Thermal Hydraulic Modeling of Once-Through Steam Generator by Two-Fluid U-Tube Steam Generator Code

The THERMIT U-tube steam generator (THERMIT-UTSG) code was used for evaluation for the parametric study of a scaled once-through pressurized water reactor steam generator (OTSG) made by Babcock & Wilcox. The results of the code were compared to the experimental data of the 19-tube OTSG and a simple heat transfer code that was developed by Osakabe. The main calculated thermodynamic parameters were primary-secondary fluid temperatures, tube wall internal and external temperatures that were subjected to primary and the secondary fluid, and the secondary fluid vapor quality. The assessed code can be used for modeling the OTSGs with some modification. The results of THERMIT-UTSG were in agreement with the experimental results and the prediction of Osakabe’s numerical model

Thermal Hydraulic Modeling of Once-Through Steam Generator by Two-Fluid U-Tube Steam Generator Code

The THERMIT U-tube steam generator (THERMIT-UTSG) code was used for evaluation for the parametric study of a scaled once-through pressurized water reactor steam generator (OTSG) made by Babcock & Wilcox. The results of the code were compared to the experimental data of the 19-tube OTSG and a simple heat transfer code that was developed by Osakabe. The main calculated thermodynamic parameters were primary-secondary fluid temperatures, tube wall internal and external temperatures that were subjected to primary and the secondary fluid, and the secondary fluid vapor quality. The assessed code can be used for modeling the OTSGs with some modification. The results of THERMIT-UTSG were in agreement with the experimental results and the prediction of Osakabe's numerical model

Computation of concentration changes of heavy metals in the fuel assemblies with 1.6% enrichment by ORIGEN code for VVER-1000

ORIGEN code is a widely used computer code for calculating the buildup, decay, and processing of radioactive materials. During the past few years, a sustained effort was undertaken by ORNL to update the original ORIGEN code [4] and its associated data bases. The results of this effort were updated on the reactor model, cross section, fission product yields, decay data, decay photon data and the ORIGEN computer code itself. In this paper we have obtained concentration changes of uranium and plutonium isotopes by ORIGEN code at different burn-up and then the results have been compared with VVER-1000 results in the first fuel cycle for fuel assemblies with 1.6% enrichment in the BUSHEHR Nuclear Power Plant

Extending Lyapunov redesign method for robust stabilization of non-affine quadratic polynomial systems

The Lyapunov redesign method is basically used for robust stabilization of nonlinear systems with an affine structure. In this paper, for the first time, by suggestion of a simple but effective idea, this approach is developed for robust stabilization of non-affine quadratic polynomial systems in the presence of uncertainties and external disturbances. In the proposed method, according to the upper bound of an uncertain term, a quadratic polynomial is constructed and with respect to the position of the roots of this polynomial, the additional feedback law is designed for robustness of the quadratic polynomial system. The proposed technique is also used for robust stabilizing of a magnetic ball levitation system. When the coil current is the control input of the magnetic ball levitation system, equations of this system are increasingly nonlinear with respect to control input and have quadratic polynomial structure. The effectiveness of the proposed control law is also demonstrated through computer simulations

Study of temperature distribution of fuel, clad and coolant in the VVER-1000 reactor core during group-10 control rod scram by using diffusion and point kinetic methods

In this paper, through the application of two different methods (point kinetic and diffusion), the temperature distribution of fuel, clad and coolant has been studied and calculated during group-10 control rod scram, in the Bushehr Nuclear Power Plant (Iran) with a VVER-1000 reactor core. In the reactor core of Bushehr NPP, 10 groups of control rods are used of which, group-10 control rods contain the highest amount of injected negative reactivity in terms of quantity as compared to other groups of control rods. In this paper we explain impacts of negative reactivity, caused by a complete or minor scram of group-10 control rods, on thermoneutronic parameters of the VVER-1000 nuclear reactor core. It should be noted that through these calculations and by using the results, we can develop a sound understanding of impacts of this controlling element in optimum control of the reactor core and, on this basis, with careful attention and by gaining access to a reliable simulation (on the basis of results of calculations made in this survey) we can monitor the VVER-1000 reactor core through a smart control system. In continuation, for a more accurate survey and for comparing results of different calculation systems (point kinetic and diffusion), by using COSTANZA-R,Z calculation code (in which neutronic calculations are based on diffusion model) and using WIMS code at different areas and temperatures (for calculation of constant physical coefficients and temperature coefficients needed in COSTANZAR, Z code) for the VVER-1000 reactor core of Bushehr NPP, calculation of temperature distribution of fuel elements and coolant by using diffusion model is made in the course of group-10 control rods scram and afterwards

A study of the effects of changing burn-up and gap gaseous compound on the gap convection coefficient (in a hot fuel pin) in VVER-1000 reactor

In this article we worked on the result and process of calculation of the gap heat transfer coefficient for a hot fuel pin in accordance with burn-up changes in the VVER-1000 reactor at the Bushehr nuclear power plant (Iran). With regard to the fact that in calculating the fuel gap heat transfer coefficient, various parameters are effective and the need for designing a model is being felt, therefore, in this article we used Ross and Stoute gap model to study impacts of different effective parameters such as thermal expansion and gaseous fission products on the hgap change rate. Over time and with changes in fuel burn-up some gaseous fission products such as xenon, argon and krypton gases are released to the gas mixture in the gap, which originally contained helium. In this study, the composition of gaseous elements in the gap volume during different times of reactor operation was found using ORIGEN code [3]. Considering that the thermal conduction of these gases is lower than that of helium, and by using the Ross and Stoute gap model, we find first that the changes in gaseous compounds in the gap reduce the values of gap thermal conductivity coefficient, but considering thermal expansion (due to burn-up alterations) of fuel and clad resulting in the reduction of gap thickness we find that the gap heat transfer coefficient will augment in a broad range of burn-up changes. These changes result in a higher rate of gap thickness reduction than the low rate of decrease of heat conduction coefficient of the gas in the gap during burn-up. Once these changes have been defined, we can proceed with the analysis of the results of calculations based on the Ross and Stoute model and compare the results obtained with the experimental results for a hot fuel pin as presented in the final safety analysis report of the VVER-1000 reactor at Bushehr [2]. It is noteworthy that the results of accomplished calculations based on the Ross and Stoute model correspond well with the existing experimental results for this reactor

Numerical simulation of the PEM fuel cell performance enhancement by various blockage arrangement of the cathode serpentine gas flow channel outlets/inlets

In this paper, performance enhancement of polymer electrolyte membrane fuel cells by changing the outlet/inlet configuration of parallel-serpentine flow field is investigated. The geometrical changes of the channel outlets/inlets are designed to amplify the effects of transverse over-rib convection in the gas diffusion and catalyst layers. A three-dimensional and two-phase simulation of the fuel cell performance with four flow fields of parallel-serpentine, serpentine-baffled, serpentine-interdigitated and serpentine-stepped channel is conducted and the results are presented in the form of polarization curves, contours of velocity, oxygen concentration, liquid water saturation, local current density, and the dissolved water content. The results show that the liquid saturation volume coverage is reduced from 0.832 for the parallel-serpentine flow field to 0.514 for the serpentine-baffled flow field. Also, the regions with high concentration of oxygen was improved by 26.7% between these two cases. Due to the increase in oxygen delivery to the catalyst layer and better water removal on the cathode side, the serpentine-baffled, serpentine-interdigitated, and serpentine-stepped flow channel geometries showed a significant increase in performance compared to the parallel-serpentine case. The highest net power has resulted for the serpentine-baffled case so that at a current density of 1.5 A/cm(2), a performance increase of 38.5% was achieved compared to the parallel-serpentine case. (C) 2021 Elsevier Ltd. All rights reserved

Peridotites from the Khoy Ophiolitic Complex, NW Iran : evidence of mantle dynamics in a supra-subduction-zone context

The Khoy Ophiolitic Complex as a part of the Tethyan ophiolites is exposed in the northwestern part of the Iranian-Azerbaijan province, extending to the Anatolian ophiolites in southeastern Turkey. Petrography, geochemistry and microstructural studies of the residual mantle sequence in the Khoy Ophiolitic Complex provide important information about the degree of partial melting and deformation in the oceanic mantle lithosphere. Ultramafic tectonites dominantly composed of lherzolite and clinopyroxene-bearing harzburgite (TiO₂ = 0.012-0.024 wt.%; Al₂O₃ = 1.36-1.81 wt.%). Chondrite-normalized rare-earth-element patterns are characteristically U-shaped. These peridotites can be divided into two types: (1) type 1 peridotites with Al-rich spinels (Cr number of 0.16-0.26, and Mg number of 0.64-0.76), resembling the fertile abyssal peridotites, supposed to have originated as the residue from 20% partial melting, followed by segregation of basaltic magmas. Microstructural fabrics of olivine grains in peridotites highlight a sequence of dislocation creep on the (0 1 0) [1 0 0] slip system, plus subsidiary slip along the (0 0 1) [1 0 0] slip system. These systems, as well as coarse and fine-grained porphyroclastic textures, indicate deformation at high temperatures of ~1000–1250 ℃. The observed subsidiary (0 0 1) [1 0 0] slip system is considered to have been triggered by elevated H₂O activity, and that deformation phases took place in a wet subduction-related environment. The geochemical and microstructural data suggest that the mantle sequence of the Khoy Ophiolitic Complex is consistent with a supra-subduction-zone environment in relation to a slow-spreading back-arc basin.16 page(s

The Dehshir ophiolite (central Iran) : geochemical constraints on the origin and evolution of the inner Zagros ophiolite belt

The Late Cretaceous Dehshir ophiolite is an important element within the Inner Zagros (Nain-Baft) ophiolite belt and contains all components of a complete "Penrose ophiolite," including tectonized harzburgites, gabbros, sheeted dike complexes, pillowed basalts, and rare ultramafic-mafic cumulates. The cumulate rocks of this ophiolite are composed of plagioclase lherzolite, clinopyroxenite, leucogabbro, and pegmatite gabbro. All the massifs in the Inner Zagros ophiolite belt are overlain by Turonian-Maastrichtian pelagic limestones (93.5-65.5 Ma). Clinopyroxene compositions of Dehshir mafic rocks are similar to those of both boninites and island-arc tholeiites. Nearly all spinels from the inner ophiolite belt are similar to those of highly depleted harzburgites from intra-oceanic forearcs, although some Dehshir harzburgite spinels plot within the field for abyssal (mid-ocean-ridge basalt) peridotites. All components of the Dehshir and other ophiolites of this belt show strong suprasubduction-zone affinities, from harzburgitic mantle to ophiolitic lavas. Volcanic rocks have a mixture of dominantly arc-like (island-arc tholeiite, boninite, and calc-alkaline) and subordinate mid-ocean-ridge basalt–like compositional features, usually with mid-ocean-ridge basalt–like rocks at the base and arc-like rocks at the top. Our data for the Dehshir ophiolite and the similarity of these results to those for Iranian inner and outer belt ophiolites compel the conclusion that a geographically long, broad, and continuous tract of forearc lithosphere was created at about the same time during the earliest stages of subduction along the southern margin of Eurasia in Late Cretaceous time.32 page(s