Oumar Sanogo

Fast and accurate dating of nuclear events using La-140/Ba-140 isotopic activity ratio

This study reports on a fast and accurate assessment of zero time of certain nuclear events using La-140/Ba-140 isotopic activity ratio. For a non-steady nuclear fission reaction, the dating is not possible. For the hypothesis of a nuclear explosion and for a release from a steady state nuclear fission reaction the zero-times will differ. This assessment is fast, because we propose some constants that can be used directly for the calculation of zero time and its upper and lower age limits. The assessment is accurate because of the calculation of zero time using a mathematical method, namely the weighted least-squares method, to evaluate an average value of the age of a nuclear event. This was done using two databases that exhibit differences between the values of some nuclear parameters. As an example, the calculation method is applied for the detection of radionuclides La-140 and Ba-140 in May 2010 at the radionuclides station JPP37 (Okinawa Island, Japan).

Experimental and modeling study of the effect of CF3CHFCF3 on the chemical structure of a methane-oxygen-argon flame

The chemical structure of stoichiometric methane–oxygen–argon flames seeded or not with 1% heptafluoropropane (CF3CHFCF3) was measured by the molecular beam-mass spectrometry technique. Both flames were stabilized on a water-cooled flat-flame burner under low pressure (4.2 kPa). Mole fraction profiles were computed by a simulation code as well. Modeling of the unseeded flame was performed with an updated version of a mechanism issued from Warnatz. Two submechanisms were considered to model the chemistry of fluorinated species: (i) a mechanism proposed by Westbrook to model flame inhibition by CF3Br, (ii) a modified version of (i) validated recently by Sanogo in a modeling study of the effect of C2F6 on a methane flame. Both submechanisms were compared on the basis of their reaction pathways. They have in common a key role played by CF2 in the consumption of the fluorinated additive. The consumption of this radical forms CF that is consumed very slowly with Westbrook mechanism,in contradiction with experim...

Experimental and computational study of the effect of C2F6 on premixed methane flames

The objective of this work was to specify the mechanism of flame inhibition by compounds that do not contain bromine. Mole fraction profiles have been measured by molecular beam-mass spectrometer technique in a stoichiometric CH 4 /O 2 /Ar low-pressure flame seeded with and without 1% hexafluoroethane (C 2 F 6 ). For both flames, stable and reactive species concentrations have been computed and compared with experimental results in order to validate a detailed mechanism. Extension of the mechanism to atmospheric pressure was carried out by substituting the rate constant of a few reactions by high-pressure values. Mole fraction profiles computed in 1-atm-pressure stoichiometric methane-air flame were in very good agreement with Bechtels experimental results. Thus validated, the mechanism was used to compute the reduction in flame velocity that results from the addition of increasing amounts of the inhibitor to a methane-oxygen-nitrogen flame. Calculated flame velocities are in very close agreement with experimental values obtained with a premixed flame stabilized on an open tubular burner. This shows that inhibition efficiency of fluorinated compounds can be predicted very accurately.

Impact of pre-treatment by torrefaction and carbonization on temperature field, energy efficiency and tar content during the gasification of cotton stalks

The present study focused on the gasification of raw and pre-treated cotton stalks (CS) by torrefaction and carbonization. Temperature fields, mass balance, energy balance, energy efficiency and tar content of the gas were investigated for the gasification of different types of biomass materials (raw, torrefied and carbonized CS). High temperature and thick reduction zone were obtained during the gasification of pre-treated CS comparatively to the gasification of raw CS. Thus, the thermal and catalytic cracking of the tars may be more pronounced for the gasification of pre-treated biomass particularly for the carbonized biomass. Mass and energy balances have shown a reduction of biomass conversion during the gasification of torrefied and carbonized CS. Indeed, the energy efficiency of 58.7, 46.5 and 38.4% were obtained for raw, carbonized and torrefied CS, respectively. The lowest energetic performances were found during the gasification of torrefied CS due probably to the severe degree of the torrefaction. However, the tar content in gas was drastically decreased by the pre-treatment of the CS. Indeed, the tar contents of 4.41, 2.24 and 0.10 g/Nm3 were obtained for the gasification of raw, torrefied and carbonized CS, respectively. Key words: Biomass gasification, pre-treatment, tar content, energy efficiency.

Nuclear event zero time determination using analytical solutions of radioxenon activities under in-growth condition

Motivated by simplifying the calculation process of radioxenon isotopic activity used by scientist community in nuclear event characterization, the analytical formulas of the numbers of nuclides and isotopic activities of CTBT relevant radioxenon Xe-135, Xe-133m, Xe-133 and Xe-131m proposed in this work can be useful and incorporated in the calculation algorithms for nuclear event studies. The calculated ages using analytical formulas and radioxenon activity data from real observations compare well with the reported ages and show good results of event timing precision.