Taneaki Yahata

Kinetic studies of the fluorination of uranium oxides by fluorine—I: The fluorination of U3O8 and UO3

Abstract The reactions of U 3 O 8 and UO 3 with fluorine have been studied in the temperature range from 350 to 440°C with a thermobalance. The overall reaction consists of two steps. In the first step reaction, these oxides change to uranyl fluorides and in the second to UF 6 . In the case of U 3 O 8 , the first step reaction influenced the rate of the second step, so that the formation of the UF 6 was slow at first, where an induction period was seen, and finally followed the linear law. The rate of the first step reaction of UO 3 was much faster than the second step, and the great part of the overall reaction followed the linear law. The activation energies of the second step reactions for U 3 O 8 and UO 3 were 21·3 and 22·0 kcal/mole respectively. An almost linear relationship was found to exist between the reaction rate and the partial pressure of fluorine. For U 3 O 8 , the formation rate of UF 6 was nearly proportional to the surface area determined by gaseous adsorption.

The variation of lattice parameter with hydrogen content of non-stoichiometric plutonium dihydride

Abstract The relation between composition and lattice parameter of non-stoichiometric plutonium dihydride (cub.) has been studied. The samples were prepared by two different methods, namely, thermal decomposition of PuH3.0 and hydrogenation reaction of the lower hydrides. As the H/Pu mole ratio increased from 2·0 to 2·7, the lattice parameter of PuH2+x lineally decreased from 5·360 to 5·340A˚. The influence of the oxidation on the lattice parameter was also given.

Treatment of Ion-Exchange Resins by Fluidized Bed Incinerator Equipped with Copper Oxide Catalyst Fundamental Studies

Thermal decomposition behavior for ion-exchange resins in air flow was examined by differential thermobalance. The resins were decomposed in three steps: first, by water evaporation; second, by functional group decomposition, and finally by base polymers combustion. Following this work, the incineration of resins was examined, using a fluidized bed incinerator with copper oxide catalyst, which had been installed at the freeboard. The resins were burned at about 750°C in fluidized bed. Any combustibles remaining in the off-gas were incinerated by catalytic oxidation at the surface of the copper oxide catalyst at 650°C. From this experiment, it was confirmed that the incineration with copper oxide catalyst is feasible for treatment of ion-exchange resins. In-situ desulfurization of nascent sulfur dioxide in fluidized bed by Ca(OH)2 was also examined, and was found effective. However, the excess Ca(OH)2 would be adsorbed on the surface of the catalyst or accumulated in pipelines, and further block the gas fl...

Electrical conductivity anomaly in near-stoichiometric plutonium dioxide

The variation of the electrical conductivity with oxygen pressure has been measured for plutonium dioxide at temperatures between 950 and 1100°C and in the oxygen partial pressure range from 2.1 × 104to 10−11 Pa. Minima in electrical conductivity and corresponding transitions from n- to p-type conduction as function of the oxygen partial pressure were observed. These minima could occur by the presence of some impurities, but the possibility of the existence of hyperstoichiometric PuO2 also could not be excluded by considering the concentration of the impurities. An intrinsic band-gap energy of 2.5 eV was calculated from the temperature dependence of the minimum electrical conductivity. The slopes of the plot of log o against log PO2 for the n-type region were −14.99, −14.72, −14.77 and −14.81 at 950,1000, 1050 and 1100°C, respectively, which are in good agreement with the values reported previously. The ionized oxygen vacancy model seems to be reasonable in the n-type region.

A study of ammonium plutonium(IV) fluorides—II: The thermal decomposition of ammonium plutonium(IV) fluorides, ammonium cerium(IV) fluoride and ammonium uranium(IV) fluoride

Abstract Thermal decomposition of PuF 4 · 7 6 NH 4 F (or PuF4·NH4F), PuF4·2NH4F, CeF 4 · 7 6 NH 4 F (or CeF4·NH4F) and UF 4 · 7 6 NH 4 F (or UF4·NH4F) have been studied under vacuum and in inert gas flow, using a microthermobalance. The anhydrous PuF3, CeF3 and UF4 were obtained as the decomposition products. The following reactions appeared to occur in thermal decomposition of these double salts. 1 M F 4 · 7 6 NH 4 F = M F 3 + 5 6 NH 4 F + 8 6 HF + 1 6 N 2 (M = Pu and Ce ) 2 UF 4 · 7 6 NH 4 F = UF 4 + 7 6 NH 4 F .

A study of ammonium plutonium(IV) fluorides—I: The preparation of ammonium plutonium(IV) fluorides

Abstract The preparation of ammonium plutonium(IV) fluorides from the mixed solution of 0–10M NH4F and 0–10M HF has been studied. The valency of Pu(IV) was adjusted by controlled potential electrolysis or by addition of NH4NO2 solution. The precipitates obtained from Pu(IV) adjusted by controlled potential electrolysis were pink 6PuF4·7NH4F (or PuF4 · NH4F) and green PuF4·2NH4F; the former was precipitated from 0·5-2M NH4F, while the latter from 4–10M NH4F, and mixed precipitates were obtained in the concentration region of 2–4M NH4F. The solubility of plutonium has a minimum at 0·5M NH4F and then increases rapidly with the concentration of NH4F. The precipitates obtained from Pu(IV) adjusted by NH4NO2 solution were a pink 6PuF4·7NH4F(or PuF4 ·NH4F) and a red new compound showing a different X-ray pattern and PuFNH3 mole ratio 1·0:5·6-5·8:0·7-0·8.

Preparation of Plutonium Metal, (I)

Ammonium plutonium(IV) fluorides, PuF4.7/6NH4F and PuF4.2NH4F, were prepared by the addition of an acidic solution containing Pu(IV) to a mixed solution of NH4F and HF. Anhydrous PuF3 was obtained by thermal decomposition of the ammonium plutonium(IV) fluorides under reduced pressure or else in an inert gas flow. The anhydrous fluoride was then reduced with Li vapor to Pu metal. Cerium metal was prepared by the same method.

Fluorination of Uranium Metal by Fluorine Gas

A study has been made on the fluorination of uranium metal chips to UF6 with fluorine gas in the temperature range of 100° to 400°C. The formation of UF6 was influenced by the concentration and the flow rate of fluorine gas and by the reaction temperature. The reaction occurred apparently above 200°C. Uranium metal was first converted to low fluorine content compound such as UF3 or UF4-x, then to UF4 and finally to UF6. The intermediate compounds were confirmed by X-ray analysis and by their color.

Preparation of Plutonium Metal, (I):Preparation of Plutonium Metal by Lithium Reduction of Ammonium Plutonium(IV) Fluoride

A method of producing Pu metal by the reduction of sodium plutonium(IV) fluoride is reported. After the valency of Pu in acidic solution was adjusted to tetravalent state by addition of nitrite (e.g. NaNO2), sodium plutonium (IV) fluoride was precipitated by adding hydrofluoric acid in the presence of sodium ion in the solution. The double salt obtained by the wet method was dried under reduced pressure at 110°C, and then reduced with Ca metal in Ar atmosphere. Over 80% Pu yield was obtained by reducing 1 g batch of the double salt.