• 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.

• 방사성폐기물학회지
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• 제20권3호
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• pp.339-347
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• 2022

Major accidents at nuclear power plants generate huge amounts of radioactive waste in a short period of time over a wide area outside the plant boundary. Therefore, extraordinary efforts are required for safe management of the waste. A well-established remediation plan including radioactive waste management that is prepared in advance will minimize the impact on the public and environment. In Korea, however, only limited plans exist to systematically manage this type of off-site radioactive waste generating event. In this study, we developed basic strategies for off-site radioactive waste management based on recommendations from the IAEA (International Atomic Energy Agency) and NCRP (National Council on Radiation Protection and Measurements), experiences from the Fukushima Daiichi accident in Japan, and a review of the national radioactive waste management system in Korea. These strategies included the assignment of roles and responsibilities, development of management methodologies, securement of storage capacities, preparation for the use of existing infrastructure, assurance of information transparency, and establishment of cooperative measures with international organizations.

• 방사성폐기물학회지
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• 제20권4호
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• pp.511-521
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• 2022

Decommissioning of nuclear power plants generates a large amount of radioactive waste in a short period. Moreover, Radioactive waste has various forms including a large volumes of metal, concrete, and solid waste. The disposal of decommissioning waste using 200 L drums is inefficient in terms of economics, work efficiency, and radiation safety. Therefore, The Korea Radioactive Waste Agency is developing large containers for the packaging, transportation, and disposal of decommissioning waste. Assessing disposability considering the characteristics of the radioactive waste and facility, convenience of operation, and safety of workers is necessary. In this study, the exposure dose rate of workers during the disposal of new containers was evaluated using Monte Carlo N-Particle Transport code. Six normal and four abnormal scenarios were derived for the assessment of the dose rate in a near surface disposal facility operation. The results showed that the calculated dose rates in all normal scenarios were lower than the direct exposure dose limitation of workers in the safety analysis report. In abnormal scenarios, the work hours with dose rates below 20 mSv·y^-1 were calculated. The results of this study will be useful in establishing the optimal radiation work conditions.

• 방사성폐기물학회지
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• 제21권2호
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• pp.283-294
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• 2023

APro, developed in KAERI for the process-based total system performance assessment (TSPA) of deep geological disposal systems, performs finite element method (FEM)-based multiphysics analysis. In the FEM-based analysis, the mesh element quality influences the numerical solution accuracy, memory requirement, and computation time. Therefore, an appropriate mesh structure should be constructed before the mesh stability analysis to achieve an accurate and efficient process-based TSPA. A generic reference case of DECOVALEX-2023 Task F, which has been proposed for simulating stationary groundwater flow and time-dependent conservative transport of two tracers, was used in this study for mesh stability analysis. The relative differences in tracer concentration varying mesh structures were determined by comparing with the results for the finest mesh structure. For calculation efficiency, the memory requirements and computation time were compared. Based on the mesh stability analysis, an approach based on adaptive mesh refinement was developed to resolve the error in the early stage of the simulation time-period. It was observed that the relative difference in the tracer concentration significantly decreased with high calculation efficiency.

• Nuclear Engineering and Technology
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• 제56권6호
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• pp.2388-2394
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• 2024

In our previous works, two different spherical burnable poison particles (BPPs) as B₄C and Gd₂O₃ in pin-in block type HTGR core had utilized to suppress the excess reactivity and to control long-term reactivity during the burnup period. In the present work, we performed the neutronic analysis of a prismatic HTGR operating at 850 ℃ with thermal power of 100 MW containing spherical and cylindrical BPPs and then studied the self-shielding effect of BPPs and shape effect. The calculations were performed when the surface area (1) or volume (2) of cylindrical BPPs equals to that of the spherical BPPs. The calculations showed that the neutronic parameters were slightly better for the second case than the first one, such as the excess reactivity of the reactor core at the beginning of the cycle were more suppressed, the core lifetime were more extended, and the fuel-burning were more efficiently. The neutron spectrum in each region of the cylindrical BBPs slightly differs than that of the spherical BPPs. Therefore, the self-shielding effect of BPPs on reactor core performance depends on the particle's geometrical shape.

• Nuclear Engineering and Technology
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• 제11권4호
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• pp.263-274
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• 1979

국내도입이 예상되는 900MWe급 가압경수로형 (PWR) 원자력 발전소와 캐나다형가압중수로형 (PHWR-CANDU) 원자력발전소에 대하여 throwaway 핵연료주기를 가상하여 두 노형의 상대적인 경제성을 비교 검토 하였다. 계산을 목적으로 발전단가를 발전소 투자비, 운전보수비, 운전자본비 및 핵연료비로 구분했으며 건설단가는 보완된 ORCOST 전산코드를 그리고 발전단가는 보완된 POWERCO-50 전산코드를 사용하여 구하였다. 계산에 요구되는 각종의 경제인자에 대하여는 단일의 수치값을 갖는 상수보다는 어떤 범위의 수치대를 이루는 통계적인 변수로 처리하였으며 ORCOST 및 POWERCO-50을 통한 무작위 추출법을 통하여 발전소 건설비 및 발전단가의 화율돗수 분포도를 얻었다. 계산결과 두노형간의 발전단가 분포도는 서로 겹치고 있으며 발전 단가의 기대치는 1986년도 미화로 PHWR의 발전단가가 PWR의 발전단가, 39.41mills/kwh보다 약 0.4mill/kwh만큼 적지만 PHWR의 건설기간이 PWR 보다 1년정도 더 걸리게되는 경우 차이가 없음을 알았다. 따라서 두 노형간의 경제성은 거의 우열을 가릴 수 없으며 한국에서 원자력발전소 노형을 선정할 때 기술전수, 국산화 등 경제외적 인자도 경제적 인자로 수량화하여 검토하는 것이 필요하다고 결론을 내렸다.

• Asian Journal of Atmospheric Environment
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• 제5권4호
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• pp.263-277
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• 2011

Global atmospheric $CO_2$ distributions were simulated with a chemical transport model (GEOS-Chem) and compared with space-borne observations of $CO_2$ column density by GOSAT from April 2009 to January 2010. The GEOS-Chem model simulated 3-D global atmospheric $CO_2$ at $2^{\circ}{\times}2.5^{\circ}$ horizontal resolution using global $CO_2$ surface sources/sinks as well as 3-D emissions from aviation and the atmospheric oxidation of other carbon species. The seasonal cycle and spatial distribution of GEOS-Chem $CO_2$ columns were generally comparable with GOSAT columns over each continent with a systematic positive bias of ~1.0%. Data from the World Data Center for Greenhouse Gases (WDCGG) from twelve ground stations spanning $90^{\circ}S-82^{\circ}N$ were also compared with the modeled data for the period of 2004-2009 inclusive. The ground-based data show high correlations with the GEOS-Chem simulation ($0.66{\leq}R^2{\leq}0.99$) but the model data have a negative bias of ~1.0%, which is primarily due to the model initial conditions. Together these two comparisons can be used to infer that GOSAT $CO_2$ retrievals underestimate $CO_2$ column concentration by ~2.0%, as demonstrated in recent validation work using other methods. We further estimated individual source/sink contributions to the global atmospheric $CO_2$ budget and trends through 7 tagged $CO_2$ tracers (fossil fuels, ocean exchanges, biomass burning, biofuel burning, net terrestrial exchange, shipping, aviation, and CO oxidation) over 2004-2009. The global $CO_2$ trend over this period (2.1 ppmv/year) has been mainly driven by fossil fuel combustion and cement production (3.2 ppmv/year), reinforcing the fact that rigorous $CO_2$ reductions from human activities are necessary in order to stabilize atmospheric $CO_2$ levels.

• 방사성폐기물학회지
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• 제15권3호
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• pp.219-230
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• 2017

본 연구는 경주 중 저준위처분장 2단계 표층처분시설의 폐쇄 후 안전성에 대한 불확실성을 예측 평가하기 위하여 수행되었다. 다중덮개와 처분고의 건전/열화를 고려한 총4가지의 시나리오를 도출하여 강우침투 시 예상되는 처분시설 내부의 유체 이동을 모사하였다. 강우 조건은 총 30년(1985~2014) 간의 월평균 데이터를 적용하였으며, 시뮬레이션 기간은 제도적 관리기간인 300년으로 설정하였다. 처분덮개와 처분고 콘크리트 모두 건전성을 유지하는 조건의 기본 시나리오 평가 결과, 처분시설 내부의 처분고를 완전히 포화시키지 못하는 것을 확인할 수 있었다. 다중 덮개층을 구성하는 8개 층의 각 매질의 모세관 압력과 투과도 차이로 인하여 다중 덮개층이 효과적으로 차수 배수 역할을 하는 것으로 나타났다.

• 방사성폐기물학회지
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• 제20권1호
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• pp.43-63
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• 2022

The aim of this review is to communicate some essential knowledge of the underlying mechanism of the corrosion of structural containment alloys during molten salt reactor operation in the context of prospective online monitoring in future MSR installations. The formation of metal halide species and the progression of their concentration in the molten salt do reflect containment corrosion, tracing the depletion of alloying metals at the alloy salt interface will assure safe conditions during reactor operation. Even though the progress of alloying metal halides concentrations in the molten salt do strongly understate actual corrosion rates, their prospective 1^st order kinetics followed by near-linearly increase is attributed to homogeneous matrix corrosion. The service life of the structural containment alloy is derived from homogeneous matrix corrosion and near-surface void formation but less so from intergranular cracking (IGC) and pitting corrosion. Online monitoring of corrosion species is of particular interest for molten chloride systems since besides the expected formation of chromium chloride species CrCl₂ and CrCl₃, other metal chloride species such as FeCl₂, FeCl₃, MoCl₂, MnCl₂ and NiCl₂ will form, depending on the selected structural alloy. The metal chloride concentrations should follow, after an incubation period of about 10,000 hours, a linear projection with a positive slope and a steady increase of < 1 ppm per day. During the incubation period, metal concentration show 1^st order kinetics and increasing linearly with time^1/2. Ideally, a linear increase reflects homogeneous matrix corrosion, while a sharp increase in the metal chloride concentration could set a warning flag for potential material failure within the projected service life, e.g. as result of intergranular cracking or pitting corrosion. Continuous monitoring of metal chloride concentrations can therefore provide direct information about the mechanism of the ongoing corrosion scenario and offer valuable information for a timely warning of prospective material failure.

• 방사성폐기물학회지
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• 제14권4호
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• pp.343-356
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• 2016

한국원자력환경공단에서는 국내 경수로 원전에서 발생한 사용후핵연료를 건식으로 저장하기 위하여 안전성을 최우선으로 국내/외 기술기준을 준수하여 금속겸용용기를 개발하였다. 이러한 금속용기는 50년 동안 주요 안전성요소(구조, 열제거, 격납, 임계방지, 방사선차폐 등)에 대한 건전성을 유지하고, 운영기간 중 유지보수 과정에 폐기물의 발생을 최소화 하고 이를 안전하게 관리할 수 있도록 설계하였다. 본 논문은 설계수명이 종료된 금속용기 본체 및 내/외부 구조물에 대한 방사화 평가를 통해 정량적인 방사능 재고량에 대한 정보를 제공한다. 본 논문에서는 금속용기 본체 및 구성품의 방사화 방사능 재고량은 MCNP5 ORIGEN-2 평가체계를 이용하여 계산하였으며, 각 구성품의 화학조성, 중성자속 분포, 반응률 및 저장기간 동안 중성자조사 기간을 반영하여 평가하였다. 평가결과, 설계수명 이후 10년 경과시 모든 금속재질에서 $^{60}Co$의 방사능이 기타 핵종들에 비하여 가장 큰 방사능을 띄는 것으로 나타났으며, 중성자차폐체인 수지에서는 수명직후 $^{28}Al$ 및 $^{24}Na$등의 고에너지 감마선을 방출하는 핵종은 반감기가 짧아 0.5년 이후에는 무시할 수 있는 수준으로 나타났다. 또한, 사용후핵연료 제거후 캐니스터 및 금속용기 본체에 대한 표면 선량률 평가결과, 상당히 낮은 값을 나타내어, 해체 시 작업자가 받는 피폭선량은 무시할 수 있는 수준으로 평가되었다. 본 평가방법은 사용후핵연료 금속겸용용기 해체 시 계획의 수립 및 해체작업 종사자의 피폭선량 예측, 방사성폐기물의 관리/재활용 등의 기본자료로 활용할 수 있을 것으로 사료된다.