[en] Useful materials are separated as products or unnecessary materials are eliminated to remove from spent fuels in nuclear reactors by irradiaitng laser beams to atom beams or molecular beams as an object by utilizing the fact that the wavelength of the laser agrees with the spectral absorption band of aimed atoms and molecules. Further, for obtaining the atom or molecule beams, the spent fuels in the nuclear reactor are evaporated and thermally decomposed by electron beams. This enables not only the separation of uranium and plutonium but also concentration of uranium simultaneously. (T.M.)

[en] The fractional distillation characteristics of the materials used for the reactor pressure vessel made of ASTM A302B and the structures in reactor made of SUS304 which are the radioactive metallic waste of Japan Power Demonstration Reactor (JPDR) were analyzed numerically. In the simulation, the vaporization rates of the components of the waste were calculated by using the Langmuir's equation and Henry's law. As the result of simulation, it was calculated that ¹⁵²Eu, ¹⁵⁴Eu, ¹⁴C and ⁹⁴Nb can be reduced to less than clearance level by the fractional distillation. On the ASTM A302B case, it was pointed out that the other radioactive nuclei which are ⁵⁴Mn, ⁶⁰Co, ⁵⁹Ni and ⁶³Ni satisfy clearance level after 77 years cooling down. On the SUS304 case, it was pointed out that ⁵⁹Ni and ⁶³Ni must be separated to satisfy clearance level using isotope separation. (author)

[en] We measured and simulated the characteristics of vacuum distillation for duralumin (Aluminum alloy 7075: Al-5.6Zn-2.5Mg-1.6Cu-0.25Cr). In the experiment, the duralumin (378.7 mg) was heated to 1500 degC (the rate is 200 degC/h) and vaporized. The ion current of its components within the vapor was measured using quadrupole mass spectrometer. In the simulation, the vaporization rate of the components within vapor was calculated by using the formula of Langmuir and the law of Raoult. The simulation agreed well with the experiment, and it was found that the group of Al, Cu and Cr, and the group of Mg and Zn could be separated by the vacuum distillation. These results show that the reduction of metallic radioactive wastes can be attained using the vacuum distillation. (author)

[en] For the remote analysis of a next generation nuclear fuel material containing minor actinide (MA), we applied laser-induced breakdown spectroscopy (LIBS) to uranium oxide (U_3O_8), which included a small amount of neodymium oxide (Nd_2O_3), as a simulated sample of MA. By using a deconvolution technique for the Nd spectra in U, we separated the complex, overlapped, and confused spectra and determined their actual intensities. As a result, a calibration curve with good linearity and a detection limit of less than 700 ppm were demonstrated. (author)

[en] The fractional distillation characteristics at between 0 degC and 2500 degC (the rate is 200 degC/h) of radioactive metallic waste for JPDR which mainly consists of stainless steel were analyzed numerically. In the simulation, the vaporization rates of the components of JPDR waste were calculated by using the Langmuir's equation and Henry's law. As the results, it was calculated that ^152,154Eu, ¹⁴C and ⁹⁴Nb can be removed by the fractional distillation. On the other hand, ⁵⁴Mn and ⁵⁵Fe can be reduced by cooling them for about 30 years. Therefore, by removing ^59,63Ni and ⁶⁰Co using laser separation method, it will be possible to reduce the radioactive metallic waste by less than one hundredth. (author)

[en] For the separation of radionuclide from the radioactive metallic waste generated by the decommissioning of nuclear facilities, a new method combined with the distillation and laser separation is being developed. The characteristics of fractional distillation for duralumin (Aluminum alloy 7075: Al-5.6Zn-2.5Mg-1.6Cu-0.25Cr) are studied experimentally and theoretically for the first step. In the experiment, the duralumin (378.7 mg) is heated to 1773 K with the rate of 200 K/h and vaporized. The ion current of its components within the vapor is measured using quadrupole mass spectrometer. In the simulation, the vaporization rate of the components from the melt is calculated by using the Langmuir's equation and the Henry's law. The results of the simulation agree well with the experimental ones, and it is indicated that Al, Mg and Zn could be fractionated from duralumin. (author)

[en] Isotope shift of the recycled uranium atoms including the ²³⁶U was measured by laser induced fluorescence method. Eight even levels at 2 eV and three odd levels at 4 eV were measured with isotope shifts among ²³⁸U, ²³⁶U and ²³⁵U obtained. As for the measurement of the 4 eV levels, the Doppler free two photon absorption method was used, and the hyperfine structure of the ²³⁵U was analyzed simultaneously. The isotope shift of ²³⁴U was also observed in the three transition. (J.P.N.)

[en] Emission characteristics of gadolinium (Gd) oxide are studied, using ns and fs laser pulses for ablation in double-pulse laser induced breakdown spectroscopy (LIBS). In the current conditions of pulse energy and signal detection timing, emission intensity enhancement in the reheating mode is 25-fold, but little effect can be observed in a pre-pulse mode. It is shown that the optimum focus position of the ablation pulse is about 5 mm apart from the sample surface in the reheating mode. Although little emission can be observed in the single-pulse configuration with fs ablation pulses, the intense emission can be observed in the reheating mode in the double-pulse configuration. (orig.)

[en] For applying Laser-induced breakdown Spectroscopy (LIBS) to the analysis of nuclear fuel materials, it is very important to investigate the analytical method to identify the emission spectrum and its intensity on impurities intermingled within complex emission spectra of matrix elements such as uranium (U) and plutonium (Pu). Experiments using gadolinium (Gd) as simulated sample, in which several 100 ppm of copper (Cu) was contained, were performed and the analytical performance was estimated. The spectrum was decomposed into each peak of some spectra component on Gd and Cu. And the result, intensity of Cu component intermingled in Gd was determined quantitatively. In order to evaluate the linearity in the impurity analysis, the experiments with various concentration of Cu were carried out. The detection limit was determined to be about 70 ppm from the equivalent noise level which was estimated from the standard deviation in wavelength. The results curried out under the other laser conditions (intensity and wavelength) ware also evaluated. (author)

[en] We built a computation code for the coupled nonlinear Maxwell-Density Matrix equations of multi-level atomic systems including transverse and time-dependent variations. Numerical solutions for two-level atomic systems shown as a function of laser detuning in Na and U are in good agreement with the experimental result. Applying this code to the laser beam propagation through medium with two-step photo-ionization, it is concluded that the group velocity in the spatial edge of a laser pulse is slower than that in the center, and the self-focusing and the temporal reshaping of the laser pulse used for the first-excitation are more distinguished than that used for ionization. (author)