bluuebunny/crossref_metadata_2025 huggingface dataset:
The Visualization of Thin Film Evaporation on Thin Micro Sintered Copper Mesh Screen
Authors: Li Chen , Peterson G. P. , Li Ji , Koratkar Nikhil
Published: July 2009

The thin film evaporation process through use of thin micro-scale sintered copper mesh screen was proven to be a very effective heat transfer mechanism with high critical heat flux (CHF). This efficient heat transfer mechanism is widely used in designing heat pipe, Capillary Pumped Loops (CPL), and drying process, however, the nucleation process and meniscus dynamics at the liquid-vapor-solid interface are not directly observed and systematically studied. Very few visual investigation in thin film evaporation has been conducted. In the existing two visual studies, the interface thermal resistance between coating and the heated wall was not seriously considered, and the heat flux was limited below 35 W/cm2. In this visualization investigation, the nucleation process and meniscus dynamics from initial condition to drying out were observed and well documented. To minimize the interface thermal resistance, the micro scale wicking was sintered to heated wall directly. High quality images were acquired through a well-designed visualization system. The majority of nucleate bubbles, whose diameters are at a magnitude of 10 μm, were found to form on the top wire surfaces instead of inside the porous media at moderate heat flux. Few large size bubbles were observed to grow inside capillary wicks, however, their presence did not seem to stop the evaporation process as reported before. The menisci receding process was visually captured for the first time. The minimum menisci radius was found to form at the smallest corners and pores. It is also illustrated the thin liquid area increases when the menisci recede and the thin liquid film evaporation is the dominant heat transfer mode at high heat flux. The present work visually confirms the heat transfer regimes of evaporation on micro porous media, which was proposed by Li and Peterson [2], and further improves the understanding to the nucleate boiling and thin liquid film evaporation on the surfaces of micro sintered copper mesh screen.
Tip Leakage Flow and Heat Transfer Characteristics on Rotor Casing and Blade Tip in an Axial Gas Turbine Engine: Steady Analysis
Authors: Rahman Md Hamidur , Kim Sung In , Hassan Ibrahim
Published: July 2009

Steady simulations have been performed to investigate tip leakage flow and heat transfer characteristics on the casing and rotor blade tip in a single stage turbine engine. A turbine stage of stator and rotor was modeled with a pressure ratio of 3.2. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data. The effects of tip clearance height and rotor rotational speed on the blade tip and casing heat transfer characteristics are mainly considered. It is observed that the tip leakage flow structure is highly dependent on the height of the tip gap as well as speeds of the rotor blade. In all cases, flow separates just around the corner of the pressure side of the blade tip. The region of recirculating flow increases with the increase of the clearance height. Then the flow reattaches on the tip surface near the suction side beyond the flow separation. This flow reattachment enhances surface heat transfer. The leakage flow interaction with the reverse cross flow, induced by relative casing motion, is found to have significant effect on the blade tip and casing heat transfer distribution. Critical region of high heat transfer on the casing exists near the blade tip leading edge and along the pressure side edge at all clearance height. Whereas, at high speed rotation, it tends to move towards the trailing edge due to the change of inflow angle.
Numerical Prediction of Heat Transfer Enhancement in a Semiconductor Device With a Swiveled Module Board
Authors: Bhatta S. G. , Seetharam T. R.
Published: July 2009

A three dimensional study of heat transfer from an array of heated blocks is presented. Heated blocks represent electronic modules mounted on horizontal circuit board in a rectangular channel. Numerically obtained average heat transfer coefficients for the top surface of the heated blocks are compared with experimentally obtained values, and it is found that there is a good agreement between the two at lower Reynolds numbers, 7600 to 22000. Further, the horizontal module board affixed with heated modules is swiveled upwards longitudinally in the vertical plane about the front end of the plate for the same Reynolds numbers. The influence of angle of orientation of the heated bottom plate on the heat transfer enhancement from the heated modules is studied, and it is observed that there is a remarkable improvement in heat transfer even for low angle of swivel. It is observed that heat transfer enhancement is accompanied with a penalty in terms of increase in pressure drop; and for low angle of swivel, the pressure drop increase is noted to be moderate.
PIV Measurements in the Condenser Region of a Gas-Loaded Thermosyphon
Authors: Cleary Martin , Grimes Ronan , Hodes Marc , North Mark T.
Published: July 2009

Thermosyphons are passive devices used to transfer heat via a liquid-vapor phase change cycle. By adding a secondary non-condensable gas (NCG) to the vapor phase of the thermosyphon it is possible to provide some control over the evaporator temperature as heat load and or ambient temperature vary. The objective of this paper is to perform measurements on the vapor phase in the condenser region of a gas-loaded thermosyphon using particle image velocimetry (PIV). An optically-accessible water/air thermosyphon with a 34.5 mm diameter was designed, constructed and characterized for a range of fill ratios, heat loads, coolant temperatures and masses of NCG. Smoke particles, added with the NCG, were used to seed the flow. The flow field in the condenser was found to be unsteady except with low masses of NCG. It was found that there was no discernable vapor/NCG front present. A large amount of mixing of the vapor and NCG and recirculation of the NCG was observed. Due to the complex 3-dimensional non-axisymmetric nature of the flow it is very difficult to obtain useful quantitative measurements, however, PIV was found to be a very useful tool in visualizing the flow providing an insight in to the flow structures in the condenser.
Piezoelectric Fans: Heat Transfer Enhancements for Electronics Cooling
Authors: Petroski James , Arik Mehmet , Gursoy Mustafa
Published: July 2009

Piezoelectric fans have been investigated for electronics cooling over the last decade. The primary usage or method has been to place the vibrating fan near the surface to be cooled. The piezofan used in the current study is composed of a piezo actuator attached to a flexible metal beam. It is operated at up to 120VAC and at 60 Hz. While most of the research in the literature focused on cooling bare surfaces, larger heat transfer rates are of interest in the present study. A proposed system of piezoelectric fans and heat sink is presented as a more efficient method of system cooling with these fans. In this paper, a heat sink and piezoelectric fan system demonstrated a capability of cooling an area of about 75 cm2 (about 1 C/W) where electronic assemblies can be mounted. The heat sink not only provides surface area, but also flow shaping for the unusual three-dimensional flow field of the fans. A volumetric coefficient of performance (COPv) is proposed, which allows a piezofan and heat sink system volume to be compared against the heat dissipating capacity of a similar heat sink of the same volume for natural convection. A piezofan system is shown to have a COPv of five times of a typical natural convection solution. The paper will further discuss the effect of nozzles in flow shaping obtained via experimental and computational studies. A three-dimensional flow field of the proposed cooling scheme with a piezofan is obtained via laser Doppler anemometry (LDA) flow visualization method. Velocities at the heat sink in the order of 1.5 m/s were achieved through this critical shaping. Finally, the overall system characterization to different heat loads and fan amplitudes will be discussed.
Validation of a Computational Polymer Electrolyte Fuel Cell Model
Authors: Fu Richard S. , Pasaogullari Ugur
Published: July 2009

Computational models of polymer electrolyte fuel cells (PEFCs) of various degrees of complexities have been reported in the recent years and are capable of simulating detail transport phenomena within the PEFCs where experimental methods cannot. A thorough model validation is necessary for the model results to be used in analysis and design. Water transport in PEFCs has a strong effect on the performance regardless of the operating conditions. In low humidity cases, especially, the amount of water exchange from anode to cathode has a strong role in governing the water content in the anode side of the polymer electrolyte membrane (PEM), consequently on the ionic conductivity of the anode side of the membrane and catalyst layer. In this work, we present results on validation of the previously developed CFD based PEFC model for low humidity conditions using current density and species distribution data along the flow direction provided in the open literature. An excellent current density profile was obtained and species profiles were found to capture the data trend well, especially for the first half of the flow distance. Our findings suggest that, an accurate water transport modeling is paramount in capturing the overall PEFC behavior.
Three-Dimensional CFD Modelling and Analysis of the Thermal Entrainment in Open Refrigerated Display Cabinets
Authors: Gaspar Pedro Dinis , Carrilho Gonc¸alves L. C. , Pitarma R. A.
Published: July 2009

This study presents a three-dimensional Computational Fluid Dynamics (CFD) simulation of the air flow pattern and the temperature distribution in a refrigerated display cabinet. The thermal entrainment is evaluated by the variations of the mass flow rate and thermal power along and across the air curtain considering the numerical predictions of abovementioned properties. The evaluation on the ambient air velocity for the three-dimensional (3D) effects in the pattern of this type of turbulent air flow is obtained. Additionally, it is verified that the longitudinal air flow oscillations and the length extremity effects have a considerable influence in the overall thermal performance of the equipment. The non uniform distribution of the air temperature and velocity throughout the re-circulated air curtain determine the temperature differences in the linear display space and inside the food products, affecting the refrigeration power of display cabinets. The numerical predictions have been validated by comparison with experimental tests performed in accordance with the climatic class n.° 3 of EN 441 Standard (Tamb = 25 °C, φamb = 60%; νamb = 0,2 m s−1). These tests were conducted using the point measuring technique for the air temperature, air relative humidity and air velocity throughout the air curtain, the display area of conservation of food products and nearby the inlets/outlets of the air mass flow.
Heat Transfer From Solids With Variable Thermal Conductivity and Uniform Internal Heat Generation Using Homotopy Perturbation Method
Authors: Gul Rahim , Khan Zafar H. , Khan Waqar A.
Published: July 2009

Homotopy perturbation method (HPM) is employed to investigate the effects of temperature dependent thermal conductivity and internal heat generation on the dimensionless temperature distribution and heat transfer from solids of arbitrary shapes (rectangular, cylindrical and spherical). Dirichlet and Robin boundary conditions are applied at the outer boundary of the solids.
CFD Modeling and Analysis of a Shell-and-Tube Heat Exchanger
Authors: Ozden Ender , Tarı I˙lker
Published: July 2009

A shell-and-tube heat exchanger is modeled and numerically analyzed using a commercial finite volume CFD package. The heat exchanger is small, has a single shell and a single tube pass, and its shell side is baffled. The baffles are 25% or 36% cut single-segmental baffles. Tube layout is the staggered layout with a triangular pitch. There is no leakage from baffle orifices and no gap between the baffles and the shell. It is observed that the shell side flow and the temperature distributions are very sensitive to modeling choices such as mesh, order of discretization and turbulence modeling. Various turbulence models are tried for the first and second order discretizations using two different mesh densities. CFD predictions of shell side pressure drop and overall heat transfer coefficient are obtained and compared with Kern and Bell-Delaware method results. After selecting the best modeling approach, the sensitivity of the results to flow rates and the baffle spacing is investigated. It is observed that the flow and temperature fields obtained from CFD simulations can provide valuable information about the parts of the heat exchanger design that need improvement. Correlation based approaches may indicate the existence of the weakness but CFD simulations can also pin point the source and the location of it. Using CFD together with experiments may speed up the design process and may improve the final design.
Thermal Analysis of Radiator Core in Heavy Duty Automobile
Authors: Kolachalama Srikanth , Kuppa Kalyan , Mattam Dhananjay , Shukla Mukul
Published: July 2009

Background: Heat dissipation is one of the most critical considerations in engine design and with an efficient cooling system; performance of the engine can be dramatically improved. All internal combustion engines convert chemical energy into mechanical power. Around 70% of the energy is converted into heat and therefore, the primary job of the cooling system is to keep the engine from overheating by transferring this heat to the air. A radiator transfer’s heat from the hot coolant to the air and an effective design of radiator will ultimately lead to enhanced engine performance by reducing the heating effect. Methods and results: A mathematical expression for the rate of heat dissipation from the radiator core was derived and a modification in the design was proposed in the radiator core by changing the structure of the tubes from cylindrical to helical. The rate of heat dissipation for both designs was compared with similar boundary conditions by varying the magnitude of all design parameters in a specific range that have same magnitude of area of cross section, length of the radiator core and coefficient of thermal conductivity for the tube. Enhanced rate of heat dissipation for helical structure confirms the efficacy of the proposed design.
Experimental Aero-Thermal Characterization of a Circular Jet Impinging a Plate: Influence of Impingement Flow Mach Number on Convective Heat Exchange Radial Distribution
Authors: Lalizel Gildas , David Christophe , Fe´not Matthieu , Dorignac Eva
Published: July 2009

Impingement jets are known to be efficient mechanisms for the exchange of heat between fluid and structure. They are generally used in industry for cooling, heating or drying. Several experimental and numerical studies have been realized to study convective heat transfers and/or to correlate the convective heat transfers to the wall with the unsteady flow of the jet (O’Donovan et al. [9] [10]). But these studies have been performed at low Mach number whereas higher Mach number are found in industrial applications as fan cooling processes for instance (M = 0.5 to 0.8). So, we propose to study the influence of Mach number of the impingement flow, ranging from 0.1 to 0.8, on convective heat exchange between a circular jet and a round axisymmetric plate. The aerodynamic of the fluid and the heat transfers depend on the following parameters: the D hydraulic diameter of the jet, the H distance to the wall, the Re Reynolds number of the flow, the M Mach number and the Tj temperature of the jet. The local convective heat transfer coefficients are experimentally determined by an inverse method based on a measurement of steady state temperature fields by infrared thermography (Fe´not et al. [2]) for 1 ≤ H/D ≤ 5 and 0.1 ≤ M ≤ 0.8. An experimental study of radial velocity fluctuations of the fluid in nearby wall has also been realized from hot wire anemometry. A spatial and temporal turbulent study (turbulence spectrum, integral turbulent scales, dissipation rate) allows to correlate convective heat transfer to the wall to aerodynamic phenomena.
Designing Si/Si1−xGex Superlattices With Tailored Thermal Transport Properties
Authors: Landry E. S. , McGaughey A. J. H.
Published: July 2009

Si/Si1−xGex superlattices are promising candidates for thermoelectric energy conversion applications [1, 2], as the phonon transport through them can be inhibited while maintaining desirable electrical transport properties. No comprehensive experimental study has been performed to map the thermal conductivity design space accessible by Si/Ge nanocomposites. By using atomistic modeling tools, interesting areas of the design space can be identified and then further explored experimentally.
Experimental and Theoretical Analysis of the Nanoscale Crater Generation With a Near Field Scanning Optical Tip
Authors: Wen Sy-Bor
Published: July 2009

Different nano-patterns have been generated with the same near field scanning optical microscope (NSOM) tips with multiple femtosecond laser pulses in different background gases. It is demonstrated that significant energy was transferred from the NSOM probe to a pure silicon surface for the generation of nano-protrusions and nano-craters, which shows the possibility of nano-fabrication with the present experimental configuration. In order to understand the heating effect of the target and the relationship between the generations of nano-craters, a corresponding theoretical analysis considering the wave format light propagation within a single tapering NSOM probe (first order approximation) and the subsequent light absorption in a target is established. This analysis show that electron temperature of around the nano-scale laser spot of target can be very high (>∼10,000 K) during the laser pulse. However, both the photoexcited electron number density and lattice temperature are much less the threshold for a thermal and non-thermal evaporation. Therefore, supplementary mechanisms in additional to pure pulsed light absorption are required for generation of nano-craters on a target if a single tapering angle NSOM probe is applied.
Development of a Dynamic Simulation Code for a VHTR-Aided SI Process
Authors: Shin Youngjoon , Chang Jiwoon , Kim Jihwan , Lee Kiyoung , Lee Wonjae , Chang Jonghwa
Published: July 2009

In order to establish the optimal start-up method and to understand the dynamic behavior of the SI process coupled to a VHTR through an Intermediate Heat Exchanger (IHX), the development of a dynamic simulation code is necessary. Perturbation of the flow rate or temperature in input streams may result in various transient states. An understanding of the dynamic behavior due to these factors is very important to establish a safe operation method for a hydrogen production plant including a VHTR. Based on the mass and energy balance sheets of an electrodialysis-embedded SI process, proposed by KAERI, equivalent to a 200 MWth VHTR, not only the establishment of a thermal pathway (draft) between the SI process and the VHTR system but also the equipment sizing required in the SI process was carried out. A dynamic simulation code for the SI –2nd Skid (sulfuric acid concentration and decomposition part) was prepared at first for each chemical reactor. The reliability of the computer code has been confirmed by the convergence value at a steady state. This confirmation has been performed for the primary and secondary sulfuric acid distillation columns, the sulfuric acid vaporizer, the sulfuric acid decomposer, and the sulfur trioxide decomposer, respectively. An integrated computer code with a visualization function has been prepared by coupling each proven computer code, according to the thermal pathway. The dynamic behaviors of the integrated the SI-2nd Skid according to several anticipated scenarios were evaluated and the dominant and mild factors are discussed.
Reliability and Integrity Management Program for PBMR Helium Pressure Boundary Components
Authors: Fleming Karl N. , Fletcher John , Broom Neil , Gamble Ron , Gosselin Steve
Published: July 2009

The purpose of this paper is to present the results of a study to establish strategies for the reliability and integrity management (RIM) of passive metallic components for the PBMR. The RIM strategies investigated include design elements, leak detection and testing approaches, and non-destructive examinations. Specific combinations of strategies are determined to be necessary and sufficient to achieve target reliability goals for passive components. This study recommends a basis for the RIM program for the PBMR Demonstration Power Plant (DPP) and provides guidance for the development by the American Society of Mechanical Engineers (ASME) of RIM requirements for Modular High Temperature Gas-Cooled Reactors (MHRs).
Demonstration of Nuclear Hydrogen Production Utilizing the Japan’s HTTR: Control Scheme Evaluation of the HTTR-IS Nuclear Hydrogen Production System
Authors: Sato Hiroyuki , Sakaba Nariaki , Sano Naoki , Ohashi Hirofumi , Tachibana Yukio , Kunitomi Kazuhiko
Published: July 2009

One of the key technology requirements to achieve the nuclear hydrogen demonstration is the establishment of control scheme which harmonizes the reactor operation with chemical plant operation. This study focused on developing the control scheme to be considered in the HTTR-IS nuclear hydrogen production system, which are in case of (a) abnormal shut-down and (b) restart-up of the IS process. The key parameters and equipments have been determined and the control operations are simulated. The simulation results show that the impact of abnormal events initiated in the IS process on the reactor operation can be effectively minimized by the rapid initiation of diverter valves using model-based fault diagnosis method. Furthermore, the thermal shock to components in the IS process can be prevented in case of restart-up operation of the IS process by controlling the helium gas flow-rate of primary and secondary cooling system. It is confirmed by the analysis that the control scheme developed enable to maintain the reactor operation normally under all conditions and supply heat from nuclear reactor to the IS process hydrogen production system flexibly.
A Contribution on the Investigation of the Dynamic Behaviour of Rotating Shafts With a Hybrid Magnetic Bearing Concept (HMBC) for Blower Application
Authors: Gronek Martin , Rottenbach Torsten , Worlitz Frank
Published: July 2009

Within a subproject of the RAPHAEL-Program, which is part of the 6th EURATOM Framework Program supervised by the European Commission it was investigated whether the use of a Hybrid Magnetic Bearing Concept (HMBC) will be beneficial for a blower application. As in the RAPHAEL program the subproject “Component Development” deals with R&D on components of High Temperature Reactor Technology (HTR), a major focus is on safety- and reliability-related issues. That implies special requirements for the support of high speed rotating shafts in HTR-Applications that only can be satisfied by using Active Magnetic Bearings (AMB). Regarding safety and competitiveness, AMBs are considered key components for the support of rotating HTR-components due to their technical features. AMBs are characterized by an electromagnetic actuator that is generating the bearing force depending on the clearance between stator and rotor, in which the rotor is levitated. Therefore an active control of the coil current is necessary. Furthermore, Touch Down Bearings (TDB) are needed to avoid damages in case of an emergency shut down or in case of energy supply losses. This contribution provides an internal insight on the advantages of a Hybrid Magnetic Bearing Concept that is characterized by a completely Active Magnetic Bearing-supported vertical arranged rotor and an additional permanent magnetic Radial Bearing. One benefit of the HMBC is an additional radial guidance of the shaft that may reduce the loads while dropping into the Touch Down Bearings e.g. in case of energy supply losses of the AMBs. Reduced loads on the TDBs will increase their life cycle and the availability of the AMB supported component. The Scope of this R&D-Project, which will be described more detailed in this contribution, includes the analytical modeling and simulation of the dynamic behavior of the Hybrid Magnetic Bearing System, the modification of the completely AMB-supported test facility FLP500 with a radial PMB and the experimental tests and validation of the analytical models to provide recommendations for the investigated blower application as an HTR-component. Furthermore, the effects occurring during the modification of the test facility and the approach that was necessary to solve unexpected problems will be described.
Results of Tests to Demonstrate a Six-Inch Diameter Coater for Production of TRISO-Coated Particles for Advanced Gas Reactor Experiments
Authors: Barnes Charles M. , Marshall Douglas W. , Hunn John , Tomlin Bruce L. , Keeley Joe T.
Published: July 2009

The Next Generation Nuclear Plant (NGNP)/Advanced Gas Reactor (AGR) Fuel Development and Qualification Program includes a series of irradiation experiments in Idaho National Laboratory’s (INL’s) Advanced Test Reactor. TRISO-coated particles for the first AGR experiment, AGR-1, were produced at Oak Ridge National Laboratory (ORNL) in a two-inch diameter coater. A requirement of the NGNP/AGR Program is to produce coated particles for later experiments in coaters more representative of industrial scale. Toward this end, tests have been performed by Babcock and Wilcox (B&W) in a six-inch diameter coater. These tests are expected to lead to successful fabrication of particles for the second AGR experiment, AGR-2. While a thorough study of how coating parameters affect particle properties was not the goal of these tests, the test data obtained provides insight into process parameter/coated particle property relationships. Most relationships for the six-inch diameter coater followed trends found with the ORNL two-inch coater, in spite of differences in coater design and bed hydrodynamics. For example the key coating parameters affecting pyrocarbon anisotropy were coater temperature, coating gas fraction, total gas flow rate and kernel charge size. Anisotropy of the outer pyrolytic carbon (OPyC) layer also strongly correlates with coater differential pressure. In an effort to reduce the total particle fabrication run time, silicon carbide (SiC) was deposited with methyltrichlorosilane (MTS) concentrations up to 3 mol %. Using only hydrogen as the fluidizing gas, the high concentration MTS tests resulted in particles with lower than desired SiC densities. However when hydrogen was partially replaced with argon, high SiC densities were achieved with the high MTS gas fraction.
Deep Burn Strategy for Pure Reactor-Grade Plutonium in Pebble Bed High Temperature Gas-Cooled Reactors
Authors: Mulder Eben , Serfontein Dawid , Teuchert Eberhard
Published: July 2009

In this article an advanced fuel cycle for pebble bed reactors is introduced that can safely and efficiently incinerate pure reactor-grade Pu [Pu(LWR)], thereby fulfilling the bulk of the GNEP waste incineration requirements. It is shown below that the very high fissile content of the Pu(LWR)-fuel enables it to convert practically all of the 240Pu to 241Pu and incinerate it. Since the fuel contains no 238U, no fresh 239Pu is produced. The 239Pu is reduced in-situ by 99.5% and the 240Pu by 97.6%. The only significant fissile isotope remaining is 241Pu, however, it will decay with a half life of 14.4 years to the fertile 241Am by β-decay.
Neutron Flux Measurements for the PBMR DPP
Authors: Procter Gordon , Artaud Clark J.
Published: July 2009

For the Pebble Bed Modular Reactor (PBMR) Demonstration Power Plant (DPP) several neutron flux measurements are made, both within the Reactor Pressure Vessel (RPV) and outside the RPV. The measurements within the RPV are performed by the Core Structures Instrumentation (CSI) system. While those outside the RPV are performed by the Nuclear Instrumentation System (NIS). The PBMR has a long annular core with a relative low power density, requiring flux monitoring over the full 11 M of the active core region. The core structures instrumentation measures the neutron flux in the graphite reflector. Two measurement techniques are used; Fission Chamber based channels with high sensitivity for initial fuel load and low power testing and SPND channels for measurements at full and near full power operation. The CSI flux monitoring supports data acquisition for design Verification and Validation (V&V), and the data will also be used for the characterization of the NIS for normal reactor start-ups and low power operation. The CSI flux measurement channels are only required for the first few years of operation; the sensors are not replaceable. The Nuclear Instrumentation System is an ex core system that includes the Post Event Instrumentation. Due to the long length of the PBMR core, the flux is measured at several axial positions. This is a fission chamber based system; full advantage is taken of all the operating modes for fission chambers (pulse counting, mean square voltage (MSV), and linear current). The CSI flux monitoring channels have many technical and integration challenges. The environment where the sensors and their associated signal cables are required to operate is extremely harsh; temperature and radiation levels are very high. The selection and protection of the fission chambers warranted special attention. The selection criteria for sensors and cables takes cognizance of the fact that the assemblies are built in during the assembly of the reactor internal structures, and that they are not replaceable. This paper describes the challenges in the development of the monitoring systems for the measurement of neutron flux both within the RPV and the ex core region. The selection of detector configuration and the associated signal processing will be discussed. The use of only analogue signal processing techniques will also be elaborated on.
Active Chemistry Control for Coolant Helium Applying High-Temperature Gas-Cooled Reactors
Authors: Sakaba Nariaki , Hamamoto Shimpei , Takeda Yoichi
Published: July 2009

Lifetime extension of high-temperature equipment such as the intermediate heat exchanger of high-temperature gas-cooled reactors (HTGRs) is important from the economical point of view. Since the replacing cost will cause the increasing of the running cost, it is important to reduce replacing times of the high-cost primary equipment during assumed reactor lifetime. In the past, helium chemistry has been controlled by the passive chemistry control technology in which chemical impurity in the coolant helium is removed as low concentration as possible, as does Japan’s HTTR. Although the lifetime of high-temperature equipment almost depends upon the chemistry conditions in the coolant helium, it is necessary to establish an active chemistry control technology to maintain adequate chemical conditions. In this study, carbon deposition which could occur at the surface of the heat transfer tubes of the intermediate heat exchanger and decarburization of the high-temperature material of Hastelloy XR used at the heat transfer tubes were evaluated by referring the actual chemistry data obtained by the HTTR. The chemical equilibrium study contributed to clarify the algorism of the chemistry behaviours to be controlled. The created algorism is planned to be added to the instrumentation system of the helium purification systems. In addition, the chemical composition to be maintained during the reactor operation was proposed by evaluating not only core graphite oxidation but also carbon deposition and decarburization. It was identified when the chemical composition could not keep adequately, injection of 10 ppm carbon monoxide could effectively control the chemical composition to the designated stable area where the high-temperature materials could keep their structural integrity beyond the assumed duration. The proposed active chemistry control technology is expected to contribute economically to the purification systems of the future very high-temperature reactors.
The Feasibility Study of AGR 7-Position Fuel Testing Assembly in NEFT Position
Authors: Chang Gray S. , Grover Blaine , Maki John T. , Lillo Misti A.
Published: July 2009

In order to support the Next Generation Nuclear Plant (NGNP) Program 2018 deployment schedule, the Advanced Gas Reactor (AGR) Fuel Development and Qualification Program must reduce the AGR fuel irradiation testing time in the Advanced Test Reactor (ATR) from approximately 2 1/2 calendar years to 1 1/2 calendar years. The AGR fuel irradiation testing requirements are: (a) burn-up of at least 14% FIMA; (b) Fast neutron fluence (E > 0.18 MeV) – maximum < 5.1 × 1025 n/m2; (c) limit of fission power density is 350 W/cc; and (d) irradiation time < 1 1/2 calendar years. The accelerated testing could be accomplished by utilizing the ATR North East flux trap (NEFT) position, which can provide more control of the thermal neutron flux rate than the ATR B-10 position currently being used for the AGR-1 fuel testing, which is regulated to achieve the fuel temperature and burn-up rate requirements. In addition, the Fast (E > 1.0 MeV) to Thermal (E < 0.625 eV) neutron flux ratio (F/T) for the NEFT is much harder (higher) than the F/T ratio for the B-10 position. Thus, an appropriate configuration of Beryllium (Be) and water will need to be determined in order to soften (lower) the F/T ratio to the desired value. The proposed AGR 7-position fuel test configuration in the NEFT will utilize a graphite holder consisting of six fuel specimen positions arranged around the perimeter of the graphite holder with a seventh fuel specimen position in the center of the holder. To soften the neutron spectrum in the fuel compacts, the water volume in the outer water annulus can be increased. To reduce the compact power density, a hafnium filter could be incorporated around the graphite holder. After several trials, a hafnium filter with a thickness of 0.008 inches appeared to adequately reduce the power density to achieve the fuel testing requirements. It was also determined that the chosen beryllium-tube and water annulus configuration would adequately soften the neutron spectrum to achieve the fuel testing requirement. This neutronics study is based upon typical ATR cycle operation of 50 effective full power days (EFPD) per cycle for seven proposed irradiation cycles, and a NE lobe power of the 14 MW. The MCWO-calculated fuel compact power density, burnup (% FIMA), and fast neutron fluence (E > 0.18 MeV) results indicate that the average fuel compact burnup and fast neutron fluence reach 14.79% FIMA and 4.16 × 1025 n/m2, respectively. The fuel compact peak burnup reached 16.68% FIMA with corresponding fast neutron fluence for that fuel compact of 5.06 × 1025 n/m2, which satisfied the fuel testing requirements. It is therefore concluded that accelerating the AGR fuel testing using the proposed AGR 7-position fuel test configuration in the NEFT is very feasible.
PBMR Technology Development Projects at Stellenbosch University, South Africa
Authors: Dobson R. T.
Published: July 2009

PBMR has initiated a research and development program wherein a network of expertise relating to PBMR-specific technology is to be established. As a result of this initiative four specific PBMR sponsored technology development projects have been initiated at Stellenbosch University. The work done and still to be done towards these projects will be presented. The first project relates to the characterization of the flow dynamics of particles (ions, atoms and clusters) in a high pressure and velocity (9 MPa and 120 m/s) stream of helium due to various body-force fields (magnetic, electric and centrifugal); the ultimate objective of this project is to develop a graphite dust and particle scrubbing system. The second project relates to an entirely passive reactor cooling system (RCCS) using thermosyphon-type heat pipes with no pumps and active controls. The third project relates to the fuel temperature measurement under normal and loss of coolant pressure conditions using a fibre-optic Bragg-grating method. A fourth project relates to energy efficiency improvement by the conversion of waste, decay, after and residual heat into electrical power. This project makes use of two-phase closed loop thermosyphon-type heat pipes to transport the heat to an external heat engine, such as free piston type Stirling engine or organic Rankine cycle system. The research activities needed to meet the objectives of the above projects will be presented and discussed in this paper.
The Re-Evaluation of the AVR Melt-Wire Experiment Using Modern Methods With Specific Focus on Bounding the Bypass Flow Effects
Authors: Viljoen Carel F. , Sen Sonat , Reitsma Frederik , Ubbink Onno , Pohl Peter , Barnert Heiko
Published: July 2009

The AVR (Arbeitsgemeinschaft Versuchsreaktor) is a pebble bed type helium cooled graphite moderated high temperature reactor that operated in Germany for 21 years and was closed down in December 1988 [1]. The AVR melt-wire experiments [2], where graphite spheres with melt-wires of different melting temperatures were introduced into the core, indicate that measured pebble temperatures significantly exceeded temperatures calculated with the models used at the time [3]. These discrepancies are often attributed to the special design features of the AVR, in particular the control rod noses protruding into the core, and to inherent features of the pebble bed reactor. In order to reduce the uncertainty in design and safety calculations the PBMR Company is re-evaluating the AVR melt-wire experiments with updated models and tools. 3-D neutronics thermal-hydraulics analyses are performed utilizing a coupled VSOP99-STAR-CD calculation. In the coupled system VSOP99 [4] provides power profiles on a geometrical mesh to STAR-CD [5] while STAR-CD provides the fuel, moderator and solid structure temperatures to VSOP99. The different fuel histories and flow variations can be modelled with VSOP99 (although this is not yet included in the model) while the computational fluid dynamics (CFD) code, STAR-CD, adds higher-order thermal and gas flow modelling capabilities. This coupling therefore ensures that the correct thermal feedback to the neutronics is included. Of the many possible explanations for the higher-than-expected melt-wire temperatures, flow bypassing the pebble core was identified as potentially the largest contributor and was thus selected as the first topic to study. This paper reports the bounding effects of bypass flows on the gas temperatures in the top of the reactor. It also presents preliminary comparisons between measured temperatures above the core ceiling structure and calculated temperatures. Results to date confirm the importance of correctly modelling the bypass flows. Plans on future model improvements and other effects to be studied with the coupled VSOP99-STAR-CD tool are also included.
Modeling of the SB-CVD Process Used for TRISO Coated Fuels Fabrication
Authors: Mendes Alexandra , Cellier Franc¸ois , Ablitzer Carine , Perrais Christophe , Dolliet Alain , Flamant Gilles
Published: July 2009

For a few years, AREVA and the Commissariat a` l’Energie Atomique (CEA) have been conducting an extensive R&D program on V/HTR fuels with the objective is to optimize the TRISO fuel coatings produced in a Spouted Bed Chemical Vapor Deposition (SB-CVD) reactor. Numerical simulation models of this SB-CVD process have been developed in this work, describing physical and chemical phenomena occurring in high temperature spouted bed reactors. These models have been used to link external operating conditions (gas flow rate, precursor concentration, temperature, etc.) to local deposition conditions (concentration and temperature fields, deposition rate profiles, etc...). The adopted strategy has been to develop simplified models based on a process engineering approach, which require low computational efforts but can handle complex chemical systems and provide relatively accurate predictions. A model based on a hydrodynamic stream tube formulation (pseudo 2D model) and including a complete description of heat and mass transfer has thus been developed. Bed hydrodynamic has been described using high temperature correlations developed in the frame of this work. Radiation and heat transfer at reactor walls, which are of key importance for an accurate description of coupled transfer phenomena, have been implemented in the model formulation. The heterogeneous and homogeneous chemical mechanisms involved in the SB-CVD process have been first selected from the literature, then developed and reduced according to the main reaction paths. The pseudo 2D model developed and the specific high temperature correlations used have been validated by in-situ pressure and temperature profile measurement in 2″ and 3″ diameter SB-CVD reactors and finally by measurements of deposition rates on coated ZrO2 and UO2 kernels. The results presented in this paper show that the model is capable of handling rather large chemical schemes and combines simplicity and relatively good accuracy; hence it can be used for preliminary design and optimization of HTR fuel coating fabrication. Calculations have shown that particular attention must be paid to the heat transfer description in high temperature spouted bed reactors. A forthcoming work will focus on further model validation by varying the experimental conditions and using different SB-CVD furnace sizes and configurations. In addition further analyses and optimization studies of the chemical mechanisms involved are planned, which aim to increase the model accuracy and reliability. A better understanding of the SB-CVD process through accurate modeling will be very helpful for the optimization of coating deposition parameters on an industrial scale and for the design and scale up of large SB-CVD reactors.
A Comparison Between Recent Advances in Cylindrical Nodal Diffusion Methods
Authors: Colameco David V. , Ivanov Kostadin N. , Prinsloo Rian H. , Tomasevic Djordje I. , Theron Suzanne
Published: July 2009

The resurgence of High Temperature Reactor (HTR) technology has prompted the development and application of modern calculation methodologies, many of which are already utilized in the existing power reactor industry, to HTR designs. To this end, the use of nodal diffusion methods for full core neutronic analysis is once again considered for both their performance and accuracy advantages. Recently a number of different approaches to Two-Dimensional (2D) and 3D multigroup cylindrical nodal diffusion methods were proposed by various institutions for use in HTR, and specifically Pebble Bed Modular Reactor (PBMR), reactor calculations. In this regard we may mention the NEM code from the Pennsylvania State University (PSU), based on the Nodal Expansion Method; and the OSCAR code from NECSA, utilizing a conformal mapping approach to the Analytic Nodal Method. In this work we will compare these two approaches in terms of accuracy and performance. Representative problems, selected to test the methods thoroughly, were devised and based on both a modified version of the PBMR 400 MW benchmark problem and a “cylindrisized” version of the IAEA two-group problem. The comparative results between OSCAR and NEM are given, focusing on global reactivity estimation, as well as power and flux errors as compared to reference finite-difference solutions. These results indicate that both OSCAR and NEM recover the global reference solution for the IAEA problem, and show power errors which are generally acceptable for nodal methods. For the PBMR problem the accuracy is similar, but some convergence difficulties are experienced at the outer boundaries of the system due to the very large dimensions of the reflector (when compared to typical water-moderated reactors). For both codes a significant performance increase was found as compared to finite-difference calculations, which is the method currently employed by the PBMR (Pty) Ltd company. In conclusion it seems that nodal methods have potential for use in the HTR analysis, and specifically PBMR calculational arena, although cylindrical geometry based nodal methods will have to develop toward maturity before becoming the industry standard.
Preliminary Cost Estimates for Massive Hydrogen Production Using SI Process
Authors: Yang K. J. , Lee K. Y. , Lee T. H.
Published: July 2009

As a preliminary study of cost estimates for nuclear hydrogen systems, the hydrogen production costs of the nuclear energy sources benchmarking GT-MHR and PBMR are estimated in the necessary input data on a Korean specific basis. G4-ECONS was appropriately modified to calculate the cost for hydrogen production of SI process with VHTR as a thermal energy source rather than the LUEC. The estimated costs presented in this paper show that hydrogen production by the VHTR could be competitive with current techniques of hydrogen production from fossil fuels if CO2 capture and sequestration is required. Nuclear production of hydrogen would allow large-scale production of hydrogen at economic prices while avoiding the release of CO2. Nuclear production of hydrogen could thus become the enabling technology for the hydrogen economy. The major factors that would affect the cost of hydrogen were also discussed.
Corrosion Issues of HTR Structural Metallic Materials
Authors: Cabet Celine , Duprey Brigitte , Girardin Gouenou , Page`s Annie , Blat Martine
Published: July 2009

Within the framework of the ANTARES program, AREVA NP, EDF and the CEA have launched a joint R&D program on metallic materials for VHTR. Reference alloys for circuit and Intermediate Heat eXchanger (IHX) are nickel-based with about 22%wt. of chromium. Compatibility with the HTR primary helium appears to be a determining property for the material selection and qualification. The coolant is actually polluted by a low level of impurities that can interact with metals at high temperature. Oxidation, carburization and/or decarburization occur, in relation to atmosphere characteristics, temperature and alloy chemical composition. As these corrosion effects can notably influence the mechanical properties, they often are determining to the component service life. Since the corrosion behavior is highly sensitive to environmental conditions, material studies require dedicated facilities that shall allow for a strict control of the environment throughout the entire specimen exposure. AREVA NP, CEA, and EDF have developed experimental loops respectively under the names the Chemistry Loop, CORINTH and CORALLINE, ESTEREL; these high temperature helium flow systems are equipped with high accuracy hygrometers and gas analyzers. A benchmark was defined to cross-validate the lab devices and procedures. It is composed of two tests. The joint protocol sets the operating parameters in terms of material, specimen preparation, temperature and heating program, gas pressure and flow rate, time, gas composition. Corrosion is assessed by mass change associated to observations and analyses of the corroded coupons considering the surface scales (nature, morphology and thickness), the internal oxidation (nature, distribution and depth) and the possible carburization/decarburization (type and depth). For benchmark test 1, AREVA NP, CEA, and EDF produced similar results in terms of operation of the tests as well as about the corrosion criteria. On the other hand, benchmark test 2 showed a difference in the residual water vapor level between loops that was shown to strongly influence the specimen behavior. Discrepancies in the alloy corrosion were studied regarding gas flow rates and effective oxygen potential in helium. As a consequence, the experimental tools and procedures have been upgraded. French laboratories have now efficient corrosion facilities and methods at their disposal to study and qualify the corrosion behavior of structural materials in HTR environment.