Hisayoshi Mitamura

Crystalline phases in a devitrified simulated high-level waste glass containing the elements of the platinum group

Abstract A borosilicate glass containing 20 wt% simulated high-level waste oxides was subjected to heat treatment at 700°C for 1000 h. Seven crystalline phases were newly formed by the treatment in addition to two phases, (Ru, Rh)O2 and (Pd, Rh, Te), which had already existed in the as-prepared simulated high-level waste glass. Among the new seven phases, five phases were certainly identified to be (RE)BSiO5, CeO2, SiO2, (RE)PO4 and (Sr, Ba, RE)MoO4. Of two unidentified phases, one was rich in silicon, chromium and rare earth elements (RE), and the other was rich in nickel and chromium. The crystalline phases of the elements of the platinum group facilitated the occurrence of the other phases and suppressed crystal growth.

Segregation of the elements of the platinum group in a simulated high-level waste glass

Segregation of the elements of the platinum group occurred during vitrification of the borosilicate glass containing 20 wt% simulated high-level waste oxides. The segregated materials were composed of two crystalline phases: one was the solid solution of ruthenium and rhodium dioxides and the other was that of palladium and rhodium metals also with tellurium. The segregated materials were not distributed homogeneously throughout the glass: (i) on the surface of the glass, there occurred palladium, rhodium and tellurium alloy alone; and (ii) at the inner part of the glass, the agglomerates of the two phases were concentrated in one part and dispersed in the other.

Development of ceramic waste forms for actinide-rich waste : Radiation stability of perovskite and phase and chemical stabilities of Zr- and Al-based ceramics

Abstract Ceramics are considered as most promising materials for conditioning of long-lived radionuclides because of their outstanding durability for long term. The Japan Atomic Energy Research Institute (JAERI) has developed ceramic waste forms, e.g. Synroc and zirconia-based ceramics, for the actinide-rich wastes arising from partitioning and transmutation processes. In the present study, α-decay damage effects on the density and leaching behavior of perovskite (one of three main minerals forming Synroc) were investigated by an accelerated experiment using the actinide doping technique. A decrease in density of Cm-doped perovskite reached 1.3 % at a dose of 9 × 10 17 α-decays·g −1 . The leach rates (MCC-1 leach test inpH ∼ 2 solution at 90°C for 2 months) of perovskite specimens with accumulated doses of 1.6 × 10 17 , 4.0 × 10 17 and 8.3 × 10 17 α-decays·g −1 were 1.7, 2.3 and 3.0 μ·m −2 ·day −1 , respectively. Application of zirconia- and alumina-based ceramics for incorporating actinides was also investigated by the experiments using non-radioactive elements (Ce and Nd) with an emphasis on crystallographic phase stability and chemical durability. The yttria-stabilized zirconia was stable crystallographically in the wide ranges of Ce and/ or Nd content and had excellent chemical durability.

Formation of goethite and hematite from neodymium-containing ferrihydrite suspensions

The effects of neodymium (Nd) on the transformation of ferrihydrite to iron oxides was studied. The possible isomorphous substitution of Nd3+ for Fe3+ in iron oxides was examined also. Nd was used as an inactive substitute of trivalent radioactive actinide elements. Hydrolysis of ferric nitrate solution containing 0–30 mole % of Nd formed Nd, Fe-rich ferrihydrite as initial precipitates, which were poorly crystalline. Aging of the Nd-containing ferrihydrite in 0.3 M OH− at 40°C and at pH 9.2 at 70°C formed Nd-free goethite and Nd-substituted hematite. The abundance of these crystalline phases was related to Nd in the parent solutions. Phase abundance, unit-cell parameters, and peak width were estimated by use of the Rietveld method.

Chemical Durability of Yttria-Stabilized Zirconia for Highly Concentrated TRU Wastes

Neptunium has an extremely long half-life and will be the main toxic element in the later stage of disposal. Yttria-Stabilized Zirconia (YSZ), with a fluorite structure, samples doped with Np-237 in high concentration (20, 30, 40 mol %) were fabricated (sintered in Air or Ar, at 1773 K, for 80 hours), and their leaching test (in deionized water, at 423 K, for 84 days) was carried out. The results indicated that the obtained leaching rates were much smaller than those of the Synroc and glass waste form, and that the increase in Np content did not cause any drastic changes in the leaching rates of Zr, Y, or Np. They were also compared to the results of YSZ doped with Ce or Nd used as surrogates for actinides. The work showed that YSZ doped with Np in high concentration has an excellent chemical durability

Small calciner for drying and calcination of SYNROC slurry

A laboratory scale calciner was developed in which a batch of SYNROC slurry could be dried and then calcined. A SYNROC sample was demonstratively prepared from a hydroxide-route slurry with the calciner. Results of x-ray diffraction and leach tests revealed that the calciner formed a SYNROC sample of good quality. It is also shown that the calciner is well adapted to a hot-cell apparatus for SYNNROC fabrication.

Well-type NaI(Tl) spectrometry for quantitative analysis of 244Cm leached from curium-doped synroc

Abstract The count rates in the 42.8-keV peak of 244Cm are integrated from 32.0 to 52.5 keV, and the net area under this peak is computed. The 244Cm activity is obtained by multiplying this area with the calibration factor, which is measured as a function of the volume of the curium solution. In the static leach test at 90°C, the normalized curium-leach rate does not vary significantly with time, and averages 1.1 × 10−3 g m−3 day−1 with an estimated total uncertainty of 75%.

Synthesis and Characterization of Copper Hydroxide Acetate With a Layered Discoid Crystal

Titration of copper acetate solution with a dilute NaOH solution to pH 6.5 and subsequent aging at 313 K yielded copper hydroxide acetate with an analytical composition of Cu2(OH)3.1(OCOCH3)0.9nH2O (n ∼ 0.7) and layered discoid crystals. The chemical composition, structure, and holistic trend in thermal behavior are similar to those of the previously known Cu2(OH)3(OCOCH3)H2O phase with layered rectangular crystals. The most obvious difference between the two compounds is morphology of the crystals. The other major differences are found in stability of bonding of the interlayer acetate ions to solid phase and behavior in anion-containing solutions. The interlayer acetate ions in the present compound begin to be dissociated from the solid phase at ∼343 K while those in the previous compound are not dissociated below 383 K. The reaction of the present compound is topotactic in Cl− and NO3− aqueous solutions but reconstructive in a SO42− aqueous solution while the reaction of the previous compound in those solutions is topotactic.

Radiation stability of ceramic waste forms determined by in situ electron microscopy and He ion irradiation

The radiation stability of polyphase titanate ceramic waste forms was studied using analytical transmission electron microscopy, in combination with in situ irradiation by 30 keV He{sup +} ions, followed by staged annealing. Two experiments were conducted. In the first, a reconnaissance investigation was made of the stabilities of the synthetic minerals hollandite, zirconolite, and perovskite when subjected to a total dose of 1.8 x 10{sup 17} He{sup +} cm{sup {minus}2}. It was found that all phases amorphized at approximately the same rate, but perovskite recovered its structure more rapidly and at lower temperatures than the other phases. In particular, annealing for 10 minutes at 1000{degrees}C was sufficient for perovskite to completely regain its crystallinity, while zirconolite and hollandite were only partially restored by these conditions. In the second experiment, the response of a thin hollandite crystal to irradiation was examined by selected area electron diffraction. At a dose of 1.5 x 10{sup 15} He{sup +} cm{sup {minus}2} its incommensurate superstructure was disrupted, but even at a dose of 3 x 10{sup 16} He cm{sup {minus}2} the hollandite subcell was largely intact. For this dose, total recovery was achieved by annealing for 1 minute at 1000{degrees}C.

Quantitative X-ray diffraction analysis of titanate waste forms and its application to damage ingrowth

Quantitative powder X-ray diffraction was used to analyze the phase assemblages of titanate nuclear waste ceramics doped with {sup 224}Cm and accumulating {alpha}-decay doses up to 1.24 {times} 10{sup 18} alpha-decay-events g{sup -1}. Among the Cm-bearing phases, perovskite is more susceptible to damage than zirconolite. Phases devoid of curium (hollandite and freudenbergite) experience a flux of ionizing radiation, and may also undergo radiation-induced structural degradation. The analysis demonstrated that a dose of 1.24 {times} 10{sup 18} alpha-decay-events g{sup -1} approximately 20 wt% of the waste phases remain aperiodic after annealing for 2 hours at 800{degrees}C.