Tatsuo Sasayama

Synthesis of plutonium sesquicarbide by the reduction of dioxide with graphite

Abstract Plutonium sesquicarbide was synthesized by the carbothermic reduction of dioxide both in vacuum and in flowing helium in order to investigate the mechanism and kinetics of its formation. The CO gas concentration during reduction in flowing helium was used to determine the rate of formation of sesquicarbide. For powder samples the reduction was found to be controlled by a surface reaction. For compacted samples the reduction was controlled by the diffusion of CO gas through the carbide layer. The activation energy was 375 and 385 kJ/mol for powder and compacted samples, respectively. It was inferred that three kinds of plutonium oxide, fcc PuO2 − x bcc Pu2O3, and hexagonal Pu2O3 exist as intermediate phases at 1680 K.

Mass spectroscopic study on the carbothermic reduction of plutonium dioxide

Abstract Mass spectroscopic measurements of actinide-bearing species, effusing from the Knudsen cell containing a mixture of PuO 2 + 3C, were performed in the temperature range from 1593 to 1673 K. The change of P Pu and p Puo accompanied by the progress of the carbothermic reduction indicated that the reaction proceeded on the Pu-C-O phase diagram to the final product, PuC x O y + PuC 1.5 . The Pco in the reaction process was calculated from p Pu and P PuO values with a thermodynamical aid. It was confirmed that P co above the PuC x O y + PuC 1.4 region became less than p Pu and an invariable chemical composition of plutonium monoxycarbide in equilibrium with PuC 1.5 was attained.

Mass spectrometric study of the evaporation of LiCrO2 as a corrosion product in the compatibility experiment of Li2O pellets with Fe-Ni-Cr alloys

Abstract The measurement of the vapor species and pressures over Li 5 FeO 4 as a corrosion product in the compatibility experiment of Li 2 O pellets with Fe-Ni-Cr alloys has been done in the temperature range 1200–1500 K by means of the Knudsen effusion mass spectrometric technique. The evaporation process of liquid Li 5 FeO 4 was established and expressed by the reaction Li 5 FeO 4 (1) = LiFeO 2 (s) + 4 Li(g) + O 2 (g). The enthalpy of formation of Li 5 FeO 4 at 298 K was derived to be 1950 kJ/mol from the third-law treatment. Although a congruent process was suggested for the sublimation, it could not be confirmed in detail.

Carbothermic Synthesis of Uranium-Plutonium Mixed Carbide

Mechanically blended powder of UO2, PUO2 and graphite and its compact were heated in a vacuum to have some informations on the formation of mixed carbide (U, Pu)C. It was experimentally confirmed that PUO2 was reduced to sesquicarbide without forming a solid solution with UO2 in the reduction process. Larger quantity of sesquicarbide was formed in the compacted sample than in the powder one in the intermediate products. Compacts of UO2, PUO2 and graphite were also heated at 1,665-1,920 K in He, in order to investigate the effects of reduction temperature, He flow rate and blending time on the rate constant of reduction. The reaction proceeded from the surface toward the center of the compact. It was inferred that the rate-determining step was the reaction at the interfacial boundary between the reacted layer and the unreacted zone. The activation energy for the reduction was determined to be 375±20 kJ/mol. The Pu loss due to vaporization could be sufficiently suppressed, when compacted samples were reduce...

Mass spectrometric study on the vaporization of ternary compounds PuMC2(M = Fe, Co, Ni)

The thermochemical properties of ternary compounds PuFeC2, PuCoC2 and PuNiC2 were investigated in the temperature range 1420–1853 K by means of the Knudsen effusion mass spectrometric technique. The peritectic reactions at 1650, 1610 and 1670 K were suggested for these three compounds, respectively. Below the peritectic temperature, their vaporization process was incongruent, as the vapor pressures of Fe, Co and Ni were much higher than that of Pu. The free energies of formation of PuFeC2, PuCoC2 and PuNiC2 have been determined from the vapor pressure data.