T he ACOG Ethics Committee is to be commended for continuing to offer guidance for the admittedly and necessarily “evolving ethic” regarding obstetrician/gynecologist responsibilities in cases complicated by human immunodeficiency virus (HIV). This most recent revision replaced the 1990 Committee Opinion on the subject.’ When clinical realities warrant terms such as “plague” and “epidemic,” the stakes are obviously high and the emotions run deep.* We have written this commentary with the practicing obstetrician/gynecologist in mind. The need for a revised statement apparently stemmed from the need for ethical reflection to keep pace with the epidemiological and clinical information being gathered about HIV infection. The revised statement reflects both format and content changes. The organization of the statement into sections makes for a much more coherent statement. Data about patient-to-professional risk of transmission are referenced as confirmation of the committee’s earlier argument that, with universal precautions, the risk is very slight (with hepatitis as a point of contrast now included).3 The revised statement recognizes that HIV infection has spread into all socioeconomic levels.

Compressive and tensile creep were measured on UO2 doped with 0.4 wt % niobia at controlled oxygen potentials. Kinetic results were almost identical, irrespective of the nature of the applied stress, but differences in after-test microstructures were observed. Formation of “plastic” UO2 with increases in strain rate of more than two orders of magnitude were recorded when oxygen potential changed from −560 to −410 kJ/mol; this was associated, primarily, with the formation of the Nb4+ ion. Over the same range of oxygen potential, creep activation energy decreased linearly from −425 to −225 kJ/ mol. In contrast, strain rate and activation energy for undoped UO2 remain almost constant under these conditions.

The effect of additions of up to 0.33 wt % titania on the grain growth and densification of UO2 has been studied. It is shown that the solubility of titania in UO2 lies between 0.07 and 0.13 wt % at 1650°C in hydrogen and that the grain growth rate is proportional to the concentration of added titania up to the solubility limit, remaining constant thereafter. Titania in excess of the solubility limit forms a liquid eutectic with UO2. This eutectic, which has a solidification temperature in the 1600–1620° C range, inhibits grain growth at temperatures below 1600°C but can enhance it at higher temperatures where the eutectic is liquid. TiO2 is not as effective as the lower oxides in promoting grain growth.

Compacted mixtures of UO2 and MgO with MgU ratios up to 0·07 readily form solid solutions when heated at 1600° in a slightly oxidizing atmosphere such as a 5% H2-95% CO2 mixture. No oxygen vacancies are associated with these solid solutions which can always be represented as UxMg1−xO2+z where z cannot be negative. The reduction of these solid solutions has been studied. The amount of magnesium remaining in solution depends not only on the oxygen potential of the reducing gas but also on the concentration of dissolved magnesium prior to reduction. This concentration effect is most marked at the higher concentrations of dissolved magnesia. It is shown that the quantity of magnesia which can be dissolved in UO2 at a given oxygen potential is less than the quantity retained in solution when a solid solution, prepared in a more oxidizing atmosphere, is reduced at that oxygen potential. Magnesia precipitates from solution during reduction in the form of small clusters which are distributed both inter- and intra-granularly in the compacts.

An out-reactor instrumented defected fuel experiment using a fuel element simulator (FES) was conducted for the first time. The experiment simulated both reactor coolant pressures and temperatures during and after the sheath (clad) of a single CANDU fuel element (fuel pin) containing UO2 pellets was defected. A mechanistic fuel oxidation model with discrete radial fuel cracks was adapted to represent the defected fuel element for the purpose of model validation. The duration of the experiment lasted ≈5.2 days at a total electrical power of 16.5 kW (or ≈20 kW m−1 of linear power). Post-test coulometric titration (CT) measurements of the fuel oxygen potential and the hyperstoichiometric oxygen, in the out-reactor UO2 fuel were consistent with a 3D fuel oxidation model results in the vicinity of the sheath defect. These results were supported by lattice parameter measurements, using X-ray diffraction (XRD), converted to hyperstoichiometric oxygen x. Away from the sheath defect, in the fuel element axial upstream direction, both the CT measurements and the 3D fuel oxidation model results showed a decline in hyperstoichiometric fuel, though this decline was more pronounced in the model. This discrepancy was believed to be a result of the model not including dynamic radial fuel crack geometry and that additional oxygen was introduced to the samples during sample preparation. Considering that most of the x measurements using the XRD lattice parameter technique closely agreed with the model results, it is believed that the fuel oxidation model was close to simulating the oxidation in the out-reactor instrumented defected fuel experiment after ≈5.2 days of heating.

Beryllia powders have been prepared from crude beryllium hydroxide via beryllium sulphate. Two routes have been used to purify the hydroxide, (1) crystallisation of beryllium sulphate and (2) solvent extraction with acetyl-acetone/carbon tetrachloride. In both cases the beryllium sulphate has been decomposed at temperatures in the range 900–1000° C to produce beryllia powders having surface areas of 10–15 m2/g.