Decommissioning of the Plutonium Research Building No.1 (Plan and Present Status)

Komuro, Michiyasu; Kanazawa, Hiroyuki; Kokusen, Junya; Shimizu, Osamu; Honda, Junichi; Harada, Katsuya; Otobe, Haruyoshi; Nakada, Masami; Inagawa, Jun

JAEA-Technology 2021-042, 197 Pages, 2022/03

JAEA-Technology-2021-042.pdf:16.87MB

Plutonium Research Building No.1 was constructed in 1960 for the purpose of establishing plutonium handling technology and studying its basic physical properties. Radiochemical research, physicochemical research and analytical chemistry regarding solutions and solid plutonium compounds had been doing for the research program in Japan Atomic Energy Agency (JAEA). In 1964, the laboratory building was expanded and started the researching plutonium-uranium mixed fuel and reprocessing of plutonium-based fuel, playing an advanced role in plutonium-related research in Japan. Since then, the research target has been expanded to include transplutonium elements, and it has functioned as a basic research facility for actinides. The laboratory is constructed by concrete structure and it has the second floor, equipped with 15 glove boxes and 4 chemical hoods. Plutonium Research Building No.1 was decided as one of the facilities to be decommissioned by Japan Atomic Energy Agency Reform Plan in September 2014. So far, the contamination survey of the radioactive materials in the controlled area, the decontamination of glove boxes, and the consideration of the equipment dismantling procedure have been performed as planned. The radioisotope and nuclear fuel materials used in the facility have been transfer to the other facilities in JAEA. The decommissioning of the facility is proceeding with the goal of completing by decommissioning the radiation controlled area in 2026. In this report, the details of the decommissioning plan and the past achievements are reported with the several data.

Carrying-out of whole nuclear fuel materials in Plutonium Research Building No.1

Inagawa, Jun; Kitatsuji, Yoshihiro; Otobe, Haruyoshi; Nakada, Masami; Takano, Masahide; Akie, Hiroshi; Shimizu, Osamu; Komuro, Michiyasu; Oura, Hirofumi*; Nagai, Isao*; et al.

JAEA-Technology 2021-001, 144 Pages, 2021/08

JAEA-Technology-2021-001.pdf:12.98MB

Plutonium Research Building No.1 (Pu1) was qualified as a facility to decommission, and preparatory operations for decommission were worked by the research groups users and the facility managers of Pu1. The operation of transportation of whole nuclear materials in Pu1 to Back-end Cycle Key Element Research Facility (BECKY) completed at Dec. 2020. In the operation included evaluation of criticality safety for changing permission of the license for use nuclear fuel materials in BECKY, cask of the transportation, the registration request of the cask at the institute, the test transportation, formulation of plan for whole nuclear materials transportation, and the main transportation. This report circumstantially shows all of those process to help prospective decommission.

Laser ablation absorption spectroscopy for isotopic analysis of plutonium; Spectroscopic properties and analytical performance

Miyabe, Masabumi; Oba, Masaki; Jung, K.; Iimura, Hideki; Akaoka, Katsuaki; Kato, Masaaki; Otobe, Haruyoshi; Khumaeni, A.*; Wakaida, Ikuo

Spectrochimica Acta, Part B, 134, p.42 - 51, 2017/08

https://doi.org/10.1016/j.sab.2017.05.008

Spectroscopic properties of atomic species of plutonium were investigated by combining laser ablation and resonance absorption techniques for the analysis of a plutonium oxide sample. For 17 transitions of Pu atoms and ions, the absorbance, isotope shift, and hyperfine splitting were determined via Voigt profile fitting of the recorded absorption spectra. Three transitions were selected as candidates for analytical use. Using these transitions, we investigated the analytical performance that was attainable and determined a correlation coefficient R2 between the absorbance and plutonium concentration of 0.9999, a limit of detection of 30-130 ppm, and a relative standard deviation of approximately 6% for an abundance of Pu of 2.4%. These results demonstrate that laser ablation absorption spectroscopy is applicable to the remote isotopic analysis of highly radioactive nuclear fuels and waste materials containing multiple actinide elements.

Deposition of uranium oxide following the reduction in weak acid solution using Electrochemical Quartz Crystal Microbalance (EQCM)

Ouchi, Kazuki; Otobe, Haruyoshi; Kitatsuji, Yoshihiro; Yamamoto, Masahiro

ECS Transactions, 75(27), p.51 - 57, 2017/01

https://doi.org/10.1149/07527.0051ecst

We investigated the deposition of U(IV) following a valence change of U as electrodeposition using an electrochemical quartz crystal microbalance (EQCM). When measurements of the reduction of U(VI) in a weak acid solution were performed, deposits of U(IV) were observed on the electrode surface. From deposition rates, pH dependence of them, and oxidation potentials of deposits, we proposed the following deposition mechanism. The deposition is divided into the three phases; First, in the induction phase, U(IV) produced by the disproportionation forms U(IV) hydroxide nucleus. Next, in the growth phase, U(IV) deposits begin to grow. In this phase, the deposits catalyze the reduction of U(V) to U(IV), resulting an increase of the reduction current. Finally, in the transformation phase, U(IV) hydroxide species transform into U dioxide having more stable state.

Measurement of uranium spectrum using laser induced breakdown spectroscopy; High resolution spectroscopy (350-470 nm)

Akaoka, Katsuaki; Oba, Masaki; Miyabe, Masabumi; Otobe, Haruyoshi; Wakaida, Ikuo

JAEA-Research 2015-012, 48 Pages, 2015/10

JAEA-Research-2015-012.pdf:2.22MB

It is important to analyze the next generation nuclear fuel material containing minor actinide (MA) and the fuel debris generated at the accident of Fukushima Daiichi Nuclear Power Station. Therefore, the remote analysis for nuclear fuel materials using Laser Induced Breakdown Spectroscopy (LIBS) is studied. For applying Laser Induced Breakdown Spectroscopy (LIBS) to the analysis of nuclear fuel materials, it is very important 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). Then, the high resolution spectra of natural uranium of wavelength region of 350-470 nm are measured using LIBS, 247 atomic spectra and 294 single ion spectra were identified. We have confirmed that the measured wavelength and oscillator strength of spectra are consistent with published values.

Corrosion of uranium and plutonium dioxides in aqueous solutions

Otobe, Haruyoshi; Kitatsuji, Yoshihiro; Kurata, Masaki; Takano, Masahide

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 11 Pages, 2014/10

The chemical and transport behaviors of Pu and U in the corroded debris must be understood for the criticality safety control of Pu and U in the debris, especially for the removal operations and storage. Therefore, the chemical changes of UO and PuO powders, disks and U and Pu metal disks in HO aqueous solution have been checked, where HO is formed by the radiolysis of HO. As a result, UO changed to hydrated uranium peroxide, whereas the PuO remained unchanged. U metal was more reactive with HO aqueous solution than Pu metal. The chemical changes of the mixed UO/PuO powders in HO aqueous solution have been investigated. The dried slurry of the middle zone of HO aqueous solution was mainly composed of hydrated uranium peroxide, whereas the dried powder of the bottom zone was mainly composed of PuO.

Oxygen defects of actinide, lanthanide oxides, and their solid solutions

Otobe, Haruyoshi

Journal of Nuclear Materials, 442(1-3), p.394 - 399, 2013/11

https://doi.org/10.1016/j.jnucmat.2013.07.015

The chemical properties (ex. atomic diffusion), the thermal properties (ex. melting point and thermal diffusivity) and the mechanical properties of oxide fuels are significantly dependent on the oxygen defects of the oxide fuels. For the first step to specify the oxygen defects of oxide fuels, we have tried the thermodynamic approaches to the oxygen defects by comparing the relations between the molar ratio of oxygen to metal (O/M) and the oxygen potentials of Pu, Am, Cm, Ce oxides and several solid solutions including Zr and Np dioxides. Consequently, we have found the consistent properties in the relations between O/M and the oxygen potentials of actinide, lanthanide oxides and their solid solutions, in addition to the dependence of the relations on the crystal structures.

Oxygen potentials of pyrochlore-type AmZrO

Otobe, Haruyoshi; Takano, Masahide; Hayashi, Hirokazu; Arai, Yasuo

Journal of the American Ceramic Society, 94(10), p.3596 - 3599, 2011/10

https://doi.org/10.1111/j.1551-2916.2011.04617.x

The relations between the oxygen potentials and the oxygen-nonstoichiometry () of the pyrochlore-type AmZrO for 1333 K were measured by the electrochemical method using a zirconia solid electrolyte and the mass changes by the oxidation and reduction. It was found that the oxygen potential of AmZrO smoothly increased from -516.52 to 0 kJ/mol with increasing from 0.0 to 0.56 at 1333K. The oxygen potentials of AmZrO were higher than those of AmO at the corresponding O/M by approximately 130 kJ/mol. The difference of the oxygen potentials between AmZrO and AmO was consistent with that between PuZrO and PuO considering the difference of the ionic radii between Am and Pu. This leads to the systematical understanding of the thermodynamic properties of the transuraniumm oxides.

Laser induced breakdown spectroscopy analysis of the uranium including calcium; Dependence of laser power (Contract research)

Akaoka, Katsuaki; Maruyama, Yoichiro; Oba, Masaki; Miyabe, Masabumi; Otobe, Haruyoshi; Wakaida, Ikuo

JAEA-Research 2010-036, 14 Pages, 2010/10

JAEA-Research-2010-036.pdf:2.18MB

For the remote analysis of low DF TRU (Decontamination Factor Transuranic) fuel, Laser Induced Breakdown Spectroscopy (LIBS) was applied to uranium oxide including a small amount of calcium oxide (3306ppm(weight)) as a sample, and the spectrum emitted from laser-breakdown plasma was examined. The characteristics, such as spectrum intensity and plasma excitation temperature as a function of laser power, were measured using time-resolved spectroscopy. As a result, the laser power of around 5 mJ was found optimum to obtain the stable intensity and narrow line width of spectrum.

Oxygen potential measurements of CmPuO by EMF method

Otobe, Haruyoshi; Akabori, Mitsuo; Arai, Yasuo

IOP Conference Series; Materials Science and Engineering, 9, p.012015_1 - 012015_7, 2010/05

https://doi.org/10.1088/1757-899X/9/1/012015

The dependence of the oxygen potentials on oxygen nonstoichiometry () and temperature of CmPuO was measured by electromotive force (EMF) measurements. The coulomb titration has been made for the sample at the intervals of 40 K between 1173 and 1333 K over the range of 0.018 0.053. The oxygen potentials decreased gradually from -31.02 to -117.48 kJmol with increasing from 0.018 to 0.045, and the rapidly decreased from -117.48 to -283.74 kJmol up to 0.053. The temperature dependence of the oxygen potentials was also measured between 1173 and 1333 K for several constant values. The temperature dependence was almost linear over the and temperature ranges concerned.