• Nuclear Engineering and Technology
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• 제29권4호
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• pp.320-326
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• 1997

The nuclide transport in the one-dimensional porous medium is considered as a first step in developing a decay chain transport in multidimensional inhomogeneous media. A method of solving conventional advection-dispersion equation with decay chain of arbitrary length by using the method of characteristics (MOC) is introduced. In specific cases where the advection are dominant rather than dispersion, the method is known to be useful : one of the most distinctive advantages in applying the model is that the MU minimizes the numerical dispersion, which is distinguished in such common numerical schemes as finite element method and finite difference method. The suggested model is considered to be effective through several illustrations for the case that decay chain of arbitrary length is involved during transport which is difficult to solve by standard numerical solutions if the medium becomes more complicated.

• Nuclear Engineering and Technology
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• 제26권2호
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• pp.277-284
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• 1994

폐기물 고화체로부터 주위의 Near-field로의 단일 핵종의 이동에는 많은 연구가 수행되고 있으나, 방사성 핵종 사슬의 이동에 관한 연구는 매우 제한되어 있다. 본 논문에서는 조화 유출되는 방사성 핵종 사슬의 이동을 분석하고, 유한 크기의 다공성 매질에서의 일반적인 비순환 해석해를 제시하였다. 또한 이해를 사용후 핵연료에서 가장 중요한 핵종사슬인 $^{234}$ U$\longrightarrow$$^{230}$ Th$\longrightarrow$$^{226}$ Ra 에 적용하여 보았다. 본 연구는 방사성 폐기물의 처분장 성능평가에 유용하고 중요하게 사용될 것이다.

• Nuclear Engineering and Technology
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• 제26권4호
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• pp.453-460
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• 1994

암반(Porous Rock Matrix)과 균열(fracture)에서 일차원의 이동 방정식(Migration Equation)을 3-Member Decay Chain까지 화장하고, Laplace Transform을 이용하여 초기조건이 Delta Function과 Bateman Equation인 각각에 대해 해석해를 구한다. 그 해를 이용하여 Actinide Chain 중 4n＋1과 4n＋2 Chain에서 선택된 Np$^{241}$-U$^{233}$ -Th$^{229}$ 와 U$^{234}$ -Th$^{230}$ -Ra$^{226}$ Chain의 각 핵종들의 균열에서의 농도를 상대농도로 나타낸다. 이핵종들의 지연계수(Retardation Coefficient)는 화강암에 대한 것을 사용하여 균열에서의 농도 변화를 볼 수 있다. 본 연구에 의한 결과로는 U$^{233}$ , Th$^{229}$ , Th$^{230}$ Ra$^{226}$ 같은 핵종들은 비록 초기 inventory에는 작은 양일지라도 균열과 암반에서 모핵종의 붕괴(decay)에 의해 생기므로써 처분장으로부터 먼 거리에서는 중요한 핵종이 된다는 것을 알 수 있다.

• Nuclear Engineering and Technology
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• 제34권3호
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• pp.218-231
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• 2002

Using a three-dimensional numerical code, B3R developed for nuclide transport of an arbitrary length of decay chain in the buffer between the canister and adjacent rock in a high- level radioactive waste repository by adopting a finite difference method utilizing the control- volume scheme, some illustrative calculations have been done. A linear sorption isotherm, nuclide transport due to diffusion in the buffer and the rock matrix, and advection and dispersion along thin rigid parallel fractures existing in a saturated porous rock matrix as well as diffusion through the fracture wall into the matrix is assumed. In such kind of repository, buffer and rock matrix are known to be important physico-chemical harriers in nuclide retardation. To show effects of buffer and rock matrix on nuclide transport in HLW repository and also to demonstrate usefulness of B3R, several cases of breakthrough curves as well as three- dimensional plots of concentration isopleths associated with these two barriers are introduced for a typical case of decay chain of $^{234}$ Ulongrightarrow$^{230}$ Thlongrightarrow$^{226}$ Ra, which is the most important chain as far as the human environment is concerned.

• 대한수학회지
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• 제38권4호
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• pp.723-761
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• 2001

The objects of this paper are to formulated a model for the transport of a chain of radioactive waste products in a fractured porous medium, to devise an effective and efficient numerical method for approximating the solution of the model, and to demonstrated the convergence of the numerical method. The formulation begins from a model in an unfractured (single porosity) medium, passes through a double porosity model in a fractured medium, and ends with a modified single porosity model that takes the relevant time scales of the flow and the nuclear decay.

• Nuclear Engineering and Technology
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• 제25권4호
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• pp.539-547
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• 1993

이전에 제시한 모델 1-3을 다시 확장하여 균열 암반에서의 일차원적 핵종이동에 관한 추계적인 모델을 제시하였다. 이 모델은 처분장 근처의 암반내의 균열을 통한 무한 길이를 갖는 핵종의 붕괴 사슬에 의한 이동을 연속시간 마코프 프로세스를 이용하여 모사한다. 이전의 결정론적 해석해에 의한 모델들이 균일한 다공성매질과 같은 단순성을 요구하고 핵종의 붕괴사슬의 수를 제한하며 균열암반매질내에서의 이동의 경우에는 균열에서 암반으로의 확산등이 고려되지 않거나 그 해의 형태가 복잡하다. 또다른 결정론적인 해를 제시하는 수치모델의 경우에도 해를 얻기 위한 과정이 상당히 복잡하고 정확한 해를 제공하지는 못한다. 이에 반해 이 모델은 매질에서의 핵종의 농도에 관한 기대값과 그 분산으로서 비교적 용이하게 해를 제시한다. 모델을 검증하고 그 효율성가 정착성을 예시하기 위하여 암반으로의 확산이 무시된 단순화된 매질에 대하여 3개의 붕괴 사슬을 갖는 가상의 핵종에 대하여 이동거리와 시간에 대한 농도에 대하여 정확한 해석해와의 비교가 행하여 졌다. 매질을 나눈 구획의 수에 종속 하는 수치분산을 보정하여 계산된 결과에서 이 모델이 해석해와 잘 일치하는 것을 알 수 있었다.

• 방사성폐기물학회지
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• 제20권2호
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• pp.171-183
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• 2022

The parent and daughter nuclides in a radioactive decay chain arrive at secular equilibrium once they have a large half-life difference. The characteristics of this equilibrium state can be used to estimate the production time of nuclear materials. In this study, a mathematical model and algorithm that can be applied to radio-chronometry using the radioactive equilibrium relationship were investigated, reviewed, and implemented. A Bateman equation that can analyze the decay of radioactive materials over time was used for the mathematical model. To obtain a differential-based solution of the Bateman equation, an algebraic numerical solution approach and two different matrix exponential functions (Moral and Levy) were implemented. The obtained result was compared with those of commonly used algorithms, such as the Chebyshev rational approximation method and WISE Uranium. The experimental analysis confirmed the similarity of the results. However, the Moral method led to an increasing calculation uncertainty once there was a branching decay, so this aspect must be improved. The time period corresponding to the production of nuclear materials or nuclear activity can be estimated using the proposed algorithm when uranium or its daughter nuclides are included in the target materials for nuclear forensics.

• 대한치과교정학회지
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• 제54권3호
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• pp.153-159
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• 2024

Objective: This study aimed to assess the effects of commonly consumed hot drinks on the force decay of orthodontic elastomeric chains. Methods: This in vitro experimental study evaluated 375 pieces of elastomeric chains with six rings placed on a jig. Four rings were stretched by 23.5 mm corresponding to the approximate distance between the canine and the second premolar. Fifteen pieces served as reference samples at time zero, and 360 pieces were randomized into four groups: control, hot water, hot tea, and hot coffee. Each group was further divided into six subgroups (n = 15) according to the different exposure periods. The specimens in the experimental groups were exposed to the respective solutions at 65.5℃ four times per day for 90 seconds at 5-second intervals. The control group was exposed to artificial saliva at 37℃. The force decay of the samples was measured at 1, 2, 7, 14, 21, and 28 days using a universal testing machine. Data were analyzed using repeated-measures analysis of variance. Results: Maximum force decay occurred on day 1 in all groups. The minimum force was recorded in the control group, followed by the tea, coffee, and hot water groups on day 1. At the other time points, the minimum force was observed in the tea group, followed by the control, coffee, and hot water groups. Conclusions: Patients can consume hot drinks without concern about any adverse effect on force decay of the orthodontic elastomeric chains.

• 전기학회논문지
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• 제59권12호
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• pp.2230-2234
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• 2010

This paper deals with the change of surface potential decay, surface resistivity, contact angle and XPS of ultraviolet-treated PET films. From the experimental results on the surface potential decay of UV degraded-samples, it was found that the accumulation of charge is decreased and the surface potential decay time is shortened. Also, from the result of XPS, it was found that the changes affected by the surface degradation of PET film were caused by the generation of carboxyl groups through the chain decomposition and recombination with oxygen molecules in the air.

• Nuclear Engineering and Technology
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• 제31권4호
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• pp.432-443
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• 1999

Using a two-dimensional numerical model, nuclide transport in the buffer between the canister and adjacent rock in a high-level radioactive waste repository is dealt with. Calculations are made for a typical case with a three-member decay chain, $^{234}$ U longrightarrow $^{230}$ Th longrightarrow $^{226}$ Ra. The solution method used here is based on a physically exact formulation by a control volume method directly integrating the governing equation over each control volume.