[en] The performance of a continuous neutron source using an electron accelerator was evaluated by computer simulation codes (EGS4 and MCNP) in terms of neutron yield, neutron flux distribution, neutron spectrum, and heat distribution. Electrons with energies from 10 to 100 MeV were injected into a tungsten converter in order to generate photons by bremsstrahlung. When the photon irradiated a heavy water (DS₂O) target, neutrons were produced by photonuclear reaction in the D₂O target. This type of source was optimized for target geometry and electron energy from the point of neutron yield. The neutron spectrum was found to have two characteristic peaks, at the low-energy (thermal) region and the high-energy (million-electron-volt) region. The maximum photoneutrons per 1,000 MeV of electron energy was 0.56 at the electron energy of 30 MeV. In the case of irradiation by a 30-MeV, 33-mA continuous electron beam, the maximum thermal neutron flux was on the order of 10¹¹ cm^-2·s^-1

[en] Two transmutation methods, the spallation neutron and the muon-catalyzed fusion methods, both which use an accelerator, are employed for the transmutation of long-lived nuclides in high-level radioactive wastes. The transmutation energies and the effective half-lives of ⁹⁹ T_c for both transmutation methods are calculated by the Monte Carlo simulation codes for particle transport, the NMTC/JAERI code and the MCNP code. Both methods could obtain short effective half-lives, which are 17 times smaller than those of a fission reactor. The transmutation energies are calculated to be 25 to 55 MeV for both methods. These calculated transmutation energies reveal that it is possible for the foregoing two methods for transmutation of ⁹⁹ T_c to meet the energy balance criterion

[en] The mass yield distributions and the nuclear transmutation ratios of ²³⁷Np and ²³⁸U by photofission were measured by using the bremsstrahlung beam of 20-, 30- and 60-MeV energies. (author)

[en] The recoil properties in photonuclear (γ,n) reactions were measured by catcher foil method using natural copper and cesium chloride targets for the application to the transmutation of long-lived radioisotopes such as ¹³⁷Cs in high radioactive waste. The targets were prepared by a vacuum evaporation method. A stack consisting of target, catcher and beam monitor foils was placed in an evacuated chamber and irradiated with uncollimated electron-free bremsstrahlung. The recoil range was estimated from the radioactivities observed in the target and catcher foil, and the recoil energy calculated from a range-energy relation. As a result, it was found that the range caused by absorption of incident bremsstrahlung was one order of magnitude lower than the range caused by neutron emission from target nuclei in an excited state. This technique was applied to measurement of (γ,n) reaction cross section from radioisotope target of ¹³⁷Cs. (author)

[en] This paper shows the absolute yields for the mass distribution of photofission products of ²³⁸U, ²³⁷Np and ²³⁹Pu. The thin targets of ²³⁸U, ²³⁷Np and ²³⁹Pu were irradiated with the bremsstrahlung beam whose end-point energy was 20-, 30- and 60-MeV. Fission fragments recoiled out from the target were catched on the aluminum foil. The mass-yield distributions of fission fragments were obtained by measuring gamma-ray activities with a pure-Ge detector. Our mass distribution curves showed good agreement with the other experimental results. (author)

[en] Two transmutation methods of ¹³⁷Cs using a proton accelerator were evaluated in terms of the effective half life and the transmutation energy. One was the proton method which mainly used high energy proton spallation reaction for transmutation, and the other was the spallation neutron method which mainly used thermal neutron capture reaction. The transmutation energies and the effective half lives for the two transmutation methods were calculated by Monte Carlo simulation codes for particle transport, the NMTC/JAERI code and the MCNP code. The calculated transmutation energies were 510 MeV and 570 MeV for the spallation neutron method and the proton method, respectively, for an effective half life of 2 yr for ¹³⁷Cs. (author)

[en] In Japan Atomic Energy Agency (JAEA), an innovative centrifugal contactor system has been developed for a future reprocessing plant. It was confirmed that it had a higher extraction capacity through the uranium test already. But it was necessary that it had the higher mechanical reliability to be applied in a reprocessing plant. In this study, two types of driving units that use a ball bearing or a magnetic bearing have been developed for it. It was confirmed that they had enough abilities trough endurance tests. The driving unit with ball bearing could be operated continuously for 5000 hours that was equal to a term of an annual operation. It was found that it could be operated for a year without maintenance. JAEA will continue to improve them and select more advantageous one on the basis of economy and lifetime in near future. (authors)

[en] The Japan Atomic Energy Agency has been developing centrifugal contactors for solvent extraction to apply to next-generation reprocessing plants. The centrifugal contactor has some attractive advantages such as more compact design and shorter liquid residence times than conventional contactors. Many kinetic studies using a miniature centrifugal contactor have been carried out worldwide. However, there are few engineering-scale studies in which stage efficiencies, transition behavior of concentration profiles, and robustness under maloperation conditions have been comprehensively discussed for a contactor cascade system. In this study, we carried out extraction and stripping tests of an engineering-scale centrifugal contactor cascade system based on a flowsheet of 10 kg-HM/h using uranyl nitrate solution. As a result, the stage efficiencies on uranium extraction and stripping were quite high, nearly 100% for extraction and 97-98% for stripping. The uranium concentration profiles became stable within 10 minutes for both extraction and stripping sections. No overflow or entrainment was observed under normal operation during the extraction and stripping tests. During the stripping test, it was estimated that an increase in temperature of the feed stripping solution from 308 to 333 K or a decrease in the flow rate ratio of the organic to aqueous phase from 1.0 to 0.8 corresponded to the distribution capacity of the two contactors. The maloperation test, in which a motor at a stage of the contactor cascade system was intentionally stopped, showed that the system could maintain stable operation with no emergency shutdown following the installation of at least two additional stages. (author)

[en] The electrowinning process is pyrochemical reprocessing method for spent oxide fuel and includes severe corrosion environment due to high temperature and corrosive gas. As one of important subjects in electrowinning process, the improvement of corrosion resistance should be required to make the process fit for practical use. The application of cold crucible technology is useful option to achieve it. In this study, the corrosion tests of several metals in molten 2CsCl-NaCl mixed salt blowing chlorine gas were carried out under the controlled material temperature by air cooling to discuss the application of cold crucible induction melting (CCIM) technology on the electrowinning process. As results, it is experimentally shown that HASTELLOY C-22 exhibited the best corrosion resistance in both molten salt and vapor phases and the corrosion rate was less than 0.1 mm/y by cooling the material surface at 200degC. It is due to lower temperature of material surface and scull barrier of solidificated salt. From above results, are remarkable improvement of corrosion resistance was achieved by the application of cold crucible technology and HASTELLOY alloy could be proposed as promising candidate material for the crucible. Based on the results of corrosion test, the crucible made of HASTELLOY alloy was actually manufactured to demonstrate the heat performance on engineering scale and 2CsCl-NaCl mixed salt was melted in the crucible by CCIM device. The heat performance of HASTELLOY crucible on induction heating was efficiently good and the induction heating gave rapid melting of salt. It shows excellent adaptation to apply CCIM to pyrochemical electrolyzer. These results gave the promising prospect to solve the corrosion problem in electrowinning process. (author)

[en] The thermo-chemical and electrolytic hybrid hydrogen production process has been developed by Japan Nuclear Cycle Development Institute (JNC). The process is based on sulfuric acid (H₂SO₄) synthesis and decomposition process developed earlier (Westinghouse process) and sulfur trioxide (SO₃) decomposition process is facilitated by electrolysis with ionic oxygen conductive solid electrolyte at 500degC-550degC. Stable hydrogen and oxygen production for several hours by the process was already confirmed in the experiments performed by JNC. The experiment for about 60 hours was performed to investigate the durability of the experimental apparatus by the hybrid process. In the experiment, 50wt% sulfuric acid was circulated in the experimental apparatus at the flow rate of 0.6 ml/min, and SO₃ electrolysis cell was operated at 550degC. The cell voltage of SO₃ electrolysis cell and SO₂ solution electrolysis cell were kept to 0.13 V and 0.9 V, respectively. Stable oxygen generation from SO₃ electrolysis cell was observed during the experiment and no degradation were observed in the Pt plated YSZ electrolyte. Nevertheless, outlet pipe of SO₃ electrolysis cell was corroded by high temperature sulfuric acid and hydrogen generation rate in SO₂ solution electrolysis cell decreased in several hours. The cause of the corrosion of outlet pipe of SO₃ electrolysis cell and the decrease of hydrogen generation rate was investigated and the technical problems for manufacturing a higher performance (1NL/h) experimental apparatus were extracted. (author)