-ITB remained unchanged or even grew, when the stiffness feature was weak in the T_e profile. The density fluctuation level at the ITB seemed unchanged during ECH; however, the correlation length became longer in the T_i-ITB degradation case and shorter in the T_i-ITB unchanging case.