CFD Calculations of Natural Circulation in a High Temperature Gas Reactor Following Pressurized Circulator Shutdown

Multiple Paths ◽

Core Depth ◽

It is anticipated that in the event of the failure of the gas circulator in a prismatic gas-cooled very high temperature gas reactor (VHTR), there will develop natural convection currents in the core with the helium coolant. It is of interest to know the amount of energy transported by the helium plumes impinging on material surfaces in the upper plenum. Additionally, in the event of a rupture in an intermediate heat exchanger which contains water, it will be of great interest to understand the potential for free convection as it will convect water vapor, which will have detrimental effects on the core graphite. It is well known that heating a gas causes it to rise because the buoyant forces overcome gravitational forces. In the reactor, there will be hot walls that can provide heating to the helium, though the temperature of the coolant channel walls will be a function of the core depth, which makes the presence of free convection dependent on the particular conditions. In addition to the uncertainty of whether there will be sufficient buoyant forces to drive free convection, there is uncertainty as to what paths the helium will take in forming natural circulation loops. Computational fluid dynamic (CFD) calculations are reported herein that demonstrate the potential for the occurrence of natural circulation considering the core itself along with upper and lower plena and including flow paths in the gaps between the graphite blocks that allow bypass flow to occur. It is shown that multiple paths are possible for circulating flow.

Conceptual Core Design Study of the Very High Temperature Gas-Cooled Reactor (VHTR) Upgrading the Core Performance by Using Multihole-Type Fuel

Transactions of the Atomic Energy Society of Japan ◽

10.3327/taesj.j07.005 ◽

2008 ◽

Vol 7 (1) ◽

pp. 32-43 ◽

Author(s):

Kazutaka OHASHI ◽

Tetsuo NISHIHARA ◽

Kazuhiko KUNITOMI ◽

Masaaki NAKANO ◽

Yujiro TAZAWA ◽

...

Keyword(s):

High Temperature ◽

Design Study ◽

The Core ◽

Conceptual Core ◽

Very High ◽

Type Fuel ◽

Fourth International Topical Meeting on High Temperature Reactor Technology, Volume 1 ◽

Active Chemistry Control for Coolant Helium Applying High-Temperature Gas-Cooled Reactors

10.1115/htr2008-58096 ◽

2008 ◽

Author(s):

Nariaki Sakaba ◽

Shimpei Hamamoto ◽

Yoichi Takeda

Keyword(s):

Heat Transfer ◽

High Temperature ◽

Heat Exchanger ◽

Chemical Composition ◽

Structural Integrity ◽

Carbon Deposition ◽

Control Technology ◽

Equilibrium Study ◽

Lifetime extension of high-temperature equipment such as the intermediate heat exchanger of high-temperature gas-cooled reactors (HTGRs) is important from the economical point of view. Since the replacing cost will cause the increasing of the running cost, it is important to reduce replacing times of the high-cost primary equipment during assumed reactor lifetime. In the past, helium chemistry has been controlled by the passive chemistry control technology in which chemical impurity in the coolant helium is removed as low concentration as possible, as does Japan’s HTTR. Although the lifetime of high-temperature equipment almost depends upon the chemistry conditions in the coolant helium, it is necessary to establish an active chemistry control technology to maintain adequate chemical conditions. In this study, carbon deposition which could occur at the surface of the heat transfer tubes of the intermediate heat exchanger and decarburization of the high-temperature material of Hastelloy XR used at the heat transfer tubes were evaluated by referring the actual chemistry data obtained by the HTTR. The chemical equilibrium study contributed to clarify the algorism of the chemistry behaviours to be controlled. The created algorism is planned to be added to the instrumentation system of the helium purification systems. In addition, the chemical composition to be maintained during the reactor operation was proposed by evaluating not only core graphite oxidation but also carbon deposition and decarburization. It was identified when the chemical composition could not keep adequately, injection of 10 ppm carbon monoxide could effectively control the chemical composition to the designated stable area where the high-temperature materials could keep their structural integrity beyond the assumed duration. The proposed active chemistry control technology is expected to contribute economically to the purification systems of the future very high-temperature reactors.

Air Ingress Analysis: Computational Fluid Dynamics Models

2010 14th International Heat Transfer Conference, Volume 7 ◽

10.1115/ihtc14-23083 ◽

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.

Development of Plate-Fin Heat Exchanger for Intermediate Heat Exchanger of High-Temperature Gas Cooled Reactor

Transactions of the Atomic Energy Society of Japan ◽

10.3327/taesj.j09.017 ◽

2010 ◽

Vol 9 (2) ◽

pp. 219-232 ◽

Cited By ~ 2

Author(s):

Yorikata MIZOKAMI ◽

Toshihide IGARI ◽

Keiichi NAKASHIMA ◽

Fumiko KAWASHIMA ◽

Noriyuki SAKAKIBARA ◽

...

Keyword(s):

High Temperature ◽

Heat Exchanger ◽

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

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44417 ◽

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 ◽

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.

Volume 2: Structural Integrity; Safety and Security; Advanced Applications of Nuclear Technology; Balance of Plant for Nuclear Applications ◽

Allegro: The European Gas Fast Reactor Demonstrator Project

10.1115/icone17-75326 ◽

2009 ◽

Author(s):

Christian Poette ◽

Vale´rie Brun-Magaud ◽

Franck Morin ◽

Jean-Franc¸ois Pignatel ◽

Richard Stainsby ◽

...

Keyword(s):

High Temperature ◽

Fast Reactor ◽

Heat Removal ◽

Reactor System ◽

Large Temperature ◽

The Core ◽

Current Design ◽

Ceramic Fuel ◽

High Temperature Components

In the Gas Fast Reactor development plan, ALLEGRO is the first necessary step towards the electricity generating prototype GFR. The ALLEGRO start of operation is planned by 2020. This needs to define all design options in 2010 and to start detailed design studies in 2013. ALLEGRO is a low power Gas Cooled Fast Reactor studied in the European framework. It is a loop type, non electricity generating reactor. Its power is about 80 MW. Several objectives are assigned to ALLEGRO. At first, it will demonstrate the viability of the GFR reactor system, no reactor of this type having been built in the past. Most of the GFR architecture, materials and components features are considered at reduced scale in ALLEGRO, excluding the energy conversion system. ALLEGRO will rely on the same safety options as the reactor system. In addition, the ALLEGRO core will allow the progressive qualification of the GFR ceramic fuel, with the possibility to load some ceramic carbide or nitride sub-assemblies in a first MOX core, with SiC/SiCf cladding and wrappers. When such unit test will be considered convincing enough, the diagrid and circuits are designed to accept full high temperature ceramic cores. The core neutrons can also be used to irradiate structural materials with fast neutron spectrum and in a large temperature range. The core can also include innovative irradiation fuel devices (samples or full bundles) for other reactor systems. Finally, branches on the main intermediate heat exchanger will allow the testing and validation of high temperature components and processes. The pre-conceptual design of ALLEGRO is shared between European partners through the GCFR 6th R&D Framework Program. After recalling the role of the European partners in the different design and safety tasks, the paper will give an overview of the current design with recent progresses in various areas like: • Core design and neutron performances, • The design of experimental advanced ceramic GFR fuel sub-assemblies included in several locations of the MOX core, • Fuel handling principles and solutions, • System design and global reactor architecture which is largely influenced by the Decay Heat Removal strategy (DHR) for depressurized accidents.

Source Term Analysis of the Irradiated Graphite in the Core of HTR-10

Science and Technology of Nuclear Installations ◽

10.1155/2017/2614890 ◽

2017 ◽

Vol 2017 ◽

pp. 1-6 ◽

Cited By ~ 5

Author(s):

Xuegang Liu ◽

Xin Huang ◽

Feng Xie ◽

Fuming Jia ◽

Xiaogui Feng ◽

...

Keyword(s):

High Temperature ◽

Source Term ◽

Pressurized Water Reactor ◽

Sample Collection ◽

Analytical Methodology ◽

Pressurized Water ◽

The Core ◽

Irradiated Graphite ◽

Term Analysis ◽

The high temperature gas-cooled reactor (HTGR) has potential utilization due to its featured characteristics such as inherent safety and wide diversity of utilization. One distinct difference between HTGR and traditional pressurized water reactor (PWR) is the large inventory of graphite in the core acting as reflector, moderator, or structure materials. Some radionuclides will be generated in graphite during the period of irradiation, which play significant roles in reactor safety, environmental release, waste disposal, and so forth. Based on the actual operation of the 10 MW pebble bed high temperature gas-cooled reactor (HTR-10) in Tsinghua University, China, an experimental study on source term analysis of the irradiated graphite has been done. An irradiated graphite sphere was randomly collected from the core of HTR-10 as sample in this study. This paper focuses on the analytical procedure and the establishment of the analytical methodology, including the sample collection, graphite sample preparation, and analytical parameters. The results reveal that the Co-60, Cs-137, Eu-152, and Eu-154 are the major γ contributors, while H-3 and C-14 are the dominating β emitting nuclides in postirradiation graphite material of HTR-10. The distribution profiles of the above four nuclides are also presented.

Oxide Layers Mechanical Properties for Ni Base Alloys in HTR Environment

Materials Science Forum ◽

10.4028/www.scientific.net/msf.595-598.501 ◽

2008 ◽

Vol 595-598 ◽

pp. 501-509

Author(s):

Damien Kaczorowski ◽

Gouenou Girardin ◽

S. Chamousset

Keyword(s):

Mechanical Properties ◽

High Temperature ◽

Heat Exchanger ◽

Tensile Test ◽

Oxide Layers ◽

Nickel Base ◽

Very High ◽

Nickel base alloys 617 and 230 are promising candidates for the Intermediate Heat eXchanger (IHX) of GenIV Very High Temperature gas cooled Reactors. The capability to maintain an oxide layer as an efficient barrier against corrosion under mechanical loading is investigated through SEM in situ tensile test. The mechanical properties of external oxide layers are so compared between the two alloys. Cracks and spallation are observed. Few differences could be observed between these two alloys when pre oxidized in impure helium.