Download or read book Diffusion Modeling of Fission Product Release During Depressurized Core Conduction Cooldown Conditions written by and published by . This book was released on 1990 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: A simple model for diffusion through the silicon carbide layer of TRISO particles is applied to the data for accident condition testing of fuel spheres for the High-Temperature Reactor program of the Federal Republic of Germany (FRG). Categorization of sphere release of 137Cs based on fast neutron fluence permits predictions of release with an accuracy comparable to that of the US/FRG accident condition fuel performance model. Calculations are also performed for 85Kr, 9°Sr, and {sup 110m}Ag. Diffusion of cesium through SiC suggests that models of fuel failure should consider fuel performance during repeated accident condition thermal cycling. Microstructural considerations in models in fission product release are discussed. The neutron-induced segregation of silicon within the SiC structure is postulated as a mechanism for enhanced fission product release during accident conditions. An oxygen-enhanced SiC decomposition mechanism is also discussed. 12 refs., 11 figs., 2 tabs.

Download or read book Energy Research Abstracts written by and published by . This book was released on 1993 with total page 754 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modelling of Fission Product Release from TRISO Fuel During Accident Conditions written by Alastair Justin Ramlakan and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fission product release -- GETTER -- TRISO -- Benchmark -- Model -- CRP-6 -- International Atomic Energy Agency -- Diffusion.

Download or read book Analytical Modeling of Fission Product Releases by Diffusion from Multicoated Fuel Particles written by and published by . This book was released on 2003 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three levels of fission product diffusional release models are solved exactly. First, the Booth model for a homogeneous uncoated spherical fuel particle is presented and an improved implementation is suggested. Second, the release from a fuel particle with a single barrier layer is derived as a simple alternative to account for a coating layer. Third, the general case of release from a multicoated fuel particle is derived and applied to a TRISO-coated fuel. Previous approaches required approximate numerical solutions for the case of an arbitrary number of coatings with arbitrary diffusivities and arbitrary coating interface conditions.

Download or read book Surface Modification Technologies written by and published by . This book was released on 1995 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fission product release models in conacs written by A. B. Albert Barnett Reynolds and published by . This book was released on 1983 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Environmental Pollution Control written by and published by . This book was released on 1991 with total page 706 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Initial Conditions and Depressurization on Lock Exchange Flow After a Depressurized Conduction Cool Down Event in the High Temperature Test Facility written by Molly Glass and published by . This book was released on 2017 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: The High Temperature Test Facility (HTTF) is an electrically heated, scaled model of a Modular High Temperature Gas Reactor (MHTGR). Five experiments were conducted to study Depressurized Conduction Cool-Down phenomena stemming from a Double-Ended Guillotine Break (DEGB). After a DEGB, the reactor pressure vessel would depressurize until the pressures are equalized between the cavity that surrounds the reactor vessel and the vessel itself. Immediately following the depressurization there would be a large density gradient between the reactor vessel, which is full of hot helium and the cavity mixture of cold air and discharged helium. This density gradient would drive lock exchange flow, where the less dense helium would travel along the top of the pipe and the denser cavity gas would intrude into the bottom of the pipe and propagate towards the lower plenum. The cavity gas would then fill the lower plenum up to the top elevation of the hot leg pipe, which would then diffuse air into the core, potentially compromising core support and fuel integrity by graphite oxidation. Lock exchange flow is a density driven mechanism that depends on the density gradient between the cavity and the pressure vessel. Gas concentrations and temperatures greatly affect density and thus affect key time characteristics of lock exchange flow. The key time characteristics to be studied in the five experiments are: the time for the gas front to arrive at the thermocouple instrumentation in the cross-duct outside the lower plenum, the time to fill the lower plenum, and the times to reach instrumented posts in the lower plenum at various heights. The time to reach the plenum will indicate the speed at which the cold dense gas front is travelling. The time to fill the lower plenum is also the time of onset of molecular diffusion. The time the gas front reaches each instrumented post will display how the cold dense gas front propagates through the plenum. The first three of five tests were conducted at ambient temperatures with initially equalized pressures between the Reactor Cavity Simulation Tank (RCST) and the Primary Pressure Vessel (PPV). The next test was a heated depressurization, and the last test was a heated test with pressures initially equalized. These three categories of tests vary initial conditions that will change lock exchange flow time characteristics.

Download or read book Modeling of Fission Products Release Using Fuzzy Reasoning written by Adel Abdelrahman and published by LAP Lambert Academic Publishing. This book was released on 2014-03 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: The fuzzy reasoning is used to model the fractional release of fission products under severe accidents conditions comparing with the data from out of pile experiments conducted in special annealing furnaces, performed on specimens of spent nuclear fuel with high burn up. The physical phenomena of interest are migration of fission products from the severe damaged fuel matrix and its microstructure grains with associated phenomena of sweeping of fission products from inter-granular and intra-granular sites, the increase of grain size on the account of annihilation of smaller grains during high temperature annealing, and a coalescence of pores. These phenomena can be viewed and imaged as global mass transfer of imaginary packages carrying the fission products with time. So incorporating the Package Flow Model PFM to represent the migration of the imaginary fission product packages of grains, bubbles or, pores with adjusted size during the annealing tests. The predicted values have shown a good agreement with the experimental data set from ORNL VI and HI tests, CRL experiments and, CEA experiments.

Download or read book MELCOR 1 8 5 Modeling Aspects of Fission Product Release Transport and Deposition an Assessment with Recommendations written by and published by . This book was released on 2010 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Phebus and VERCORS data have played an important role in contemporary understanding and modeling of fission product release and transport from damaged light water reactor fuel. The data from these test programs have allowed improvement of MELCOR modeling of release and transport processes for both low enrichment uranium fuel as well as high burnup and mixed oxide (MOX) fuels. This paper discusses the synthesis of these findings in the MELCOR severe accident code. Based on recent assessments of MELCOR 1.8.5 fission product release modeling against the Phebus FPT-1 test and on observations from the ISP-46 exercise, modifications to the default MELCOR 1.8.5 release models are recommended. The assessments identified an alternative set of Booth diffusion parameters recommended by ORNL (ORNL-Booth), which produced significantly improved release predictions for cesium and other fission product groups. Some adjustments to the scaling factors in the ORNL-Booth model were made for selected fission product groups, including UO2, Mo and Ru in order to obtain better comparisons with the FPT-1 data. The adjusted model, referred to as 'Modified ORNL-Booth, ' was subsequently compared to original ORNL VI fission product release experiments and to more recently performed French VERCORS tests, and the comparisons was as favorable or better than the original CORSOR-M MELCOR default release model. These modified ORNL-Booth parameters, input to MELCOR 1.8.5 as 'sensitivity coefficients' (i.e. user input that over-rides the code defaults) are recommended for the interim period until improved release models can be implemented into MELCOR. For the case of ruthenium release in air-oxidizing conditions, some additional modifications to the Ru class vapor pressure are recommended based on estimates of the RuO2 vapor pressure over mildly hyperstoichiometric UO2. The increased vapor pressure for this class significantly increases the net transport of Ru from the fuel to the gas stream. A formal model is needed. Deposition patterns in the Phebus FPT-1 circuit were also significantly improved by using the modified ORNL-Booth parameters, where retention of lower volatile Cs2MoO4 is now predicted in the heated exit regions of the FPT-1 test, bringing down depositions in the FPT-1 steam generator tube to be in closer alignment with the experimental data. This improvement in 'RCS' deposition behavior preserves the overall correct release of cesium to the containment that was observed even with the default CORSOR-M model. Not correctly treated however is the release and transport of Ag to the FPT-1 containment. A model for Ag release from control rods is presently not available in MELCOR. Lack of this model is thought to be responsible for the underprediction by a factor of two of the total aerosol mass to the FPT-1 containment. It is suggested that this underprediction of airborne mass led to an underprediction of the aerosol agglomeration rate. Underprediction of the agglomeration rate leads to low predictions of the aerosol particle size in comparison to experimentally measured ones. Small particle size leads low predictions of the gravitational settling rate relative to the experimental data. This error, however, is a conservative one in that too-low settling rate would result in a larger source term to the environment. Implementation of an interim Ag release model is currently under study. In the course of this assessment, a review of MELCOR release models was performed and led to the identification of several areas for future improvements to MELCOR. These include upgrading the Booth release model to account for changes in local oxidizing/reducing conditions and including a fuel oxidation model to accommodate effects of fuel stoichiometry. Models such as implemented in the French ELSA code and described by Lewis are considered appropriate for MELCOR. A model for ruthenium release under air oxidizing conditions is also needed and should be included as part of a fuel oxidation model since fuel stoichiometry is a fundamental parameter in determining the vapor pressure of ruthenium oxides over the fuel. There is also a need to expand the MELCOR architecture for tracking fission product classes to allow for more speciation of fission products. An example is the formation of CsI and Cs2MoO4 and potentially CsOH if all Mo is combined with Cs such that excess Cs exists in the fuel. Presently, MELCOR can track only one class combination (CsI) accurately, where excess Cs is assumed to be CsOH. Our recommended interim modifications map the CsOH (MELCOR Radionuclide Class 2) and Mo (Class 7) vapor pressure properties to Cs2MoO4, which approximates the desired formal class combination of Cs and Mo. Other extensions to handle properly iodine speciation from pool/gas chemistry are also needed.

Download or read book Modeling of Thermal Hydraulic Behavior and Fission Product Releases in Degraded Cores written by and published by . This book was released on 1988 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: When core material reaches melting conditions severe degradation of the core geometry occurs. Data available on the core behavior in a severely degraded state suggest that extensive blockage of the flow channels would occur. If a sufficient bypass is available for the gas flow, such as in the LOFT LP-FP-2 test, severe retardation of the hydrogen and fission product sources from the degraded channel is suggested from the available data. This phenomena is expected to occur in an LWR core and should be considered by core models that are used for severe accident analysis. In the MAAP code it is done by preventing gas flow through molten core regions. Good agreement is obtained with all relevant data that are directly applicable to LWR accident conditions. A more mechanistic model for the freezing of core material and its effect on the coolant channel geometry is currently being investigated by the US Department of Energy Advanced Reactor Severe Accident Program (ARSAP). 8 refs., 2 figs.

Download or read book Measurement and Modelling of Postirradiation Fission Product Release from HTGR Fuel Particles Under Accident Conditions written by and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A study was performed to provide a description of the release of fission products from failed fuel particles during a core heatup event in an HTGR. The need for this study was established in the Accident Initiation and Progression Analysis program. The release of fission products was measured from laser-failed BISO ThO2, TRISO UC2, and weak acid resin (WAR) particles over a range of burnups. The burnups were 0.25, 1.4 and 15.7% FIMA for ThO2 particles, 23.5 and 74% FIMA for UC2 particles, and 60% FIMA for WAR particles. The fission products measured were nuclides of xenon, iodine, krypton, tellurium, and cesium. Two types of experiments were performed: isothermal and temperature rise experiments. The range of the temperatures was from 1200° to 2300°C. In the temperature rise experiments, the heating rates were between 50° and 450°C/h.

Download or read book Report on Simulation of Fission Gas and Fission Product Diffusion in UO2 written by and published by . This book was released on 2016 with total page 25 pages. Available in PDF, EPUB and Kindle. Book excerpt: In UO2 nuclear fuel, the retention and release of fission gas atoms such as xenon (Xe) are important for nuclear fuel performance by, for example, reducing the fuel thermal conductivity, causing fuel swelling that leads to mechanical interaction with the clad, increasing the plenum pressure and reducing the fuel-clad gap thermal conductivity. We use multi-scale simulations to determine fission gas diffusion mechanisms as well as the corresponding rates in UO2 under both intrinsic and irradiation conditions. In addition to Xe and Kr, the fission products Zr, Ru, Ce, Y, La, Sr and Ba have been investigated. Density functional theory (DFT) calculations are used to study formation, binding and migration energies of small clusters of Xe atoms and vacancies. Empirical potential calculations enable us to determine the corresponding entropies and attempt frequencies for migration as well as investigate the properties of large clusters or small fission gas bubbles. A continuum reaction-diffusion model is developed for Xe and point defects based on the mechanisms and rates obtained from atomistic simulations. Effective fission gas diffusivities are then obtained by solving this set of equations for different chemical and irradiation conditions using the MARMOT phase field code. The predictions are compared to available experimental data. The importance of the large XeU3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and high binding energy. We find that the XeU3O cluster gives Xe diffusion coefficients that are higher for intrinsic conditions than under irradiation over a wide range of temperatures. Under irradiation the fast-moving XeU3O cluster recombines quickly with irradiation induced interstitial U ions, while this mechanism is less important for intrinsic conditions. The net result is higher concentration of the XeU3O cluster for intrinsic conditions than under irradiation. We speculate that differences in the irradiation conditions and their impact on the XeU3O cluster can explain the wide range of diffusivities reported in experimental studies. However, all vacancy-mediated mechanisms underestimate the Xe diffusivity compared to the empirical radiation-enhanced rate used in most fission gas release models. We investigate the possibility that diffusion of small fission gas bubbles or extended Xe-vacancy clusters may give rise to the observed radiation-enhanced diffusion coefficient. These studies highlight the importance of U divacancies and an octahedron coordination of uranium vacancies encompassing a Xe fission gas atom. The latter cluster can migrate via a multistep mechanism with a rather low effective barrier, which together with irradiation-induced clusters of uranium vacancies, gives rise to the irradiation-enhanced diffusion coefficient observed in experiments.

Download or read book Licensing Topical Report written by and published by . This book was released on 1980 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The release of fission products from failed fuel particles was measured under simulated accident (core heatup) conditions. A generic model and specific model parameters that describe delayed fission product release from the kernels of failed HTGR fuel particles were developed from the experimental results. The release of fission products was measured from laser-failed BISO ThO2 and highly enriched (HEU) TRISO UC2 particles that had been irradiated to a range of kernel burnups. The burnups were 0.25, 1.4, and 15.7% FIMA for ThO2 particles and 23.5 and 74% FIMA for UC2 particles. The fission products measured were nuclides of xenon, iodine, krypton, tellurium, and cesium.

Download or read book Preliminary studies of fission product release from uo2 under oxidising conditions written by D. R. Mccracken and published by . This book was released on 1985 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fission product release and redistribution was studied during the exposure of uo2 in a zirconium furnace tube to steam and air at temperatures up to 910 degrees c. the fuel fragments had been exposed to less than or equal to 3.11 x 10 sup(18) n/cm sup(2) (0.3 mw.h/kg) at less than or equal to 70 degrees c in the self-serve facility of nrx. under these conditions no diffusion to grain boundaries should have occurred, and fission products should stay randomly scattered throughout the matrix. releases were small, less than or equal to 1.4 percent with only xenon and iodine being significant. the fuel oxidation occurred predominantly at less than or equal to 700 degrees c. at higher temperatures oxidation of the zirconium occurred and protected the fuel from significant high temperature oxidation. the results illustrate that fission gases distributed in the fuel matrix are not released during simple crystallographic re-arrangement. release occurs only when an atomic site or gas bubble is intersected by a crack or dislocation. significantly higher release should be expected under conditions where grain growth occurs. selective traps for fission products performed well and will be further investigated in future studies.

Download or read book Government Reports Announcements Index written by and published by . This book was released on 1991 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Government reports annual index written by and published by . This book was released on 199? with total page 1646 pages. Available in PDF, EPUB and Kindle. Book excerpt: