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Analysis Of The Gas Diffusion Process During A Hypothetical Air Ingress Accident In A Modular High Temperature Gas Cooled Reactor
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Book Synopsis Analysis of the gas diffusion process during a hypothetical air ingress accident in a modular high temperature gas cooled reactor by : Zuoyi Zhang
Download or read book Analysis of the gas diffusion process during a hypothetical air ingress accident in a modular high temperature gas cooled reactor written by Zuoyi Zhang and published by . This book was released on 1994 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Analyse Des Gasdiffusionsprozesses Während Eines Hypothetischen Lufteinbruch-Unfalls in Einem Modularen Hochtemperatur-Reaktor by : Zuoyi Zhang
Download or read book Analyse Des Gasdiffusionsprozesses Während Eines Hypothetischen Lufteinbruch-Unfalls in Einem Modularen Hochtemperatur-Reaktor written by Zuoyi Zhang and published by . This book was released on 1993 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Energy Research Abstracts written by and published by . This book was released on 1995 with total page 782 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Hypothetical Air Ingress Scenarios in Advanced Modular High Temperature Gas Cooled Reactors by :
Download or read book Hypothetical Air Ingress Scenarios in Advanced Modular High Temperature Gas Cooled Reactors written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Considering an extremely hypothetical scenario of complete cross duct failure and unlimited air supply into the reactor vessel of a modular high temperature gas cooled ractor, it is found that the potential air inflow remains limited due to the high friction pressure drop through the active core. All incoming air will be oxidized to CO and some local external burning would be temporarily possible in such a scenario. The accident would have to continue with unlimited air supply for hundreds of hours before the core structural integrity would be jeopardized.
Book Synopsis Air Ingress Analyses on a High Temperature Gas-Cooled Reactor by :
Download or read book Air Ingress Analyses on a High Temperature Gas-Cooled Reactor written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A primary-pipe break accident is one of the design-basis accidents of a high-temperature gas-cooled reactor (HTGR). When this accident occurs, air is anticipated to enter the reactor core from the break and oxidize the in-core graphite structure in the modular pebble bed reactor (MPBR). This paper presents the results of the graphite oxidation model developed as part of the Idaho National Engineering and Environmental Laboratory's Direct Research and Development effort. Although gas reactors have been tried in the past with limited success, the innovations of modularity and integrated state-ofart control systems coupled with improved fuel design and a pebble bed core make this design potentially very attractive from an economic and technical perspective. A schematic diagram on a reference design of the MPBR has been established on a major component level (INEEL & MIT, 1999). Steady-state and transient thermal hydraulics models will be produced with key parameters established for these conditions at all major components. Development of an integrated plant model to allow for transient analysis on a more sophisticated level is now being developed. In this paper, preliminary results of the hypothetical air ingress are presented. A graphite oxidation model was developed to determine temperature and the control mechanism in the spherical graphite geometry.
Book Synopsis Hypothetical Air Ingress Scenarios in Advanced Modular High Temeprature Gas Cooled Reactors by :
Download or read book Hypothetical Air Ingress Scenarios in Advanced Modular High Temeprature Gas Cooled Reactors written by and published by . This book was released on 1988 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Study on Air Ingress Mitigation Methods in the Very High Temperature Gas Cooled Reactor (VHTR). by :
Download or read book Study on Air Ingress Mitigation Methods in the Very High Temperature Gas Cooled Reactor (VHTR). written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An air-ingress accident followed by a pipe break is considered as a critical event for a very high temperature gas-cooled reactor (VHTR). Following helium depressurization, it is anticipated that unless countermeasures are taken, air will enter the core through the break leading to oxidation of the in-core graphite structure. Thus, without mitigation features, this accident might lead to severe exothermic chemical reactions of graphite and oxygen. Under extreme circumstances, a loss of core structural integrity may occur along with excessive release of radiological inventory. Idaho National Laboratory under the auspices of the U.S. Department of Energy is performing research and development (R & D) that focuses on key phenomena important during challenging scenarios that may occur in the VHTR. Phenomena Identification and Ranking Table (PIRT) studies to date have identified the air ingress event, following on the heels of a VHTR depressurization, as very important (Oh et al. 2006, Schultz et al. 2006). Consequently, the development of advanced air ingress-related models and verification and validation (V & V) requirements are part of the experimental validation plan. This paper discusses about various air-ingress mitigation concepts applicable for the VHTRs. The study begins with identifying important factors (or phenomena) associated with the air-ingress accident by using a root-cause analysis. By preventing main causes of the important events identified in the root-cause diagram, the basic air-ingress mitigation ideas can be conceptually derived. The main concepts include (1) preventing structural degradation of graphite supporters; (2) preventing local stress concentration in the supporter; (3) preventing graphite oxidation; (4) preventing air ingress; (5) preventing density gradient driven flow; (4) preventing fluid density gradient; (5) preventing fluid temperature gradient; (6) preventing high temperature. Based on the basic concepts listed above, various air-ingress mitigation methods are proposed in this study. Among them, the following two mitigation ideas are extensively investigated using computational fluid dynamic codes (CFD): (1) helium injection in the lower plenum, and (2) reactor enclosure opened at the bottom. The main idea of the helium injection method is to replace air in the core and the lower plenum upper part by buoyancy force. This method reduces graphite oxidation damage in the severe locations of the reactor inside. To validate this method, CFD simulations are addressed here. A simple 2-D CFD model is developed based on the GT-MHR 600MWt design. The simulation results showed that the helium replace the air flow into the core and significantly reduce the air concentration in the core and bottom reflector potentially protecting oxidation damage. According to the simulation results, even small helium flow was sufficient to remove air in the core, mitigating the air-ingress successfully. The idea of the reactor enclosure with an opening at the bottom changes overall air-ingress mechanism from natural convection to molecular diffusion. This method can be applied to the current system by some design modification of the reactor cavity. To validate this concept, this study also uses CFD simulations based on the simplified 2-D geometry. The simulation results showed that the enclosure open at the bottom can successfully mitigate air-ingress into the reactor even after on-set natural circulation occurs.
Book Synopsis Government Reports Annual Index by :
Download or read book Government Reports Annual Index written by and published by . This book was released on 1995 with total page 1742 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sections 1-2. Keyword Index.--Section 3. Personal author index.--Section 4. Corporate author index.-- Section 5. Contract/grant number index, NTIS order/report number index 1-E.--Section 6. NTIS order/report number index F-Z.
Book Synopsis Depressurized Core Heatup Accident Scenarios in Advanced Modular High Temperature Gas Cooled Reactors by :
Download or read book Depressurized Core Heatup Accident Scenarios in Advanced Modular High Temperature Gas Cooled Reactors written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The decay heat removal by a passive air colling system from a modular high tempeature gas cooled reactor during depressurized core heatup accident scenarios was analyzed. The effects of several design and operating parameters on the peak fuel and vessel temperatures were established. The results indicate that fuel and vessel temperatures remain well below failure levels and that significant safety margins exist in the key variables of decay heat and core thermal conductivities.
Book Synopsis Government Reports Announcements & Index by :
Download or read book Government Reports Announcements & Index written by and published by . This book was released on 1995-07 with total page 1164 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Hypothetical Core Disassembly Accident Analysis for the Gas-cooled Fast Reactor and Liquid Metal Fast Breeder Reactor by : David C. Losey
Download or read book Hypothetical Core Disassembly Accident Analysis for the Gas-cooled Fast Reactor and Liquid Metal Fast Breeder Reactor written by David C. Losey and published by . This book was released on 1979 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Computational Fluid Dynamics Analyses on Very High Temperature Reactor Air Ingress by :
Download or read book Computational Fluid Dynamics Analyses on Very High Temperature Reactor Air Ingress written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A preliminary computational fluid dynamics (CFD) analysis was performed to understand density-gradient-induced stratified flow in a Very High Temperature Reactor (VHTR) air-ingress accident. Various parameters were taken into consideration, including turbulence model, core temperature, initial air mole-fraction, and flow resistance in the core. The gas turbine modular helium reactor (GT-MHR) 600 MWt was selected as the reference reactor and it was simplified to be 2-D geometry in modeling. The core and the lower plenum were assumed to be porous bodies. Following the preliminary CFD results, the analysis of the air-ingress accident has been performed by two different codes: GAMMA code (system analysis code, Oh et al. 2006) and FLUENT CFD code (Fluent 2007). Eventually, the analysis results showed that the actual onset time of natural convection (~160 sec) would be significantly earlier than the previous predictions (~150 hours) calculated based on the molecular diffusion air-ingress mechanism. This leads to the conclusion that the consequences of this accident will be much more serious than previously expected.
Book Synopsis Implications of Air Ingress Induced by Density-Difference Driven Stratified Flow by :
Download or read book Implications of Air Ingress Induced by Density-Difference Driven Stratified Flow written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the design basis accidents for the Next Generation Nuclear Plant (NGNP), a high temperature gas-cooled reactor, is air ingress subsequent to a pipe break. Following a postulated double-ended guillotine break in the hot duct, and the subsequent depressurization to nearly reactor cavity pressure levels, air present in the reactor cavity will enter the reactor vessel via density-gradient-driven-stratified flow. Because of the significantly higher molecular weight and lower initial temperature of the reactor cavity air-helium mixture, in contrast to the helium in the reactor vessel, the air-helium mixture in the cavity always has a larger density than the helium discharging from the reactor vessel through the break into the reactor cavity. In the later stages of the helium blowdown, the momentum of the helium flow decreases sufficiently for the heavier cavity air-helium mixture to intrude into the reactor vessel lower plenum through the lower portion of the break. Once it has entered, the heavier gas will pool at the bottom of the lower plenum. From there it will move upwards into the core via diffusion and density-gradient effects that stem from heating the air-helium mixture and from the pressure differences between the reactor cavity and the reactor vessel. This scenario (considering density-gradient-driven stratified flow) is considerably different from the heretofore commonly used scenario that attributes movement of air into the reactor vessel and from thence to the core region via diffusion. When density-gradient-driven stratified flow is considered as a contributing phenomena for air ingress into the reactor vessel, the following factors contribute to a much earlier natural circulation-phase in the reactor vessel: (a) density-gradient-driven stratified flow is a much more rapid mechanism (at least one order of magnitude) for moving air into the reactor vessel lower plenum than diffusion, and consequently, (b) the diffusion dominated phase begins with a much larger flow area and a much shorter distance for air to move into the core than earlier scenarios that attribute all air ingress from the reactor cavity into the core to diffusion only. Hence, consideration of the density-gradient-driven stratified flow phenomena will likely lead to more rapid air ingress into the core and also the presence of more air for core graphite oxidation than the widely-used air ingress attributed solely to diffusion. This paper discusses the density-gradient-driven stratified flow phenomena and the implications of considering this behavior on the progression of the air ingress event. Preliminary calculations are used to underline the importance of considering the density-gradient driven stratified flow phenomena in subsequent validation experiments and software development for analyzing VHTR scenarios.
Book Synopsis Journal of Nuclear Science and Technology by :
Download or read book Journal of Nuclear Science and Technology written by and published by . This book was released on 1994 with total page 762 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Natural Circulation Patterns in the VHTR Air-Ingress Accident and Related Issues by :
Download or read book Natural Circulation Patterns in the VHTR Air-Ingress Accident and Related Issues written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A natural circulation pattern in a Very High Gas-Cooled Reactor during a hypothetical air-ingress accident has been investigated using computational fluid dynamic (CFD) methods in order to compare with the previous 1-D flow path model for the air-ingress analyses. The GT-MHR 600 MWt reactor was selected to be the reference design and modeled by a half symmetric 3-D geometry using FLUENT 6.3, a commercial CFD code. The simulation was carried out as steady-state calculations, and the boundary conditions were either assumed or provided from the 1-D GAMMA code results. Totally, 12 different cases have been estimated, and many notable findings and results have been obtained in this study. According to the simulations, the natural circulation pattern in the reactor was quite different from the previous 1-D assumptions. A large re-circulation flow with thermal stratification phenomena was clearly observed in the hot-leg and the lower plenum in the 3-D model. This re-circulation flow provided approximately an order faster air-ingress speed (0.46 m/s in superficial velocity) than previously predicted values by 1-D modeling (0.02~0.03 m/s). It indicates that the 1-D air-ingress modeling may significantly distort the air-ingress scenario and consequences. In addition, the complicated natural circulation pattern is eventually expected to lead to very complex graphite oxidations and corrosion patterns.
Book Synopsis Study on Depressurized Loss of Coolant Accident and Its Mitigation Method Framework at Very High Temperature Gas Cooled Reactor by : Izabela Gutowska
Download or read book Study on Depressurized Loss of Coolant Accident and Its Mitigation Method Framework at Very High Temperature Gas Cooled Reactor written by Izabela Gutowska and published by . This book was released on 2015 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: To understand how a Depressurized Loss of Forced Convection (D-LOFC) initiated from a double-ended guillotine break may affect further operation of a High Temperature Gas Cooled Rector (HTGR), thorough understanding of each specific stage of this event is required. Key considerations that need to be determined is the amount of air that will ingress into the reactor vessel during a Depressurized Conduction Cooldown (DCC) accident as well as the time scale of each events stage. Reactor components constructed of graphite will, at sufficiently high temperatures produce exothermic reactions in the presence of air while undergoing oxidation reaction. There is a danger that it may cause loss of core structural integrity via oxidation or surface corrosion. Thus, without any mitigation systems, this accident might result in exothermic chemical reactions of graphite and oxygen depending on the accident scenario and the design. Having the knowledge on the amount of air inside the vessel one can investigate how to reduce air concentration via specifically designed mitigation system. The main idea of the applied mitigation method is to replace air in the core with buoyancy force by insertion of secondary gas: helium, nitrogen or argon into the reactor's lower plenum. This can help to mitigate graphite oxidation inside the reactor core by reducing air volume mass fraction in the reactor components and by lowering the core and lower plenum temperatures. This dissertation presents design framework for a secondary gas insertion system that will mitigate the potential core/structure damage during DCC event. Obtained results will serve as a guidelines for future design engineers while applying the concept to existing design.
Book Synopsis A Preliminary Investigation of Rapid Depressurization Phenomena Following a Sudden DLOFC in a VHTR. by :
Download or read book A Preliminary Investigation of Rapid Depressurization Phenomena Following a Sudden DLOFC in a VHTR. written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Air ingress has been identified as a potential threat for Very High Temperature gas-cooled Reactors (VHTR). Reactor components constructed of graphite will, at high temperatures, produce exothermic reactions in the presence of oxygen. The danger lies in the possibility of fuel element damage and core structural failure. Previous investigations of air ingress mechanisms have focused on thermal and molecular diffusion, density-driven stratified flow, and natural convection. Here, we investigate the possibility of a rapid ingress of air due to a Taylor wave expansion after a hypothetical sudden loss of coolant accident (LOCA) scenario in a VHTR. Our analysis starts with a one-dimensional shock tube simulation to simply illustrate the development of a Taylor wave with resulting reentrant flow. Then, a simulation is performed of an idealized two-dimensional axisymmetric representation of the lower plenum of General Atomics GT-MHR subjected to a hypothetical catastrophic break of the hot duct. Analysis shows the potential for significant and rapid air ingress into the reactor vessel in the case of a large break in the cooling system.
