Kenji Kikuchi

Physical properties, structure, and shape of radioactive Cs from the Fukushima Daiichi Nuclear Power Plant accident derived from soil, bamboo and shiitake mushroom measurements.

We conducted an elution experiment with contaminated soils using various aqueous reagent solutions and autoradiography measurements of contaminated bamboo shoots and shiitake mushrooms to determine the physical and chemical characteristics of radioactive Cs from the Fukushima Daiichi Nuclear Power Plant accident. Based on our study results and data in the literature, we conclude that the active Cs emitted by the accident fell to the ground as granular non-ionic materials. Therefore, they were not adsorbed or trapped by minerals in the soil, but instead physically adhere to the rough surfaces of the soil mineral particles. Granular Cs* can be transferred among media, such as soils and plants. The physical properties and dynamic behavior of the granular Cs* is expected to be helpful in considering methods for decontamination of soil, litter, and other media.

Research and Development Program on Accelerator Driven Subcritical System in JAEA

For a dedicated transmutation system, Japan Atomic Energy Agency (JAEA) has been proceeding with the research and development on an accelerator-driven subcritical system (ADS). The ADS proposed by JAEA is a lead-bismuth eutectic (LBE) cooled fast subcritical core with 800 MWth. JAEA has started a comprehensive research and development (R&D) program since the fiscal year of 2002 to acquire knowledge and elemental technology that are necessary for the validation of engineering feasibility of the ADS. In this paper, the outline and the results in the first three-year stage of the program are reported. Items of R&D were concentrated on three technical areas peculiar to the ADS: (1) a superconducting linear accelerator (SC-LINAC), (2) the LBE as spallation target and core coolant, and (3) a subcritical core design and reactor physics of the ADS. For R&D on the accelerator, a prototype cryomodule was built and its good performance in electric field was examined. For R&D on the LBE, various technical data for material corrosion, thermal-hydraulics and radioactive impurity were obtained by loop tests and reactor irradiation. For R&D on the subcritical core, engineering feasibility for the LBE cooled tank-type ADS was discussed using thermal-hydraulic and structural analysis not only in normal operation but also in transient situations. Reactor physics experiments for subcritical monitoring and physics parameters of the ADS were also performed at critical assemblies.

A Challenge for a High-Resolution Ag-In-Cd Decoupler in Intensified Short-Pulsed Neutron Source

A sharp pulsed-neutron beam, which has narrow width and large attenuation, will enhance ability to separate peak position diffracted from crystal structure in time-of-flight measurement method. Traditional technique to satisfy the request above is to use Boron for decoupling higher cut-off energy. Disadvantage, however, will be an excess formation of He bubbles and large heat deposition in the materials as a result of (n,α) reaction, particularly in a MW class of neutron source. Alternative is to use a material combination of Ag-In-Cd, which has different energies for resonance absorption and often used in the control rod of pressurized water reactors with cladding stainless steel. For application of this material to pulsed-neutron source a challenge is to make sandwiches structure with Al alloy because a moderator is made of this material from points of views of heat removing. Technically hot isostatic pressing was a choice and devoted to realize a bonding strength through R&Ds. Final product was set up to MLF /J-PARC and a successful resolution was observed in a powder diffractometer.