Structural modifications of boron carbide irradiated by heavy ions

International audienc

The use of NRA to study thermal diffusion of helium in (U,Pu)O-2

International audienceA lot of work has been already done on helium atomic diffusion in UO2 samples, but information is still lacking about the fate of helium in high level damaged UOX and MOX matrices and more precisely their intrinsic evolutions under alpha self irradiation in disposal/storage conditions. The present study deals with helium atomic diffusion in actinide doped samples versus damage level. The presently used samples allow a disposal simulation of about 100 years of a UOX spent fuel with a 60 MW d kg−1 burnup or a storage simulation of a MOX spent fuel with a 47.5 MW d kg−1 burnup. For the first time, nuclear reaction analysis of radioactive samples has been performed in order to obtain diffusion coefficients of helium in (U, Pu)O2. Samples were implanted with 3He+ and then annealed at temperatures ranging from 1123 K to 1273 K. The evolution of the 3He depth profiles was studied by the mean of the non-resonant reaction: 3He(d, p)4He. Using the SIMNRA software and the second Fick's law, thermal diffusion coefficients have been measured and compared to the 3He thermal diffusion coefficients in UO2 found in the literature

Ion irradiation used as surrogate for neutron irradiation to understand nuclear graphite evolution during reactor operation: consequences for the long lived radionuclide’s behavior

International audienc

Effect of stoichiometry on UO2_2 behavior under high temperature and irradiation

International audienc

Mécanismes d’incorporation et de migration du Mo dans le dioxyde d’uranium stœchiométrique et sur-stœchiométrique

International audienc

Thermal diffusion of lithium implanted in small and large grain boron carbide

International audienceBoron carbide (B4C) is used as a neutron absorber for nuclear reactor control and installation protection in most types of reactors. When the B4C is irradiated in the reactor, large quantities of lithium and helium (up to about 1022 /cm3) are produced due to the neutron absorption reaction 10B (n, α) 7Li. This work aims at studying the Li diffusion in large grain size (20–50 µm) or small grain size (0.2 – 5 µm) B4C in the temperature range of 500–800 °C. Lithium was implanted in B4C samples at a fluence of 1014 ions/cm2 (maximum concentration of 54 at. ppm). The Li concentration profiles as a function of depth were obtained before and after each heat treatment by Time-Of-Flight Secondary Ionization Mass Spectrometry technique. A heterogeneous diffusion process was observed depending on the implantation depth. Considering diffusion in the non-damaged, bulk material beyond the implanted zone, the thermal diffusion of lithium into the grain boundaries was found to be about four orders of magnitude higher than into the grains. •TOF-SIMS analyses of Li have been performed in implanted and annealed high density, large grain boron carbide.•The diffusion coefficient of Li in boron carbide has been determined in the 500 – 800 °C range, the obtained activation energy, about 2 eV, is close to ab initio estimations.•Li diffusion is highly enhanced in the gain boundaries

Effect of high temperature on the behavior of Mo and Cs in UO2_2 and UO2+x_{2+x}

International audienc