• Nuclear Engineering and Technology
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• v.41 no.3
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• pp.279-286
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• 2009

Improving over a previous study [1], this paper provides a Monte Carlo method for the heat conduction analysis of problems with complicated geometry (such as a pebble with dispersed fuel particles). The method is based on the theoretical results of asymptotic analysis of neutron transport equation. The improved method uses an appropriate boundary layer correction (with extrapolation thickness) and a scaling factor, rendering the problem more diffusive and thus obtaining a heat conduction solution. Monte Carlo results are obtained for the randomly distributed fuel particles of a pebble, providing realistic temperature distributions (showing the kernel and graphite-matrix temperatures distinctly). The volumetric analytic solution commonly used in the literature is shown to predict lower temperatures than those of the Monte Carlo results provided in this paper.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2088-2093
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• 2008

In this study, flow field measurement of the Pebble Bed Reactor(PBR) for the High Temperature Gas-cooled Reactor(HTGR) was performed. Large number of pebbles in the core of PBR provides complicated flow channel. Due to the complicated geometries, numerical analysis has been intensively made rather than experimental observation. However, the justification of computational simulation by the experimental study is crucial to develop solid analysis of design method. In the present study, a wind tunnel installed with pebbles stacked was constructed and equipped with the Particle Image Velocimetry(PIV). We designed the system scaled up to realize the room temperature condition according to the similarity. The PIV observation gave us stagnation points, low speed region so that the suspected high temperature region can be identified. With the further supplementary experimental works, the present system may produce valuable data to justify the Computational Fluid Dynamics(CFD) simulation method.

• Journal of applied mathematics & informatics
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• v.42 no.1
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• pp.77-83
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• 2024

Chung defined a pebbling move on a graph G as the removal of two pebbles from one vertex and the addition of one pebble to an adjacent vertex. The monophonic pebbling number guarantees that a pebble can be shifted in the chordless and the longest path possible if there are any hurdles in the process of the supply chain. For a connected graph G a monophonic path between any two vertices x and y contains no chords. The monophonic pebbling number, µ(G), is the least positive integer n such that for any distribution of µ(G) pebbles it is possible to move on G allowing one pebble to be carried to any specified but arbitrary vertex using monophonic a path by a sequence of pebbling operations. The aim of this study is to find out the monophonic pebbling numbers of the sun graphs, (C_n × P₂) + K₁ graph, the spherical graph, the anti-prism graphs, and an n-crossed prism graph.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.339-352
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• 2023

Prediction of the time-related traits of pebble flow inside pebble-bed HTGRs is of great significance for reactor operation and design. In this work, an image-driven approach with the aid of a convolutional neural network (CNN) is proposed to predict the remaining time of initially loaded pebbles and the time interval of paired flow images of the pebble bed. Two types of strategies are put forward: one is adding FC layers to the classic classification CNN models and using regression training, and the other is CNN-based deep expectation (DEX) by regarding the time prediction as a deep classification task followed by softmax expected value refinements. The current dataset is obtained from the discrete element method (DEM) simulations. Results show that the CNN-aided models generally make satisfactory predictions on the remaining time with the determination coefficient larger than 0.99. Among these models, the VGG19+DEX performs the best and its CumScore (proportion of test set with prediction error within 0.5s) can reach 0.939. Besides, the remaining time of additional test sets and new cases can also be well predicted, indicating good generalization ability of the model. In the task of predicting the time interval of image pairs, the VGG19+DEX model has also generated satisfactory results. Particularly, the trained model, with promising generalization ability, has demonstrated great potential in accurately and instantaneously predicting the traits of interest, without the need for additional computational intensive DEM simulations. Nevertheless, the issues of data diversity and model optimization need to be improved to achieve the full potential of the CNN-aided prediction tool.

• Nuclear Engineering and Technology
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• v.18 no.2
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• pp.122-134
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• 1986

• Economic and Environmental Geology
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• v.29 no.1
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• pp.25-33
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• 1996

Stable isotopic ratios of the carbonate rocks and chemical compositions of the matrix of pebble bearing phyllitic rocks known as the Hwanggangri Formation, which are in hot debate on their origin such as tillite, debris flow and turbidite, were determined to interpret their depositional environment. Argillaceous matrix of the pebble bearing phyllitic rocks has a high content of CaO (av. 19.5%) and MgO (av. 8.3%), corresponding to calcareous sandy shale. No difference of chemical compositions including trace elements and REE is in the matrices between the Hwanggangri and the Kunjasan Formations. Carbonate rocks from the Okchon zone and outside of the zone range $-2.5{\sim}+6.1$‰ in ${\delta}^{13}C$ and $+5.8{\sim}+25.9$‰ in ${\delta}^{18}O$, indicating normal marine limestone. However, unusally $^{13}C$ enriched carbonate rocks might be deposited in the highly evaporated sedimentary basin. A wide variation of ${\delta}^{18}O$ values is responsible for metamorphism with a $^{18}O$ depleted meteoric water. Isotopic equilibrium temperatures by graphite-calcite geothermometer show a higher metamorphic temperature ($547{\sim}589^{\circ}C$) in the Okchon zone than those ($265{\sim}292^{\circ}C$) in the Samtaesan Formation of the Chosun group. Rhythmic alternation of relatively thin shale with thin limestone in the Kounri Formation is not cherty layer but thin limesilicate bed by metasomatic replacement. Judging from the isotopic and chemical compositions of the carbonate rocks and calcareous matrix of the pebble bearing phyllitic rocks, the Hwangganari Formation was deposited in the shallow marine environment favorable to debris flow.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.244-249
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• 2005

Flow distribution and pressure drop analysis for an inlet plenum of a Pebble Bed Modular Reactor (PBMR) have been performed using Computational Fluid Dynamics. Three-dimensional Navier-Stokes equations have been solved in conjunction with $k-{\epsilon}$ model as a turbulence closure. Non-uniformity in flow distribution is assessed for the reference case and parametric studies have been performed for rising channels diameter, Reynolds number and angle between the inlet ports. Also, two different shapes of the inlet plenum namely, rectangular shape and oval shape, have been analysed. The relative flow mal-distribution parameter shows that the flow distribution in the rising channels for the reference case is strongly non-uniform. As the rising channels diameter decreases, the uniformity in the flow distribution as well as the pressure drop inside the inlet plenum increases. Reynolds number is found to have no effect on the flow distribution in the rising channels for both the shapes of the inlet plenum. The increase in angle between the inlet ports makes the flow distribution in the rising channels more uniform.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.357-373
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• 2022

The high-temperature gas-cooled reactor pebble-bed module project is the first commercial Generation-IV NPP(Nuclear Power Plant) in China. A new joint is used for the vertical support of RPV(Reactor Pressure Vessel). The steel corbel is integrally embedded into the reactor-cabin wall through eight asymmetrically arranged pre-stressed high-strength bolts, achieving the different path transmission of shear force and moment. The vertical monotonic loading test of two specimens is conducted. The results show that the failure mode of the joint is bolt fracture. There is no prominent yield stage in the whole loading process. The stress of bolts is linearly distributed along the height of corbel at initial loading. As the load increases, the height of neutral axis of bolts gradually decreases. The upper and lower edges of the wall opening contact the corbel plate to restrict the rotation of the corbel. During the loading, the pre-stress of some bolts decreases. The increase of the pre-stress strength ratio of bolts has no noticeable effect on the structure stiffness, but it reduces the ultimate bearing capacity of the joint. A simplified calculation model for the elastic stage of the joint is established, and the estimation results are in good agreement with the experimental results.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.10a
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• pp.115-115
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• 2001

• Proceedings of the Korean Nuclear Society Conference
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• 2005.05a
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• pp.45-46
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• 2005