• Nuclear Engineering and Technology
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• 제16권4호
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• pp.202-216
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• 1984

Nodal method가 소격격자 해석방법의 하나로 정립됨으로써, 계산격자가 비교적 크더라도 각 격자의 평균출력분포를 정확히 계산할 수 있게 하는 균질화변수틀 찾는 방법이 중요하게 되었다. 본 연구에서는 simplified equivalence theory와 approximate node equivalence theory의 두가지 근사방법을 가압경수형 원자로 문제에 적응하여 시험하여 보았다. 균질화계산과 노심분석계산 방법으로서 analytic nodal method에 기초를 둔 ANM 코드를 개발하였다. 여러 균질화 방법외 정확성을 KTDD 코드에 의한 reference solution과 비교하여 본 결과, 균질화 계산은 핵연료영역에서는 영역별 핵연료집합체 계산으로, baffle과 reflector의 공존 격자영역은 이들을 포함하는 color set 계산으로 수행할 수 있음을 알았다. Approximate node equivalence theory에 입각해서 approximate homogenized cross-section들과 approximate discontinuity factor들의 균질화 변수를 사용하면 출력분포와 임계도가 각각 0.8%, 0,1% 오차 범위내에서 예측되었다.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1195-1208
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• 2019

This paper introduces a new two-step procedure for PWR depletion analyses. This procedure adopts the albedo-corrected parameterized equivalence constants (APEC) method to correct the lattice-based raw cross sections (XSs) and discontinuity factors (DFs) by accounting for neutron leakage. The intrinsic limitations of the conventional two-step methods are discussed by analyzing a 2-dimensional SMR with the commercial DeCART2D/MASTER code system. For a full-scope development of the APEC correction, the MASTER nodal code was modified so that the group constants can be corrected in the middle of a microscopic core depletion. The basic APEC methodology is described and color-set problems are defined to determine the APEC functions for burnup-dependent XS and DF corrections. Then the new two-step method was applied to depletion analyses of the SMR without thermal feedback, and its validity was evaluated in terms of being able to predict accurately the reactor eigenvalue and nodal power profile. In addition, four variants of the original SMR core were also analyzed for a further evaluation of the APEC-assisted depletion. In this work, several combinations of the burnup-dependent and -independent XS and DF corrections were also considered. The results show that the APEC method could enhance the nodal equivalence significantly with inexpensive additional costs.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제11B권4호
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• pp.137-145
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• 2001

The magnetic force calculation methods, the Maxwell＇s stress tensor method, virtual work method, and nodal force method, are reviewed and the equivalence of them are theoretically proved. The methods are applied to the magnetic force calculation of 2D linear and nonlinear problems, and 3D nonlinear problem. As the results, the convergence of the methods as the number of elements increases, accuracy of the methods, and integral path dependence of the methods are discussed. Finally some recommendations on the usage of the methods, including the determination of the integral path, are given.

• 한국해양공학회지
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• 제29권1호
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• pp.45-55
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• 2015

Because of the high stress concentration near the toe of a welded joint, the calculation of local stress using the finite element method which is relevant to the fatigue strength of the weld toe crack, is a challenging task. This is mainly caused by the sensitivity of finite element analysis, which usually occurs near the area of a dramatically changing stress field. This paper presents a novel numerical method through which a less mesh-sensitive local stress calculation can be achieved based on the 3D solid finite element, strictly sticking to the original definition of hot spot stress. In order to achieve the goal, a traction stress, defined at 0.5t and 1.5t away from the weld toe, was calculated using either a force-equivalent or work-equivalent approach, both of which are based on the internal nodal forces on the imaginary cut planes. In the force-equivalent approach, the traction stress on the imaginary cut plane was calculated using the simple force and moment equilibrium, whereas the equivalence of the work done by both the nodal forces and linearized traction stress was employed in the work-equivalent approach. In order to confirm the validity of the proposed method, five typical welded joints widely used in ships and offshore structures were analyzed using five different solid element types and four different mesh sizes. Finally, the performance of the proposed method was compared with that of the traditionally used surface stress extrapolation method. It turned out that the sensitivity of the hot spot stress for the analyzed typical welded joints obtained from the proposed method outperformed the traditional extrapolation method by far.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2230-2245
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• 2023

KANT (KAIST Advanced Nuclear Tachygraphy) is a PWR core simulator recently developed at Korea Advance Institute of Science and Technology, which solves three-dimensional steady-state and transient multigroup neutron diffusion equations under Cartesian geometries alongside the incorporation of thermal-hydraulics feedback effect for multi-physics calculation. It utilizes the standard Nodal Expansion Method (NEM) accelerated with various Coarse Mesh Finite Difference (CMFD) methods for neutronics calculation. For thermal-hydraulics (TH) calculation, a single-phase flow model and a one-dimensional cylindrical fuel rod heat conduction model are employed. The time-dependent neutronics and TH calculations are numerically solved through an implicit Euler scheme, where a detailed coupling strategy is presented in this paper alongside a description of nodal equivalence, macroscopic depletion, and pin power reconstruction. For validation of the steady, transient, and depletion calculation with pin power reconstruction capacity of KANT, solutions for various benchmark problems are presented. The IAEA 3-D PWR and 4-group KOEBERG problems were considered for the steady-state reactor benchmark problem. For transient calculations, LMW (Lagenbuch, Maurer and Werner) LWR and NEACRP 3-D PWR benchmarks were solved, where the latter problem includes thermal-hydraulics feedback. For macroscopic depletion with pin power reconstruction, a small PWR problem modified with KAIST benchmark model was solved. For validation of the multi-physics analysis capability of KANT concerning large-sized PWRs, the BEAVRS Cycle1 benchmark has been considered. It was found that KANT solutions are accurate and consistent compared to other published works.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(1)
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• pp.148-153
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• 1996

In this paper, an effective method for resolving difficulty resulting from the heterogeneity of the PWR baffle/reflector region is developed on the basis of the AFEN method. The essential difference of the new method from the conventional approach based on the equivalence theory is that the heterogeneous baffle/reflector is directly, without homogenization, considered as a node in nodal calculation Numerical results show that AFEN method with the new method can accurately predict both the multiplication factor and the power distribution of thermal reactors with baffle explicitly modeled.