Motoharu Mizumoto

Review of research and development of accelerator-driven system in Japan for transmutation of long-lived nuclides

Abstract Active and comprehensive studies on an accelerator-driven subcritical system (ADS) for transmutation of long-lived nuclides have been carried out at the Japan Atomic Energy Research Institute (JAERI). In the late 1970s, JAERI started the basic study of this subject and later, comprehensive studies have been performed under the “OMEGA” program of Japan: the long-term program for research and development on partitioning and transmutation (P&T) technology. Based on a design study of a dedicated transmutation system, JAERI decided to concentrate its efforts for transmutation study on the development of ADS. The construction of an experimental facility for the ADS development was proposed as a part of the Neutron Science Project of JAERI, which aimed at the construction of the world most powerful spallation neutron source. Since 1998, JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing a High-Intensity Proton Accelerator Project. An ADS experimental facility composed of a subcritical assembly and a liquid lead-bismuth target/coolant engineering facility will be constructed under this project. In this paper, the development of ADS at JAERI, together with related technologies of P&T, both under the OMEGA program and the joint proposal, is reviewed. Other activities on ADS study in Japan are also reviewed.

Partitioning and transmutation studies at JAERI both under OMEGA program and high-intensity proton accelerator project

Abstract At the Japan Atomic Energy Research Institute (JAERI), active and comprehensive studies on partitioning and transmutation (P&T) of long-lived nuclear waste from the reprocessing processes of spent fuel has been carried out under the OMEGA program. Studies at JAERI include a design study of dedicated transmutation systems both of an MA burner fast reactor (ABR) and an accelerator-driven subcritical system (ADS), and the development of a high intensity proton accelerator as well as the development of partitioning process, nitride fuel fabrication/dry separation process technologies and nuclear data studies. During the course of studies, JAERI developed the concept of the double-strata fuel cycle, in which a dedicated system is used for transmutation. Comparing the various transmutation systems, such as thermal neutron spectrum or fast neutron spectrum systems, power reactors or dedicated systems, from the viewpoints of reactor physics, nuclear fuel cycle and socio-technical issues, it was concluded that the ADS is the best option for transmutation of minor actinide(MA). JAERI, therefore, decided to concentrate its R&D efforts on the development of ADS and related technologies. One of the goals of R&D is to provide a basis for designing demonstration facilities of ADS, aqueous partitioning process and nitride fuel fabrication and dry separation technologies. As the initial step toward this purpose, the construction of an ADS experimental facility is planned under the High-Intensity Proton Accelerator Project which JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing since 1998. The paper discusses the some of the results of P&T studies and the outline of the High-Intensity Proton Accelerator Project under which ADS experimental facility will be constructed.

FEASIBILITY OF LEAD-BISMUTH-COOLED ACCELERATOR-DRIVEN SYSTEM FOR MINOR-ACTINIDE TRANSMUTATION

The feasibility for the lead-bismuth-cooled accelerator-driven system (ADS) to transmute minor actinides partitioned from high-level radioactive waste is discussed. Since lead-bismuth will cause considerable corrosion and erosion effects at high temperature, the fuel-clad temperature must be kept as low as possible. Moreover, the most critical issue of the ADS design is the engineering viability of the high-power spallation target and the beam window. The thermal-hydraulic and structural analysis was carried out for both the fuel assembly and the beam window. In addition to the analysis in steady state, the transient behaviors were also studied during typical transient and unprotected accidents. The results showed that engineering viability is reasonably achievable in the nominal operation. For the beam trip, which will be the most frequent transient, the number of events to cause the failure of the beam window is estimated as more than 105. For safety aspects of the ADS during unprotected accidents, the estimated results showed that unprotected loss of flow would cause the most significant problem, if the beam operation was kept. Therefore, high reliability of the beam shutdown is required for the ADS safety.

Consistent description of collective level structure and neutron interaction data for 12C in the framework of the soft-rotator model

Abstract We have measured the neutron elastic and inelastic scattering angular distributions of 12C at 28.2 MeV. This data, together with information from other works, was used to construct a neutron scattering data-base in the energy region from 20 to 40 MeV. Then, a systematic analysis of nuclear structure and neutron interaction data for 12C was carried out in the framework of the soft-rotator model. The model was firstly applied to analyse the low-lying collective level structure of the 12C nucleus successfully. The intrinsic wave function obtained in such an analysis was then used to construct the coupling potentials in the coupled-channels formalism to calculate the neutron total and scattering cross sections. The quadrupole deformation parameter obtained in the present analysis was 0.164, which was much smaller in the absolute sense than the value used in the rotation-vibration model employed frequently in the past, i.e. ≈0.6. When averaged over the β-vibration function, however, the present result yields an effective quadrupole strength of about the same scale as the previous studies due to softness of the 12C wave function with respect to β2 degree of freedom. The soft-rotator model was found to be very successful in reproducing both the structure and neutron scattering data consistently for the first time in this mass region.

Development of a H− ion source for the high intensity proton linac at Japan Atomic Energy Research Institute

A volume production type negative ion source has been designed and tested for the high intensity proton linear accelerator at Japan Atomic Energy Research Institute. The dimensions of the plasma chamber are 150 mm in diameter and 200 mm in length. The beam extractor consists of four electrodes with a single aperture of 8 mm in diameter. Negative ion current (density) of 40 mA (80 mA/cm2) was achieved with a duty factor of 5%.

Differential α-Production Cross Sections of Iron and Nickel for 4.3 to 14.1 MeV Neutrons

Differential α-Production Cross Sections of Iron and Nickel for 4.3 to 14.1 MeV Neutrons Mamoru BABA a , Nobuo ITO a , Isamu MATSUYAMA a , Shigeo MATSUYAMA a , Naohiro HIRAKAWA a , Satoshi CHIBA b , Tokio FUKAHORI b , Motoharu MIZUMOTO b , Kazuo HASEGAWA b & Shinichiro MEIGO b a Department of Nuclear Engineering , Tohoku University , Aramaki, Aoba-ku, Sendai , 980-77 b Japan Atomic Energy Research Institute , Tokai-mura, Ibraki-ken , 319-11 Published online: 15 Mar 2012.

The influence of water absorption in samples for neutron capture cross section measurements

Abstract Sample-related corrections for average neutron capture cross section measurements are complicated in the keV region due to the resonance structure. In particular, light mass nuclei present in chemical compounds of rare earth materials make corrections for neutron multiple-scattering and self-shielding difficult. Moreover, samples of chemical compounds such as oxides are hygroscopic. A Monte Carlo method has been developed by taking into account the effects caused by neutron slowing down into the resonance region due to the scattering from hydrogen and oxygen atoms. The validity of the calculated corrections has been investigated by comparing experimental data of oxide and metallic samples. The calculation method and related problems will be discussed.

Neutron resonances in 133Cs

Neutron capture and neutron transmission measurements on 133Cs were made to obtain neutron resonance parameters. Neutron capture areas up to 2 keV and neutron widths up to 5.9 keV for each resonance were derived. Below 100 eV five neutron radiative capture widths were obtained from the shape analysis of the transmission data. The following average s-wave resonance parameters were obtained: S0 = (0.77 ± 0.09) × 10−4, D = 22.4 ± 1.5 eV, \qGγ = 119 ± 3 meV. The distribution of the level spacings is consistent with the two-population Wigner distribution predicted theoretically. The statistic Δ3 is in good agreement with the value which Dyson and Mehta derived by using the orthogonal ensemble.

Neutron resonance parameters and radiative capture cross sections of 147Sm and 149Sm

Abstract Neutron capture and transmission measurements have been carried out on the separated isotopes of 147 Sm (98.34 %) and 149 Sm (97.72 %) at the 55 m time-of-flight station of the Japan Atomic Energy Research Institute electron linear accelerator. Resonance energies and neutron widths for a large number of resolved resonances were determined up to 2 keV for 147 Sm and 520 eV for 149 Sm. Radiation widths for 5 resonances in 147 Sm + n and 7 resonances in 149 Sm + n were derived. The s-wave strength functions, average level spacings and average radiation widths were obtained to be: 10 4 S 0 = 4.8 ± 0.5, D = 5.7 ± 0.5 eV and Γ γ = 69 ± 2 meV for 147 Sm ; a 10 4 S 0 = 4.6 ± 0.6, D = 2.2 ± 0.2 eV and Γ γ = 62 ± 2 meV for 149 Sm . The average capture cr sections were deduced from 3.3 to 300 keV with an estimated accuracy of 5 to 15 %. The measured capture cross sections for 149 Sm are largely different from the evaluated data, which are obtained based on the statistical model calculation. Possible reasons for this disagreement are discussed.

Development of a high brightness negative hydrogen ion source

A high brightness negative hydrogen ion source has been developed for a high intensity proton linear accelerator. The ion source is volume production type. Negative ions are generated in a magnetically filtered multicusp plasma generator. The negative ion production is enhanced by seeding a small amount of cesium into the plasma generator. A negative hydrogen ion beam of 36 mA was extracted from a single aperture at an acceleration voltage of 50 kV. To obtain a higher ion beam current, the focusing of beamlets extracted from the multiaperture grid has been demonstrated with an aperture displacement technique.