Effect of oxygen and nitrogen impurities on the thermodynamic properties of uranium-plutonium mixed carbide fuel

The mixed carbide fuel being developed as an alternative to the mixed oxide to fuel fast breeder reactors consists of uranium-plutonium monocarbide with an admixture of 10-20 vol% of the sesqui-carbide. The monocarbide phase contains oxygen and nitrogen as dissolved impurities. These impurities as well as the sesquicarbide phase affect the performance of the fuel. The quantities of interest in assessing the performance of the fuel are its carbon potential and the partial pressures of carbon monoxide and plutonium. Both carbon potential and CO pressures are important in clad carburisation, the latter being involved in a gas phase carburisation mechanism. In the present study the partial pressures of CO, Pu and N2 as well as the carbon potential of the fuel have been calculated as a function of plutonium fraction, impurity (O, N) concentration, sesquicarbide content and temperature. Two different caculational methods were used - one based on a set of equilibrium relations between the co-existing phases and the other based on free energy minimisation employing the computer programme SOLGASMIX-PV. The results are presented graphically and trends in the values are discussed

Thyroid hormone profile in per1transplant period in live donor kidney transplantation

Chronic renal failure, characterised by two factors acting in opposite directions with respect to the serum thyroid hormone levels was chosen for the study. Healthy controls, donors undergoing nephrectomy and renal transplant recipients were studied. In transplant recipients, presurgical levels of total thyroxine(TT4),free triiodothyronine(FT3) and free thyroxine(FT4) were lower than controls, and immediately after the release of arterial clamps, there was an upsurge of total triiodothyronine (TT3),TT4, FT3 and FT4 due to administered and/or endogeneously secreted catecholamines. The levels of the 7th day were comparable to the presurgical levels. The changes observed in donors and recipients were similar indicating that the hormonal changes observed are mostly due to surgical stress. Recovery in the hormonal status did not start in the first week of posttransplant period

A SEMIAUTOMATIC APPROACH FOR GENERATION OF SITE MODELS FROM CARTOSAT-2 MULTIVIEW IMAGES

In the last decade there has been a paradigm shift in creating, viewing and utilizing geospatial data for planning, navigation and traffic management of urban areas. Realistic, three-dimensional information is preferred over conventional two dimensional maps. The paper describes objectives, methodology and results of an operational system being developed for generation of site model from Cartosat-2 multiview images. The system is designed to work in operational mode with varying level of manual interactivity. A rigorous physical sensor model based on collinearity condition models the "step n stare" mode of image acquisition of the satellite. The relative orientation of the overlapping images is achieved using coplanarity condition and conjugate points. A procedure is developed to perform digitization in mono and stereo modes. A technique for refining manually digitized boundaries is developed. The conjugate points are generated by establishing a correspondence between the points obtained on refined edges to analogous points on the images obtained with view angles ±26 deg. It is achieved through geometrically constrained image matching method. The results are shown for a portion of multi-view images of Washington City obtained from Cartosat-2. The scheme is generic to accept very high resolution stereo images from other satellites as input

Dissimilar joining of zircaloy-4 to type 304L stainless steel by friction welding process

Zirconium- and titanium-based dissolver vessels containing highly radioactive and concentrated corrosive nitric acid solution needs to be joined to the rest of fuel reprocessing plant made of AISI type 304L stainless steel (SS), which demands high integrity and corrosion resistant dissimilar joints. Solid-state joining process of friction welding was proposed in the present work to join zircaloy-4 and type 304L SS since fusion welding processes produce brittle intermetallic precipitates at the interface which reduce the mechanical strength as well as the corrosion resistance of the joint. The present study attempts to optimize joining parameters, without and with thin Ta and Ni interlayers that can prevent brittle intermetallic formation. Tensile test, three-point bend test, and microhardness measurements were performed on the joints. Characterization techniques such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were employed. A good friction weld joint of zircaloy-4 to 304L SS was achieved with the joint strength (~540 MPa) greater than that of the base of zircaloy-4, without using any interlayer. A bend ductility of 5° was only obtained without using any interlayer. However, XRD patterns indicated the presence of intermetallics in the friction-welded joints without interlayers. Corrosion test carried out on zircaloy-4 to 304L SS friction joint in boiling 11.5 M nitric acid exhibited corrosion rate of 225 μm/year after 240 h. SEM examination of the corroded joint indicated severe intergranular corrosion attack over stainless steel and preferential dissolution at the interface

High burn-up issues in fast breeder reactor fuels and structural materials

Fast breeder reactors (FBR) are essential to enhance the share of nuclear power to meet the growing energy demands in India. For economic viability and sustainability of nuclear power, there is urgent need to achieve higher fuel burn-up so as to reduce the fuel cycle cost and supply power at competitive rates. Indian energy scenario demands development of high burn-up and high breeding capable fuels working with high safety and performance levels typical of FBRs. However, this poses many challenges in the development of advanced fuels as well as structural materials which can cope up with the rigorous environment in fast reactors. Prospective fuels for FBRs include mixed oxide, carbide, nitride and metallic fuels. Choice of core structural materials range from the conventional austenitic stainless steel to ferritic steels and oxide dispersion strengthened (ODS) steels. Various issues limiting the achievable burn-up in fuels and structural materials of fast breeder reactors are discussed in this paper