scholarly journals Computational Fluid Dynamics Analyses on Very High Temperature Reactor Air Ingress

2009 ◽  
Author(s):  
Chang H. Oh ◽  
Eung S. Kim ◽  
Richard Schultz ◽  
David Petti ◽  
Hyung S. Kang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Temperature ◽  
System Analysis ◽  
Onset Time ◽  
The Core ◽  
Very High Temperature Reactor ◽  
High Temperature Reactor ◽  
Air Ingress ◽  
Very High

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 2D 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.

Air Ingress Analysis: Computational Fluid Dynamics Models

2010 ◽  
Author(s):  
Chang H. Oh ◽  
Eung S. Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Temperature ◽  
Fluid Dynamic ◽  
Department Of Energy ◽  
Validation Data ◽  
The Core ◽  
Air Ingress ◽  
Dynamics Models ◽  
Very High

Idaho National Laboratory (INL), under the auspices of the U.S. Department of Energy (DOE), is performing research and development that focuses on key phenomena important during potential scenarios that may occur in very high temperature reactors (VHTRs). Phenomena identification and ranking studies to date have ranked an air ingress event, following on the heels of a VHTR depressurization, as important with regard to core safety. Consequently, the development of advanced air-ingress-related models and verification and validation data are a very high priority. Following a loss of coolant and system depressurization incident, air will enter the core of the High Temperature Gas Cooled Reactor through the break, possibly causing oxidation of the core and reflector graphite structure. Simple core and plant models indicate that, under certain circumstances, the oxidation may proceed at an elevated rate with additional heat generated from the oxidation reaction itself. Under postulated conditions of fluid flow and temperature, excessive degradation of lower plenum graphite can lead to a loss of structural support. Excessive oxidation of core graphite can also lead to a release of fission products into the confinement, which could be detrimental to reactor safety. Computational fluid dynamics models developed in this study will improve our understanding of this phenomenon. This paper presents two-dimensional (2-D) and three-dimensional (3-D) computational fluid dynamic (CFD) results for the quantitative assessment of the air ingress phenomena. A portion of the results from density-driven stratified flow in the inlet pipe will be compared with the experimental results.

CFD Analysis on the Influence of Coolant Distribution Blocks on the Core Hot Spot Temperature in a Prismatic Very High Temperature Reactor

2011 ◽  
Author(s):  
Min-Hwan Kim ◽  
Nam-il Tak ◽  
Jae Man Noh ◽  
Goon-Cherl Park
Keyword(s):  
High Temperature ◽  
Hot Spot ◽  
Maximum Velocity ◽  
Unit Cell ◽  
Normal Operation ◽  
The Core ◽  
Very High Temperature Reactor ◽  
Velocity Deviation ◽  
High Temperature Reactor ◽  
Very High

Two design options of core distribution block (CDB) for a cooled-vessel design in the Very High Temperature Reactor (VHTR) were developed and the influence on the core hot spot was investigated by the commercial computational fluid dynamics (CFD) code, CFX-11. Isothermal CFD analyses were performed to estimate the coolant flow variation at the inlet of the coolant channel. The results predicted about 5% of the maximum velocity deviation when applying the core pressure drop of NHDD PMR200. A unit-cell CFD model was used to access the effect of the velocity deviation on the core hot spot. The unit-cell analyses were carried out for the velocity deviation of 0%, 5%, and 10%. Not only a constant power but also a local maximum power profile was considered. According to the results, the maximum fuel temperature was increased by about 30°C for the velocity deviation of 10% but still below the normal operation limit of 1250°C.

Air Ingress Phenomena in a Depressurization Accident of the Very-High-Temperature Reactor

2008 ◽  
Author(s):  
Tetsuaki Takeda
Keyword(s):  
High Temperature ◽  
Natural Circulation ◽  
Reactor Core ◽  
Fission Products ◽  
Design Criterion ◽  
Very High Temperature Reactor ◽  
High Temperature Reactor ◽  
Air Ingress ◽  
High Degree ◽  
Very High

The inherent properties of the Very-High-Temperature Reactor (VHTR) facilitate the design of the VHTR with high degree of passive safe performances, compared to other type of reactors. However, it is still not clear if the VHTR can maintain a passive safe function during the primary-pipe rupture accident, or what would be a design criterion to guarantee the VHTR with the high degree of passive safe performances during the accident. The primary-pipe rupture accident is one of the most common of accidents related to the basic design regarding the VHTR, which has a potential to cause the destruction of the reactor core by oxidizing in-core graphite structures and to release fission products by oxidizing graphite fuel elements. It is a guillotine type rupture of the double coaxial pipe at the nozzle part connecting to the side or bottom of the reactor pressure vessel, which is a peculiar accident for the VHTR. This study is to investigate the air ingress phenomena and to develop the passive safe technology for the prevention of air ingress and of graphite corrosion. The present paper describes the influences of a localized natural circulation in parallel channels onto the air ingress process during the primary-pipe rupture accident of the VHTR.

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