[en] The organophosphate insecticide chlorpyrifos was irradiated under different photochemical conditions and the products characterized by gas chromatography, mass spectrometry, and NMR spectroscopy. Irradiation of chlorpyrifos in hexane yielded dechlorinated photoproducts and cleavage products. In methanol, besides these products, chlorpyrifos gave oxons. Several new photoproducts, the formation of which apparently occurs by the displacement of 5-chloro by a methoxy substituent in the pyridyl moiety. The possibility of formation of such products on glass, soil, and leaf surfaces under the influence of UV and solar simulated light have also been explored and many new products presumably formed due to simultaneous photo-dechlorination, oxidation and hydrolytic processes were detected. Photodegradation of chlorpyrifos was rapid on a soil surface but comparatively slow on glass and leaf surfaces

No abstract available

[en] Sol-gel Processes have revolutionized conventional ceramic technology by providing extremely fine and uniform powders for the fabrication of ceramics. The use of this technology for nuclear fuel fabrication has also been explored in many countries. Unlike the conventional sol-gel process, sol-gel process for nuclear fuels tries to eliminate the preparation of powders in view of the hazards associated with their handling in powder form. Elimination of powder handling also makes the process more amenability to automation and remotisation. In sol-gel process metal nitrate solution is directly converted into metal oxide gel particles avoiding generation of powder. Additional advantage of sol-gel process is that the gel particles can be directly used for the fabrication of different types of fuel pins, viz. vipac fuel pin for fast reactor, coated particle fuel for High Temperature Reactor (HTR) or conventional pellet fuel for thermal or fast reactors. The suitability of the gel particles for the fabrication of desired fuel pin greatly depends upon the physical characteristics of the gel. The present report deals with the study of the variation of physical characteristics of gel particles with chemical conditions under which they are prepared. Further, adaptation this process in tailoring the gel properties for specific application is also discussed

[en] Full text: Sol-gel processes have revolutionized conventional ceramic technology by providing extremely fine and uniform powders for the fabrication of ceramics. The use of this technology for nuclear fuel fabrication has also been explored in many countries. Unlike the conventional sol-gel process, sol-gel process for nuclear fuels tries to eliminate the preparation of powders in view of the toxic nature of the powders particularly those of plutonium and ²³³U. The elimination of powder handling thus makes this process more readily amenable for use in glove boxes or for remote handling. In this process, the first step is the preparation of microspheres of the fuel material from a solution which is then followed by vibro-compaction of these microspheres of different sizes to obtain the required smear density of fuel inside a pin. The maximum achievable packing density of 92 % makes it suitable for fast reactors only. With a view to extend the applicability of sol-gel process for thermal reactor fuel fabrication the concept of converting the gel microspheres derived from sol-gel process, to the pellets, has been under investigation for several years. The unique feature of this process is that it combines the advantages of sol-gel process for the preparation of fuel oxide gel microspheres of reproducible quality with proven irradiation behavior of the pellet fuel. One of the important pre-requisite for the success of this process is the preparation of soft oxide gel microspheres suitable for conversion to dense pellets free from berry structure. Studies on the internal gelation process, one of the many variants of sol-gel process, for obtaining soft oxide gel microspheres suitable for gel pelletisation is now under investigation at BARC. Some of the recent findings related to Sol-Gel Microsphere Pelletisation (SGMP) in urania-plutonia and thoria-urania systems will be presented

[en] Internal gelation process has been developed to prepare high density ThO₂-3%UO₂ pellets. The study indicated that by carefully controlling the feed composition and the heat treatment scheme, soft mixed oxide microspheres could be obtained which are amenable for pelletisation at relatively low compaction pressures (200-250 MPa). The green pellets could be sintered in air up to 97% of TD at 1350 deg. C. The fractured and polished surface of the pellets showed a smooth surface without any berry structure. The shrinkage behaviour of these pellets was also studied in Ar + 8% H₂ atmosphere using a dilatometer. These studies revealed that the densification starts at a low temperature of 1100 deg. C. The SEM studies indicated uniform microstructure in the pellets with 3-5 μm grain size with uniform pores (∼1 μm) distributed homogeneously in the pellet

[en] Highlights: • First time reporting of enthalpy increment and heat capacity data of UPb_3 compound. • First time reporting of high temperature calorimetric determination of enthalpy of formation of UPb_3 compound. • Miedema model was used to calculate enthalpies of formation of UPb_3 and UPb. • Thermodynamic table of the compound UPb_3 was generated. - Abstract: Interaction of uranium based metallic fuels and lead coolant can lead to formation of intermetallic compounds of U-Pb system. To understand U-Pb interactions, it is important to know thermodynamic properties of intermetallic compounds present in this system, UPb_3 and UPb. In the present work, enthalpy increment, heat capacity and enthalpy of formation of UPb_3 intermetallic compound were determined. The enthalpy increment was determined by high temperature Calvet calorimeter and heat capacity was determined using DSC. The heat capacity data was used to calculate thermodynamic parameters of the compound as a function of temperature. The enthalpy of formation at 843 K was determined using successive precipitation method, by direct reaction calorimetry. The enthalpy of formation at 843 K, from Pb(l) and U(l), was −28.9 kJ at-mol"−"1 and after adjusting enthalpy increments of pure elements and compound, the enthalpy of formation of the compound at 298 K, from Pb(s) and U(α) was found to be −20.0 kJ at-mol"−"1.

[en] The suitability of the gel particles for the fabrication of desired fuel pin greatly depends upon the physical characteristics of the gel. The present report deals with the study of the variation of gel properties with chemical parameters and its adaptation to tailoring of the gel properties for specific application

[en] High temperature X-ray diffraction measurements were carried out for pure palladium and palladium-rich alloys of compositions Pd_0_._7_7Ag_0_._2_3 and Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3 in the temperature range of 298–1023 K at an interval of 50 K. The lattice parameters, coefficient of thermal expansion and X-ray Debye temperature of these materials were calculated as a function of temperature from the XRD data. The lattice parameter of Pd_0_._7_7Ag_0_._2_3 alloy was found to be higher than that of palladium, whereas the lattice parameter of Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3 was found to be lower than that of palladium in the temperature range of investigation. Further, the lattice parameters of both the palladium alloys show negative deviation from Vegard's law and the deviation was found to increase with increase in temperature. The average value of coefficient of linear thermal expansion was found to follow the trend: α_T (Pd)>α_T (Pd_0_._7_7Ag_0_._2_3)>α_T (Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3). The X-ray Debye temperatures of Pd_0_._7_7Ag_0_._2_3 and Pd_0_._7_7Ag_0_._1_0Cu_0_._1_3 alloys were calculated and found to be 225±10 and 165±10 K, respectively.

[en] Titania-silica microspheres have been prepared by sol-gel process. Internal gelation route, which use hexamethylenetetramine as the source of ammonia was used for the preparation spherical gel particles. A cationic surfactant, cetrimide was added in the feed broth for introducing meso-porosity in the gel network. Further paraffin oil emulsion was incorporated in the feed broth before gelation for the formation of larger pores in the gel network. The spherical gel particles thus obtained were washed and heat treated under controlled conditions to remove the entrapped surfactant, paraffin oil and other organic compounds resulting in highly porous intact titania-silica microspheres. The material was characterized by surface area, porosity and by SEM photomicrographs. The ion exchange property of this material was studied using the sorption of plutonium on this material from carbonate medium by distribution coefficient studies and ion exchange column loading and elution experiments. (author)

[en] The sorption behaviour of Pu(IV) from carbonate medium on titanium microspheres prepared by sol-gel procedure has been investigated. Distribution ratios (D) of Pu(IV) between titania microspheres and aqueous carbonate medium for its sorption on this ion exchanger have been determined. The high D values (∼ 1000) shown by this exchanger from various carbonate/bicarbonate media indicate the suitability of this material for the removal of plutonium from sodium carbonate waste streams. (author)