[en] Reactivity insertion limits imposed by clad melting temperature and their sensitivity with respect to safety parameters have been investigated in a typical pool type research reactor. Simulations were conducted using modified PARET code for High Enriched Uranium (HEU) having UAl_x-Al fuel and Low Enriched Uranium (LEU) cores having $ 1 were investigated for less than one second. Reactor was kept at a low power. Scram disabled transients for ramp reactivity insertions were studied. The meltdown was observed at $ 2.0, $ 1.9 and $ 2.2 per 0.5 sec in above mentioned three cores. In LEU (U₃Si₂-Al) core the clad failure is predicted for step reactivity insertions of $2.1. The behaviour of the core with scram enabled at 12 MW power has also been Oscillations in the power, fuel and clad temperatures have been observed. The secondary power peak within 0.1 sec of the primary peak causes a non linear rise in temperatures within the fuel which leads to the clad meltdown. The sensitivity analysis conducted for LEU (U₃Si₂-Al) core indicates the LEU's reactivity insertion limits are quite insensitive to the variation of B_eff/, Doppler and coolant temperature coefficients. However reactivity limits are sensitive to the void coefficient of reactivity. These sensitivities can be partially attributed due to a poor hydrodynamic model used in the PARET code. (author)

[en] In this work a c-language based program DRF (Dynamics of Fusion Reactor) has been developed to study the time behavior of plasma parameter's in typical Toroidal Fusion Reactor based on Magnetic Confinement. The Modeling of torus reactor without and with impurities have been done. This program is based on plasma volume averaged density and energy balance equations for single predominant ion behaviors. Two major sources of plasma heating (i.e. auxiliary heating and alpha heating) have been used in this work. A simplified model for Bremsstrahlung and Cyclotron loss has also been employed in the work. Effect of MHD instabilities have been add in energy confinement time through plasma Beta (ratio of kinetic pressure to magnetic pressure). Design parameters (ratio of kinetic pressure to magnetic pressure). Design parameters of TFTR have been used in this work. Simulation shows that stable reactor operation in feasible for N = 5.4 x10/sup -13/cm/sup -3/, T= 11 keV and auxiliary heating of 30 MW for first five seconds. An optimum volume with an optimum minor radius comes to be 1.5 x 10/sup -8/cm/sup -3/ and 50 cm respectively. The effect of change in initial fuel density and magnetic field has been studied. The effect of change in T, N, Tau, P/sub alpha/, P/sub cyc/, P/sub brem/, P/sub conv/ due to change in impurity concentration have also been studied in this work. Result shows acceptable impurity concentration limit for carbon, oxygen, silicon, iron, molybdenum and tungsten (wolfram) are 9.47 x 100/sup -2/, 5.45x 10/sup -2/, 2.7x 10/sup -2/, 1.065 x 10/sup -2/, 3.3x 10/sup -3/ and 6.75 x 10/sup -4/ respectively. (author)

[en] The neutronics analysis of the current core of the TRIGA Mark II research reactor is performed at the Atominstitute (ATI) of Vienna University of Technology. The current core is a completely mixed core having three different types of fuels i.e. aluminium clad 20 % enriched, stainless steel clad 20 % enriched and SS clad 70 % enriched (FLIP) Fuel Elements (FE(s)). The completely mixed nature and complicated irradiation history of the core makes the reactor physics calculations challenging. This PhD neutronics research is performed by employing the combination of two best and well practiced reactor simulation tools i.e. MCNP (general Monte Carlo N-particle transport code) for static analysis and ORIGEN2 (Oak Ridge Isotop Generation and depletion code) for dynamic analysis of the reactor core. The PhD work is started to develop a MCNP model of the first core configuration (March 1962) employing fresh fuel composition. The neutrons reaction data libraries ENDF/B-VI is applied taking the missing isotope of Samarium from JEFF3.1. The MCNP model of the very first core has been confirmed by three different local experiments performed on the first core configuration. These experiments include the first criticality, reactivity distribution and the neutron flux density distribution experiment. The first criticality experiment verifies the MCNP model that core achieves its criticality on addition of the 57th FE with a reactivity difference of about 9.3 cents. The measured reactivity worths of four FE(s) and a graphite element are taken from the log book and compared with MCNP simulated results. The percent difference between calculations and measurements ranges from 4 to 22 %. The neutron flux density mapping experiment confirms the model completely exhibiting good agreement between simulated and the experimental results. Since its first criticality, some additional 104-type and 110-type (FLIP) FE(s) have been added to keep the reactor into operation. This turns the current core into a complete mixed core. To analyze the current core, a good knowledge of burned fuel material composition is essential. Because of the complications of experimental methods for measuring each FE, the ORIGEN2 computer code is selected for burn up and relevant material composition calculation. These calculations are verified by measuring the Cesium isotope (Cs-137) for six spent FE(s). Modifying the confirmed ORIGEN2 model for 104 and 110 (FLIP) FE(s), the burn up calculations of all 83 FE(s) of the current core are completed and applied to the already developed MCNP model. The detailed MCNP model of the burned core is verified by three local consistent experiments performed in June 2009. The criticality experiment confirms the model that the current core achieves its criticality on addition of 78th FE. The five FE(s) from different ring positions are measured to confirm the theoretical results. The percent deviation between MCNP predictions and experimental observations ranges from 3 to 19 %. The radial and axial neutron flux density distribution experiment verifies the MCNP theoretical results in the core. The theoretical and experimental perturbation study in the Central Irradiation Channel (CIR) of the core is performed. The reactivity effect of three small cylindrical samples (void, Cadmium and heavy water) are measured and compared with the MCNP predictions for verification. Applying the current core MCNP model, the void coefficient of reactivity is calculated as 11 cents per %-void. To perform the calculation in the experimental facilities outside the reactor core, the MCNP model is extended to the thermal column, radiographic collimator, four beam tubes and biological shielding. The MCNP results are verified in the thermal column and the beam tube A region. The percent difference between the simulated and experimental neutron diffusion length is 13 %. (author)

[en] Strongly correlated electron systems (SCES) represent a class of intermetallic compounds where electron-electron correlations result in extraordinary low temperature properties like heavy-fermion behavior or superconductivity. Pressure as a clean thermodynamic variable can re-scale microscopic mechanisms responsible for the observed anomalous properties. Therefore, pressure dependent studies of such materials essentially contribute towards a better understanding of the materials and the novel phenomena involved. This work summarizes the experimental findings regarding the evolution of the ground state and other physical properties of some SCES compounds under high pressure and magnetic fields. Mainly two types of materials have been studied here: (i) Yb-based Kondo lattices, which include Yb₂Pd₂In_(1-x)Sn_x and YbPd_(2-x)Pt_xSi, (ii) materials exhibiting superconductivity, namely Mo₃Sb₇ and Ce₂PdIn₈. The effect of pressure and field has been assessed by measuring the temperature dependent electrical resistivity under different hydrostatic pressures and in applied magnetic fields. Further, physical properties like specific heat or magnetic susceptibility has also been studied for many samples. The data were analyzed in terms of different theoretical models available in the literature. In some circumstances where no appropriate models exist, analysis was made in a phenomenological manner or by comparisons. The series Yb₂Pd₂In_(1-x)Sn_x orders magnetically in a narrow Sn-rich concentration range. By applying appropriate pressure and field to a specific composition, it is possible to separate the magnetic anomaly out of a single maximum in temperature dependent eleitrical resistivity, rho(T). This demonstrated that magnetic order can significantly influence T(rho)(max), a characteristic feature of Kondo lattices. The unique pressure response of YbPd₂Si, compared to the rest of series YbPd_(2-x)Pt_xSi, is indicative of a different crystal electric field (CEF) ground state which can have some other consequences as well. In case of Mo₃Sb₇, by application of pressure it was possible to detect the presence of a hidden spin-density-wave anomaly, which was highlighted by pressure. For the non-Fermi liquid (nFl) heavy fermion superconductor Ce₂PdIn₈, both pressure and field tend to suppress superconductivity, driving the system towards a Fermi liquid state. Superconductivity emerges from the nFl state and may be mediated by Antiferromagnetic-spin fluctuations due to the proximity of a quantum critical point. (author)

[en] Two-stream instabilities in electron-positron-ion plasmas are studied. The relative motion of the ions with respect to the electron-positron plasma and of the positrons with respect to the electron-ion plasma can give rise to such instabilities. The growth rates depend upon the percentage concentration of different species. A comparison of this work with the two stream instabilities studied previously in pure electron-positron and electron-ion plasmas is also made. The relevance of the present investigation to astrophysical and laboratory plasmas is pointed out

[en] A methodology has been described to study the effect of number of fuel plates per fuel element on critical cores of Material Testing Reactors (MTR). When the number of fuel plates are varied in a fuel element by keeping the fuel loading per fuel element constant, the fuel density in the fuel plates varies. Due to this variation, the water channel width needs to be recalculated. For a given number of fuel plates, water channel width was determined by optimizing k_infinity using a transport theory lattice code WIMS-D/4. The dimensions of fuel element and control fuel element were determined using this optimized water channel width. For the calculated dimensions, the critical cores were determined for the given number of fuel plates per fuel element by using three dimensional diffusion theory code CITATION. The optimization of water channel width gives rise to a channel width of 2.1 mm when the number of fuel plates is 23 with 290 g ''2''3''5U fuel loading which is the same as in the case of Pakistan Reactor-1 (PARR-1). Although the decrease in number of fuel element results in an increase in optimal water channel width but the thickness of standard fuel element (SFE) and control fuel element (CFE) decreases and it gives rise to compact critical and equilibrium cores. The criticality studies of PARR-1 are in good agreement with the predictions

[en] Purpose: To develop a new radiotherapy plan optimization technique that, for a given organ geometry, will find the optimal photon beam energies and fluences to produce a desirable dose distribution. This new modulated (both in energy and fluence) photon radiotherapy (XMRT) was compared with intensity modulated radiotherapy (IMRT) for a simple organ geometry. Methods: The XMRT optimization was formulated using a linear programming approach where the objective function is the mean dose to the healthy organs and dose-point constraints were assigned to each organ of interest. The organ geometry consisted of a target, two organs at risk (OARs), and normal tissue. A seven-equispaced-coplanar beam arrangement was used. For conventional IMRT, only 6 MV beams were available, while XMRT was optimized using 6 and 18 MV beams. A prescribed dose (PD) of 72 GY was assigned to the target, with upper and lower bounds of 110% and 95% of the PD, respectively. Both OARs were assigned a maximum dose of 64 Gy, while the normal tissue was assigned a maximum dose of 66 Gy. A numerical solver, Gurobi, generated solutions for the XMRT and IMRT problems. The dose-volume histograms from IMRT and XMRT solutions were compared. Results: The maximum, minimum, mean, and homogeneity of the dose to the target were comparable between IMRT and XMRT. Though IMRT had improved dose conformity relative to XMRT, XMRT reduced the mean dose to both OARs by more than 1 Gy. For normal tissue, an increase of 5 Gy in mean dose and 27 percent in integral dose was seen for IMRT relative to XMRT. Conclusion: This work demonstrates the benefits of simultaneously modulating photon beam energy and fluence using our XMRT approach in a given phantom geometry. While target coverage was comparable, dose to healthy structures was reduced using XMRT

[en] This study examined the long-term effects of hydrocarbon exposure on the gonadal development of fish. Mature Atlantic cod (Gadus morhua) were exposed to low concentrations of water accommodated fractions (WAFs) of polycyclic aromatic hydrocarbons (PAHs) in an ambient flowthrough seawater system. Some PAH-exposed cod groups were depurated afterwards for 38 to 287 days. Mortality was rare, and external lesions occurred only in the PAH-exposed groups. The gonado-somatic index revealed that gonadal development was disrupted in both sexes and spawning and spermiation was delayed in the 33 depurated PAH-groups. The findings indicate that chronic exposure to WAFs in the water column may have an adverse effect on reproduction in Atlantic cod.

[en] Potatoes (Varieties: Cardinal and Patrones) were irradiated at a dose of 0.10 kGy in Co-60 irradiator and stored at 20 degree centigrade for a period of 4 months. There was 5 and 3 percent rotting in control and 9 and 5 percent rotting in irradiated tubers in Cardinal and Patrones respectively at the end of 4 months storage period. The sprouting percentage at the end of 4 months was 51 and 59 in unirradiated tubers in Cardinal and Patrones varieties whereas no sprouting was observed in the irradiated potatoes in both the varieties. The weight loss was more (8.3 and 6.6%) in the control than the irradiated tubers (6.7 and 5.7%) in Cardinal and Patrones varieties at the end of 4 months storage period. Effect of radiation and storage was significant on ascorbic acid but negligible on sugars. Sensory quality was improved as a result of radiation treatment. The cost economics for food irradiation based on a source strength of 59 kCi was Rs. 290 per tone

[en] The perovskite based SrFeO₃ and SrFe_0.5Nb_0.5O₃ materials have been synthesized by solid state reaction methods. The structural properties are investigated using a combination of X-ray diffraction and X-ray absorption fine structure spectroscopic techniques. From the Rietveld refinement of the X-ray diffraction data it has been observed that SrFeO₃ has a simple cubic perovskite structure, which is consistent with the previous literature results; whereas SrFe_0.5Nb_0.5O₃ shows a tetragonal structure within P4mm space group. X-ray absorption results demonstrate that the valence state of Fe in SrFeO₃ is (IV); however, it changes to (III) when 50% Nb⁵⁺ is substituted at the Fe sites. - Highlights: → Structural studies by employing XRD and XANES spectroscopic techniques. → Rietveld refinement confirmed SrFeO₃ has cubic structure, space group Pm-3m. → It is revealed that SrFe_0.5Nb_0.5O₃ has tetragonal structure, in P4mm space group. → From XANES results it is observed that Fe has valence state of (IV) in SrFeO₃. → Doping of 50% Nb⁵⁺ at Fe sites, changes Fe valence to (III) in SrFe_0.5Nb_0.5O₃.