Transport and Diffusion of Fission Products in Graphite PDF Download
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Author: J. Bromley
Publisher:
ISBN:
Category :
Languages : en
Pages : 46
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Book Description
Author: J. Bromley
Publisher:
ISBN:
Category :
Languages : en
Pages : 46
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The transport of fission products from points of origin in unclad graphite matrix-type fuels to the reactor circulating system involves, as one of the steps. diffusion through the graphite matrix to the fuel element surface. As pointed out by Rosenthal. the fraction of a given fission product chain actaally reaching the fuel element surface will be small if the time for transport through the graphite is long compared to the half-lives of the volatile members. An important problem, therefore, is the determination of the effective transport rates of the various mobile elements and their daughter products of interest through various graphites suitable for use as fuel element compacts. as functions of temperature over the range of greatest immediate interest to reactor designers. The upper end of the range need not exceed about 1000 deg C. The transport of helium and arbon through various graphites has been the subject of considerable study by Watson. Evans, and other, . and a prelimilnary investigation of the high temperature transport of some ordinarily non-volatile elements has been carried out by Saunders. This work is briefly reviewed in relation to the final problem and the areas in which further information is needed most by reactor designers is indicated. (auth).
Author: A. R. Saunders
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Category : Fission products
Languages : en
Pages : 42
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Author: Lukas M. Carter
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ISBN:
Category :
Languages : en
Pages : 190
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Release of radioactive fission products from nuclear fuel during normal reactor operation or in accident scenarios is a fundamental safety concern. Of paramount importance are the understanding and elucidation of mechanisms of chemical interaction, nuclear interaction, and transport phenomena involving fission products. Worldwide efforts to reduce fossil fuel dependence coupled with an increasing overall energy demand have generated renewed enthusiasm toward nuclear power technologies, and as such, these mechanisms continue to be the subjects of vigorous research. High-Temperature Gas-Cooled Reactors (HTGRs or VHTRs) remain one of the most promising candidates for the next generation of nuclear power reactors. An extant knowledge gap specific to HTGR technology derives from an incomplete understanding of fission product transport in major core materials under HTGR operational conditions. Our specific interest in the current work is diffusion in reactor graphite. Development of methods for analysis of diffusion of multiple fission products is key to providing accurate models for fission product release from HTGR core components and the reactor as a whole. In the present work, a specialized diffusion cell has been developed and constructed to facilitate real-time diffusion measurements via ICP-MS. The cell utilizes a helium gas-jet system which transports diffusing fission products to the mass spectrometer using carbon nanoparticles. The setup was designed to replicate conditions present in a functioning HTGR, and can be configured for real-time release or permeation measurements of single or multiple fission products from graphite or other core materials. In the present work, we have analyzed release rates of cesium in graphite grades IG-110, NBG-18, and a commercial grade of graphite, as well as release of iodine in IG-110. Additionally we have investigated infusion of graphite samples with Cs, I, Sr, Ag, and other surrogate fission products for use in release or profile measurements of diffusion coefficients.
Author: Kevin Graydon
Publisher:
ISBN:
Category :
Languages : en
Pages : 55
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The next generation of nuclear reactors (Generation IV) are specified to use graphite as the choice material for neutron moderation and structural components. For this reason, study of diffusion behavior of the fission product, ruthenium (Ru), in the candidate graphite grades, POCO AXF-5Q & ZXF-5Q, IG-110, NBG-18 and PCEA, is necessary. Diffusion data for Ru in these grades is absent due to the lack of prior studies and this work aims to fill this void and begin the study of this metallic fission product’s diffusion behavior. By utilizing physical vapor deposition (PVD), dynamic secondary ion mass spectroscopy (SIMS), and the thin film solution to the diffusion equation coupled with a short circuit diffusion correction term, the diffusivities and Arrhenius temperature dependence are determined in the range of 500-1000°C and reported for the first time. Diffusion of Ru in this range is slow, with both lower activation energies and diffusion coefficients than other metallic fission products. Simulations of Ru diffusion on a graphene plane give activation energies similar to those acquired in this study. This is consistent with Ru behaving as an intercalating species and using the region in between graphene-like basal planes of graphite to travel through the lattice.
Author: Hahn-Meitner Institut fur Kernforschung
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Category :
Languages : en
Pages :
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Author:
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Category :
Languages : en
Pages :
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The experimental work on the diffusion of fission products in graphite matrices at high temperatures is reviewed and the possible mechanisms of mass transport are discussed. Preliminary data are given on diffusion in these systems. It is shown that the rates of diffusion for fission products introduced by a recoil process into the moderatcr lattice can be correlated based on a random wahk solid state diffusion model. An expression is derived for the coefficient of diffusion in terms of the lattice parameters giving the coefficients of diffusion for different atomic species as an exponential function of the atomic radii. The possibility of other controlling mechanisms above 1000 deg C and the effect of carbide formation and other reactions is evaluated. (auth).
Author:
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ISBN:
Category :
Languages : en
Pages : 24
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High and Very High Temperatures Gas Reactors (HTGRs/VHTRs) have five barriers to fission product (FP) release: the TRISO fuel coating, the fuel elements, the core graphite, the primary coolant system, and the reactor building. This project focused on measurements and computations of FP diffusion in graphite, FP adsorption on graphite and FP interactions with dust particles of arbitrary shape. Diffusion Coefficients of Cs and Iodine in two nuclear graphite were obtained by the release method and use of Inductively Coupled Plasma- Mass Spectroscopy (ICP-MS) and Instrumented Neutron Activation Analysis (INAA). A new mathematical model for fission gas release from nuclear fuel was also developed. Several techniques were explored to measure adsorption isotherms, notably a Knudsen Effusion Mass Spectrometer (KEMS) and Instrumented Neutron Activation Analysis (INAA). Some of these measurements are still in progress. The results will be reported in a supplemental report later. Studies ofFP interactions with dust and shape factors for both chain like particles and agglomerates over a wide size range were obtained through solutions of the diffusion and transport equations. The Green's Function Method for diffusion and Monte Carlo technique for transport were used, and it was found that the shape factors are sensitive to the particle arrangements, and that diffusion and transport of FPs can be hindered. Several journal articles relating to the above work have been published, and more are in submission and preparation.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 24
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Book Description
High and Very High Temperatures Gas Reactors (HTGRs/VHTRs) have five barriers to fission product (FP) release: the TRISO fuel coating, the fuel elements, the core graphite, the primary coolant system, and the reactor building. This project focused on measurements and computations of FP diffusion in graphite, FP adsorption on graphite and FP interactions with dust particles of arbitrary shape. Diffusion Coefficients of Cs and Iodine in two nuclear graphite were obtained by the release method and use of Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) and Instrumented Neutron Activation Analysis (INAA). A new mathematical model for fission gas release from nuclear fuel was also developed. Several techniques were explored to measure adsorption isotherms, notably a Knudsen Effusion Mass Spectrometer (KEMS) and Instrumented Neutron Activation Analysis (INAA). Some of these measurements are still in progress. The results will be reported in a supplemental report later. Studies of FP interactions with dust and shape factors for both chain-like particles and agglomerates over a wide size range were obtained through solutions of the diffusion and transport equations. The Green's Function Method for diffusion and Monte Carlo technique for transport were used, and it was found that the shape factors are sensitive to the particle arrangements, and that diffusion and transport of FPs can be hindered. Several journal articles relating to the above work have been published, and more are in submission and preparation.
Author: Thomas R. Boyle
Publisher:
ISBN:
Category : Electronic Dissertations
Languages : en
Pages : 83
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Book Description
Measuring and quantifying the diffusion of fission products in reactor materials is a critical element of the future success of Very High Temperature Reactors (VHTRs). While the extreme temperatures, which may be in excess of 1000 °C, allow for a potentially very high efficiency, they also can be problematic due to the increase in fission product transport. The aim of this work was to explore a repeatable, accurate, and cost effective process to measure the diffusion coefficients of fission products in VHTR materials. This work focuses on the diffusion of silver in graphite. We constructed graphite cells which could be filled with a silver diffusant. This diffusant may take the form of silver flakes, silver power, or a silver-laden graphite powder. The cells were hermetically sealed and heated to temperatures comparable to those found in VHTRs. These cells were imaged using microtomography and electron microscopy. Neutron Activation Analysis (NAA) was used to determine actual diffusion profiles in the cells.
