Heat Transfer Analysis of Pebble Bed Reactors and Comparison with Prismatic Cores PDF Download
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Languages : en
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The general analytical equations relating the core-power density and the gas-film temperature drop at the fuel surface to the pnincipal reactor parameters are presented for both axial-flow and radial-flow pebble bed cores. Charts are included which show the power density and gas-film temperature drop as functions of fuel-ball diameter, pumping power-to-heat removal ratio, gas temperature rise per unit length of gas passage, and the gas pressure. The effects of voidage, system temperature and gas properties are considered along with factors causing hot spots. The effects on interior temperature of variations in the gas film heat transfer coefficient around the fuel surface were investigated. Neglecting hot spots, the power density obtainable in the prismatic core is more than four times that of the pebble bed core for equal maximum fuel temperatures. The extra degree of freedom available in design of prismatic core coolant passages permits the designer always to select a combination of parameters that is superior to the optimum combination for the pebble bed reactor. It is therefore clear that the fuel handling system, including perhaps the reactor maintenance, will have to be considerably more economical in the case of the pebble bed reactor in order for that reactor to compete with its prismatic counterpart. (auth).
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Category :
Languages : en
Pages :
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Book Description
The general analytical equations relating the core-power density and the gas-film temperature drop at the fuel surface to the pnincipal reactor parameters are presented for both axial-flow and radial-flow pebble bed cores. Charts are included which show the power density and gas-film temperature drop as functions of fuel-ball diameter, pumping power-to-heat removal ratio, gas temperature rise per unit length of gas passage, and the gas pressure. The effects of voidage, system temperature and gas properties are considered along with factors causing hot spots. The effects on interior temperature of variations in the gas film heat transfer coefficient around the fuel surface were investigated. Neglecting hot spots, the power density obtainable in the prismatic core is more than four times that of the pebble bed core for equal maximum fuel temperatures. The extra degree of freedom available in design of prismatic core coolant passages permits the designer always to select a combination of parameters that is superior to the optimum combination for the pebble bed reactor. It is therefore clear that the fuel handling system, including perhaps the reactor maintenance, will have to be considerably more economical in the case of the pebble bed reactor in order for that reactor to compete with its prismatic counterpart. (auth).
Author: Shengyao Jiang
Publisher: Springer Nature
ISBN: 9811595658
Category : Science
Languages : en
Pages : 510
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Book Description
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.
Author: Benjamin L. Nelson
Publisher:
ISBN:
Category : Gas cooled reactors
Languages : en
Pages : 112
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Book Description
The Very High Temperature Reactor (VHTR) has two possible core configurations, a hexagonal prismatic and a pebble bed. It is essential that an experimental facility be built for the validation of computer codes for the safe operation of the VHTR. The scaling of the prismatic core configuration has been analyzed previously for a large break loss of coolant accident. This is a scaling analysis for the pebble bed core configuration. As part of the full scaling analysis, the bottom up scaling of the pebble bed core for pressure drop and radial heat transfer were conducted. Radiation is the dominant form of heat transfer at high temperatures and was scaled using the two methods of treating radiation in a packed bed of spheres. The results of scaling were compared using FLUENT, a computational fluid dynamics code, using the setup, run, and comparison of a 1/80 azimuthally and 1/4 radial full scale prototype and scaled model. The temperature profiles across the core under natural circulation like conditions were determined for both models. The model and prototype temperature profiles had significant variation at the boundary, but only a few degree variation away from the boundary. Additionally, the radiation transport equation and radiation conductivity were compared, and distortions quantified for the FLUENT models.
Author:
Publisher:
ISBN:
Category : Nuclear energy
Languages : en
Pages : 938
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Author:
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ISBN:
Category : Nuclear energy
Languages : en
Pages : 1162
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Author: Lakshana Ravindranath Huddar
Publisher:
ISBN:
Category :
Languages : en
Pages : 165
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Book Description
ABSTRACT Heat Transfer in Pebble-Bed Nuclear Reactor Cores Cooled by Fluoride Salts By Lakshana Ravindranath Huddar Doctor of Philosophy in Engineering - Nuclear Engineering University of California, Berkeley Professor Per F. Peterson, Chair With electricity demand predicted to rise by more than 50% within the next 20 years and a burgeoning world population requiring reliable emissions-free base-load electricity, can we design advanced nuclear reactors to help meet this challenge? At the University of California, Berkeley (UCB) Fluoride-salt-cooled High Temperature Reactors (FHR) are currently being investigated. FHRs are designed with better safety and economic characteristics than conventional light water reactors (LWR) currently in operation. These reactors operate at high temperature and low pressure making them more efficient and safer than LWRs. The pebble-bed FHR (PB-FHR) variant includes an annular nuclear reactor core that is filled with randomly packed pebble fuel. It is crucial to characterize the heat transfer within this unique geometry as this informs the safety limits of the reactor. The work presented in this dissertation focused on furthering the understanding of heat transfer in pebble-bed nuclear reactor cores using fluoride salts as a coolant. This was done through experimental, analytical and computational techniques. A complex nuclear system with a coolant that has never previously been in commercial use requires experimental data that can directly inform aspects of its design. It is important to isolate heat transfer phenomena in order to understand the underlying physics in the context of the PB-FHR, as well as to make decisions about further experimental work that needs to be done in support of developing the PB-FHR. Certain organic oils can simulate the heat transfer behaviour of the fluoride salt if relevant non-dimensional parameters are matched. The advantage of this method is that experiments can be done at a much lower temperature and at a smaller geometric scale compared to FHRs, thereby lowering costs. In this dissertation, experiments were designed and performed to collect data demonstrating similitude. The limitations of these experiments were also elucidated by underlining key distortions between the experimental and the prototypical conditions. This dissertation is broadly split into four parts. Firstly, the heat transfer phenomenology in the PB-FHR core was outlined. Although the viscous dissipation term and the thermal diffusion term (including thermal dispersion) were similar in magnitude, they were overshadowed by the advection term which was about 104 times bigger during normal operation and 105 times bigger during accident transients in which natural circulation becomes the main mode of fluid flow. Thus it is safe to neglect the viscous dissipation and the thermal diffusion terms in the PB-FHR core without a significant loss of accuracy. Secondly, separate effects tests (SET) were performed using simulant oils, and the results were compared to the prototypical conditions using flinak as the fluoride salt. The main purpose of these experiments was to study natural convection heat transfer and identify any distortions between the two cases. An isolated copper sphere was immersed in flinak and a parallel experiment was performed using simulant oil. A large discrepancy between the flinak and the oil was noted, due to distortions from assuming quasi-steady state conditions. A steady state experiment using a cylindrical heater immersed in oil was also performed, and the results compared to a similar experiment done at Oak Ridge National Laboratory (ORNL) using flinak. The Nusselt numbers matched within 10% for laminar flows. This supports the conclusion that natural convection similitude does exist for oils used in scaled experiments, allowing natural convection data to be used for for FHR and MSR modeling. This is important, due to the lack of significant experimental data showing natural convection in fluoride salts, so these SETs add to the overall understanding of their heat transfer properties. With the knowledge of the distortions between the oil and the salt, an experiment to measure heat transfer coefficients within a pebble-bed test section was designed, constructed and performed. Oil was pumped through a test section filled with randomly packed copper spheres. The temperature of the oil was pulsed at a constant frequency, which caused a temperature difference between the pebbles and the oil. An excellent match was found between the measured heat transfer coefficients and the literature. This data provides an essential closure parameter for multiphysics modeling of the PB-FHR. Using frequency response techniques in scaled experiments is an innovative approach for extracting dynamic responses to coolant-structure interactions. Finally, an integrated model of the passive decay heat removal system was presented using Flownex and the simulations compared to experimental data. A good match was found with the data, which was within 14%. The work presented in this dissertation shows fundamental details on heat transfer in the PB-FHR core using experimental data and simulations, leading us closer to developing advanced nuclear reactors that can later be commercialized. Advanced nuclear reactors such as the PB-FHR have immense potential in reducing greenhouse gas emissions and combating climate change while being exceedingly safe and providing reliable electricity.
Author: Shengyao Jiang
Publisher:
ISBN: 9789811595660
Category :
Languages : en
Pages : 0
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Book Description
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. .
Author: U.S. Atomic Energy Commission
Publisher:
ISBN:
Category :
Languages : en
Pages : 252
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Author:
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ISBN:
Category : Feasibility studies
Languages : en
Pages : 342
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Book Description
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.
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Languages : en
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A one-dimensional computational model was developed to evaluate the heat removal capabilities of both prismatic-core and pebble-bed modular HTGRs during depressurized heatup transients. A correlation was incorporated to calculate the temperature- and neutron-fluence-dependent thermal conductivity of graphite. The modified Zehner-Schluender model was used to determine the effective thermal conductivity of a pebble bed, accounting for both conduction and radiation. Studies were performed for prismatic-core and pebble-bed modular HTGRs, and the results were compared to analyses performed by GA and GR, respectively. For the particular modular reactor design studied, the prismatic HTGR peak temperature was 2152.2/sup 0/C at 38 hours following the transient initiation, and the pebble-bed peak temperature was 1647.8/sup 0/C at 26 hours. These results compared favorably with those of GA and GE, with only slight differences caused by neglecting axial heat transfer in a one-dimensional radial model. This study found that the magnitude of the initial power density had a greater effect on the temperature excursion than did the initial temperature.
