scholarly journals FINAL REPORT on Experimental Validation of Stratified Flow Phenomena, Graphite Oxidation, and Mitigation Strategies of Air Ingress Accidents

2011 ◽  
Author(s):  
Chang H. Oh ◽  
Eung S. Kim ◽  
Hee C. NO ◽  
Nam Z. Cho
Keyword(s):  
Experimental Validation ◽  
Stratified Flow ◽  
Mitigation Strategies ◽  
Final Report ◽  
Graphite Oxidation ◽  
Flow Phenomena ◽  
Air Ingress

scholarly journals Study on Air Ingress Mitigation Methods in the Very High Temperature Gas Cooled Reactor (VHTR)

2011 ◽  
Author(s):  
Chang H. Oh ◽  
Eung S. Kim
Keyword(s):  
High Temperature ◽  
Root Cause ◽  
The Core ◽  
Graphite Oxidation ◽  
Simulation Results ◽  
Oxidation Damage ◽  
Air Ingress ◽  
Mitigation Methods ◽  
Very High ◽  
High Temperature Gas

An air-ingress accident followed by a pipe break is considered as a critical event for a very high temperature gas-cooled reactor (VHTR) safety. 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 depending on the accident scenario and the design. 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 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; (6) preventing fluid density gradient; (7) preventing fluid temperature gradient; (7) preventing high temperature. Based on the basic concepts listed above, various air-ingress mitigation methods are proposed in this study. Among them, the following one mitigation idea was extensively investigated using computational fluid dynamic codes (CFD) in terms of helium injection in the lower plenum. 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 was developed based on the GT-MHR 600MWt as a reference design. The simulation results showed that the helium replaces the air flow into the core and significantly reduces 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 influence of nuclear graphite oxidation on air ingress accident of HTR-PM

2017 ◽  
Vol 110 ◽  
pp. 1242-1248 ◽  
Author(s):  
Wei Xu ◽  
Jun Sun ◽  
Yanhua Zheng ◽  
Lei Shi
Keyword(s):  
Graphite Oxidation ◽  
Nuclear Graphite ◽  
Air Ingress

Numerical Simulation of Graphite Oxidation in HTGR

2012 ◽  
Author(s):  
Yao Wang ◽  
Peng Wang ◽  
Suyuan Yu
Keyword(s):  
Weight Loss ◽  
Reaction Rate ◽  
Calculation Model ◽  
Structure Design ◽  
Oxidation Degree ◽  
Reactor Graphite ◽  
Graphite Oxidation ◽  
Graphite Structure ◽  
Air Ingress ◽  
Time Accumulation

The oxidation of the bottom reflector graphite in HTR-10 of Tsinghua University during air ingress accident were studied numerically based on a theoretical calculation model, which considered the changes of chemical reaction rate and mass transfer speed with weight loss in oxidation process. The results showed that oxidation degree of the bottom reflector increased nearly exponentially with temperature; the oxidation corrosion quantity increased significantly over time accumulation; weight loss calculated by this model is larger than previous models, so reactor graphite structure design should be paid more attention.

Stratified flow-induced air-ingress accident assessment of the GAMMA code in HTGRs

2011 ◽  
Vol 241 (8) ◽  
pp. 3216-3223 ◽  
Author(s):  
Hyung Gon Jin ◽  
Hee Cheon No ◽  
Hyeon Il Kim
Keyword(s):  
Stratified Flow ◽  
Air Ingress

scholarly journals Nonuniform Oxidation on the Surface of Fuel Element in HTR

2016 ◽  
Vol 2016 ◽  
pp. 1-9
Author(s):  
Peng Liu ◽  
Yanhua Zheng ◽  
Wei Xu ◽  
Lei Shi
Keyword(s):  
Fuel Element ◽  
Computer Technology ◽  
Shape Function ◽  
Accident Analysis ◽  
Packed Beds ◽  
Sphere Surface ◽  
Graphite Oxidation ◽  
Air Ingress ◽  
Cfd Method ◽  
The Relationship

The graphite oxidation of fuel element has obtained high attention in air ingress accident analysis of high temperature gas-cooled reactor (HTR). The shape function, defined as the relationship between the maximum and the average of the oxidation, is an important factor to estimate the consequence of the accident. There are no detailed studies on the shape function currently except two experiments several decades ago. With the development of computer technology, CFD method is used in the numerical experiment about graphite oxidation in pebble bed of HTR in this paper. Structured packed beds are used in the calculation instead of random packed beds. The result shows the nonuniform distribution of oxidation on the sphere surface and the shape function in the condition of air ingress accident. Furthermore, the sensitive factors of shape function, such as temperature and Re number, are discussed in detail and the relationship between the shape function and sensitive factors is explained. According to the results in this paper, the shape function ranges from 1.05 to 4.7 under the condition of temperature varying from 600°C to 1200°C and Re varying from 16 to 1600.

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