Effect of bed configuration on pebble flow uniformity and stagnation in the pebble bed reactor

In the pebble bed reactor, large number of fuel pebbles’ movement law and moving state can affect the reactor’s design, operation and safety directly. Therefore the pebble flow, which is based on the theory of particle streaming, is one of the most important research subjects of the pebble bed reactor engineering. The in-core pebble flow is a very slow particle flow (or called quasi-static particle flow), which is very different from the usual particle motion. How to accurately describe the characteristics of in-core pebble flow is a central issue for this subject. Due to the presence of random flow, the cross-mixing phenomenon will occur inevitably. In the present paper, the mixing phenomenon of pebble flow is generalized on the basis of experiment results. The pebble flow cross-mixing probability serves as the parameter which describes both the regularity and the randomness of pebble flow. The results are provided in the form of diagrammatic presentation.

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Experimental and Numerical Study of the Movement Mechanism and Characteristics of the Quasi-Static Pebble Flow

Volume 2: Plant Systems, Construction, Structures and Components; Next Generation Reactors and Advanced Reactors ◽

10.1115/icone21-15371 ◽

2013 ◽

Author(s):

Xinlong Jia ◽

Nan Gui ◽

Xingtuan Yang ◽

Jiyuan Tu ◽

Shengyao Jiang

Keyword(s):

Numerical Study ◽

Mixing Zone ◽

Force Analysis ◽

Particle Movement ◽

Pebble Bed ◽

Dem Simulation ◽

Pebble Bed Reactor ◽

Pebble Bed Reactors ◽

Movement Mechanism ◽

Pebble Flow

Quasi-static pebble flow, or so-called the very slow pebble flow, in a pebble bed reactor, with evident randomicity and dispersibility, is extremely complex. Improving the knowledge of the movement mechanism of quasi-static pebble flow can be beneficial to the safety of the pebble bed reactor. This study utilizes a phenomenological method and a discrete element method to investigate the interface features of two regions composed of differently colored pebbles. A pseudo-two dimensional experimental setup is established to facilitate the observation of movement of pebble. Then, the DEM simulation is carried out to analyze the further details of particle movement mechanism. To some extent, the two methods are closely related and mutually confirmed. In this study, some special phenomena are observed, such as the non-uniformity, mixing zone, stagnant zones, the propagation of voids, slow flow zone, etc. Moreover, some basic issues on the movement mechanism and characteristics of quasi-static pebble flow are discussed, e.g. the interpretation of force analysis inside the pebble packing, propagation and distribution of voids, formation of equilibrium arches, the effects of stagnant zone on the flow field, and so on. These characteristics of the quasi-static pebble flow are very different from the continuous flow, and the understanding of these characteristics is very helpful for the design and analysis of pebble bed reactors.

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Mechanism analysis of quasi-static dense pebble flow in pebble bed reactor using phenomenological approach

Nuclear Engineering and Design ◽

10.1016/j.nucengdes.2012.06.011 ◽

2012 ◽

Vol 250 ◽

pp. 247-259 ◽

Cited By ~ 38

Author(s):

X.T. Yang ◽

W.P. Hu ◽

S.Y. Jiang ◽

K.K.L. Wong ◽

J.Y. Tu

Keyword(s):

Phenomenological Approach ◽

Mechanism Analysis ◽

Pebble Bed ◽

Pebble Bed Reactor ◽

Pebble Flow

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Preliminary neutronic study on Pu-based OTTO cycle pebble bed reactor

Kerntechnik ◽

10.3139/124.110793 ◽

2017 ◽

Vol 82 (6) ◽

pp. 643-647 ◽

Cited By ~ 4

Author(s):

T. Setiadipura ◽

D. Irwanto ◽

Zuhair

Keyword(s):

Otto Cycle ◽

Pebble Bed ◽

Pebble Bed Reactor

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Analysis of the impact of random summing on passive assay of pebble bed reactor fuel using gamma-ray spectrometry

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment ◽

10.1016/j.nima.2007.04.064 ◽

2007 ◽

Vol 579 (1) ◽

pp. 297-300

Author(s):

J. Chen ◽

A.I. Hawari

Keyword(s):

Gamma Ray ◽

Reactor Fuel ◽

Gamma Ray Spectrometry ◽

Pebble Bed ◽

Pebble Bed Reactor ◽

The Impact

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A Safety Re-Evaluation of the AVR Pebble Bed Reactor Operation and Its Consequences for Future HTR Concepts

Fourth International Topical Meeting on High Temperature Reactor Technology, Volume 2 ◽

10.1115/htr2008-58336 ◽

2008 ◽

Cited By ~ 15

Author(s):

Rainer Moormann

Keyword(s):

Fission Product ◽

End Of Life ◽

Fission Products ◽

Normal Operation ◽

Primary Circuit ◽

Pebble Bed ◽

Pebble Bed Reactor ◽

Hot Gas ◽

Design Basis ◽

Gas Tight

The AVR pebble bed reactor (46 MWth) was operated 1967–1988 at coolant outlet temperatures up to 990°C. Also because of a lack of other experience the AVR operation is a basis for future HTRs. This paper deals with insufficiently published unresolved safety problems of AVR and of pebble bed HTRs. The AVR primary circuit is heavily contaminated with dust bound and mobile metallic fission products (Sr-90, Cs-137) which create problems in current dismantling. The evaluation of fission product deposition experiments indicates that the end of life contamination reached several percent of a single core inventory. A re-evaluation of the AVR contamination is performed in order to quantify consequences for future HTRs: The AVR contamination was mainly caused by inadmissible high core temperatures, and not — as presumed in the past — by inadequate fuel quality only. The high AVR core temperatures were detected not earlier than one year before final AVR shut-down, because a pebble bed core cannot be equipped with instruments. The maximum core temperatures were more than 200 K higher than precalculated. Further, azimuthal temperature differences at the active core margin were observed, as unpredictable hot gas currents with temperatures > 1100°C. Despite of remarkable effort these problems are not yet understood. Having the black box character of the AVR core in mind it remains uncertain whether convincing explanations can be found without major experimental R&D. After detection of the inadmissible core temperatures, the AVR hot gas temperatures were strongly reduced for safety reasons. Metallic fission products diffuse in fuel kernel, coatings and graphite and their break through takes place in long term normal operation, if fission product specific temperature limits are exceeded. This is an unresolved weak point of HTRs in contrast to other reactors and is particularly problematic in pebble bed systems with their large dust content. Another disadvantage, responsible for the pronounced AVR contamination, lies in the fact that activity released from fuel elements is distributed in HTRs all over the coolant circuit surfaces and on graphitic dust and accumulates there. Consequences of AVR experience on future reactors are discussed. As long as pebble bed intrinsic reasons for the high AVR temperatures cannot be excluded they have to be conservatively considered in operation and design basis accidents. For an HTR of 400 MWth, 900°C hot gas temperature, modern fuel and 32 fpy the contaminations are expected to approach at least the same order as in AVR end of life. This creates major problems in design basis accidents, for maintenance and dismantling. Application of German dose criteria on advanced pebble bed reactors leads to the conclusion that a pebble bed HTR needs a gas tight containment even if inadmissible high temperatures as observed in AVR are not considered. However, a gas tight containment does not diminish the consequences of the primary circuit contamination on maintenance and dismantling. Thus complementary measures are discussed. A reduction of demands on future reactors (hot gas temperatures, fuel burn-up) is one option; another one is an elaborate R&D program for solution of unresolved problems related to operation and design basis accidents. These problems are listed in the paper.

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Modeling of Fuel Elements Cycling System in Pebble Bed Reactor Based on Timed Places Control Petri Nets

Energy and Power Engineering ◽

10.4236/epe.2013.54b098 ◽

2013 ◽

Vol 05 (04) ◽

pp. 510-516

Author(s):

Hongbing Liu ◽

Peng Shen ◽

Dong Du ◽

Xin Wang ◽

Haiquan Zhang

Keyword(s):

Petri Nets ◽

Pebble Bed ◽

Pebble Bed Reactor ◽

Cycling System ◽

Fuel Elements

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Physical Analysis of the Initial Core and Running-In Phase for Pebble-Bed Reactor HTR-PM

Science and Technology of Nuclear Installations ◽

10.1155/2017/8918424 ◽

2017 ◽

Vol 2017 ◽

pp. 1-6

Author(s):

Jingyu Zhang ◽

Fu Li ◽

Yuliang Sun

Keyword(s):

Physical Parameters ◽

Physical Analysis ◽

Fuel Management ◽

Fuel Temperature ◽

Pebble Bed ◽

Pebble Bed Reactor ◽

Pebble Bed Reactors ◽

Management Scheme ◽

Typical Scheme ◽

Scheme Evaluation

The pebble-bed reactor HTR-PM is being built in China and is planned to be critical in one or two years. At present, one emphasis of engineering design is to determine the fuel management scheme of the initial core and running-in phase. There are many possible schemes, and many factors need to be considered in the process of scheme evaluation and analysis. Based on the experience from the constructed or designed pebble-bed reactors, the fuel enrichment and the ratio of fuel spheres to graphite spheres are important. In this paper, some relevant physical considerations of the initial core and running-in phase of HTR-PM are given. Then a typical scheme of the initial core and running-in phase is proposed and simulated with VSOP code, and some key physical parameters, such as the maximum power per fuel sphere, the maximum fuel temperature, the refueling rate, and the discharge burnup, are calculated. Results of the physical parameters all satisfy the relevant design requirements, which means the proposed scheme is safe and reliable and can provide support for the fuel management of HTR-PM in the future.

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