Download or read book MCNP4B Modeling of Pebble bed Reactors written by Julian Robert Lebenhaft and published by . This book was released on 2001 with total page 722 pages. Available in PDF, EPUB and Kindle. Book excerpt: The applicability of the Monte Carlo code MCNP4B to the neutronic modeling of pebblebed reactors was investigated. A modeling methodology was developed based on an analysis of critical experiments carried out at the HTR-PROTIEUS and ASTRA facilities, and the critical loading of the HTR-10 reactor. A body-centred cubic lattice of spheres with a specified packing fraction approximates the pebble bed, and exclusion zones offset the contribution of partial spheres generated by the geometry routines in MCNP4B at the core boundaries. The coated fuel particles are modeled in detail and are distributed over the fuelled region of the fuel sphere using a simple cubic lattice. This method predicted the critical core loading accurately in all cases. The calculation of control-rod worths in the more decoupled tall annular ASTRA core gave results within 10% compared to the reported experiments. An approximate method was also developed for the MCNP4B modeling of pebble-bed reactors with burnup. The nuclide densities of homogenized layers in the VSOP94 reactor model are transferred to the corresponding MCNP4B model with the lattice of spheres represented explicitly. The method was demonstrated on the PBMR equilibrium core, and used for a parallel study of burnup k- and isotopics on a single pebble. Finally, a study was carried out of the proliferation potential of a modular pebble-bed reactor for both normal and off-normal operation. VSOP94 analysis showed that spent fuel from pebble-bed reactors is proliferation resistant at high discharge burnup, because of its unfavourable plutonium isotopic composition and the need to divert -157,000 pebbles to accumulate sufficient 239Pu for a nuclear weapon. The isotopics of first-pass fuel pebbles are more favourable, but even more pebbles ( -258,000) would be needed. However, a supercell MOCUP model was used to demonstrate that -20,000 pebbles would be needed if loaded with depleted uranium. But the associated reactivity loss would necessitate a compensatory increase in core height of approximately 50 cm. Such a change in core loading, as well as the properties of the special pebbles, would be noticed in a safeguarded facility.

Download or read book Multiphase Flow and Heat Transfer in Pebble Bed Reactor Core written by Shengyao Jiang and published by Springer Nature. This book was released on 2020-11-19 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book introduces readers to gas flows and heat transfer in pebble bed reactor cores. It addresses fundamental issues regarding experimental and modeling methods for complex multiphase systems, as well as relevant applications and recent research advances. The numerical methods and experimental measurements/techniques used to solve pebble flows, as well as the content on radiation modeling for high-temperature pebble beds, will be of particular interest. This book is intended for a broad readership, including researchers and practitioners, and is sure to become a key reference resource for students and professionals alike.

Download or read book A COMPARISON OF PEBBLE MIXING AND DEPLETION ALGORITHMS USED IN PEBBLE BED REACTOR EQUILIBRIUM CYCLE SIMULATION written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recirculating pebble-bed reactors are distinguished from all other reactor types by the downward movement through and reinsertion of fuel into the core during operation. Core simulators must account for this movement and mixing in order to capture the physics of the equilibrium cycle core. VSOP and PEBBED are two codes used to perform such simulations, but they do so using different methods. In this study, a simplified pebble-bed core with a specified flux profile and cross sections is used as the model for conducting analyses of two types of burnup schemes. The differences between the codes are described and related to the differences observed in the nuclide densities in pebbles discharged from the core. Differences in the methods for computing fission product buildup and average number densities lead to significant differences in the computed core power and eigenvalue. These test models provide a key component of an overall equilibrium cycle benchmark involving neutron transport, cross section generation, and fuel circulation.

Download or read book METHODS FOR MODELING THE PACKING OF FUEL ELEMENTS IN PEBBLE BED REACTORS written by Abderrafi M. Ougouag and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Two methods for the modeling of the packing of pebbles in the pebble bed reactors are presented and compared. The first method is based on random generation of potential centers for the pebbles, followed by rejection of points that are not compatible with the geometric constraint of no (or limited) pebbles overlap. The second method models the actual physical packing process, accounting for the dynamic of pebbles as they are dropped onto the pebble bed and as they settle therein. A simplification in the latter model is the assumption of a starting point with very dilute packing followed by settling. The results from the two models are compared and the properties of the second model and the dependence of its results on many of the modeling parameters are presented. The first model (with no overlap allowed) has been implemented into a code to compute Dancoff factors. The second model will soon be implemented into that same code and will also be used to model flow of pebbles in a reactor and core densification in the simulation of earthquakes. Both methods reproduce experimental values well, with the latter displaying a high level of fidelity.

Download or read book Fuel Element Development Program for the Pebble Bed Reactor written by and published by . This book was released on 1961 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Design and Feasibility Study of a Pebble Bed Reactor steam Power Plant written by and published by . This book was released on 1958 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt: Originally issued as S and P 1963A, Parts I and II. This report covers a design and feasibility study of a pebble bed reactor-steam power plant of 125 megawatt electrical output. The reactor design which evolved from this study is a two-region thermal breeder, operating on the uranium-thorium cycle, in which all core structural materials are graphite. Fuel is in the form of unclad spherical elements of graphite, containing fissile and fertile material. The primary loop consists of the reactor plus three steam generators and blowers in parallel. Plant design and system analysis including cost analysis and capital cost summary are given.

Download or read book Development of a Radioactive Pebble Bed Chemical Reactor System written by C. H. Collins and published by . This book was released on 1966 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fuel Element Development Program for the Pebble Bed Reactor written by Sanderson & Porter, Inc and published by . This book was released on 1959 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Numerous types of high temperature ceramic fuel elements for the Pebble Bed Reactor are being evaluated. Specimens are 1-1/2 in diameter uranium graphite spheres with external coatings such as silicon carbide or pyrolytically deposited high density graphite and feul particle coatings such as alumina. Low diffusion product leakage rates at high temperatures have been observed for some of these coatings. High level irradiation damage to either the silicon carbide coating or the coating-graphite bond.

Download or read book Multiscale Analysis of Pebble Bed Reactors written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: - The PEBBED code was developed at the Idaho National Laboratory for design and analysis of pebble-bed high temperature reactors. The diffusion-depletion-pebble-mixing algorithm of the original PEBBED code was enhanced through coupling with the THERMIX-KONVEK code for thermal fluid analysis and by the COMBINE code for online cross section generation. The COMBINE code solves the B-1 or B-3 approximations to the transport equation for neutron slowing down and resonance interactions in a homogeneous medium with simple corrections for shadowing and thermal self-shielding. The number densities of materials within specified regions of the core are averaged and transferred to COMBINE from PEBBED for updating during the burnup iteration. The simple treatment of self-shielding in previous versions of COMBINE led to inaccurate results for cross sections and unsatisfactory core performance calculations. A new version of COMBINE has been developed that treats all levels of heterogeneity using the 1D transport code ANISN. In a 3-stage calculation, slowing down is performed in 167 groups for each homogeneous subregion (kernel, particle layers, graphite shell, control rod absorber annulus, etc.) Particles in a local average pebble are homogenized using ANISN then passed to the next (pebble) stage. A 1D transport solution is again performed over the pebble geometry and the homogenized pebble cross sections are passed to a 1-d radial model of a wedge of the pebble bed core. This wedge may also include homogeneous reflector regions and a control rod region composed of annuli of different absorbing regions. Radial leakage effects are therefore captured with discrete ordinates transport while axial and azimuthal effects are captured with a transverse buckling term. In this paper, results of various PBR models will be compared with comparable models from literature. Performance of the code will be assessed.

Download or read book Modelling a 100 MWe pebble bed modular reactor PBMR nuclear power plant written by Trevor Herbert Dudley and published by . This book was released on 2004 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fuel Element Development Program for the Pebble Bed Reactor written by and published by . This book was released on 1959 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Pebble Bed Reactor Dust Production Model written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The operation of pebble bed reactors, including fuel circulation, can generate graphite dust, which in turn could be a concern for internal components; and to the near field in the remote event of a break in the coolant circuits. The design of the reactor system must, therefore, take the dust into account and the operation must include contingencies for dust removal and for mitigation of potential releases. Such planning requires a proper assessment of the dust inventory. This paper presents a predictive model of dust generation in an operating pebble bed with recirculating fuel. In this preliminary work the production model is based on the use of the assumption of proportionality between the dust production and the normal force and distance traveled. The model developed in this work uses the slip distances and the inter-pebble forces computed by the authors' PEBBLES. The code, based on the discrete element method, simulates the relevant static and kinetic friction interactions between the pebbles as well as the recirculation of the pebbles through the reactor vessel. The interaction between pebbles and walls of the reactor vat is treated using the same approach. The amount of dust produced is proportional to the wear coefficient for adhesive wear (taken from literature) and to the slip volume, the product of the contact area and the slip distance. The paper will compare the predicted volume with the measured production rates. The simulation tallies the dust production based on the location of creation. Two peak production zones from intra pebble forces are predicted within the bed. The first zone is located near the pebble inlet chute due to the speed of the dropping pebbles. The second peak zone occurs lower in the reactor with increased pebble contact force due to the weight of supported pebbles. This paper presents the first use of a Discrete Element Method simulation of pebble bed dust production.

Download or read book PEBBLES Mechanics Simulation Speedup written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Pebble bed reactors contain large numbers of spherical fuel elements arranged randomly. Determining the motion and location of these fuel elements is required for calculating certain parameters of pebble bed reactor operation. These simulations involve hundreds of thousands of pebbles and involve determining the entire core motion as pebbles are recirculated. Single processor algorithms for this are insufficient since they would take decades to centuries of wall-clock time. This paper describes the process of parallelizing and speeding up the PEBBLES pebble mechanics simulation code. Both shared memory programming with the Open Multi-Processing API and distributed memory programming with the Message Passing Interface API are used in simultaneously in this process. A new shared memory lock-less linear time collision detection algorithm is described. This method allows faster detection of pebbles in contact than generic methods. These combine to make full recirculations on AVR sized reactors possible in months of wall clock time.

Download or read book Modular Pebble Bed Reactor Project University Research Consortium Annual Report written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This project is developing a fundamental conceptual design for a gas-cooled, modular, pebble bed reactor. Key technology areas associated with this design are being investigated which intend to address issues concerning fuel performance, safety, core neutronics and proliferation resistance, economics and waste disposal. Research has been initiated in the following areas: · Improved fuel particle performance · Reactor physics · Economics · Proliferation resistance · Power conversion system modeling · Safety analysis · Regulatory and licensing strategy Recent accomplishments include: · Developed four conceptual models for fuel particle failures that are currently being evaluated by a series of ABAQUS analyses. Analytical fits to the results are being performed over a range of important parameters using statistical/factorial tools. The fits will be used in a Monte Carlo fuel performance code, which is under development. · A fracture mechanics approach has been used to develop a failure probability model for the fuel particle, which has resulted in significant improvement over earlier models. · Investigation of fuel particle physio-chemical behavior has been initiated which includes the development of a fission gas release model, particle temperature distributions, internal particle pressure, migration of fission products, and chemical attack of fuel particle layers. · A balance of plant, steady-state thermal hydraulics model has been developed to represent all major components of a MPBR. Component models are being refined to accurately reflect transient performance. · A comparison between air and helium for use in the energy-conversion cycle of the MPBR has been completed and formed the basis of a master's degree thesis. · Safety issues associated with air ingress are being evaluated. · Post shutdown, reactor heat removal characteristics are being evaluated by the Heating-7 code. · PEBBED, a fast deterministic neutronic code package suitable for numerous repetitive calculations has been developed. Use of the code has focused on scoping studies for MPBR design features and proliferation issues. Publication of an archival journal article covering this work is being prepared. · Detailed gas reactor physics calculations have also been performed with the MCNP and VSOP codes. Furthermore, studies on the proliferation resistance of the MPBR fuel cycle has been initiated using these code · Issues identified during the MPBR research has resulted in a NERI proposal dealing with turbo-machinery design being approved for funding beginning in FY01. Two other NERI proposals, dealing with the development of a burnup "meter" and modularization techniques, were also funded in which the MIT team will be a participant. · A South African MPBR fuel testing proposal is pending ($7.0M over nine years).

Download or read book A Preliminary Study of the Effect of Shifts in Packing Fraction on K effective in Pebble Bed Reactors written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A preliminary examination of the effect of pebble packing changes on the reactivity of a pebble-bed reactor (PBR) is performed. As a first step, using the MCNP code, the modeling of a PBR core as a continuous and homogenous region is compared to the modeling as a collection of discrete pebbles of equal average fuel density. It is shown that the two modeling approaches give the same trends inasmuch as changes in keff are concerned. It is thus shown that for the purpose of identifying trends in keff changes, the use of a homogeneous model is sufficient. A homogenous model is then used to assess the effect of pebble packing arrangement changes on the reactivity of a PBR core. It is shown that the changes can be large enough to result in prompt criticality. It is shown that for uranium fueled PBRs, thermal feedback could have the potential to offset the increase in activity, whereas for plutonium fueled systems, thermal feedback may not be sufficient for totally offsetting the packing-increase reactivity insertion and could even exacerbate the initial response. It is thus shown that a full study, including reactor kinetics, thermal feedback, and the dynamics of energy deposition and removal is warranted to fully characterize the potential consequences of packing shifts.

Download or read book On the Use of Large Eddy Simulation and Direct Numerical Simulation to Improve Near Wall Modeling in Porous Media Models of Pebble Bed Reactors written by David Reger and published by . This book was released on 2024 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work aims to improve capabilities for modeling localized effects in porous media models of Pebble Bed Reactors (PBRs). The wall-channel effect is the primary local phenomena of interest in a PBR, where the presence of the reflector wall disrupts the pebble packing, causing the pebbles near the wall to pack less efficiently and creating large void regions. Accurate modeling of the near-wall region is important as it will affect core bypass flow and temperature predictions. Failing to properly model this region therefore leads to increased uncertainty in the prediction of maximum fuel temperatures and thus larger safety margins are necessary. Porous media models are commonly used for design scoping and plant-level simulations of PBRs. Although these models have some capabilities to model the near-wall region, the correlations that are available in porous media codes are often inaccurate when a multi-region model is used to discretize the near-wall region. A high-to-low methodology is therefore developed in this work to improve local modeling capabilities in porous media codes. NekRS, a spectral-element computational fluid dynamics (CFD) code, is used to generate a large high-fidelity flow dataset with Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). An analysis of the Turbulent Kinetic Energy (TKE) budget is performed, revealing notable regions of negative TKE production near pebble contact points. Further investigation reveals that the amount of negative production in a given region can be linked to the local porosity of that region. This investigation of the flow physics helps to provide a better understanding of the differences in flow behavior across the various regions of the bed. Porous media models equivalent to the high-fidelity models are created and simulated with Idaho National Laboratory's Pronghorn porous media code. The KTA correlation is used for the pressure drop calculation in Pronghorn and is the correlation that is targeted for improvement. Results between NekRS and Pronghorn are compared to determine areas of discrepancy between the two codes. A method is then developed to extract the form loss coefficients from the high-fidelity dataset where the bed is split into several concentric ring subdomains and flow data is averaged in each region. An improved pressure drop correlation is determined with the extracted form coefficients and is implemented in Pronghorn, reducing the error in the near-wall velocity prediction from greater than 30\% to less than 5\%. A similar high-to-low investigation is performed on the interphase heat transfer closure. Several correlations are compared to the high-fidelity results where it is found that the KTA heat transfer correlation is capable of accurately predicting the local Nusselt numbers that were determined in the high-fidelity simulation. Comparison of the radial solid temperature profiles, however, reveal discrepancies between NekRS and Pronghorn. It is discovered that the implementation of the interphase heat transfer coefficient that exists in many current porous media codes is not valid when local porosities are modeled. Instead, it is suggested that the interphase heat transfer coefficient should be dependent on the local porosity, the Nusselt number, and the local solid surface-to-volume ratio. Implementation of this change produces improvement in the agreement between NekRS and Pronghorn while using the KTA heat transfer correlation.

Download or read book Neutronics Analysis of a Modified Pebble Bed Advanced High Temperature Reactor written by Jorge Abejón Orzáez and published by . This book was released on 2009 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The objective of this research is to, based on the original design for the Pebble Bed Advanced High Temperature Reactor (PB-AHTR), develop an MCNPX model of the reactor core with the objective to attain criticality and to breed new fuel. A brief but complete description of a first approach to the PB-AHTR will be provided and a MCNPX model will be run in order to ascertain the difficulties of that configuration. On the second part, a modification of the original model will be evaluated and compared in order to resolve the difficulties encountered in the original design. Finally, in an effort to optimize the design, an evolutionary approach will be analyzed, based on the previous model, and conclusions will be attained.