bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerothermal Analysis of Small Payloads Delivered Into Low Earth Orbit From an Airborne Launch Platform
Authors: Guillot Martin J. , McNab Ian
Published: July 2009

In recent years there has been an ever increasing need to launch small payloads (∼1–100 kg) into low earth orbit (LEO). Examples include the defense and telecommunications industries. Permanent human presence in LEO, such as the international space station, requires continual re-supply from earth. Additionally, NASA’s stated mission of launching a manned mission to Mars requires many tonnes of raw materials to be economically launched into LEO and assembled there. Conventional rocket launch from earth is prohibitively expensive for small mass payloads. Estimates range from $7000–$20,000 to launch 1 kg of mass into low earth orbit. Several concepts have been proposed to economically launch small payloads from earth, including light gas guns, electromagnetic launchers and the so called “slingatron” concept. The goal of these concepts is to reduce the cost per kg (to under $1000) to achieve LEO. Each of these concepts involves launching small payloads that traverse the atmosphere and then placed into low earth orbit using thrusters to turn the velocity vector into a stable circular orbit. As the launch vehicle traverses the dense lower portion of the atmosphere it experiences severe thermal heating loads that must be absorbed by a thermal protection system (TPS) if the payload is to survive the transit. The University of Texas is currently heading a multi-university research initiative (MURI) to study the feasibility of launching small payloads into low earth orbit from an electromagnetic gun housed in an airborne platform. As part of the study, the aerothermal issues associated with traverse through the atmosphere and propellant mass required to achieve a stable circular orbit are investigated. The effort focuses on quantifying the required parasitic mass of the thermal protection system (TPS) and propellant need to place a nominal 10 kg launch mass into a circular low earth orbit from an electromagnetic launcher at 16 km altitude. The TPS is assumed to be graphite or carbon-carbon composite. In this effort, we consider ballistic trajectories only. Circular orbit is achieved using rocket thrusters at the terminal altitude. Total parasitic mass (TPS + propellant) is estimated for various launch angles.
Modeling the Retention of Water Droplets on Topographically-Modified, Micro-Grooved Aluminum
Authors: Sommers Andrew D. , Jacobi Anthony M.
Published: July 2009

In this research, a method for fabricating controlled micro-scale, anisotropic topographical features on aluminum is described for the purpose of exploiting those features to affect the surface wettability. Experimental data have shown that droplets placed on these micro-grooved aluminum surfaces using a micro-syringe exhibit an increased apparent contact angle, and for droplets condensed on these etched surfaces, up to a 50% reduction in the volume needed for the onset of droplet sliding is manifest. No chemical surface treatment is necessary to achieve this water repellency; it is accomplished solely by the anisotropic surface morphology that manipulates droplet geometry and creates and exploits discontinuities in the three-phase contact line. In an effort to provide guidance for the development of these surfaces, a mechanistic model for droplet retention on micro-grooved aluminum surfaces will also be presented. This work will show that current models, tacitly based on an assumption of isotropic wetting, do not provide reliable prediction of water retention on these new surfaces.
Effect of Reduced Temperature and Cathode Porosity on the Performance of Tubular Solid Oxide Fuel Cell
Authors: Sleiti A. K.
Published: July 2009

The effect of decreasing the inlet temperature and the cathode porosity of tubular Solid Oxide Fuel Cell with one air channel and one fuel channel was investigated using CFD approach. A CFD model of the cell was developed using the commercial CFD software Fluent 6.2. A Fluent based SOFC model was used to simulate the electrochemical effects. The cathode and the anode of the cell were resolved in the model and the convection and conduction heat transfer modes were included. The results of the CFD model are presented at inlet temperatures of 700°C, 600°C, and 500°C and with cathode porosity of 30%, 20% and 10%. The resulting thermal, electrical, and flow fields are presented and discussed. It was found that the Fluent based SOFC model is effective tool for analyzing the complex and highly interactive three-dimensional electrical, thermal, and fluid flow fields, generally associated with the SOFCs. The comprehensive current density and thermal fields generated with the Fluent based model are necessary to assist a life-cycle analysis of the cell through prediction of thermal stresses.
Effect of Variable Thermal Conductivity on Heat Transfer From a Hollow Sphere With Heat Generation Using Homotopy Perturbation Method
Authors: Khan Zafar H. , Gul Rahim , Khan Waqar A.
Published: July 2009

Homotopy perturbation method (HPM) is employed to investigate steady-state heat conduction with temperature dependent thermal conductivity and heat generation in a hollow sphere. Analytical models are developed for dimensionless temperature distribution and heat transfer using mixed boundary conditions (Dirichlet, Neumann and Robin). The effects of dimensionless heat generation parameter and temperature dependent thermal conductivity on temperature distribution and heat transfer from hollow spheres are analyzed graphically. It is demonstrated that the heat transfer is strongly dependent on the dimensionless heat generation parameter and temperature dependent thermal conductivity. Finally the HPM results are compared with Kirchhoff Transformation results.
Effects of Exit Vent Location on Fire Room Conditions During PPV
Authors: Beal Colin M. , Ezekoye Ofodike A.
Published: July 2009

Positive Pressure Ventilation (PPV) is a widely used fire fighting tactic in which a fan is used to push hot products of fire out of a burning structure. There is a recent body of research that has been conducted regarding the advantages and disadvantages of PPV. Studies of PPV most commonly use full scale experimental fires and/or computational simulations to evaluate its effectiveness. This paper presents computational simulations that have been conducted using Fire Dynamic Simulator (FDS) version 5 to evaluate the effects of exit vent location on resulting fire room conditions during the application of PPV to a ventilation constrained fire. The simulations use a simple one room structure with an adjacent hallway. We are simulating this geometry because we are in the process of designing and constructing a similar experimental compartment. Cold flow simulations are first conducted to understand how much the presence of the fire heat release affects the flow patterns. Then, two simulations which employ PPV with different exit vent locations are compared. The differences between the two simulations are detailed and a physical explanation for the differences is presented.
Validation of Dynamic Models for an Air-Cooled CPU Chip Cooling Device
Authors: Zhang R. , Zhang C. , Jiang J.
Published: July 2009

In this paper, the proposed novel technique using computational fluid dynamics (CFD) approach to design control systems is validated experimentally for a chip cooling device. Both experimental approach and CFD simulations are employed to extract the dynamic characteristics from the non-linear chip cooling system around a specific operating point, which are then used to construct the linear dynamic model for the chip cooling system. The linear dynamic model has two inputs, the heat load generated by the chip and the cooling fan voltage. The output is the temperature of the case housing the chip. The results from the linear dynamic model obtained by the CFD approach are compared with those obtained experimentally under the same dynamic conditions to validate the feasibility of using the CFD approach to design a control system for a thermal-fluid system.
Solution of Heat Conduction Problem in Automotive Clutch and Brake Systems
Authors: Al-Shabibi Abdullah M.
Published: July 2009

This paper is investigating the transient solution for a heat conduction problem in solids with insulated boundary. This class of problem is often encountered in automotive brake and clutch systems where the frictional heat generated at contact surface is much larger than that the system is capable of dissipating. The heat conduction equation can be solved through the superposition of the homogenous solution and the particular solution. The use of the steady state solution as a particular solution can however result in a lack of numerical accuracy because of its order of magnitude driven by the nearly insulated boundary. A special solution form is proposed for the particular solution to account for such boundary condition. The proposed solution was tested in the context of a typical clutch disk sliding between two non-conductive rigid bodies. The solution has proven to be time efficient and free of numerical accuracy associated with the order of magnitude of the particular solution.
Nozzle Track and CHF Prediction of Spray Cooling for Inclined Sprays
Authors: Guo Yongxian , Jia Jianyuan , Wang Weidong , Zhou Shaorong
Published: July 2009

The tracks of the nozzles were studied during spray cooling with different inclination angles, based on the study of Visaria [1,2] and the critical heat flux (CHF) criterion, which means that CHF will be achieved when the spray is configured on the condition that the spray impact area just inscribes a square test surface. The predictions of the tracks of the nozzles were made. It indicates that the nozzle tracks are parts of some ellipses as keeping the four borderline of the square test surface being the tangent line of the elliptical spray impact area. A new CHF model was established and new expression of CHF was derived based on the nozzle track model and the study of Visaria. The effects of spray inclination angle on CHF were predicted. Three different nozzles with different cone angles and volume flux were used. Simulation results indicate that CHF increases slightly with increasing inclination angle. The maximum difference of CHF of the three nozzles is about 13.1%. One reason for the difference between the established model and the results derived by Visaria is attributed to the difference of the spray impact area.
Heat Transfer Enhancement in Triangular Fin
Authors: Shokouhmand H. , Moghaddami M. , Jafari H.
Published: July 2009

Fins are widely utilized in many industrial applications for example, fins are used in air cooled finned tube heat exchangers like car radiators, heat rejection devices, refrigeration systems and in condensing central heat exchangers. In this paper, heat transfer inside the fin system composed of a primary rectangular fin with a number of rectangular fins (secondary fins), which are attached on its surface, is modeled and analyzed numerically. The length of the secondary fins decreases linearly from the base of the primary fin to its tip. This modified triangular fin is a kind of improved tree fin networks. The effectiveness of the modified triangular fin is compared with the effectiveness of triangular fin which is calculated analytically. The results show that adding secondary fins increases the effectiveness of triangular fin significantly. Also, it is found that increasing the number of secondary fins in a constant length of primary fin will increase the effectiveness. In addition, by comparing the results it can be concluded that by shortening the length of the primary fin in modified triangular fin, the effectiveness will increase significantly to the contrary of the triangular fin, so smaller heat exchangers can be built by using the modified triangular fin. It is found that in a constant length of primary fin, there is an optimum thickness of secondary fins which maximize the effectiveness of the fin.
Thermo-Physical Features of Extreme Activity of Metallic Nano-Particles
Authors: Shokri Babak , Yaghmaee Maziar S. , Rahimipour M. Reza
Published: July 2009

In order to understand the physics behind the strange behaviors of materials at nano-scale, one of the most important factors is to investigate their extreme activity in different environments. This information comes directly from the cohesion (binding) energy of materials. In this report, we first review a simple thermodynamic-based theory for size dependence feature of total cohesion energy of metallic nano-particles. Then, regarding the size dependency of cohesion energy, simple theory for size dependency of enthalpy and Gibbs free energy formation of metallic nano-particles is developed. Moreover, to describe the relative activity of metallic nano-particles, hypothesis through the modified classical physico-chemical formalism of activity in a reactive medium will be presented. Series of computations for size dependency of relative activity (via relative reaction constant: nano/macro) for Zn, Al, Ag, Ga and W nano-particles in a reactive solution will be presented. Our computational results show that by decreasing the size of the particles less than 100 nm, the equilibrium reaction constant and consequently the relative activity of particles increases, which confirms the tendency observed in experiments so far. The suggested concept of size dependence reaction constant provides a quantitative scale for studying the reactions contain nano-particles.
Heat Flux Estimation in Direct Chill Casting Using Experimental and Inverse Finite Element Method
Authors: Nallathambi Ashok Kumar , Alam Umair , Specht Eckehard
Published: July 2009

In Direct Chill (DC) non-ferrous metal casting, water is used as a cooling medium to extract the heat from the solidified outer layer of the ingot which supports the inner molten metal. Insufficient or excessive water supply changes the heat flux which is favorable for the growth of micro-cracks. This work presents the combined experimental and numerical technique to estimate the heat flux in the DC nickel casting. Experimental techniques are explained for the measurement of temperature. A two-dimensional Inverse Heat Conduction Problem (IHCP) is solved through the non-iterative Finite Element Method (FEM) using the experimental temperature data. Wetting front which separates the film boiling and nucleate boiling zone, changes the order of the heat flux. Maximum heat flux position and its propagation velocity are plotted as a function of time. It is demonstrated that increase in water velocity decreases the maximum heat flux and delays the wetting front movement.
The Temperature Distributions of Trapezoidal Fin Under Periodic Thermal Conditions
Authors: Shokouhmand H. , Khabazi N. , Taghavi S. M. , Jafari H.
Published: July 2009

This paper investigates the effects of periodic thermal conditions on the thermal performance of a convective fin. The environment heat transfer coefficient and thermal conductivity coefficient are assumed to be constant. The periodic oscillation of the base temperature is considered. An efficient numerical method which is called collocation method is used to solve the linear hyperbolic heat conduction equation. The results obtained lead to the conclusion that the efficiency of the fin is decreased if the frequency of the temperature oscillation goes up. Good agreement between numerical results and similar previous special cases confirm the validity of the presented algorithm.
Experimental Study of Mixed Convection Shell-and-Coil Heat Exchanger
Authors: Ghorbani Mianroudi Nasser , Gorji Mofid , Taherian Hessam
Published: July 2009

In this study the mixed convection heat transfer in a coil-in-shell heat exchanger for various Reynolds numbers, various tube-to-coil diameter ratios and different dimensionless coil pitch was experimentally investigated. The experiments were conducted for both laminar and turbulent flow inside coil. Effects of coil pitch and tube diameters on shell-side heat transfer coefficient of the heat exchanger were studied. Different characteristic lengths were used in various Nusselt number calculations to determine which length best fits the data and several equations were proposed. The particular difference in this study in comparison with the other similar studies was the boundary conditions for the helical coils. The results indicate that the equivalent diameter of shell is the best characteristic length.
Proposed Concept Design for the High Temperature Sulphuric Acid Decomposition Reactor Applicable to the Hybrid Sulphur (HyS) Process
Authors: Coetzee M. D. , Blom P. W. E.
Published: July 2009

The utilization of alternate sources of energy is becoming more important due to the constantly growing world-wide demand for energy. The production of hydrogen via the Hybrid Sulphur process is a possible alternative that may contribute to alleviating the pressure on energy resources. The current field of interest is to investigate the operation of the sulphuric acid decomposition reactor operating at pressure ranges between 8 and 9 MPa. The reduction of SO3 to SO2 is, however, favoured at low pressures while maintaining high operating temperatures. Considering this, the need to investigate the possibility of operating at lower operating pressures is important in striving for higher process efficiencies. The proposed decomposition reactor is a multi-stage reactor system operated adiabatically with inter-stage heating in order to simplify the reactor design and improve the over-all conversion and efficiency of the process. At a pressure of 8–9 MPa and temperature of 900°C, the maximum conversion of SO3 to SO2 that can be achieved is between 48% and 54%. The proposed multi-stage reactor system has 5 packed bed (catalyst) reactor stages with 4 intermediate heat exchangers, and by lowering the operating pressure to 3 kPa, a maximum conversion of 72% could be achieved. The viability of the HyS process mainly depends on the performance of the SO3 decomposition reactor.
Non-Catalytic Plasma-Arc Reforming of Natural Gas With Carbon Dioxide as the Oxidizing Agent for the Production of Synthesis Gas or Hydrogen
Authors: Basson Gert W. , Blom P. W. E.
Published: July 2009

The world’s energy consumption is increasing constantly due to the growing population of the world. The increasing energy consumption has a negative effect on the fossil fuel reserves of the world. Hydrogen has the potential to provide energy for all our needs by making use of fossil fuel such as natural gas and nuclear-based electricity. Hydrogen can be produced by reforming methane with carbon dioxide as the oxidizing agent. Hydrogen can be produced in a Plasma-arc reforming unit making use of the heat energy generated by a 500 MWt Pebble Bed Modular Reactor (PBMR). The reaction in the unit takes place stoichiometrically in the absence of a catalyst. Steam can be added to the feed stream together with the Carbon Dioxide, which make it possible to control the H2/CO ratio in the synthesis gas between 1/1 and 3/1. This ratio of H2/CO in the synthesis gas is suitable to be used as feed gas to almost any chemical and petrochemical process. To increase the hydrogen production further, the Water-Gas Shift Reaction can be applied. A techno-economic analysis was performed on the non-catalytic plasma-arc reforming process. The capital cost of the plant is estimated at $463 million for the production of 1132 million Nm3/year of hydrogen. The production cost of hydrogen is in the order of $12.81 per GJ depending on the natural gas cost and the price of electricity.
Fabrication, Properties and Irradiation Performance of Molded Block Fuel Elements for HTGRs
Authors: Hrovat Milan F. , Grosse Karl-H. , Seemann Richard
Published: July 2009

The molded block fuel element (FE) also called monolith is a molded body, consisting of a substantially isotropic highly crystalline graphite matrix, fuel regions within the same matrix and cooling channels. The fuel regions contain the fuel in the form of coated particles which are well bonded to the remaining graphite matrix, so that both parts of the block form a monolithic structure. The monolith meets the requirements for the very high temperature reactors attaining helium outlet temperatures above 1000°C. To fabricate the molded blocks FE demonstration plant was erected and put into operation. The equipment worked without malfunction. The produced block FEs meet the specifications of GA machined block FEs. All specimens and block segments irradiated at temperature up to 1600°C and max. fast fluence E > 0, 1 MeV of 11×1021 n/cm2 show perfect behaviour without any damage.
Evaluation of Design, Leak Monitoring, and NDE Strategies to Assure PBMR Helium Pressure Boundary Reliability
Authors: Fleming Karl N. , Smit Kobus
Published: July 2009

This paper discusses the reliability and integrity management (RIM) strategies that have been applied in the design of the PBMR passive metallic components for the helium pressure boundary (HPB) to meet reliability targets and to evaluate what combination of strategies are needed to meet the targets. The strategies considered include deterministic design strategies to reduce or eliminate the potential for specific damage mechanisms, use of an on-line leak monitoring system and associated design provisions that provide a high degree of leak detection reliability, and periodic non-destructive examinations combined with repair and replacement strategies to reduce the probability that degradation would lead to pipe ruptures. The PBMR RIM program for passive metallic piping components uses a leak-before-break philosophy. A Markov model developed for use in LWR risk-informed inservice inspection evaluations was applied to investigate the impact of alternative RIM strategies and plant age assumptions on the pipe rupture frequencies as a function of rupture size. Some key results of this investigation are presented in this paper.
Development of an ASME PRA Standard for Non-LWRs
Authors: Fleming Karl N. , Lusse Lemmer , Budnitz Bob , Siu Nathan , Tinsley Grant
Published: July 2009

The ASME Committee on Nuclear Risk Management (CNRM) has established a working group to pursue the development of a PRA standard that can be used for advanced non-LWR plants. The applications of such PRAs include the performance of PRAs to support licensing and design decisions, and to meet NRC requirements for Design Certifications and Construction and Operating Licenses. The purpose of this paper is to summarize the significant progress that has been made to date in developing a new PRA standard for non-LWRs from the personal point of view of the working group chairman.
Fabrication Process and Product Quality Improvements in Advanced Gas Reactor UCO Kernels
Authors: Barnes Charles M. , Richardson W. C. , Husser DeWayne , Ebner Matthias
Published: July 2009

A major element of the Next Generation Nuclear Plant (NGNP)/Advanced Gas Reactor (AGR) Fuel Development and Qualification Program is developing fuel fabrication processes to produce high quality uranium-containing fuel kernels, TRISO-coated particles and fuel compacts needed for planned irradiation tests. The goals of the program also include developing the fabrication technology to mass produce this fuel at low cost. Kernels for the first AGR test, AGR-1, consisted of uranium oxycarbide (UCO) microspheres that were produced by an internal gelation process followed by high temperature steps to convert the UO3 + C “green” microspheres to UO2 + UCx. The high temperature steps also densified the kernels. Babcock and Wilcox (B&W) fabricated UCO kernels in their Lynchburg facility for the AGR-1 irradiation experiment, which went into the Advanced Test Reactor (ATR) at Idaho National Laboratory in December 2006. An evaluation of the kernel process prior and after these kernels were produced led to several recommendations to improve the fabrication process. These recommendations included testing alternative methods of dispersing carbon during broth preparation, evaluating the method of broth mixing, optimizing the broth chemistry, optimizing sintering conditions, and demonstrating fabrication of larger diameter UCO kernels needed for the second AGR irradiation test, AGR-2. Based on these recommendations and requirements, a test program was defined and performed. Certain portions of the test program were performed by Oak Ridge National Laboratory (ORNL), while tests at larger scale were performed by B&W. The tests at B&W have demonstrated improvements in both kernel properties and process operation. Changes in the form of carbon black used and the method of mixing the carbon prior to forming kernels led to improvements in the phase distribution in the sintered kernels, greater consistency in kernel properties, a reduction in forming run time, and simplifications to the forming process. Process parameter variation tests in both forming and sintering steps led to an increased understanding of the acceptable ranges for process parameters and additional reduction in required operating times. Another result of this test program was to double the kernel production rate. Following the development tests, approximately 40 kg of natural uranium UCO kernels have been produced for use in coater scale up tests, and approximately 10 kg of low enriched uranium UCO kernels for use in the AGR-2 experiment.
Update on Overcoating and Compacting Activities for Coated Particles With 425 µm Kernels
Authors: Pappano Peter J. , Hunn John D.
Published: July 2009

The Advanced Gas Reactor (AGR) program is tasked with developing and qualifying fuel for the Next Generation Nuclear Plant (NGNP) [1, 2]. The first experiment, AGR-1, focused on TRISO coating 350 μm uranium oxide/uranium carbide (UCO) kernels and compacting them into a right circular cylinder fuel form using an overcoating and compacting process. The AGR-1 fuel compacts are currently being irradiated at the Advanced Test Reactor (ATR). The AGR-2 experiment will focus on overcoating and compacting TRISO coated 425 μm UCO kernels. This paper summaries the work that has been done to date on preparing to make AGR-2 compacts.
A Novel Concept of the Modular HTGR and Its New Application
Authors: Tian Jiafu
Published: July 2009

The Ordered Bed Modular HTGR (OBMR) core is filled with an ordered bed of fuel spheres, which has great structural stability. It is able to adapt its configuration to ship space, create stability in ships at large and work in vibrating and possibly bumping environment, which are suitable for ship applications. The modular HTGR has features of inherent safety, high-cycle efficiency, and coupling with gas turbine power conversion system, would make a great advantage for marine use. The OBMR design for ship applications allows the option for a shorter refueling period and lower fuel cost, and reaches deep burn-up of this fuel element. It uses significantly less fuel costs than that of the PWR powered and oil powered ships. In addition, this technology also displays promising aspects in the distributed energy applications, particularly in combined heating and power applications. Therefore, development of the OBMR should still be taken into account to expand its use for purposes other than electricity generation, and can make a significant contribution to the reduction of global carbon-dioxide emissions.
Preliminary Results of the HFR-EU1 Fuel Irradiation of INET and AVR Pebbles in the HFR Petten
Authors: Marmier Alain , Fu¨tterer Michael A. , Laurie Mathias , Tang Chunhe
Published: July 2009

The irradiation experiment HFR-EU1 in the HFR Petten is currently being conducted by the European Commission’s Joint Research Centre – Institute for Energy (JRC-IE). The irradiation targets are 5 spherical High Temperature Reactor (HTR) fuel pebbles, 2 of INET production and 3 of former German production. Both types are made of TRISO coated particles and are tested for their potential for very high temperature performance and high burn-up. The irradiation started on 29 September 2006 and, by 24 February 2008, had accumulated 12 reactor cycles totaling 332.8 efpd and a calculated maximum burn-up of 8.9% FIMA (INET) and 11.2% FIMA (AVR). The objective of the HFR-EU1 test is to irradiate 5 HTR fuel pebbles at conditions beyond the characteristics of current HTR reactor designs with pebble bed cores, e.g. HTR-Modul, HTR-10 and PMBR. This should demonstrate that pebble bed HTRs are capable of enhanced performance in terms of sustainability (further increased power conversion efficiency, improved fuel use) and thus reduced waste production. The surface temperature of all pebbles was held constant during the irradiation, with the exception of HFR downtime and power transients. HFR-EU1 should demonstrate the feasibility of low coated particle failure fractions under normal operating conditions and more specifically: • high fuel surface temperature of 900°C (INET) and 950°C (AVR); • very high burn-up of 17% FIMA (INET) and 20% FIMA (AVR) which is significantly higher than the license limit of the HTR-Modul (approx. 8% FIMA); it will be explained in this paper why this objective had to be somewhat reduced due to excessive irradiation time requirements and technological difficulties. This paper provides the irradiation history of the experiment performed so far including data on fission gas release.
PBMR Confinement Analysis During Helium Pressure Boundary Breaks
Authors: Fontanet Joan , Herranz Luis E. , Ramlakan Alastair , Naicker Lolan
Published: July 2009

A scoping study on a confinement approach to a PBMR type plant was performed to quantify its performance in terms of retention and thermal-hydraulics in case of a postulated breach in the Helium Pressure Boundary. This paper introduces a simulation strategy for accident analyses of a PBMR confinement. Based on two accident sequences characterized by Helium Pressure Boundary breaches, a small (AOO) and a large (DBA) break, the estimates from the ASTEC and CONTAIN codes are presented and compared to check their capabilities and consistency. The results obtained indicate that both codes predict very similar thermal-hydraulic responses of the confinement both in magnitude and timing. As for the aerosol behaviour, both codes predict that most of inventory coming into the confinement is eventually depleted on the walls and only about 1% of the aerosol dust is released to environment. The cross-comparison of codes states that largest differences are in the inter-compartmental flows and the in-compartment gas composition. Concerning the capabilities of the codes, CONTAIN has shown to be more robust in dealing with the injection of large aerosol mass flow and with a very small injection of fission products. ASTEC however has an ad-hoc model for aerosol retention in filters.
VHTR Core Preliminary Analysis Using NEPHTIS3 / CAST3M Coupled Modelling
Authors: Damian Fre´de´ric
Published: July 2009

Along with the GFR another gas-cooled reactor identified in the Gen IV technology roadmap, the VHTR is studied in France. Some models have been developed at CEA relying on existing computational tools essentially dedicated to the prismatic block type reactor. These models simulate normal operating conditions and accidental reactor transients by using neutronic [1], thermal-hydraulic, system analysis codes [2], and their coupling [3, 4]. In the framework of the European RAPHAEL project, this paper presents the results of the preliminary investigations carried out on the VHTR design. These studies aimed at understanding the physical aspects of the annular core and to identify the limits of a standard block type VHTR with regard to a degradation of its passive safety features. Analysis was performed considering various geometrical scales: fuel cell and fuel column located at the core hot spot, 2D and 3D core configurations including the coupling between neutronic and thermal-hydraulic. From the thermal analysis performed at the core hot spot, the capability to reduce the maximum fuel temperature by modifying the design parameters such as the fuel compact and the fuel block geometry was assessed. The best performances are obtained for an annular fuel compact geometry with coolant flowing inside and outside the fuel compact (ΔT > 50°C). The reliability of such design option should however be addressed with respect to its performance during the LOFC transient (the residual decay heat will be evacuated by radiation during the transient instead of conduction through graphite). As far as the fuel element geometry is concerned, a gain of approximately 50°C can be achieved by making limited changes on the fuel compact distribution in the prismatic block: reduction of the number of fuel compact in the outer ring of the fuel element where the average ratio between coolant channels and fuel compact is smaller. On the other hand, the adopted modifications should also be evaluated with respect to the maximum temperature gradient achieved in the fuel (amoeba effect). In the end, calculations performed on the full core configuration taking into account the thermal feedback showed that the radial positioning of the fuel elements allows to reduce significantly the power peaking factor and the maximum fuel temperature. The gain on the fuel temperature, which varies during the core irradiation, is in the range 100 – 150°C. Several modifications such as the increase of the bypass fraction and the replacement of a part of the graphite reflector by material with better thermal properties were also addressed in this paper.
System for High Temperature Spectral Emissivity Measurement of Materials for VHTR Applications
Authors: Slattery Stuart R. , Malaney Tamara L. , Weber Scott J. , Anderson Mark H. , Sridharan Kumar , Allen Todd R.
Published: July 2009

An experimental system for in situ high temperature measurements of spectral emissivity of VHTR materials has been designed and constructed. The design consists of a cylindrical block of silicon carbide with several machined cavities for placement of test samples, as well as a black body cavity. The block is placed inside a furnace for heating to temperatures up to 1000°C. A shutter system allows for selective exposure of any given test sample for emissivity measurements. An optical periscope guides the thermal radiation from the sample to a Fourier Transform Infra Red (FTIR) spectrometer which is used for real-time measurements of spectral emissivity over a wavelength range of 0.8μm to 10μm. To specifically address the needs of VHTR applications, the system has been designed for studies with VHTR grade helium environments and air transients. Inlet and outlet gas compositions are measured using a gas chromatograph, which in conjunction with ex situ analysis of the samples by electron microscopy and x-ray diffraction will allow for the correlation of surface corrosion of the materials and their spectral emissivities under different operating and accident conditions.
Regulatory Viewpoint on Innovative VHTR Development in Korea
Authors: Lee Hun-Joo , Ahn Sang-Kyu , Oh Kju-Myeng , Lee Chang-Ju
Published: July 2009

This paper addresses that major changes in the safety approach, for instance the increased use of Probabilistic Risk Assessment (PRA), have been made. All commercial reactors in operation today belong to the Generations II and III. Generation IV International Forum (GIF) has launched several programs aimed at developing the next generation of nuclear energy systems. Part of the research effort is focused on new reactor concepts, such as the Very High Temperature Reactor (VHTR), currently developing in Korea. In parallel to the design process of VHTR currently underway, regulatory approach is moving forward to define new licensing rules. So, Korea Institute of Nuclear Safety (KINS) is defining, as a goal to risk-inform, the regulation and developing the regulatory framework and licensing process more efficient, predictable, and stable. However, the licensing of NPPs has focused until now on Light Water Reactors (LWRs) and has not incorporated systematically insights and benefits from PRA. In the meantime, USNRC and IAEA have recently drafted a risk-informed regulation and technology-neutral framework (TNF) for new plant licensing along with the innovative Gen-IV system design. KINS also expects that advanced NPPs will show enhanced margins of safety, and that advanced reactor designs will comply with the national safety goal policy statement. In order to meet these expectations, PRA tools are currently being considered by KINS; among them are frequency-consequence (F-C) curves, which plot the frequency of having Consequence. This paper discusses the role and the usefulness of such curves in risk-informing the licensing process in Korea, and shows that the use of F-C curve allows the implementation of both structural and rational Defence-In-Depth (DID). This paper focuses on F-C curves as means to assess the licensing basis events (LBEs) from the regulatory viewpoint on the innovative small and medium reactor (SMR) sized VHTR deployment in Korea. The principle underlying the F-C curve is that event frequency and dose are inversely related, i.e., the higher the dose consequences, the lower is the allowed event frequency.
Structural Integrity Code and Regulatory Issues in the Design of High Temperature Reactors
Authors: O’Donnell William J. , Hull Amy B. , Malik Shah
Published: July 2009

Since the 1980s, the ASME Code has made numerous improvements in elevated-temperature structural integrity technology. These advances have been incorporated into Section II, Section VIII, Code Cases, and particularly Subsection NH of Section III of the Code, “Components in Elevated Temperature Service.” The current need for designs for very high temperature and for Gen IV systems requires the extension of operating temperatures from about 1400°F (760°C) to about 1742°F (950°C) where creep effects limit structural integrity, safe allowable operating conditions, and design life. Materials that are more creep and corrosive resistant are needed for these higher operating temperatures. Material models are required for cyclic design analyses. Allowable strains, creep fatigue and creep rupture interaction evaluation methods are needed to provide assurance of structural integrity for such very high temperature applications. Current ASME Section III design criteria for lower operating temperature reactors are intended to prevent through-wall cracking and leaking and corresponding criteria are needed for high temperature reactors. Subsection NH of Section III was originally developed to provide structural design criteria and limits for elevated-temperature design of Liquid-Metal Fast Breeder Reactor (LMFBR) systems and some gas-cooled systems. The U.S. Nuclear Regulatory Commission (NRC) and its Advisory Committee for Reactor Safeguards (ACRS) reviewed the design limits and procedures in the process of reviewing the Clinch River Breeder Reactor (CRBR) for a construction permit in the late 1970s and early 1980s, and identified issues that needed resolution. In the years since then, the NRC, DOE and various contractors have evaluated the applicability of the ASME Code and Code Cases to high-temperature reactor designs such as the VHTGRs, and identified issues that need to be resolved to provide a regulatory basis for licensing. The design lifetime of Gen IV Reactors is expected to be 60 years. Additional materials including Alloy 617 and Hastelloy X need to be fully characterized. Environmental degradation effects, especially impure helium and those noted herein, need to be adequately considered. Since cyclic finite element creep analyses will be used to quantify creep rupture, creep fatigue, creep ratcheting and strain accumulations, creep behavior models and constitutive relations are needed for cyclic creep loading. Such strain- and time-hardening models must account for the interaction between the time-independent and time-dependent material response. This paper describes the evolving structural integrity evaluation approach for high temperature reactors. Evaluation methods are discussed, including simplified analysis methods, detailed analyses of localized areas, and validation needs. Regulatory issues including weldment cracking, notch weakening, creep fatigue/creep rupture damage interactions, and materials property representations for cyclic creep behavior are also covered.
Development of a Coupling Process Heat Exchanger Between a VHTR and a Sulfur-Iodine Hydrogen Production System
Authors: Kim Yong Wan , Park Jae Won , Lee Won Jae , Chang Jonghwa
Published: July 2009

A heat exchanger to transfer the heat generated from a nuclear reactor to a sulfur-iodine hydrogen production system has been developed. This heat exchanger operates in the extreme environments of a high corrosion, a high temperature, and a high differential pressure. A coating and ion beam mixing surface modification technology are applied to the process heat exchanger in order to enhance its corrosion resistance without loosing the manufacturability of the metal. A Ni-based super alloy is coated with a silicon carbide to enhance its corrosion resistance. The development of heat exchanger including shape design, thermal sizing, ion beam mixing process, stress analysis, and the manufacturing of small scale mock-up heat exchanger are discussed in this paper. The heat exchanger is a hybrid type to meet the design pressure requirements between a nuclear system and a hydrogen production system. A thermal sizing procedure for the process heat exchanger by considering the heat of sulfuric acid gas decomposition is developed. A finite element stress analysis is carried out by using the temperature profile obtained from the thermal sizing calculation. The finite element models were studied to simulate the stress state of the heat exchanger. Two-dimensional analysis was performed at the entrance region of the heat exchanger. A three-dimensional analysis for a single effective heat transfer channel was performed to investigate three-dimensional stress state. Stress analysis results have shown that the developed heat exchanger can withstand the required pressure difference at the elevated temperature condition. A small size heat exchanger was fabricated in order to test it in a high temperature nitrogen-gas loop. The fabrication of the heat exchanger includes a machining of the flow path, a coating and ion beam mixing, and a diffusion bonding of the heat transfer plate.
Deposition of TRISO Particles With Superhard SiC Coatings and the Characterization of Anisotropy by Raman Spectroscopy
Authors: Lo´pez-Honorato Eddie , Meadows Philippa J. , Tan Jun , Xiang Yang , Xiao Ping
Published: July 2009

In this work we have deposited SiC at 1300°C with the addition of small amounts of propylene. The use of propylene and high concentrations of methyltrichlorosilane (9 vol%) allowed the deposition of superhard SiC coatings (42 GPa). The superhard SiC could result from the presence of a SiC-C solid solution, undetectable by X-ray diffraction but visible by Raman spectroscopy. Another sample obtained by the use of 50 vol% Argon, also showed the formation of SiC with good properties. The use of a flat substrate together with the particles showed the importance of carrying out the analysis on actual particles rather than in flat substrates. We show that it is possible to characterize the anisotropy of PyC by Raman spectroscopy.
Evaluation of the Thermodynamics of Deep Burnup HTGR Fuel With Plutonium Kernels
Authors: Ponomarev-Stepnoy N. N. , Makarov V. M. , Ivanov A. S. , Belov I. A. , Rusinkevich A. A. , Lindemer T. , McEachern D. , Razvi J.
Published: July 2009

Rosatom of the Russian Federation and the U.S. National Nuclear Security Administration are developing the Gas-Turbine Modular Helium Reactor (GT-MHR) for the disposition of weapons-grade plutonium. Cost effective disposition of this plutonium material can be achieved by use of very high burnup coated particle fuel in the GT-MHR. In this way essentially all of the valuable energy of the Pu can be efficiently converted to electricity in one pass of the fuel through the GT-MHR.
Electrolysis of the CuCl/HCl Aqueous System for the Production of Nuclear Hydrogen
Authors: Stolberg Lorne , Boniface Hugh A. , McMahon Stacey , Suppiah Sam , York Sandra
Published: July 2009

The copper-chlorine (Cu-Cl) thermochemical cycle uses both heat and electricity to carry out a series of chemical and electrochemical reactions with the net reaction being the splitting of water into hydrogen and oxygen. The process forms a closed loop with all intermediate chemicals being recycled. All of the chemical and electrochemical reactions can be carried out at temperatures that do not exceed about 530°C. Thus, the heat requirement of this process can be satisfied by intermediate temperature nuclear reactors such as the Super Critical Water Reactor (SCWR) developed in Canada by Atomic Energy of Canada Limited (AECL). AECL is particularly interested in developing the electrochemical reactions that comprise the Cu-Cl cycle. There are two variations on the Cu-Cl cycle. In the original cycle copper metal is produced electrochemically by the disproportionation of cuprous chloride (CuCl), which is dissolved in hydrochloric acid (HCl) electrolyte. It is expected that this reaction will be carried out at a temperature that is below 100°C. Hydrogen gas is then produced by a chemical reaction that takes place between the copper metal and gaseous HCl at a temperature of 430–475°C. It was recognized by AECL that these two reaction steps could be replaced by a single electrochemical reaction that generates hydrogen directly. It is expected that this step will also be carried out at a temperature below 100°C. In this process, referred to as the CuCl/HCl electrolysis step, hydrogen gas is produced at the cathode of an electrochemical cell by the reduction of protons that are supplied by aqueous 6 M HCl while cupric chloride (CuCl2) is produced at the anode by the oxidation of CuCl, which is dissolved in 6 M HCl. The CuCl2 that is formed is recycled and is used in a reaction with steam at 400°C to produce a copper oxychloride. This reaction is common to both versions of the Cu-Cl cycle. It is the purpose of this paper to present electrochemical results from both half-cell and single-cell studies carried out to verify and understand the CuCl/HCl electrolysis step. Half-cell electrochemical data is presented that demonstrates the practicality of the electrode reactions. Electrochemical data is presented to show that the CuCl/HCl electrolysis step can be carried out in a single-cell. In both the half-cell and single-cell experiments platinum electrocatalysts are used to carry out the desired reactions.
System Analysis of Nuclear-Assisted Syngas Production From Coal
Authors: Harvego E. A. , McKellar M. G. , O’Brien J. E.
Published: July 2009

A system analysis has been performed to assess the efficiency and carbon utilization of a nuclear-assisted coal gasification process. The nuclear reactor is a high-temperature helium-cooled reactor that is used primarily to provide power for hydrogen production via high-temperature electrolysis. The supplemental hydrogen is mixed with the outlet stream from an oxygen-blown coal gasifier to produce a hydrogen-rich gas mixture, allowing most of the carbon dioxide to be converted into carbon monoxide, with enough excess hydrogen to produce a syngas product stream with a hydrogen/carbon monoxide molar ratio of about 2:1. Oxygen for the gasifier is also provided by the high-temperature electrolysis process. Results of the analysis predict 90.5% carbon utilization with a syngas production efficiency (defined as the ratio of the heating value of the produced syngas to the sum of the heating value of the coal plus the high-temperature reactor heat input) of 64.4% at a gasifier temperature of 1866 K for the high-moisture-content lignite coal considered. Usage of lower moisture coals such as bituminous can yield carbon utilization approaching 100% and 70% syngas production efficiency.