• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2004년도 학술논문집
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• pp.105-114
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• 2004

This study investigated the thermal behavior of the nuclear graphite waste generated from the decommissioning of the Korean nuclear research reactor, The first part study investigated the decomposition rate of the nuclear graphite waste up to $1000^{\circ}C$ under various oxygen partial pressures using a thermo-gravimetric analyzer (TGA). Tested graphite waste sample not easily destroyed in the oxygen-deficient condition. However, the gas-solid oxidation reaction was found to be very effective in the presence of oxygen. No significant amount of the product of incomplete combustion was formed even in the limited oxygen concentration of 4% $O_2$. The influence of temperature and oxygen partial pressure was evaluated by the theoretical model analysis of the thermo-gravimetric data. The activation energy and the reaction order of graphite oxidation were evaluated as 128 kJ/mole and 1.1, respectively. The second part of this study investigated the behavior of radioactive elements under graphite oxidation atmosphere using thermodynamic equilibrium model. $^{22}Na$, $^{134}Cs$ and $^{137}Cs$ were found be the semi-volatile elements. Since volatile uranium species can be formulated at high temperatures above $1050^{\circ}C$, the temperature of incinerator furnace should be minimized. Other corrosion/activation products, fission products and uranium were found to be the non-volatile species.

• 융복합기술연구소 논문집
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• 제4권2호
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• pp.47-50
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• 2014

Voloxidation is a process for converting $UO_2$ into $U_3O_8$ while removing some volatile products in spent fuels (SF). Various oxidative gas conditions including air and mixture of Ar and $O_2$ could be adopted for the process. The gas flows into a reactor under high temperature ($>500^{\circ}C$) and components of SF are reacted with the gas. SF is composed of various components such as actinides, lanthanides, and alkali metals. Therefore, it is of significance to understand their behavior during the reactions for process development. However, due to the limit of available experiments, phase diagram analysis should be preceded. TPP diagram is constructed with respect to temperature-pressure-pressure. It shows a stable phase depending on partial pressures of gas components as well as temperature. In this work, we investigated TPP diagrams for actinides, lanthanides and other oxides to determine stable oxide forms under different gas conditions. The results would be used to set up a material balance under a pyroprocessing scheme of SF and compare the gas conditions for the optimization of fission products removal.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1892-1900
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• 2023

A protective oxide layer forms on the material surfaces of a Nuclear Power Plant during operation due to high temperature. These oxides can host radionuclides, the activated corrosion products of fission products, resulting in decommissioning workers' exposure. These deposited oxides are iron oxides such as Fe₃O₄, Fe₂O₃ and mixed ferrites such as nickel ferrites, chromium ferrites, and cobalt ferrites. Developing a new chemical decontamination technology for domestic CANDU-type reactors is challenging due to variations in oxide compositions from different structural materials in a Pressurized Water Reactor (PWR) system. The Korea Atomic Energy Research Institute (KAERI) has already developed a chemical decontamination process for PWRs called 'HyBRID' (Hydrazine-Based Reductive metal Ion Decontamination) that does not use organic acids or organic chelating agents at all. As the first step to developing a new chemical decontamination technology for the Pressurized Heavy Water Reactor (PHWR) system, we investigated magnetite dissolution behaviors in various HyBRID inorganic acidic solutions to assess their applicability to the PHWR reactor system, which forms a thicker oxide film.

• Journal of Radiation Protection and Research
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• 제21권1호
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• pp.27-39
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• 1996

DUPIC핵연료주기로 인해 변화되는 경수로 사용 후 핵연료 물질의 핵종별 농도, 방사능, 붕괴열, 위해지수 및 방사선원항등을 시간의 함수로 그 변화특성을 분석하고, 각 인자별로 크게 영향을 미치는 주요핵종의 거동을 물질농도 측면에서 추적 분석평가하였다. 방사성물질 농도에 있어서 연소도 19,000 MWD/MTU의 사용 후 DUPIC핵연료에 존재하는 악티나이드 양은 연소도 35,000 MWD/MTU의 경수로 사용후 핵연료에 비해 약 2% 감소한 반면 핵분열생성물의 양은 약 20% 증가된 것으로 나타났다. 그리고 사용 후 DUPIC핵연료의 방사능 및 붕괴열은 일반적인 사용후핵연료 특성과는 달리, 방사성물질 농도 변화와 비례하지 않는 것으로 나타났다. 사용후 DUPIC핵연료가 갖는 감마 스펙트럼을 경수로핵연료의 경우와 비교해 볼 때, 전체적인 특징은 사용후 DUPIC핵연료의 경우가 $0.01{\sim}0.575MeV$의 낮은 에너지 범위에서는 경수로핵연료 보다 약 $40{\sim}50%$ 낮은 감마선 세기를 보여주고 있으나, 3.5 MeV이상의 높은 에너지 범위에서는 사용후 DUPIC핵연료의 감마선 세기가 휭씬 크게 나타났다. 중성자 선원항은 모두 악티나이드 물질의$({\alpha},\;n)$ 반응 및 자발핵분열에 의해 결정되고 있고, 특히 Cm-244의 자발 핵분열에 의한 중성자선원이 지배적인 것으로 나타났다. 이런 이유 때문에 Cm-244의 농도가 약 3.3배 큰 사용후 DUPIC핵연료의 중성자 선원이 경수로핵연료보다 4배 이상 크게 나타났다.

• 방사성폐기물학회지
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• 제3권4호
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• pp.301-307
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• 2005

조사후 핵연료 가열(PIA장비)를 이용한 고연소도 UO2 사용후 핵연료의 산화 및 가열후 미세조직의 변화를 관찰하였다. 울진 2호기에서 한국원자력연구소 조사후시험시설로 이송된 국산 경수로용 고연소도 사용후 핵연료는 봉평균 연소도가 57,000 MWd/tU-rod avg.이였다. 본 시험에 사용된 시편은 국부연소도 65,000 MWd/tU UO2 소결체의 고형체 200 mg을 사용하였다. 본 시편을 사용후 핵 연료 가열(PIA) 시험장비를 이용하여 핫셀 내에서 3시간의 산화시험과 연속적으로 $1,400^{\circ}C$ 까지 가열하였다. 결정립경계까지의 산화를 위하여 $500^{\circ}C$에서 헬륨 50 ml, 표준공기 100 ml를 흔합한 산화분위기로 3시간을 유지하였다. 핵분열기체 방출거동을 알기위해 시험 전과정중에 85Kr의 방출량을 베타 측정기와 감마 측정기를 이용하여 실시간으로 측정 하였다. 가열시험이 종료된 후 전자주사현미경을 이용하여 미세구조의 변화를 관찰하였다. 시험결과 가열하는 동안 핵분열생성물은 UO2기지의 결정립경계와 표면으로 이동된 것을 관찰하였다. 이 시편은 환원과정을 통하여 재구조화 되었고, $5\~10\;{\mu}m$ 정도의 결정립크기를 가진 것으로 나타났다.

• 방사성폐기물학회지
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• 제17권3호
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• pp.279-298
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• 2019

사용후핵연료의 효율적 관리를 위하여 한국원자력연구원에서 수행 중인 파이로 공정으로부터 발생되는 폐기물 처리기술에 대한 최근 연구동향을 종합적으로 고찰하였다. 파이로 폐기물 처리기술은 처분 대상 폐기물의 감용 및 포장, 저장과 최종 처분에 적합한 고화체 제조를 목표로 하고 있다. 한국원자력연구원에서 수행 중인 파이로 폐기물 처리 기술개발 접근 방향은 공정 흐름으로부터 발생한 폐기물내 주요 핵종들을 분리하고 회수한 물질 등을 재사용함으로서 폐기물 발생량을 최소로 하며 동시에 분리한 핵종을 별도로 고화처리하는 것이다. 폐기물 처리 주요 기술 특성은 먼저 전해환원용 원료물질 제조를 위하여 전처리 고온 열처리 공정을 사용하며, LiCl 과 LiCl-KCl 염으로부터 핵종을 분리하고 회수염의 재사용 및 핵종 함유량을 증대시킨 최종 고화체 제조 기술을 개발하는 것이다. 따라서 실험실 규모 실험 결과를 토대로 최근에는 공정 용량 증대를 위한 자료 확보를 목적으로 공학규모 시험을 수행 중에 있다.

• 한국방사선학회논문지
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• 제5권4호
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• pp.217-221
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• 2011

$^{237}Np$ is very important material in the fission products of nuclear reactors. Resonance integral(RI) tests of this material is necessary to check between the experiments and the evaluated data. Such feedback to the evaluated data is very important to correct data and improve of codes. The RI for the $^{237}Np(n,{\gamma})^{238}Np$ reaction were measured by using the 46-MeV electron linear accelerator (linac) at the Research Reactor Institute, Kyoto University (KURRI). The measurement was performed in the energy region from 0.005 eV and 10 keV. RI obtained as 804.7 barns, compared with those of the evaluated data in JENDL-4.0 and Mughabghab.

• Bulletin of the Korean Chemical Society
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• 제24권6호
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• pp.829-831
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• 2003

Various theoretical studies of σ-bond activation of organic molecules by transition metal complexes arereviewed. In the homolytic σ-bond activation, the d orbital energy level of the central metal is an importantfactor, as well known. At the same time, the electron-withdrawing substituent which stabilizes the sp3 orbitalaccelerates the homolytic σ-bond activation. In the heterolytic C-H σ-bond activation of RH by $MXL_n$, the XHbond formation is an important driving force, where $MRL_n$ and HX are formed as products. The heterolytic σ-bond activation is also understood in terms of the electrophilic attack of the metal center to the substrate.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2004년도 학술논문집
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• pp.397-398
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• 2004

It is important to estimate the radiation activity of the nuclear fuel which is a source term of the loss of coolant accident. The purpose of this study is to identify the most important parameters of the source term calculation based on three fuel types: typical natural uranium CANDU fuel, slightly enriched uranium and DUPIC fuel. The characteristics of the radiation source term were analyzed through sensitivity calculations of the linear power, fuel turnup, and the power shape.(omitted)

• Nuclear Engineering and Technology
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• 제52권8호
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• pp.1638-1649
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• 2020

In the case of a severe accident in a Light Water Reactor, the issue of late release of fission products, from the primary circuit surfaces is of particular concern due to the direct impact on the source term. CsI is the main iodine compound present in the primary circuit and can be deposited as particles or condensed species. Its chemistry can be affected by the presence of molybdenum, and can lead to the formation of gaseous iodine. The present work studied chemical reactions on the surfaces involving gaseous iodine release. CsI and MoO₃ were used to highlight the effects of carrier gas composition and oxygen partial pressure on the reactions. The results revealed a noticeable effect of the presence of molybdenum on the formation of gaseous iodine, mainly identified as molecular iodine. In addition, the oxygen partial pressure prevailing in the studied conditions was an influential parameter in the reaction.