• 제목/요약/키워드: Reduction of fuel materials

검색결과 271건 처리시간 0.024초

Acceleration of reduction of U3O8 to UO2 by particle rearrangement in a vertically-shaken bed

  • Byoungjin So;Ju Ho Lee;Jae Won Lee;Yung Zun Cho
    • Nuclear Engineering and Technology
    • /
    • 제56권11호
    • /
    • pp.4837-4842
    • /
    • 2024
  • The stabilization technology for damaged nuclear fuels requires physically-stable pellets, so powders that are used for the process must have high sinterability. Due to safety limitations in H2 concentration, fuel materials are reduced with high gas flow rates or for long times in cyclic oxidation and reduction process. We attempted to shorten the reaction time by shaking the powder reactor vertically. This method reduced the reaction time for the reduction process by two-thirds compared to that required in the static condition. The shaking process had a negligible effect on the quality of the powder. Therefore, this method can be applied to the reduction processes that require large volumes and long reaction times.

EXPERIMENTAL INVESTIGATION AND COMPARISON OF SPRAY AND COMBUSTION CHARACTERISTICS OF GTL AND DIESEL FUELS

  • Kim, K.S.;Beschieru, V.;Jeong, D.S.;Lee, Y.
    • International Journal of Automotive Technology
    • /
    • 제8권3호
    • /
    • pp.275-281
    • /
    • 2007
  • GTL (Gas To Liquid) has the potential to be used in diesel engines as a clean alternative fuel due to advantages in emission reduction, particularly soot reduction. Since the physical properties of GTL fuel differ from those of diesel fuel to some extent, studying how this difference in characteristics of GTL and diesel fuels affects spray and combustion in diesel engines is important. In this study, visual investigation of sprays and flames from GTL and diesel fuels in a vessel simulating diesel combustion was implemented. The effects of various parameters and conditions, such as injection pressure, chamber temperature and pilot injection on liquid-phase fuel length and auto-ignition delay were investigated. It was determined that GTL has a somewhat shorter liquid-phase fuel length, which explains why there is less contact between the fuel liquid-phase and flame for GTL fuel compared to diesel fuel.

고분자전해질 연료전지용 20% Pt/C 캐소드 촉매 제조 및 산소환원반응 평가 (Synthesis and Oxygen Reduction Reaction Evaluation of 20% Pt/C for Polymer Electrolyte Fuel Cell)

  • 김진환;강석민;;류호진
    • 대한금속재료학회지
    • /
    • 제47권7호
    • /
    • pp.454-459
    • /
    • 2009
  • In order to commercialize Polymer Electrolyte Fuel Cell (PEFC), the cathode catalyst such as Platinum supported Carbon (Pt/C) need to have a high activity of Oxygen Reduction Reaction (ORR). In this study, the 20% Pt/C was synthesized using the chemical reduction method while the crystallinity of Platinum (Pt) particles were controlled under heat treatment conditions. The activity of synthesized Pt catalysts was evaluated using electrochemical measurement. Compared with the $i_{ORR}$ at 0.8 V of 20% Pt/C heat-treated at $500^{\circ}C$ and the 20% Pt/C that were not heated and commercial 20% Pt/C, the $i_{ORR}$ at 0.8 V of 20% Pt/C heattreated at $500^{\circ}C$ was 9.5 and 1.7 times higher than those of the 20% Pt/C and commercial 20% Pt/C that were not heated. It was considered that the crystallinity and particle size affect the ORR activity of the Pt/C catalysts.

Thermodynamic and experimental analyses of the oxidation behavior of UO2 pellets in damaged fuel rods of pressurized water reactors

  • Jung, Tae-Sik;Na, Yeon-Soo;Joo, Min-Jae;Lim, Kwang-Young;Kim, Yoon-Ho;Lee, Seung-Jae
    • Nuclear Engineering and Technology
    • /
    • 제52권12호
    • /
    • pp.2880-2886
    • /
    • 2020
  • A small leak occurring on the surface of a fuel rod due to damage exposes UO2 to a steam atmosphere. During this time, fission gas trapped inside the fuel rod leaks out, and the gas leakage can be increased due to UO2 oxidation. Numerous studies have focused on the steam oxidation and its thermodynamic calculation in UO2. However, the thermodynamic calculation of the UO2 oxidation in a pressurized water reactor (PWR) environment has not been studied extensively. Moreover, the kinetics of the oxidation of UO2 pellet also has not been investigated. Therefore, in this study, the thermodynamics of UO2 oxidation under steam injection due to a damaged fuel rod in a PWR environment is studied. In addition, the diminishing radius of the UO2 pellet with time in the PWR environment was calculated through an experiment simulating the initial time of steam injection at the puncture.

하이브리드용 가솔린엔진의 EGR을 통한 연비향상에 관한 연구 (Study on Fuel Consumption Improvement in SI Engine with EGR for Hybrid Electric Vehicle)

  • 박철웅;최영;김창기
    • 한국자동차공학회논문집
    • /
    • 제16권2호
    • /
    • pp.128-135
    • /
    • 2008
  • EGR(exhaust gas recirculation) is considered as a most effective method to reduce the NOx emissions. But high EGR tolerance is always pursued not only for its advantages of the pumping loss reduction and fuel economy benefit in Gasoline-Hybrid engine. However, the occurrence of excessive cyclic variation with high EGR normally prevents substantial fuel economy improvements from being achieved in practice. Therefore, the optimum EGR rate should be carefully determined in order to achieve low fuel consumption and low exhaust emission. In this study, 2 liters gasoline engine with E-EGR system was used to investigate the effects of EGR on fuel efficiency, combustion stability, engine performance and exhaust emissions. With optimal EGR rates, the fuel consumption was improved by 4%. This improvement was achieved while a reduction in NOx emissions of 75% was accomplished. Increase of EGR gas temperature causes the charge air temperature to affect the knock phenomenon and moreover, the EGR valve lift changes for the same control signal.

SDC계 단실형 고체산화물 연료전지용 SDC-NiO 복합음극의 최적 환원 조건 (Optimum Reduction Condition of SDC-NiO Composite Anode for SDC-based Single Chamber Solid Oxide Fuel Cells)

  • 민지현;안성진;문주호;김주선
    • 한국세라믹학회지
    • /
    • 제44권10호
    • /
    • pp.542-547
    • /
    • 2007
  • We have determined an optimal reduction condition for NiO-based anode in single chamber solid oxide fuel cells that involve samaria-doped ceria (SDC) as an electrolyte. Optimal condition should not only induce sufficient reduction of NiO to Ni, but also prevent the reduction of SDC electrolyte in order to achieve high open circuit voltage (OCV) and power output. Thermodynamic consideration allowed us to determine the optimal anode reduction condition as $96%H_2-4%H_2O$ atmosphere at $250^{\circ}C$. This finding was in a good agreement with the experimental verifications by monitoring the conductivities of SDC and NiO under different reducing conditions.

The development of membranes for high temperature PEMFC

  • Lee, Doo-Yeon;Sun, Hee-Young;Cho, Chung-Kun;Lee, Myung-Jin;Seung, Do-Young
    • 한국고분자학회:학술대회논문집
    • /
    • 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
    • /
    • pp.184-184
    • /
    • 2006
  • We have succeeded in the preparation of high molecular weight polybenzimidazoles by solution polycondensation of 3,3'-diaminobenzidine tetrahydrochloride with isophthalic acid, terephthalic acid, or with their derivatives using polyphosphoric acid both as solvent and as condensing agent. Also, we modified phosphoric acid into fluoroalkyl-phosphonic acids[F-PA]. The main reasons are as follows, first of all F-PAs are stronger acids than PA and alkylphosphonic acids which should promote proton hopping and transport. In addition, F-PA has weaker adsorption onto Pt which help to prevent electrocatalyst poisoning and promote higher oxygen reduction activity. The ionic conductivity of 85%-H3PO4 doped membranes show $10^{-2}\;Scm^{-1}\;to\;3{\times}10^{-2}\;Scm^{-1}\;at\;150^{\circ}C$ MEA with 2 %-added electrolyte shows slightly higher cell voltage than the others.

  • PDF

음이온교환막연료전지용 음이온교환막의 문제점과 해결방안 (Problems and Solutions of Anion Exchange Membranes for Anion Exchange Membrane Fuel Cell (AEMFC))

  • 손태양;김태현;김형준;남상용
    • 공업화학
    • /
    • 제29권5호
    • /
    • pp.489-496
    • /
    • 2018
  • 화학에너지를 전기에너지로 전환하는 친환경 에너지 자원으로 각광받는 연료전지에서 고분자 전해질 연료전지(proton exchange membrane fuel cell, PEMFC)의 비싼 백금촉매 사용, 고온가습조건에서의 전도도 감소 등의 문제로 음이온교환연료전지(anion exchange membrane fuel cell, AEMFC)가 주목을 받고 있다. 음이온교환연료전지는 비백금계 촉매를 사용하고 산소환원반응의 활성화 에너지가 낮아 효율이 더 우수한 장점이 있다. 하지만, 이산화탄소에 노출되어 전극손상, 이온전도도 감소 등의 문제점을 포함하여 여러 가지 해결해야 할 문제점이 있다. 따라서, 본 미니총설은 음이온 교환연료전지의 다양한 문제점을 여러 연구논문을 통해서 해결방안을 제시하고자 한다.

A Review of Ac-impedance Models for the Analysis of the Oxygen Reduction Reaction on the Porous Cathode Electrode for Solid Oxide Fuel Cell

  • Kim, Ju-Sik;Pyun, Su-Il
    • 전기화학회지
    • /
    • 제8권2호
    • /
    • pp.106-114
    • /
    • 2005
  • This article covers the theoretical ac-impedance models for the analysis of oxygen reduction on the porous cathode electrode f3r solid oxide fuel cell (SOFC). Firstly, ac-impedance models were explained on the basis of the mechanism of oxygen reduction, which were classified into the rate-determining steps; (i) adsorption of oxygen atom on the electrode surface, (ii) diffusion of adsorbed oxygen atom along the electrode surface towards the three-phase (electrode/electrolyte/gas) boundaries, (iii) surface diffusion of adsorbed oxygen atom m ixed with the adsorption reaction of oxygen atom on the electrode surface and (iv) diffusion of oxygen vacancy through the electrode coupled with the charge transfer reaction at the electrode/gas interface. In each section for ac-impedance model, the representative impedance plots and the interpretation of important parameters attributed to the oxygen reduction reaction were explained. Finally, we discussed in detail the applications of the proposed theoretical ac-impedance models to the real electrode of SOFC system.

Fabrication and Properties of Porous Ni Thin Films

  • Choi, Sun-Hee;Kim, Woo-Sik;Kim, Sung-Moon;Lee, Jong-Ho;Son, Ji-Won;Kim, Joo-Sun
    • 한국세라믹학회지
    • /
    • 제43권5호
    • /
    • pp.265-269
    • /
    • 2006
  • We have deposited NiO films by RF sputtering on $Al_2O_3/SiO_2/Si$ and 100 nm-thick Gd doped $CeO_2$ covered $Al_2O_3/SiO_2/Si$ substrates at various $Ar/O_2$ ratios. The deposited films were reduced to form porous Ni thin fllms in 4% $H_2\;at\;400^{\circ}C$. For the films deposited in pure Ar, the reduction was retarded due to the thickness and the orientation of the NiO films. On the other hand, the films deposited in oxygen mixed ambient were reduced and formed porous Ni films after 20 min of reduction. We also investigated the possibility of using the films for the single chamber operation by studying the electrical property of the films in the fuel/air mixed environment. It is shown that the resistance of the Ni film increases quickly in the mixed gas environment and thus further improvements of Ni-base anodes are required for using them in the single chamber operation.