Air-ingress analysis: Part 2—Computational fluid dynamic models

Oh, Chang Ho; Kang, Hyung Seok; Kim, Eung S.

doi:10.1016/j.nucengdes.2010.05.065

Cited by 35 publications

(9 citation statements)

References 3 publications

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“…Several works will be highlighted as they pertain to this experimental effort; however, begin with a theoretical treatment of the accident progression [5], which is the first of a two-part series. The second part is a computational treatment using FLUENT [23].…”

Section: Chang Oh Et Almentioning

confidence: 99%

Fluid Stratification Separate Effects Analysis, Testing and Benchmarking

Graves

Klein

2018

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High Temperature Gas Reactors (HTGRs) are positioned to disrupt local and global markets via their unique ability to produce carbon-free process heat, high efficiency power generation, and passively safe operational features. However, significant impediments still exist to delay deployment of this particular technology, including a lack of experimental data, verified code application, and lack of consensus with regards to severe accident progression. In particular, air ingress accidents represent a particular challenge to designers and engineers, as they represent low probability, but highly complex, accident scenarios. Including phenomena such as molecular diffusion, free convection, and complex heat and mass transfer paths, experimental and traceable data is essential to maturing the state of the industry. Therefore, this work presents an experimental investigation of the transition to natural convection in HTGR applications using the Stratified Flow Separate Effects Test Facility, housed at Oregon State University. In particular, this work will present data that challenges the assumption that molecular diffusion is a significant factor in this severe accident in the reference facility of the General Atomic 600 MWth Gas Turbine-Modular Helium Reactor (GT-MHR). Rather, experimentally produced data shows a statistically suggestive retardant effect of cross duct orientation, indicating that ingress mechanics may be fundamentally altered via facility geometry. Experimentally, this is achieved using a simplified cross duct that may be positioned in one of two ways so as to provide either horizontal or vertical access to the lower plenum area. Onset of natural convection (ONC) is measured using an oxygen sensor probe, immersed in the helium working fluid, so as to provide direct indication of air presence in the upper plenum. This document will present the doctoral dissertation produced by this work, along with its analysis, experimental data, observations, and conclusions, in addition to select documents that will highlight critical changes during the development process. Those documents will include the quality assurance plan, all subsequent change requests, and the engineering transfer from Harris Thermal in order to establish the most complete quality record possible.

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Section: Chang Oh Et Almentioning

confidence: 99%

Fluid Stratification Separate Effects Analysis, Testing and Benchmarking

Graves

Klein

2018

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“…This process involves air diffusion into the helium bubble and, potentially, a density-gradient-driven stratified flow effect as well for larger break scenarios. 15 Because of the uncertainties, ingress flow start times in these analyses are usually inputs treated parametrically.…”

Section: Air Ingressmentioning

confidence: 99%

HTGR Measurements and Instrumentation Systems

Holcomb

Çetiner

2012

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“…Unfortunately, there is currently a very limited amount of experimental data in the established literature that can be used to understand this transition from diffusion to natural circulation and validate numerical models. In a separate-effects experimental study on isothermal air ingress through horizontal ports in a helium filled scaled-vessel [17], it was found that it would take several minutes to fill the entire test chamber -a result that differs from the numerical predictions by Oh et al [5,12]. The predictive modeling of this process is quite challenging because the CFD codes don't have appropriate models for properties such as molecular diffusion in binary mixtures.…”

Section: Introductionmentioning

confidence: 96%

“…If the dominating mecha-nism is molecular diffusion, the rate of air-ingress is quite slow, whereas if the driving mode is convective transport, air circulation can start within few minutes. The analytical or computational studies performed on these hypothetical accidents in GT-MHRs suggest that due to gravity currents (lock-exchange) the convective air-ingress mode is reached instantaneously [5,12]. This air flow into the lower plenum and core with high temperature graphite can lead to adverse consequences such as oxidation of graphite and can negatively impact the passive heat removal capabilities of the reactor.…”

Section: Introductionmentioning

confidence: 99%

Transition from molecular diffusion to natural circulation mode air-ingress in high temperature helium loop

Gould

Franken

Bindra

et al. 2017

Annals of Nuclear Energy

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High Temperature Gas-cooled Reactors (HTGRs) have significantly robust passive heat removal capabilities owing largely to conduction and radiation heat transfer through graphite-fuel matrix and reactor vessel wall respectively. However, these capabilities may be significantly impacted if air was to replace Helium in the high temperature graphite under accident scenarios. In case of break in the coolant system high pressure Helium will escape into the reactor cavity leading to depressurization of the reactor. This will allow air from reactor cavity to enter the plenum or core of HTGRs via different mechanisms-diffusion, gravity currents, or natural circulation. Experimental studies were conducted in a geometrically scaled setup with a shape of small English letter 'h', to depict the role of upper plenum in this process. Main focus of these studies was to understand and observe the transition time from diffusion to natural circulation. Thermal camera is used to identify this transition and flow transducer is used to measure the flow rates. The experimental results on incipience time of natural convection after a chamber pre-filled with Helium is opened to atmosphere are qualitatively similar to observations reported in literature using 'inverse U' shaped experimental setup, but also show distinct quantitative effect of extended leg on the transition times. Prior to onset of natural circulation (ONC), molecular diffusion plays the significant role in air-ingress. However, at higher temperatures convection currents may be influencing air ingress and in-turn ONC times.

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Air-ingress analysis: Part 2—Computational fluid dynamic models

Cited by 35 publications

References 3 publications

Fluid Stratification Separate Effects Analysis, Testing and Benchmarking

Fluid Stratification Separate Effects Analysis, Testing and Benchmarking

HTGR Measurements and Instrumentation Systems

Transition from molecular diffusion to natural circulation mode air-ingress in high temperature helium loop

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