THE INFLUENCE OF LUBRICATION ON THE COMPACTABILITY OF MAGNESIUM-GREEN SALT BLENDS FOR BOMB REDUCTION

Lubrication of die surfaces with mineral oil or Dag 217 during final compacting of UF/sub 4/--Mg blends prevented seizing. Mineral oil application after every third press allowed 18 compacts before seizing became severe. Similar application of Dag 217 allowed 78 compacts. Mixing 0.33 wt.% Ceremul "C" with the powder allowed 40 compacts. Punch clearance had little effect on seizing. (T.R.H.

GAS-PRESSURE BONDING OF ZIRCALOY-CLAD FLAT-PLATE URANIUM DIOXIDE FUEL ELEMENTS

A solid-state bonding technique involving the use of gas pressure at elevated temperatures was investigated for the preparation of compartmented Zircaloy-clad flat-plate uranium dioxide fuel elements. These investigations involved development of methods for the surface preparation and assembly of fuel- element components for bonding, determination of optimum bonding parameters, development of barrier coatings for uranium dioxide to prevent reaction with Zircaloy, and extensive testing and evaluation of the bonded fuel elements. During the course of this work, the process was continually modified and refined in an effort to improve the quality of the bonded element and decrease the cost of fabrication. The surface-preparation studies indicated that satisfactory bonding could be obtained consistently with both machined and belt-abraded components. Belt abrasion is more economical and was used as the standard technique in the development phases of the program. Initially the elements were assembled into a stainless steel or Ti-Namel envelope which was evacuated and sealed prior to bonding. Later studies showed that the quality of bonded elements could be improved and process costs decreased by edge welding the Zircaloy components to form a gastight assembly that was then bonded without use of a protective envelope. Further cost reductions were incorporated into the process by the use of piece Zircaloy components to form the picture frame. Optimum bending with a minimum core-to-cladding reaction was achieved by pressure bonding at 1500 to 1550 deg F for 4 hr using a helium gas pressure of 10,000 psi. A postbonding heat treatment for 5 min at 1850 deg F in a salt bath promoted additional grain growth at the bond interface during the alpha-to-beta transformation. Barrier layers of graphite. chronaium, iron. molybdenum, nickel, niobium, palladium, and various oxides were investigated to prevent reaction between the UO/sub 2/ core and Zircaloy cladding. Graphite, in the form of a sprayed and buffed coating, and chromium were found to be relatively effective barriers. The graphite coating was easy to apply and less expensive than a chromium electroplate. (auth

Differential livelihood adaptation to social-ecological change in coastal Bangladesh

Social-ecological changes, brought about by the rapid growth of the aquaculture industry and the increased occurrence of climatic stressors, have significantly affected the livelihoods of coastal communities in Asian mega-deltas. This paper explores the livelihood adaptation responses of households of different wealth classes, the heterogeneous adaptation opportunities, barriers and limits (OBLs) faced by these households and the dynamic ways in which these factors interact to enhance or impede adaptive capacities. A mixed methods approach was used to collect empirical evidence from two villages in coastal Bangladesh. Findings reveal that households’ adaptive capacities largely depend on their wealth status, which not only determine their availability of productive resources, but also empower them to navigate social-ecological change in desirable ways. Households operate within a shared response space, which is shaped by the broader socio-economic and political landscape, as well as their previous decisions that can lock them in to particular pathways. While an adaptive response may be effective for one social group, it may cause negative externalities that can undermine the adaptation options and outcomes of another group. Adaptation OBLs interact in complex ways; the extent to which these OBLs affect different households depend on the specific livelihood activities being considered and the differential values and interests they hold. To ensure more equitable and environmentally sustainable livelihoods in future, policies and programs should aim to expand households’ adaptation space by accounting for the heterogeneous needs and complex interdependencies between response processes of different groups

Microbial contamination of laboratory constructed removable orthodontic appliances

OBJECTIVES: This study aims to determine whether laboratory constructed removable orthodontic appliances are free from microbial contamination prior to clinical use and to evaluate the dental hospital cross-infection procedures to ensure that patient-derived contamination does not enter the construction process, thereby propagating a cycle of cross-contamination.MATERIALS AND METHODS: The construction process of removable orthodontic appliances from three individuals was evaluated at every stage, from impression to final delivery of the appliance using molecular microbiological techniques. The bacterial profiles at each stage of appliance construction were obtained using denaturing gradient gel electrophoresis, along with the bacterial profiles of the three participants' saliva. This enabled the bacterial profiles found at each stage of construction to be compared directly with the saliva of the person for whom the appliance was being constructed. Bacteria were identified at each stage using 16S rDNA PCR amplification and sequence phylogeny.RESULTS: There was no evidence of bacterial cross-contamination from patients to the laboratory. The current process of disinfection of impression appears to be adequate. Contamination was found on the final removable appliances (0.97 × 10(2)-1.52 × 10(3) cfu ml(-1)), and this contamination occurred from within the laboratory itself.CONCLUSIONS: Every effort is made to reduce potential cross-infection to patients and dental professionals. Newly constructed removable appliances were shown not to be free from contamination with bacteria prior to clinical use, but this contamination is environmental. Further studies would be required to determine the level of risk this poses to patients.CLINICAL SIGNIFICANCE: Dental professionals have a duty of care to minimise or eradicate potential risks of cross-infection to patients and other members of the team. To date, much less attention has been paid to contamination from the orthodontic laboratory, so contamination and infection risks are unknown.</p

The Bonding of Molybdenum-and Niobium-Clad Fuel Elements

A solid-state bonding technique involving the use of gas pressure at elevated temperatures was utilized for the self-bonding of molybdenum and niobium. Bonding conditions and surface preparation as a function of the integrity of the bond achieved were evaluated for each material. Optimum self-bonding of niobium was achieved by bonding parameters of 2100 to 2300 deg F at 10,000 psi for 3 hr with surfaces which had been prepared by etching in a nitrichydrofluoric acid solution prior to bonding. The process as developed was used to prepare niobium- clad flat-plate- and rod-type fuel elements and flat-plate subassemblies. Niobium tubing was also fabricated by this technique. (Molyb denum self-bonding was most readily achieved by gaspressure bonding at temperatures of 2300 to 2600 deg F at 10,000 psi for periods of 3 hr. With these bonding conditions a number of different surface preparations were satisfactory. Directional ductility of the molybdenum was encountered after bonding and methods to eliminate this were evaluated. Cross rolling with respect to the original rolling direction was shown to improve the ductility of molybdenum-clad specimens. (auth

Canning Graphite for Gas-Cooled Reactors

A preliminary investigation was made of techniques and materials for canning graphite to protect it for use at high temperatures in a nitrogen--oxygen atmosphere. Fabrication techniques for cladding bare and copper--plated graphite cores either in Type 316 stainless steel or Inconel X were developed. Specimens of the various combinations of core and cladding materials were subjected to simulatedservice conditions and evaluated. In all cases the Type 316 stainless steel-clad specimens failed by carburization and subsequent oxidation in relatively short periods of time. Although considerable trouble was experienced with rupture in the vicinity of the cladding welds during thermal cycling of the Inconel X-clad specimens, this material appeared to be satisfactory in other respects and is considered promising. A specimen of silicon-coated graphite eiad with Type 316 stainless steel was tested by heat treating for 624 hr at 1800 deg F. The silicon coating alloyed with the cladding material, formed a high-silicon diifusion zone, but prevented carburization of the stainless steel. (auth