• Nuclear Engineering and Technology
• /
• 제53권8호
• /
• pp.2454-2463
• /
• 2021

The objective of this research is to the use of americium (AmO₂) as a burnable absorber effectively instead of conventional gadolinium (Gd₂O₃) for VVER-1200 reactor by analyzing its impacts on reactivity, power peaking factor (PPF), safety factor, and quality of the spent fuel. The assembly is burned to 60 GWd/t by using SRAC-2006 code and JENDL-4.0 data library for finding the optimum amount and effective way of using AmO₂ as a burnable absorber. From these studies, it is found that AmO₂ can decrease the excess reactivity like Gd₂O₃ without changing the criticality life span and enrichment of ²³⁵U. A homogeneous mixture of the 0.20% AmO₂+ 4.95% enriched UO₂ fuel rod (model MF-4) decreases the PPF than the reference assembly. The use of AmO₂+UO₂ in the integral burnable absorber (IBA) rod or the outer layer could also decrease the PPF up to 10 GWd/t but increases rapidly after 30 GWd/t, which could be a safety threat. The fuel temperature coefficient and void coefficient of the model MF-4 are the same as the reference assembly. In addition, 22% of initially loaded Am are burning effectively and contributing to the power production.

• Nuclear Engineering and Technology
• /
• 제51권7호
• /
• pp.1715-1720
• /
• 2019

Jozef Stefan Institute (JSI), TRIGA Mark II reactor employs the homogeneous mixture of uranium and zirconium hydride fuel type. Since its upgrade, a series of fresh fuel steady state experimental benchmarks have been conducted. The benchmark results have provided data for testing computational neutronics codes which are important for reactor design and safety analysis. In this work, we investigated the JSI TRIGA Mark II reactor neutronics characteristics: the effective multiplication factor and two safety parameters, namely the control rod worth and the fuel temperature reactivity coefficient using SuperMC. The modeling and real-time cross section generation methods of SuperMC were evaluated in the investigation. The calculation analysis indicated the following: the effective multiplication factor was influenced by the different cross section data libraries; the control rod worth evaluation was better with Monte Carlo codes; the experimental fuel temperature reactivity coefficient was smaller than calculated results due to change in water temperature. All the results were in good agreement with the experimental values. Hence, SuperMC could be used for the designing and benchmarking of other TRIGA Mark II reactors.

• 대한금속재료학회지
• /
• 제49권1호
• /
• pp.52-57
• /
• 2011

Nickel ferrite ($NiFe_2O_4$) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of nickel oxide (NiO) and iron oxide ($Fe_2O_3$). The pressed pellets of $NiFe_2O_4$ were isothermally reduced in pure hydrogen at 800, 900, 1000 and $1100^{\circ}C$. Based on thermogravimetric analysis, the reduction behavior and the kinetic reaction mechanisms of the synthesized ferrite were studied. The initial ferrite powder and various reduction products were characterized by XRD, SEM, reflected light microscope and VSM to reveal the effect of hydrogen reduction on the composition, microstructure, magnetic properties and reaction kinetics of the produced Fe-Ni alloy. Complete reduction of the $NiFe_2O_4$ was achieved with synthesis of homogeneous nanocrystalline Fe-Ni alloys. Arrhenius equation with the approved mathematical formulations for a gas-solid reaction was applied for calculating the activation energy ($E_a$) values and detecting the controlling reaction mechanism.

• 대한금속재료학회지
• /
• 제47권9호
• /
• pp.597-603
• /
• 2009

The hydrogen reduction behavior of ultrasonic ball-milled $WO_3-CuO$ nanopowder, which is highly related with micro-pore structure, was investigated by thermogravimetry(TG) and hygrometry system. EDS and TEM results represented that the ultrasonic ball-milled $WO_3-CuO$ nanopowder consisted of the agglomerates which was confirmed as a homogeneous mixture of $WO_3$ and CuO particles. It was found that the reduction reaction of CuO was retarded by initial micro-pores which are smaller than 40 nm in the ultrasonic ball-milled $WO_3-CuO$ nanopowder. The earlier agglomeration of Cu particles at comparably low temperature decreased the volume of micro-pores in the $WO_3-CuO$ nanopowder which caused the retardation of $WO_3$ reduction reaction. These results clearly explain that the micro-pore structure significantly affected the reduction reaction of $WO_3$ and CuO in the $WO_3-CuO$ nanopowder.

• 한국초전도ㆍ저온공학회논문지
• /
• 제22권4호
• /
• pp.20-23
• /
• 2020

Among many variables in processing the high performance MgB2 bulk superconductors, simple and important approach is to optimize the size dependence of the Mg & B raw powders. The present study is dedicated towards the variation in superconducting properties of MgB2 depending upon the various combination of Mg & B powders with the two different particle sizes respectively. From morphological investigation of the MgB2 samples, narrow and long pores are observed when the larger Mg powders are used, whereas it is rather like the oval shapes with the smaller Mg powders. Also, it can be seen that the connectivity of the MgB2 samples is much enhanced with the smaller size of the B powders. Jc-H properties of the MgB2 samples also indicate that the highest Jc can be obtained when using the smaller size of the B powder with the combination of the smaller Mg powders than that of the larger Mg powders. If the cases with the larger B powers, it is more favorable to select the larger Mg powders with the better Jc-H properties considering shorter diffusion length of Mg and more homogeneous mixture between the Mg & B powders.

• Structural Engineering and Mechanics
• /
• 제84권6호
• /
• pp.823-829
• /
• 2022

This study considered the experimental parameters (Nano-graphene oxide reinforced polycarbonate, GFRP) under low-velocity impact load and vibration analysis. The effect of nano-graphene oxide (NGO) on a polycarbonate-based composite was studied. Two test procedures were adopted to obtain experimental results, vibration analysis. The mechanical tests were performed on damaged and non-damaged specimens to determine the damaging effect on the composite specimens. After the test was carried out, the effect of NGO was measured and damping factors were ascertained experimentally. 0. 2 wt% NGO was determined as the optimum amount that best affected the Vibration Analysis. The experiments revealed that the composite's damping properties were increased by adding the nanoparticles to 0.25 wt% and decreased slightly for the specimens with the highest nanoparticles content. Cyclic sinus loading was applied at a frequency of 3.5 Hz. This paper study the frequency effect of 3.5khz frequency damage on mechanical results. Found that high frequency will worthlessly affect the fatigue life in NGO/polycarbonate composite. In 3.5 Hz frequency, it was chosen to decrease the heat by frequency. Transmission electron microscopy (TEM) micrographs were used to investigate the distribution of NGO on the polycarbonate matrix and revealed a homogeneous mixture of nano-composites and strong bonding between NGO and the polycarbonate which increased the damping properties and decreased vibration. Finally, experimental modal analysis was conducted after the high-velocity impact damage process to investigate the defect on the NGO polycarbonate composites.

• 대한기계학회논문집B
• /
• 제37권3호
• /
• pp.221-228
• /
• 2013

분무유도식 DISI엔진의 성층연소운전조건에서 분무 및 화염특성에 대한 실험적 연구가 수행되었다. 연소가시화를 통하여 성층연소 DISI의 연소는 희박 예혼합 연소와 확산연소의 성격을 모두 가지고 있는 것으로 확인되었다. 분사시기에 따른 혼합기 형성특성이 연소의 특성을 결정하는 중요한 인자임을 관찰하였다. 분무와 혼합기 가시화를 통해 낮은 분위기압에서의 over-mixing, 높은 분위기압에서의 under-mixing이 발생하는 것을 확인하였으며 이러한 혼합기 형성과정의 결과에 따라 화염특성, 연소효율 등의 연소특성이 결정되는 것을 살펴볼 수 있었다. 또한, NOx, IMEP도 분사시기에 따른 경향성을 보였으며, 분사시기에 따른 연소상의 변화에 의한 영향임을 확인하였다.

• 한국임상수의학회지
• /
• 제26권4호
• /
• pp.324-330
• /
• 2009

이 실험의 목적은 개에서 poloxamer/sodium alginate 혼합물(PX/SA)의 수술 후 복강 유착 방지 효과를 알아보는 것이다. 잡종견 15마리를 무처치군, 2% Sodium carboxymethylcellulose(SCMC)처치군, PX/SA 처치군으로 각각 5마리씩 배치하였다. 유착은 돌창자의 창자간막 대측에 1 ${\times}$ 1 cm 크기로 미세 점상 출혈 찰과상을 일으켜 유도하였다. SCMC 용액은 카테터를 통하여 복강내 주입하였고, PX/SA는 찰과상 부위에 단순히 도포하였다. 수술 전 1일과 수술 후 1일, 4일, 7일, 14일에 정맥에서 혈액을 채취하여 적혈구수, 총백혈구수, 섬유소원농도를 분석하고, 수술 후 21일에 유착정도를 computerized tensiometer를 이용하여 분석하였다. 적혈구수, 총백혈구수, 섬유소원농도는 각 군간에 유의성은 없다. 유착부 분리에 필요한 평균 장력은 무처치군에서 173.05 ${\pm}$ 113.48 gf, SCMC 처치군에서 111.42 ${\pm}$ 38.25 gf, PX/SA 처치군에서 69.00 ${\pm}$ 45.07 gf였다. PX/SA 처치군의 평균 분리 장력이 다른 두 군에 비하여 유의성 있게 낮았다 (p < 0.05). 본 실험 결과로 PX/SA는 SCMC용액과 비교하여 복강유착을 감소시키는 것으로 보아 PX/SA를 개에서 복강 수술 후 유착 방지에 적용 가능한 것으로 생각한다.

• 대한화학회지
• /
• 제33권3호
• /
• pp.326-331
• /
• 1989

Sol-gel법으로 고온 초전도체인 $YBa_2Cu_3O_{7-{\sigma}}$의 세선을 제작하였다. Y, Ba, Cu 질산염을 1:2:3의 몰비로 수용액을 제조한 후 구연산 수용액을 첨가하고, 암모니아 수용액을 첨가하여 pH를 $5.8{\sim}6.2$로 조절함으로써 균일한 colloid sol을 제조할 수 있었다. 이를 358K 로 가열하면 점차 점도가 증가하면서 gel화 반응이 진행되고 이 gel화 반응이 완결되기 전에 구연산염 precursor gel fiber를 임의의 길이 및 두께로 뽑을 수 있었다. 이 precursor를 1223K, $Po_2$=1atm. 하에서 8시간 열처리한 후 723K로 서냉하고 13시간 동안 annealing 하여 약 95K에서 전기저항이 급격히 감소($T_c$, onset), 약 82K에서는 저항 0($T_c$, offset)을 나타내었고 액체질소 비등점에서 Meissner-effect를 보임으로써 초전도체 임을 확인하였다.

• 한국식품영양과학회지
• /
• 제40권5호
• /
• pp.738-746
• /
• 2011

Microbial transglutaminase(MTGase)를 이용하여 쌀 가수분해물과 초미세 생대두 분말을 혼합하여 전두부를 제조한 후 조직감, 동적점탄성, 단백질 결합패턴 및 미세구조를 평가하였다. 40%(w/v) 쌀 용액을 Termamyl 효소처리($85^{\circ}C$, 20분) 하였을 때 점조도 값 및 환원당 함량이 각각 $1.27\;Pa{\cdot}s^n$, 9.0%로 나타났다. MWSP 18~22% 농도에서 MTGase 효소로 응고시킨 전두부의 물성을 측정한 결과 MWSP 22% 첨가구에서 전형적인 두부의 조직감을 얻었으며, 쌀 가수분해물 7.5% 첨가구의 경우 경도 639.6 dyne/$cm^2$, 탄성 0.96으로 나타났다. MTGase 5%의 첨가 조건에서 MWSP 18~22% 농도에 따라 동적점탄성을 측정한 결과 MWSP 22% 첨가 경우 반응 6분 이내 G'(5.1 Pa) 및 G''(9.0 Pa)값으로 높게 나타났다. MWSP 22% 첨가구에서 시간에 따른 SDS-PAGE 상에서 대부분의 콩 단백질은 30분 이내에 중합되어 고분자중합체를 형성하였으며, 쌀 가수분해물이 첨가된 경우에도 대부분의 콩 단백질들이 중합되는 유사한 경향을 보였다. 쌀이 첨가된 전두부의 미세구조는 균일한 입자로 채워진 네트워크 구조를 보였으나 냉장저장 2일 후에는 쌀을 첨가하지 않은 대조구에 비해 더욱 거칠어진 표면을 확인할 수 있었다.