scholarly journals Analysis of the Xenon Feedback on the Core Dynamics of High-Temperature Reactors During Heat Removal Transients Without Reactor Shutdown

1984 ◽  
Vol 64 (1) ◽  
pp. 5-13 ◽  
Author(s):  
Rahim Nabbi
Keyword(s):  
High Temperature ◽  
Heat Removal ◽  
The Core ◽  
Core Dynamics ◽  
Reactor Shutdown ◽  
High Temperature Reactors

Allegro: The European Gas Fast Reactor Demonstrator Project

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 ◽  
Intermediate Heat Exchanger ◽  
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.

Assessment of surface reactivity of thorium oxide in conditions close to chemical equilibrium by isotope exchange 229Th/232Th method

2017 ◽  
Vol 105 (6) ◽  
Author(s):  
Tomo Suzuki-Muresan ◽  
Katy Perrigaud ◽  
Johan Vandenborre ◽  
Solange Ribet ◽  
Inai Takamasa ◽  
...  
Keyword(s):  
High Temperature ◽  
Chemical Equilibrium ◽  
Isotope Exchange ◽  
Surface Reactivity ◽  
Sequential Order ◽  
Thorium Oxide ◽  
Isotope Tracer ◽  
The Core ◽  
High Temperature Reactors

AbstractThis work aims to assess the solubility and the surface reactivity of crystallized thorium at pH 3.0 in presence of three types of solids: synthesized powder at 1300°C, crushed kernel, and intact kernel. In this study, the kernel is composed by the core solid from high temperature reactors (HTR) sphere particles. The originality of this work consisted in following in a sequential order the kinetic of dissolution, the surface reactivity in presence of isotope tracer

scholarly journals Extension of lifespan of graphite in fuel blocks of high-temperature gas-cooled reactors as the resource for ensuring design values of nuclear fuel burn-up

2019 ◽  
Vol 5 (4) ◽  
pp. 289-295 ◽  
Author(s):  
Olga I. Bulakh ◽  
Oleg K. Kostylev ◽  
Vladimir N. Nesterov ◽  
Eldar K. Cherdizov
Keyword(s):  
High Temperature ◽  
Nuclear Fuel ◽  
Alternative Energy ◽  
Fuel Cycle ◽  
Reactor Core ◽  
Calculated Data ◽  
Fuel Burnup ◽  
The Core ◽  
High Temperature Reactors ◽  
High Temperature Gas

High-temperature gas-cooled reactor (HTGR) is one of promising candidates for new generation of nuclear power reactors. This type of nuclear reactor is characterized with the following principal features: highly efficient generation of electricity (thermal efficiency of about 50%); the use of high-temperature heat in different production processes; reactor core self-protection properties; practical exclusion of reactor core meltdown in case of accidents; the possibility of implementation of various nuclear fuel cycle options; reduced radiation and thermal effects on the environment, forecasted acceptability of financial performance with respect to cost of electricity as compared with alternative energy sources. The range of output coolant temperatures in high-temperature reactors within the limits of 750–950 °C predetermines the use of graphite as the structural material of the reactor core and helium as the inert coolant. Application of graphite ensures higher heat capacity of the reactor core and its practical non-meltability. Residence time of reactor graphite depends on the critical value of fluence of damaging neutrons (neutrons with energies above 180 keV). In its turn, the value of critical neutron fluence is determined by the irradiation temperature and flux density of accompanying gamma-radiation. The values of critical fluence for graphite decrease within high-temperature region of 800–1000 °C to 1·1022 – 2·1021 cm–2, respectively. The compactness of the core results in the increase of the fracture of damaging neutrons in the total flux. These circumstances predetermine relatively low values of lifespan of graphite structures in high-temperature reactors. Design features and operational parameters of GT-MHR high-temperature gas-cooled reactor are described in the present paper. Results of neutronics calculations allowing determining the values of damaging neutron flux, nuclear fuel burnup and expired lifespan of graphite of fuel blocks were obtained. The mismatch between positions of the maxima in the dependences of fuel burnup and exhausted lifespan of graphite in fuel blocks along the core height is demonstrated. The map and methodology for re-shuffling fuel blocks of the GT-MHR reactor core were developed as the result of analysis of the calculated data for ensuring the matching between the design value of the fuel burnup and expected total graphite lifespan.

Investigation of the Modified RELAP5 MOD 3.2 Capability to Simulate the Transients of the Fluoride-Salt High-Temperature Reactors

2016 ◽  
Author(s):  
Limin Liu ◽  
Qiqi Yan ◽  
Dalin Zhang ◽  
Suizheng Qiu ◽  
G. H. Su
Keyword(s):  
High Temperature ◽  
Physical Properties ◽  
Heat Removal ◽  
Forced Flow ◽  
Fluoride Salt ◽  
High Temperature Reactors ◽  
Temperature Liquid ◽  
Liquid Salts ◽  
Fluoride Salts ◽  
Thermo Physical Properties

Fluoride-salt-cooled high-temperature reactors (FHRs) are a new concept that uses solid fuel and employs high temperature liquid salts as both primary and secondary side working fluids. The thermo-physical properties of the fluoride salts and specific heat transfer correlations have been implemented into the RELAP5-MOD3.2 code to enable the code to simulate the transient thermal-hydraulic response in accidents. The thermo-physical properties calculated by the modified code have been benchmarked versus the experimental data. The results of thermal-hydraulic responses of the PB-AHTR in the steady state and simple loss of forced flow from the publications using the RELAP5-3D are used to verify the ability of the modified RELAP5-MOD3.2 to simulate the transients of the FHRs. The code can predict the variations of the thermal-hydraulic parameters well whereas some results may distinguish from that calculated by the RELAP5-3D. The unprotected loss of flow is analyzed by the modified code, indicating that the passive residual heat removal system can mitigate the consequence of the accidents.

Air Ingress Accident in a High Temperature Reactor with Prismatic Fuel

2006 ◽  
Author(s):  
H. Haque ◽  
G. Brinkmann
Keyword(s):  
High Temperature ◽  
Air Flow ◽  
Heat Removal ◽  
Safety Behavior ◽  
Potential Threat ◽  
Reaction Heat ◽  
The Core ◽  
Hypothetical Scenario ◽  
Production Of Hydrogen ◽  
Air Ingress

In this paper, the safety behavior of the new generation high temperature reactors (HTRs) with prismatic fuels during air ingress accident conditions has been investigated. These reactors conceived primarily for the production of hydrogen, are characterized by their inherent safety features with respect to passive decay heat removal through conduction, radiation and natural convection. Air ingress is an HTR specific event. The potential threat posed by air ingress lies in the chemical reaction of oxygen with hot graphite at a temperature above 500 °C leading to reaction heat and graphite corrosion. A substantial amount of graphite burn-off can take place only if sufficient amount of air enters into the core. In order to better assess the phenomena of air ingress into the reactor, it is postulated that breaks are present above and below the reactor core and that unobstructed ingress of air through them is possible. It is obvious that the air ingress incident has to be preceded by a depressurization accident. For this hypothetical scenario the maximum possible air flow rate through the core resulting solely from the pressure losses in the core is determined as a function of the break cross sections exposed above and below the core. This paper demonstrates the thermal behavior of the ANTARES reactor (operating inlet/outlet temperatures 450/850 °C) for various air flow rates with respect to graphite burn-off and maximum temperatures of fuel and bottom reflector region. It indicates the limiting time at which the graphite layer of fuel will be completely burnt-off and the pellets exposed.

Exsolution and inversion in pigeonite from the Whin Sill, Northern England

1978 ◽  
Vol 36 (1) ◽  
pp. 474-475
Author(s):  
P.P.K. Smith
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Homogeneous Nucleation ◽  
Silicate Mineral ◽  
Antiphase Boundaries ◽  
Two Phase ◽  
Primitive Form ◽  
The Core ◽  
Nucleation Mechanisms ◽  
And Inversion

Grains of pigeonite, a calcium-poor silicate mineral of the pyroxene group, from the Whin Sill dolerite have been ion-thinned and examined by TEM. The pigeonite is strongly zoned chemically from the composition Wo8En64FS28 in the core to Wo13En34FS53 at the rim. Two phase transformations have occurred during the cooling of this pigeonite:- exsolution of augite, a more calcic pyroxene, and inversion of the pigeonite from the high- temperature C face-centred form to the low-temperature primitive form, with the formation of antiphase boundaries (APB's). Different sequences of these exsolution and inversion reactions, together with different nucleation mechanisms of the augite, have created three distinct microstructures depending on the position in the grain.In the core of the grains small platelets of augite about 0.02μm thick have farmed parallel to the (001) plane (Fig. 1). These are thought to have exsolved by homogeneous nucleation. Subsequently the inversion of the pigeonite has led to the creation of APB's.

Trends in the development of flexible thermal protection systems for modern aircraft

2020 ◽  
pp. 10-21
Author(s):  
V. G. Babashov ◽  
◽  
N. M. Varrik ◽  
Keyword(s):  
High Temperature ◽  
Thermal Protection ◽  
Heat Removal ◽  
Operating Conditions ◽  
Passive Protection ◽  
Thermal Protection Systems ◽  
Heat Protection ◽  
Protection Systems ◽  
Protected Surface ◽  
Flexible Panels

The emergence of new types of space and aviation technology necessitates the development of new types of thermal protection systems capable of operating at high temperature and long operating times. There are several types of thermal protection systems for different operating conditions: active thermal protection systems using forced supply of coolant to the protected surface, passive thermal protection systems using materials with low thermal conductivity without additional heat removal, high-temperature systems, which are simultaneously elements of the bearing structure and provide thermal protection, ablation materials. Heat protection systems in the form of rigid tiles and flexible panels, felt and mats are most common kind of heat protecting systems. This article examines the trends of development of flexible reusable heat protection systems intended for passive protection of aircraft structural structures from overheating.

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