• Nuclear Engineering and Technology
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• 제39권5호
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• pp.603-616
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• 2007

Roy Huddle, having invented the coated particle in Harwell 1957, stated in the early 1970s that we know now everything about particles and coatings and should be going over to deal with other problems. This was on the occasion of the Dragon fuel performance information meeting London 1973: How wrong a genius be! It took until 1978 that really good particles were made in Germany, then during the Japanese HTTR production in the 1990s and finally the Chinese 2000-2001 campaign for HTR-10. Here, we present a review of history and present status. Today, good fuel is measured by different standards from the seventies: where $9*10^{-4}$ initial free heavy metal fraction was typical for early AVR carbide fuel and $3*10^{-4}$ initial free heavy metal fraction was acceptable for oxide fuel in THTR, we insist on values more than an order of magnitude below this value today. Half a percent of particle failure at the end-of-irradiation, another ancient standard, is not even acceptable today, even for the most severe accidents. While legislation and licensing has not changed, one of the reasons we insist on these improvements is the preference for passive systems rather than active controls of earlier times. After renewed HTGR interest, we are reporting about the start of new or reactivated coated particle work in several parts of the world, considering the aspects of designs/ traditional and new materials, manufacturing technologies/ quality control quality assurance, irradiation and accident performance, modeling and performance predictions, and fuel cycle aspects and spent fuel treatment. In very general terms, the coated particle should be strong, reliable, retentive, and affordable. These properties have to be quantified and will be eventually optimized for a specific application system. Results obtained so far indicate that the same particle can be used for steam cycle applications with $700-750^{\circ}C$ helium coolant gas exit, for gas turbine applications at $850-900^{\circ}C$ and for process heat/hydrogen generation applications with $950^{\circ}C$ outlet temperatures. There is a clear set of standards for modem high quality fuel in terms of low levels of heavy metal contamination, manufacture-induced particle defects during fuel body and fuel element making, irradiation/accident induced particle failures and limits on fission product release from intact particles. While gas-cooled reactor design is still open-ended with blocks for the prismatic and spherical fuel elements for the pebble-bed design, there is near worldwide agreement on high quality fuel: a $500{\mu}m$ diameter $UO_2$ kernel of 10% enrichment is surrounded by a $100{\mu}m$ thick sacrificial buffer layer to be followed by a dense inner pyrocarbon layer, a high quality silicon carbide layer of $35{\mu}m$ thickness and theoretical density and another outer pyrocarbon layer. Good performance has been demonstrated both under operational and under accident conditions, i.e. to 10% FIMA and maximum $1600^{\circ}C$ afterwards. And it is the wide-ranging demonstration experience that makes this particle superior. Recommendations are made for further work: 1. Generation of data for presently manufactured materials, e.g. SiC strength and strength distribution, PyC creep and shrinkage and many more material data sets. 2. Renewed start of irradiation and accident testing of modem coated particle fuel. 3. Analysis of existing and newly created data with a view to demonstrate satisfactory performance at burnups beyond 10% FIMA and complete fission product retention even in accidents that go beyond $1600^{\circ}C$ for a short period of time. This work should proceed at both national and international level.

• Nuclear Engineering and Technology
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• 제40권4호
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• pp.299-304
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• 2008

A detection system was set up to measure the neutron generation rate of a recently developed D-D neutron generator. The system is composed of a Si detector, He-3 detector, and electronics for pulse height analysis. The neutron generation rate was measured by counting protons using the Si detector, and the data was crosschecked by counting neutrons with the He-3 detector. The efficiencies of the Si and He-3 detectors were calibrated independently by using a standard alpha particle source $^{241}Am$ and a bare isotopic neutron source $^{252}Cf$, respectively. The effect of the cross-sectional difference between the D(d,p)T and $D(d,n)^3He$ reactions was evaluated for the case of a thick target. The neutron generation rate was theoretically corrected for the anisotropic emission of protons and neutrons in the D-D reactions. The attenuations of neutron on the path to the He-3 detector by the target assembly and vacuum flange of the neutron generator were considered by the Monte Carlo method using the MCNP 4C2 code. As a result, the neutron generation rate based on the Si detector measurement was determined with a relative uncertainty of ${\pm}5%$, and the two rates measured by both detectors corroborated within 20%.

• Korean Chemical Engineering Research
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• 제40권6호
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• pp.752-756
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• 2002

PDP(Plasma Display Panel)용 녹색 형광체인 $Zn_2SiO_4:Mn$ 형광체의 제조에 있어 콜로이드 분무 열분해법을 도입하고, $Zn_2SiO_4$ wellimite 결정의 $Si^{4+}$ 자리를 치환하는 $Gd^{3+}/Li^+$ 부활성제를 첨가하여 형광체의 발광특성을 향상시키고자 하였다. 14 nm 크기의 fumed silica 입자를 규소 전구체로 도입한 콜로이드 분무열분해법에 의해서 제조되어진 $Zn_2SiO_4:Mn$ 입자는 응집이 없는 구형의 형상, 작은 입자 크기 및 좁은 입도 분포를 가졌다. $Gd^{3+}/Li^+$ 함량은 $Zn_2SiO_4:Mn$ 형광체 입자의 발광특성에 영향을 끼쳤으며, 적정한 함량의 $Gd^{3+}/Li^+$ 부활성제를 첨가함으로써 진공 자외선하에서 형광체의 발광휘도를 향상시키고, 잔광시간을 크게 줄일 수 있었다. 분무 열분해법에 의한 $Gd^{3+}/Li^+$이 코도핑된 $Zn_2SiO_4:Mn$ 형광체 입자의 제조에 있어서 후열처리 온도는 형광체의 발광특성을 결정짓는 주요한 인자이다. 0.1 mol%의 $Gd^{3+}/Li^+$ 부활제를 포함하고 $1,145^{\circ}C$ 온도에서 소결된 $Zn_2SiO_4:Mn$ 형광체 입자는 상업용 형광체에 비해 5% 높은 발광 휘도과 5.7 ms의 잔광시간을 가졌다.

• Nuclear Engineering and Technology
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• 제47권5호
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• pp.608-616
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• 2015

The migration of silver (Ag) in silicon carbide (SiC) and $^{110m}Ag$ through SiC of irradiated tristructural isotropic (TRISO) fuel has been studied for the past three to four decades. However, there is no satisfactory explanation for the transport mechanism of Ag in SiC. In this work, the diffusion coefficients of Ag measured and/or estimated in previous studies were reviewed, and then pre-exponential factors and activation energies from the previous experiments were evaluated using Arrhenius equation. The activation energy is $247.4kJ{\cdot}mol^{-1}$ from Ag paste experiments between two SiC layers produced using fluidized-bed chemical vapor deposition (FBCVD), $125.3kJ{\cdot}mol^{-1}$ from integral release experiments (annealing of irradiated TRISO fuel), $121.8kJ{\cdot}mol^{-1}$ from fractional Ag release during irradiation of TRISO fuel in high flux reactor (HFR), and $274.8kJ{\cdot}mol^{-1}$ from Ag ion implantation experiments, respectively. The activation energy from ion implantation experiments is greater than that from Ag paste, fractional release and integral release, and the activation energy from Ag paste experiments is approximately two times greater than that from integral release experiments and fractional Ag release during the irradiation of TRISO fuel in HFR. The pre-exponential factors are also very different depending on the experimental methods and estimation. From a comparison of the pre-exponential factors and activation energies, it can be analogized that the diffusion mechanism of Ag using ion implantation experiment is different from other experiments, such as a Ag paste experiment, integral release experiments, and heating experiments after irradiating TRISO fuel in HFR. However, the results of this work do not support the long held assumption that Ag release from FBCVD-SiC, used for the coating layer in TRISO fuel, is dominated by grain boundary diffusion. In order to understand in detail the transport mechanism of Ag through the coating layer, FBCVD-SiC in TRISO fuel, a microstructural change caused by neutron irradiation during operation has to be fully considered.

• Applied Microscopy
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• 제39권1호
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• pp.41-48
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• 2009

본 연구는 색조화장품에 사용되는 진주광택안료의 특성을 주사전자현미경과 에너지분산분광분석기 및 열분석기를 사용하여 규명하였다. 본 연구에 사용된 인공합성 진주광택안료를 여성의 볼과 눈두덩 부위에 화장을 한 후 육안으로 관찰하였을 때 진주 광택안료는 보는 각도에 따라 흰색에서 보라색까지 다양한 색조로 빛을 반사하였다. 진주광택안료의 주사전자현미경 관찰 결과 안료는 얇은 판상의 다각형의 형태를 하고 있었으며 크기는 규격화된 모양이 아니고 다양하게 관찰되었다. 이런 조각의 크기는 약 $30{\mu}m$에서 $300{\mu}m$까지 측정되었고 안료 조각은 끝이 뾰족하거나 각진 상태로 존재하였다. 고배율의 주사전자현미경상에서 안료조각의 모서리 부위와 측면은 날카롭지 않은 타원형의 형태로 나타났으며 두께는 약 $9{\mu}m$로 측정되었다. 안료조각 표면은 직경이 약 60 nm의 이산화티탄 입자들에 의해서 피복되어 있었다. 진주광택안료의 에너지분산분석기를 사용하여 구성 원소 성분을 분석한 결과 안료의 표면은 O, Si, C, Na, Ca, Ti, Zn 등이 검출되었고 안료의 측면 부위도 동일한 성분들이 검출되었다. 이들 안료는 운모 티타니아(mica titania)로 확인되었다. 진주광택안료의 열분석 결과 초기 $100^{\circ}C$부터 $800^{\circ}C$까지 중량 감소는 큰 차이를 보이지 않았다. 열분석 결과 $115^{\circ}C$에서 1.1% 중량 감소를 하였고 $416^{\circ}C$에서 1.7% 감소하였으며 $797^{\circ}C$ 에서 1.9%의 중량이 감소된 것을 확인하였다.

• 한국전기전자재료학회논문지
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• 제25권6호
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• pp.486-490
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• 2012

$La_{7.33}Bi_2(SiO_4)_6O_2$ specimens were fabricated by standard solid-state synthesis route for solid oxide electrolytes. The calcined powders exhibited uniform particles with a mean particle size of about $28{\mu}m$. The room-temperature structure of $La_{7.33}Bi_2(SiO_4)_6O_2$ specimens was analyzed as hexagonal, space group P63 or P63/m, and the unit cell volume increased with increase a sintering temperature. The specimens sintered at $1,175^{\circ}C$ showed X-ray patterns of homogeneous apatite single phase without the second phase such as $La_2Si_2O_7$ and $La_2SiO_5$. The specimen sintered at $1,175^{\circ}C$ showed the maximum sintered density of 5.49 $g/cm^3$. Increasing the sintering temperature, total conductivities increased, activation energy decreased and the values were $1.98{\times}10^{-5}Scm-1$ and 1.23 eV, respectively.

• 한국재료학회지
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• 제23권12호
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• pp.727-731
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• 2013

In this study, green barium strontium silicate phosphor ($BaSrSiO_4:Eu^{3+}$, $Eu^{2+}$) was synthesized using a solid-state reaction method in air and reducing atmosphere. Investigation of the firing temperature indicates that a single phase of $BaSrSiO_4$ is formed when the firing temperature is higher than $1400^{\circ}C$. The effect of firing temperature and doping concentration on luminescent properties are investigated. The light-emitting property was the best when the molar content of $Eu_2O_3$ was 0.025 mol. Also, the luminescent brightness of the $BaSrSiO_4$ fluorescent substance was the best when the particle size of the barium was $0.5{\mu}m$. $BaSrSiO_4$ phosphors exhibit the typical green luminescent properties of $Eu^{3+}$ and $Eu^{2+}$. The characteristics of the synthesized $BaSrSiO_4:Eu^{3+}$, $Eu^{2+}$ phosphor were investigated using X-ray diffraction (XRD) and scanning electron microscopy. The maximum emission band of the $BaSrSiO_4:Eu^{3+}$, $Eu^{2+}$ was 520 nm.

• Nuclear Engineering and Technology
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• 제34권1호
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• pp.60-67
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• 2002

The effects of ball-milling time(0 ~4 hrs) have been investigated on the change of powder characteristics, compaction behavior (compaction pressure range : 200 ~400MPa) and sinterability (1700'c in Ha atmosphere) of two different UO$_2$ powders (ex-ADU and ex-AUC) prepared by the wet process. It is observed that, while the ex-ADU UO$_2$ was little affected, the ex-AUC UO$_2$ was largely affected by the ball-milling treatment. This may be attributed to the characteristics of particle size formed during the preparation step, i.e.., the former has a small average size of about 1.0${\mu}{\textrm}{m}$, while the latter has a relatively large average size of about 301n. It appeared that the effective size reduction by ball-milling treatment is limited to the particle size larger than l${\mu}{\textrm}{m}$, and to the extent of maximum decrease in size of about 0.5tn. In the case of ex-AUC UO$_2$, it is observed that the particle size decreased with ball-milling time and green density and sintered density of the pellets prepared from ball-milled powder increased compared with those of pellets prepared from the as-received powder under the same conditions. This may be attributed mainly to the fine particles formed during the ball-milling treatment.

• 공업화학
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• 제10권6호
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• pp.843-847
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• 1999

본 연구에서는 유동층-화학증기침투에 의해 이염화이메틸규소(DDS)와 수소로부터 생성된 탄화규소를 활성탄에 증착시킨 세라믹 탄소/탄화규소복합체가 제조되었다. 4~12, 12~20, 20~40 mesh의 활성탄이 사용되었다. 증착 후 반응물인 이염화이메틸규소의 농도, 활성탄의 크기, 반응압력, 반응시간에 따른 반응후 각 시료의 표면적과 증착량 및 증착양상을 관찰하였다. 실험결과 DDS의 농도가 낮고 반응압력이 작을수록 시료 기공내에 고른 증착을 갖는 것을 알 수 있었다. 또한 기공직경과 표면적들이 어떠한 시점에서 최소값을 갖는 것으로 기공내부 증착에서 입자외부 표면 증착으로 바뀜을 알 수 있었다. DDS의 농도가 낮고 반응압력이 낮을 때 작은 탄화규소입자가 활성탄 표면에 더욱 고르게 증착되었다. 이 결과들은 SEM, TGA, 기공도측정장치, BET에 의해 확인되었다.

• Korean Chemical Engineering Research
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• 제49권6호
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• pp.752-757
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• 2011

암모니아수와 zinc acetate로부터 액상 수열합성법에 의한 ZnO의 제조에 있어 반응온도, 반응물의 농도와 혼합방법, 용액의 pH 등 반응조건에 따른 ZnO 입자의 형상과 입자분포 등 제조특성을 고찰하고, UV 조사하에 tartrazine의 광분해를 측정하여 합성된 ZnO의 광촉매로서의 성능을 확인하였다. 반응용액의 pH가 높을수록 ZnO 입자의 평균 크기는 증가하였고, zinc acetate의 농도가 증가할수록 그리고 반응온도가 증가할수록 입자의 크기는 감소하였다. 반응용액의 혼합시 암모니아수 주입 후에 zinc acetate를 첨가하였을 경우 더 작은 입자를 얻을 수 있었다. 최소 크기의 ZnO 입자의 생성을 위한 최적 조건은 용액의 pH 11.2, zinc acetate의 농도 0.6 M, 반응온도 $90^{\circ}C$였으며, 입자 평균크기는 3.133 ${\mu}$m이었다. 합성온도 $80^{\circ}C$, zinc acetate 농도 1.0M 및 반응용액의 pH 11.2의 조건에서 합성된 ZnO에 의한 tartrazine의 광촉매 분해는 분해시간 60분에서 약 97%의 분해율을 보였다.