Scaling and design analyses of a scaled-down, high-temperature test facility for experimental investigation of the initial stages of a VHTR air-ingress accident

Arcilesi, David J.; Ham, Tae Kyu; Kim, In Hun; Sun, Xiaodong; Christensen, Richard N.; Oh, Chang Ho

doi:10.1016/j.nucengdes.2015.03.007

Cited by 8 publications

(2 citation statements)

References 20 publications

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“…One last note should be given to the overall time constant calculated by Arcelesi et al [26] which is presented in Equation 2.30. The assertion is that the overall time scale of the event is a function of the time scales of each constituent stage, which density driven air ingress (DD, or DDAI) would dominate the total time scale.…”

Section: This Is Because Heat Transfer From the Solid Structures Insimentioning

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: This Is Because Heat Transfer From the Solid Structures Insimentioning

confidence: 99%

Fluid Stratification Separate Effects Analysis, Testing and Benchmarking

Graves

Klein

2018

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“…Therefore, it is highly desired to know accurately when this natural convection would begin. It has been suggested by Oh and others [11,13,14] that the sequence of events during an air ingress accident involve : (1) depressurization, (2) density-driven stratified flow, (3) diffusion into the reactor core, and (4) global natural circulation (Fig. 2).…”

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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