Studies on the overall safety aspects during irradiation of TeO2 in the central thimble of the TRIGA research reactor

The purpose of this study is to provide a detailed safety analysis of overall system and components in terms of their ability to provide optimum output from the irradiation of TeO₂ in the central thimble of the 3 MW TRIGA MARK II research reactor at Atomic Energy Research Establishment (AERE), Savar, Dhaka, Bangladesh. It identifies safety issues relevant to ¹³¹I radioisotope production and ensures that safety analysis and design are consistent. It evaluates threats developed within the facility during the irradiation process and ultimately ensures establishment of in-core safety limits and conditions at all stages of ¹³¹I production. In-core irradiation safety not only ensures the safe operation of the reactor but also strengthens the production of radioisotopes (RI). This study attempts to review and modify all safety related events and aspects relating to RI production. The three-dimensional continuous energy Monte Carlo code MCNP is used to develop a versatile and accurate full-core model of the TRIGA core. The cross-section library and fission product inventory are generated by using NJOY and ORIGEN computer codes. The methodology to evaluate heat generation and other relevant parameters necessary to provide enough information for thermal hydraulic analysis are discussed. The neutron flux distribution inside the dry and water filled central thimble is determined in order to locate the highest neutron flux trapping position. The thermal hydraulic and safety analysis are performed by elaborate numerical analysis as well as by using GENGTC computer code. A mock-up facility has also been developed to supplement and verify the theoretically predicted results. The total energy generated during irradiation of 50 gm TeO₂ sample in dry condition is found to be 113.84 w of which 75% energy is due to neutron heating and rest of the amount is from gamma heating. Around 11.28 w of heat energy is also generated in the quartz vial. When the total generated-heat transfer is considered through conduction and radiation mechanisms, the calculated temperature of 50 g of TeO₂ reaches at 970 °C. Considering simultaneous heat transfer mechanisms, (conduction, radiation and convection) the calculated maximum temperature of the 50 g of TeO₂ powder comes down at 680 °C. It may be pointed out that very high amount of heat is generated during the irradiation of TeO₂ at 3 MW reactor power in dry condition which is nearly the melting point of TeO₂ and may be termed as unsafe mode of irradiation.     

Effect of phosphoric acid on the performance of low antimony grid of Pb‐acid cell under constant current charging and discharging

Effect of phosphoric acid on the performance of Pb‐1.7%Sb grid of lead‐acid cell is studied in 5 M H₂SO₄ by cyclic galvanostatic polarization and impedance spectroscopy. An increase in capacitance to a maximum is recorded during the initial stages of the electro‐reduction of PbO₂ into Pb(II) compounds and attributed to concurrent compositional and dimensional changes. These changes include removal of O₂ bubbles, insertion of large amounts of H₂SO₄ and H₂O. Efficiency of PbO₂ formation decreases, while its rate of self‐discharge increases with increasing the charging current and in the presence of H₃PO₄. The charge capacity increases with increasing the discharging current due to the decrease in the self‐discharge. The charge capacity is lower in the presence of H₃PO₄. On increasing the cycle number, the corrodibility of the grid increases, because more layers of the surface Pb are involved in the self‐discharge. H₃PO₄ significantly retards the effect of cycle number.     

Effect of particle properties on particle percolation behaviour in a packed bed

Spontaneous inter-particle percolation is a very important phenomenon related to the mixing/segregation of particulate materials. Many studies have been conducted to understand the mechanisms governing the percolation behaviours in the past. However, previous work has a lack of systematic investigation on the effect of particle properties. In this work, a layer of small particles passing through a packed bed under gravity is analysed by means of the discrete element method. Percolation behaviour in terms of percolation velocity and radial dispersion is studied. The effect of percolating particle properties, including sliding friction and damping coefficients between percolating and packing particles, density and diameter ratios of percolating to packing particles and Young’s modulus of percolating particles, on the percolation behaviour is considered. It is observed that the damping coefficient and diameter ratio are the two dominant parameters that significantly affect the percolation behaviour. In particular, increasing the damping coefficient or decreasing the diameter ratio would increase the percolation velocity and decrease the radial dispersion. The sliding friction coefficient, Young’s modulus and density ratio have limited effects on the percolation behaviour. Two formulas have been, respectively, proposed to describe the dependences of percolation velocity and interaction force between percolating and packing particles on damping coefficient and diameter ratio.     

Probabilistic Strength at Serviceability Limit State for Normal and SBHS Slender Stiffened Plates Under Uniaxial Compression

International Journal of Steel Structures - Stiffened plates with high slenderness parameters show large out-of-plane deflections, due to elastic buckling, which may occur before the plates reach...     

Mass transfer from outer surface of thin tubes in parallel turbulent flow

The mass transfer coefficients from the outer surface of tubes or cylinders held in parallel turbulent steams have been calculated using integral momentum and mass transfer equations. The solution uses a hydrodynamics independent constant, λ _c which depends only upon Schmidt number. The results exhibit significant effect of curvature. For Schmidt number less than 108, Sherwood number can be predicted by $Sh_d Sc^{ - 1/3} = 0.039Sc^{0.208} \times \left( {\frac{L} {d}} \right)^\alpha \operatorname{Re} _d^{0.8}$Sh_d Sc^{ - 1/3} = 0.039Sc^{0.208} \times \left( {\frac{L} {d}} \right)^\alpha \operatorname{Re} _d^{0.8}, where α = −0.169Sc^−0.0103. The effect of the curvature is insignificant where $\frac{L} {d}\operatorname{Re} _L^{ - 0.2} - 0.033 \times \ln (Sc) \leqslant 0.214$\frac{L} {d}\operatorname{Re} _L^{ - 0.2} - 0.033 \times \ln (Sc) \leqslant 0.214.     

The effect of tool edge radius on the chip formation behavior of tool-based micromachining

Chip formation behavior of micromachining is governed by the tool edge radius effect as reflected by the characteristic changes in plastic deformation at varying combinations of tool edge radius, r, and undeformed chip thickness, a. At high a/r above unity, concentrated plastic deformation takes place at the primary and secondary deformation zones akin to conventional macromachining. Decreasing a/r below unity promotes localized deformation ahead of the tool edge radius, with the expansion in fraction of the primary deformation zone and the simultaneous shrinkage in fraction of the secondary deformation zone following the reductions in total tool–chip contact length. Further decrease of a/r below a critical threshold brings forth a total suppression of secondary deformation zone and resulted in an ultimate localization of plastic deformation ahead of the tool edge radius. This is perceived as a transition in chip formation mechanism from concentrated shearing to a thrust-oriented behavior.     

CO2 methanation over Ni and Rh based catalysts: Process optimization at moderate temperature

H₂ was produced from aluminum/water reaction and reacted with CO₂ over Ni and Rh based catalysts to optimize the process conditions for CO₂ methanation at moderate temperature. Monometallic catalysts were prepared by incorporating Ni and Rh using nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) and rhodium(III) chloride trihydrate (RhCl₃·3H₂O)as a precursor chemical. The preliminary study of the catalysts revealed higher activity and CH₄ selectivity for Rh based catalyst compared to that of Ni based catalyst. Further, Rh based catalyst was investigated using response surface methodology (RSM) involving central composite design. The quadratic model was employed to correlate the effects of variable parameters including methanation temperature, %humidity, and catalyst weight with the %CO₂ conversion, %CH₄ selectivity, and CH₄ production capacity. Analysis of variance revealed that methanation temperature and humidity play an important role in CO₂ methanation. Higher response values of CO₂ conversion (54.4%), CH₄ selectivity (73.5%) and CH₄ production capacity (8.4 μmol g^?1 min^?1) were noted at optimum conditions of 206.7°C of methanation temperature, 12.5% humidity and 100 mg of the catalyst. The results demonstrated the ability of Rh catalyst supported on palm shell activated carbon (PSAC) for CO₂ methanation at low temperature and atmospheric pressure.     

Sensorless operation of surface mount permanent magnet AC (PMAC)motors

A sensorless field oriented control scheme for a surface mount permanent magnet AC (PMAC) motor with split phase stator windings is presented. This motor is obtained by splitting the phase windings of a conventional three phase motor. The six-phase motor, however is run as a three-phase motor by connecting the split phase stator windings in series, while the taps are made available for voltage measurements. By measuring the terminal voltages and the line currents, absolute position of the permanent magnet AC motor driven by a current regulated PWM inverter with a hysteresis controller is estimated. The estimated position information is independent of the stator resistance, thus this scheme is even applicable at low speeds. Results are presented to show the effectiveness of the new controller, and it is also shown that the position error is negligible     

Performance prediction of shaded pole induction motors

The authors present an analysis for evaluating the performance characteristics of reluctance-augmented shaded pole motors. The proposed model is based on the d-q axis technique and is valid for steady-state and dynamic conditions. An efficient method of predicting the steady-state operating characteristics of the triac-controlled shaded pole motor is presented. This method calculates the currents and average torque as a function of conduction and control angles of the triac. The effect of critical parameters on the motor performance is investigated. Simulated results are compared with experimental values of a two-pole single phase test induction motor     

Role of drivers' personal characteristics in understanding traffic sign symbols

This study investigated the role of age, marital status, gender, nationality, educational background and monthly income in drivers' comprehension of traffic signs. The populations sampled here were from five Arabian Gulf Countries. A total of 28 symbolic warning and regulatory signs were investigated. A questionnaire specially prepared to collect the necessary data was distributed to over 9000 drivers in the five countries; 4774 responded (53%). The results indicated substantial problems with the level of comprehension among the drivers about the traffic signs. The percentages of drivers who correctly identified the regulatory signs and warning signs were around 55 and 56%, respectively. Age, gender, education and income played major roles in determining drivers' comprehension of signs, whereas marital status showed no significant effect. Drivers who are young, female, those with lower levels of education or lower incomes understand the signs significantly worse than drivers who are older, male, with higher levels of education or higher incomes. Drivers from Europe and USA are significantly better than Asian and Arab drivers. These findings are believed to be important for the designers of road signs for international applications.