• Nuclear Engineering and Technology
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• 제53권2호
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• pp.399-413
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• 2021

The solution of the time-dependent neutron diffusion equation can be approximated using quasi-static methods that factorise the neutronic flux as the product of a time dependent function times a shape function that depends both on space and time. A generalization of this technique is the updated modal method. This strategy assumes that the neutron flux can be decomposed into a sum of amplitudes multiplied by some shape functions. These functions, known as modes, come from the solution of the eigenvalue problems associated with the static neutron diffusion equation that are being updated along the transient. In previous works, the time step used to update the modes is set to a fixed value and this implies the need of using small time-steps to obtain accurate results and, consequently, a high computational cost. In this work, we propose the use of an adaptive control time-step that reduces automatically the time-step when the algorithm detects large errors and increases this value when it is not necessary to use small steps. Several strategies to compute the modes updating time step are proposed and their performance is tested for different transients in benchmark reactors with rectangular and hexagonal geometry.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.1-18
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• 2021

The criticality analysis of VVER-1000 mock-up benchmark experiments from the LR-0 research reactor operated by the Research Center Rez in the Czech Republic has been conducted with the MCS Monte Carlo code developed at the Computational Reactor Physics and Experiment laboratory of the Ulsan National Institute of Science and Technology. The main purpose of this work is to evaluate the newest ENDF/B-VIII.0 nuclear data library against the VVER-1000 mock-up integral experiments and to validate the criticality analysis capability of MCS for light water reactors with hexagonal fuel lattices. A preliminary code/code comparison between MCS and MCNP6 is first conducted to verify the suitability of MCS for the benchmark interpretation, then the validation against experimental data is performed with both ENDF/B-VII.1 and ENDF/B-VIII.0 libraries. The investigated experimental data comprises six experimental critical configurations and four experimental pin-by-pin power maps. The MCS and MCNP6 inputs used for the criticality analysis of the VVER-1000 mock-up are available as supplementary material of this article.

• Nuclear Engineering and Technology
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• 제55권2호
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• pp.756-768
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• 2023

Neutron transport calculations are extremely challenging due to the high computational cost of large and complex problems. A multilevel octree grid algorithm (MLTG) of discrete ordinates method was developed to improve the modeling accuracy and simulation efficiency on 3-D Cartesian grids. The Balakovo-3 VVER-1000 neutron dosimetry benchmark is calculated to verify and validate this numerical technique. A simplified S₂ synthetic acceleration is used in the MLTG calculation method to improve the convergence of the source iterations. For the triangularly arranged fuel pins, we adopt a source projection algorithm to generate pin-by-pin source distributions of hexagonal assemblies. MLTG provides accurate geometric modeling and flexible fixed source description at a lower cost than traditional Cartesian grids. The total number of meshes is reduced to 1.9 million from the initial 9.5 million for the Balakovo-3 model. The numerical comparisons show that the MLTG results are in satisfactory agreement with the conventional S_N method and experimental data, within the root-mean-square errors of about 4% and 10%, respectively. Compared to uniform fine meshing, approximately 70% of the computational cost can be saved using the MLTG algorithm for the Balakovo-3 computational model.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1885-1891
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• 2023

The present work aims to fabricate Na_1+xZr₂Si_xP_3-xO₁₂ compound at various calcination temperatures based on the zircon mineral. The fabricated compound was calcinated at 250, 500, and 1000℃. The effect of calcination temperature on the structure, crystal phase, and radiation shielding properties was studied for the fabricated compound. The X-ray diffraction diffractometer demonstrates that, the monoclinic crystal phase appeared at a calcination temperature of 250℃ and 500℃ is totally transformed to a high-symmetry hexagonal crystal phase under a calcination temperature of 1000℃. The radiation shielding capacity was also qualified for the fabricated compounds using the Monte Carlo N-Particle transport code in the g-photons energy interval between 15keV and 122keV. The impacts of calcination temperature on the g-ray shielding behavior were clarified in the present study, where the linear attenuation coefficient was enhanced by 218% at energy of 122keV, when the calcination temperature increased from 250 to 1000℃, respectively.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2728-2735
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• 2022

The research on the flow and heat transfer characteristics of lead bismuth(LBE) is significant for the thermal-hydraulic calculation, safety analysis and practical application of lead-based fast reactors(LFR). In this paper, a new CFD model is proposed to solve the thermal-hydraulic analysis of LBE. The model includes two parts: turbulent model and turbulent Prandtl, which are the important factors for LBE. In order to find the best model, the experiment data and design of 19-pin hexagonal rod bundle with spacer grid, undertaken at the Karlsruhe Liquid Metal Laboratory (KALLA) are used for CFD calculation. Furthermore, the turbulent model includes SST k - 𝜔 and k - 𝜀; the turbulent Prandtl includes Cheng-Tak and constant (Pr_t =1.5,2.0,2.5,3.0). Among them, the combination between SST k - 𝜔 and Cheng-Tak is more suitable for the experiment. But in the low Pe region, the deviation between the experiment data and CFD result is too much. The reason may be the inlet-effect and when Pe is in a low level, the number of molecular thermal diffusion occupies an absolute advantage, and the buoyancy will enhance. In order to test and verify versatility of the model, the NCCL performed by the Nuclear Thermal-hydraulic Laboratory (Nuthel) of Xi'an Jiao tong University is used for CFD to calculate. This paper provides two verification examples for the new universal model.

• Composites Research
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• 제36권6호
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• pp.454-460
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• 2023

최근 온실가스 배출량에 대한 규제가 높아지면서 IMO는 온실가스 배출량을 2050년까지 순 배출량 '0'을 목표로 하며 온실가스 규제를 강화하고 있다. 또한 조선/해양 분야에서는 추진 효율 향상, 구조 경량화와 같이 운항비 절감이 중요하다. 현재 이와 관련하여 구조 경량화와 고강성을 만족하기 위하여 3D 프린트 복합재료를 이용한 위상 최적화에 대한 연구가 수행되고 있다. 본 연구에서는 3D 프린트 복합재료를 활용하여 선박 구조물인 방향타의 내부에 3가지 위상 형상(육각형, 사각형, 삼각형)을 적용하였다. 방향타에 위상 형상을 적용하였을 때 적합한 형상을 알아보기 위해 구조해석을 수행했다. 선속 8 knots의 조건에서 타 각 0°에서 30°까지 10° 간격으로 CFD 해석을 수행하였으며, CFD 해석 결과를 바탕으로 하중조건을 설정하였다. 방향타 내부 위상 형상을 고려한 구조 해석 결과 삼각형, 사각형, 육각형 위상 형상 순으로 우수한 성능을 갖는 것을 확인하였다. 사각형 위상 형상을 가지는 방향타가 삼각형 위상 형상을 가지는 방향타 대비 78.5%의 무게를 가지며 경량화 측면을 고려하였을 때 사각형 위상 형상이 우수하다고 판단된다.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3907-3912
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• 2023

Radiation portal monitors (RPMs) installed at airports and harbors to prevent illicit trafficking of radioactive materials generally use large plastic scintillators. However, their energy resolution is poor and radionuclide identification is nearly unfeasible. In this study, to improve isotope identification, a RPM system based on a multi-array plastic scintillator and convolutional neural network (CNN) was evaluated by measuring the spectra of radioactive sources. A multi-array plastic scintillator comprising an assembly of 14 hexagonal scintillators was fabricated within an area of 50 × 100 cm². The energy spectra of ¹³⁷Cs, ⁶⁰Co, ²²⁶Ra, and ⁴K (KCl) were measured at speeds of 10-30 km/h, respectively, and an energy-weighted algorithm was applied. For the CNN, 700 and 300 spectral images were used as training and testing images, respectively. Compared to the conventional plastic scintillator, the multi-arrayed detector showed a high collection probability of the optical photons generated inside. A Compton maximum peak was observed for four moving radiation sources, and the CNN-based classification results showed that at least 70% was discriminated. Under the speed condition, the spectral fluctuations were higher than those under dwelling condition. However, the machine learning results demonstrated that a considerably high level of nuclide discrimination was possible under source movement conditions.

• 한국실내디자인학회논문집
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• 제19권6호
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• pp.47-58
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• 2010

Frank Lloyd Wright(1867-1959) was regarded as the pioneer of the modern architecture in the beginning and transition period of 20th century. His works have the pure shape form which have the deep relationship with the organic architecture. Wright told himself that the Froebel System had an influence on his works a lot. This study have researched about the three dimensional application of the Froebel System in his works with assembling and disassembling. Also the two dimensional application in the diagonal and circular plans are the one of the subjects here. The following conclusions are reached. First, The similar of the Wright's works and the Froebel System was the application of the similar principles rather than the copy of the method, which are the accent of the center, the composition of the part and whole, the understanding of the composition principle through the unit system and the unfolding of the crystal by rotation. Even thought the Wright's works have the triangle, square, hexagonal shape, the way of the expansion from the centered space was same. Also the space formed by the division of the center space, unfolds making the part and whole by overlap and continuation. The 2nd Froebel make space decided by the Net and Crystal Lattices which have the crystal characteristics by the rotation. The new geometric architecture, pinwheel, was created by this method. The application of the Froebel in the Wright's works have the several sets which are the 3th, 4th, 5th, 6th Froebels, 2nd, 7th Froebels and the 3th, 5th, 9th Froebels. The geometrical analysis of the square shape and the diagonal shape of the Wright's works was possible. The unfolding of the centered space can be found in the Guggenheim Museum using the analysis of the circular geometric of the 9th Froebel. The above study proves that the Froebel was not a mere tool for the basic shape training but also the main body of Wright's works which consists of the organic idea and philosophy of the space.