A ternary compound in the UFeC system

Metallographic evidence of a ternary compound was obtained during continuing investigations at Sheffield University on the U-C-Fe system ¹). Further work has shown this compound to correspond to UFeC₂ and to lie on the UC₂-Fe join.     

Structural studies of the phase separation in the UO2–PuO2–Pu2O3 ternary system

In the oxygen hypo-stoichiometric range of (U_1?yPu_y)O_2?x mixed oxide MOX fuels, the U–Pu–O phase diagram is known to exhibit a large biphasic domain depending on the Pu content. However, the phase equilibria are still to be fully described as various representations are proposed in the literature.In the present work, we notify new insights into the phase separation occurring in the UO₂–PuO₂–Pu₂O₃ domain at room temperature. Our microstructural and X-ray diffraction results are compared to the different representations reported in the literature. We provide, for the first time in the hypo-stoichiometric domain, an indisputable experimental observation of a triphasic region at high Pu content, composed of two fluorite-type structures and of one α-Pu₂O₃ sesquioxyde type structure. These results are in contradiction with previous experimental representations of the U–Pu–O ternary system.     

Interaction between point defects in the Si–SiO2 system during the process of its formation

The results of the studies of the point defect generation kinetics in the Si–SiO₂ system by means of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) are presented. It has been established that the EPR and NMR signal intensities change non-monotonously with oxide film thickness and the maximum of the EPR and minimum of the NMR signals occur at the same oxidation time. This can be connected with the competition between the generation and transformation of the point defects, the formation of Si–O bonds and strained bonds rupture in the Si–SiO₂ system during the process of its formation. The defect structure of the Si–SiO₂ system depends on the point defects density in initial wafers. A possible mechanism to explain this interdependence has been discussed.     

Thermal conductivity of Na2O–B2O3–SiO2 melts

Borosilicate glasses are candidate materials for the immobilization of high-level radioactive waste. The values of thermal conductivity of different borosilicate melts are thus indispensable information when optimizing the temperature distribution in a glass melting furnace. In this study, the thermal effusivity of Na₂O–B₂O₃–SiO₂ melts was measured using a front heating–front detection laser-flash method. The thermal conductivity, which can be obtained by combining the measured thermal effusivity with the specific heat capacity and density, was calculated using the least-squares method; the values for the Na₂O–B₂O₃–SiO₂ melts either slightly decreased linearly with increasing temperature or remained almost constant over the investigated temperature range. The values of thermal conductivity of the Na₂O–B₂O₃–SiO₂ melts were higher than those of B₂O₃–SiO₂ melts and lower than those of CaO–B₂O₃–SiO₂ melts. Furthermore, the thermal conductivity of the Na₂O–B₂O₃–SiO₂ melts was compared with those of the B₂O₃–SiO₂ and CaO–B₂O₃–SiO₂ samples.     

Phase changes of the ZrO2—12wt%Y2O3 film with Ar^＋ irradiation

1IntroductionYttrisistabilizedzirconiawithahighresistivityandalargerelativedielectricconstant.isaveryattractiveelectricalinsulator.11]Itcanbeusedforthefabricationofsilicon-oninsulator(SOI)structuresorasthebufferlayerinhighToceramicsuperconductorsonSttoavoidthereactionbetweenStandthesuperconductorfilm.[2]Thepolymorphicbehaviourofzirconiabasedceramicscontaininglessthan20wt%Yaosstillaffectsitsthermalshock-resistancewhenitisusedoveralargetemperaturerange.Ithasbeenfoundthatthereseemsacorrelesnon…     

Fabrication of a Li4SiO4–Pb tritium breeding material

PbO₂-doped Li₄SiO₄ pebbles were successfully fabricated by a liquid-atmosphere sintering process. Those pebbles sintered at 1000 °C under atmospheric conditions were found to have an average diameter of 1.05 mm, a sphericity of 98%, a theoretical density of 90.9%, an average crush load of 24.3 N, and a main phase structure of Li₄SiO₄ with a small percentage of Li₈PbO₆. Subsequent optimization of this fabrication process yielded ceramic pebbles suitable for tritium breeding in a test blanket module (TBM).     

氚在Li2SiO3中释放行为研究

分别用堆照１０，１００ｈ的Ｌｉ２ＳｉＯ３样品，在１００－８００℃范围内用氦气载带法，研究了氚的释放规律。观察到在６００℃时，９７％的氚都已释放。研究了氚释放与温度的关系、扩散规律及加热后样品的变化。     

A Study of the Aging of α-Al2O3 Dielectric Material in DBD Plasma

The performance of dielectric material is a key factor against a long time action in dielectric barrier discharge （DBD） plasma. In this study, the aging of the Al2O3 dielectric material was studied by the Atomic Force Microscope （AFM）, X-ray Photoelectron spectrum （XPS） and Auger electron spectrum （AES） methods. The results showerd that the performance of the dielectric does not descend after an 1000 h aging experiment. Therefore the thin dielectric layers of α-Al2O3 porcelain with a purity above 99% can sustain a long time action of DBD plasma and form gas ionization discharges steadily.     

The emission spectra of NaD2O,InBe,LaBe and NaBe photoneutron sources

The energy distribution of the photoneutrons of NaD₂O, InBe, LaBe and NaBe source systems were measured by means of a proton-recoil proportional counting tube. Spherical lead-shields of various thicknesses (ranging from 1·5 to 13 cm) were used to reduce the intense gamma field accompanying the neutron spectra to be measured. The spectra of spherical heterogeneous source arrangements for three different Be-target thicknesses (0·5, 1· and 2·0 cm) were measured and compared with the theoretical distribution as obtained by Monte-Carlo calculations. The change in spectrum shape due to the lead shields was also calculated by a Monte-Carlo routine. Good agreement between theoretical predictions and experimental results shows values for the peak of the neutron distribution of 264·1 ± 0·5 keV for the NaD₂O system, 397·3 ± 0·8 keV for the InBe system, 761·7 ± 0·7 keV for the LaBe system, and 966·9 ± 0·5 keV for the NaBe source system. With the LaBe system a second neutron group of much lower intensity (6·5 per cent of the main group) could be found with a peak energy of 1097·5 +- 1·0 keV in good agreement to recent gamma-spectroscopic measurements.     

A study of the structure of Zr(CrFe)2 laves phase precipitates in a ZrCrFe alloy

C15 type Zr(CrFe)₂ Laves phase precipitates have been found in Zr-1.15 wt% Cr-0.1 wt% Fe alloy. Twinned, multiple twinned and dislocation structures have been found in the precipitates. Comparison of calculated and measured precipitate size show the growth of the Zr(CrFe)₂ Laves phase is controlled by diffusion.The orientation relationships (1̄11̄)_L//(112̄0)_α, [110]_L//[0001]_α between the Zr(CrFe)₂ Laves phase precipitates and ga-Zr matrix in the ZrCrFe alloy give the same type of model for the transformation as previously suggested for Zircaloy-4.     

Investigations of the melting behaviour of the U–Zr–Fe–O system

During a severe nuclear accident, the UO₂ fuel rods, Zircaloy cladding, guide tubes, absorber and steel structural components inside the reactor pressure vessel overheat and a series of interactions between these elements and the steam atmosphere occur. These produce more heat in addition to the decay heat and result in a liquid corium of oxidic and metallic phases depending on the exact conditions and processes. A major systems resulting from this is the U–Zr–Fe–O system. High-temperature data for this system is important in order to be able to model these interactions. The Joint Research Centre, Institute for Transuranium Elements (JRC-ITU) has been examining the melting ranges for this system over the whole FeO range by means of a specialized laser flash technique that achieves very high temperatures and avoids crucible contamination. The melted zones were examined for their structure, composition and for estimation of the liquidus and solidus temperatures. The results showed that with FeO contents of over 20mol% there was a very large melting range that would permit long liquid cooling times and extend the relocation of fuel material within the reactor pressure vessel. Based on these results, the main phase regimes expected under severe accident conditions could be identified.     

Simulation of multi-atomic interactions in H–O–W system with the MD code CADAC

For future tokamak reactors, chemical erosion of tungsten armour surfaces under impact of hot deuterium–tritium plasma that contains impurities, for instance oxygen, is an important issue. Oxygen can form volatile molecular complexes O_xW_y at the surface, and the retained H-atoms form the volatile complexes H_xO_y, which mitigates the erosion (H states for hydrogen isotopes). The plasma impact can substantially destroy the complexes.To describe this H–O–W system, the molecular dynamics (MD) code CADAC was earlier developed using only pair–atomic interactions. Now CADAC is extended for multi-body forces to simulate molecular organization of atoms near the tungsten surface. The approach uses the Abell's model of empirical bond-order potentials in addition combined, for the first time, with a valence concept. CADAC simulates chemical features using atomic valences and the Morse potentials. The new model is introduced and model parameters are estimated.     

Measurement of thick-target gamma-ray production yields of the 7Li(p,p′)7Li and 7Li(p, γ)8Be reactions in the near-threshold energy region for the 7Li(p,n)7Be reaction

The gamma-ray production reactions, ⁷Li(p, p′)⁷Li and ⁷Li(p, γ)⁸Be, occur along with the neutron production reaction ⁷Li(p, n)⁷Be in a p-Li neutron source. These gamma-ray production reactions contribute to a patient's absorbed dose in boron neutron capture therapy (BNCT) when using a neutron beam from the ⁷Li(p, n)⁷Be reaction. The present work experimentally determined the thick-target gamma-ray production yields of the ⁷Li(p, p′)⁷Li and ⁷Li(p, γ)⁸Be reactions at incident proton energies of 1.670 and 1.870 MeV. The present results were compared with previous measurements. The gamma-ray production yield of ⁷Li(p, p′)⁷Li was measured to be 30%–50% smaller than as reported by previous studies. For the ⁷Li(p, γ)⁸Be reaction, the present thick-target yield is 30% smaller than one estimated from cross-section data measured in previous studies. The results must be included in future dose evaluation for BNCT using a p–Li neutron source.     

Investigation of the PuO2F2 - HF - H2O system (20°C isotherm)

The PuO₂F₂ — HF — H₂O system was investigated by using the method of isomermic solubility at 20 °C. It was established that there are three phases in the sytem: plutonyl fluoride dihydrate PuO₂F₂ · 2H₂O, tetrafluoroxyplutonic acid H₂PuO₂F₄ · 4H₂O, and plutonium oxyfluoride PuO₂F₂, the composition of which was determined by chemical analysis and by using the Schreinmacher method. The chemical individuality of the phases was confirmed by electron absorption spectra. The existence of the H₂PuO₂ F₄ · 4H₂O acid was proved by using the electromigration and the potentiometric titration methods.     

Coulomb Correction of the p-~4He Low Energy Scattering Phase Shifts

A simple approach of Coulomb correction to the p-~4He low energy scatteringphase shift is proposed,in which the channel radius of each particle wave istaken as an adjustable parameter.By using our Coulomb correction the n-~4Hescattering observables predicted from p-~4He scattering phase shifts are in excell-     

Solid solution formation in the U3O8 → UO2 transformation

Possibilities were investigated for incorporation of various foreign elements into the crystal lattice of uranium dioxide during its formation in U₃O₈ → UO₂ transformation carried out under the following conditions :Arc-ignition in various gas environments (A, N₂, CO₂, H₂) of U₃O₈-metal oxide mixtures in a graphite electrode, under conditions analogous to those of the spectrochemical analysis of uranium. It has been found that in the rapid and complete U₃O₈→ UO₂ transformation thereby made possible, foreign elements present are incorporated to a limited extent into the lattice of the uranium dioxide formed. For specimens arced in N₂, maximum concentrations retained in solid solutions with UO₂ were: 13 mole % CdO; 4 mole % ZnO; 4 mole % MgO; 7 mole % Bi₂O₃; 1 mole % PbO; 0.1–0.4 mole % CaO, In₂O₃ or NiO; ThO₂ and La₂O₃ were not found to enter UO₂ lattice, but arc-ignition of a U₃O₈-La(NO₃)₃·6H₂O mixture resulted in ready solid solution formation. On the basis of density measurements of solid solutions containing CdO and ZnO respectively, it was concluded that fluorite-type substitutional solid solutions were formed with intact cation lattice, the anion lattice probably remaining intact as well. For specimens arced in H₂, capacity for solid solution formation is reduced.The factors influencing the behaviour of the foreign metal oxides in mixtures with U₃O₈ under investigated conditions are discussed. The possibility of solid solution formation of UO₂ with certain less stable oxides, employing rapid U₃O₈→ UO₂ transformation, is pointed out.