• The Korean Journal of Ceramics
• /
• 제6권3호
• /
• pp.209-213
• /
• 2000

Microstructural changes of AlOOH doped UO$_2$pellet after annealing up to 216h have been observed and they were compared with those of the standard pellet. Grain and pore size of UO$_2$pellet increased with the addition of AlOOH and its effect was still validated during annealing. Densification rate was reduced by the addition of AlOOH and it was attributed to coarsened pores with spherical shape. Grain and pore growth was stopped and density increase was the least after 144h of annealing. The variation of pore size resulting from annealing has a linear relationship with that of grain size.

• 공업화학
• /
• 제9권3호
• /
• pp.388-393
• /
• 1998

의료용 동위원소인 fission Mo($^{99}Mo$)를 제조하기 위한 공정중 $UO_2$ 표적의 질산용해공정의 조업조건을 확립하기 위하여 $UO_2$ pellet의 유효표면적($s:0.034{\sim}0.282cm^2/g-UO_2$), 질산농도(1.5~10N), 반응온도 ($40{\sim}105^{\circ}C$)에 따른 $HNO_3$ pellet의 용해특성을 확인하였다. 그 결과 용해속도가 $UO_2$ pellet의 유효표면적에 정비례하며 표면적이 클수록 그 경향이 뚜렸함을 확인하였고, 반응속도와의 관계가 dc/dt = 10.6s로 나타났다. 용해속도와 질산농도와의 관계는 일정온도($90^{\circ}C$)에서 [$HNO_3$]1.42에 비례하는 것으로 나타났고, 온도변화에 따른 관계는 $90^{\circ}C$까지는 온도가 증가함에 따라 용해속도가 급격히 증가하나 그 이상에서는 오히려 감소하는 것으로 나타났으며, 활성화 에너지가 36.3KJ/mol로 계산되었다.

• 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.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2007년도 추계학술대회 논문집
• /
• pp.443-444
• /
• 2007

• Nuclear Engineering and Technology
• /
• 제55권10호
• /
• pp.3860-3865
• /
• 2023

A metallic microcell UO₂ pellet has a microstructure where a metal wall is connected to overcome the low thermal conductivity of the UO₂ fuel pellet. It has been verified that metallic microcell fuel pellets provide an impressive reduction of the fuel centerline temperature through a Halden irradiation test. However, it is difficult to predict the effective thermal conductivity of these pellets and researchers have had to rely on measurement and use of the finite element method. In this study, we designed a unit microcell model using a thermal resistance circuit to calculate the effective thermal conductivity on the basis of the microstructure characteristics by using the aspect ratio and compared the results with those of reported metallic UO₂ microcell pellets. In particular, using the thermal conductivity calculated by our model, the fuel centerline temperature of Cr microcell pellets on the 5th day of the Halden irradiation test was predicted within 6% error from the measured value.

• The Korean Journal of Ceramics
• /
• 제4권4호
• /
• pp.279-285
• /
• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• 한국결정성장학회지
• /
• 제17권2호
• /
• pp.75-81
• /
• 2007

[ $UO_2$ ] 소결체와 $U_3O_8$종자를 5wt% 첨가한 $UO_2$ 소결체의 치밀화 과정 및 입자성장 양상을 소결 온도 및 시간을 변수로 하여 분석하였다. $UO_2$ 성형체와 5wt% $U_3O_8$ 종자 첨가 성형체를 수소분위기에서 $1300^{\circ}C$에서 $1700^{\circ}C$로 온도를 올려가며 0시간에서 4시간 소결하여 밀도와 입자크기를 측정하였다. $1300^{\circ}C$까지는 종자 첨가에 상관없이 거의 같은 밀도를 가졌지만 온도가 올라가면서 종자 첨가 소결체의 치밀화가 저하되었다가 $1700^{\circ}C$ 근처에서 거의 비슷한 밀도를 가지게 된다. 입자성장의 경우, $1600^{\circ}C$에서는 종자 입자를 제외하면 기지상의 입자 크기는 거의 비슷하지만 $1700^{\circ}C$ 이후에서는 종자첨가 $UO_2$ 소결체의 입자성장이 종자가 첨가되지 않을 경우에 비하여 2배 이상 빠르게 진행되었다.

• Nuclear Engineering and Technology
• /
• 제35권4호
• /
• pp.299-308
• /
• 2003

Fabrication technique of $(Th,U)O_2$ pellets has been investigated. Powder mixtures of $ThO_2\;and\;UO_2$ were milled in two different ways-dry and wet milling. Milled powder was compacted and sintered to $(Th,U)O_2$ pellets. The wet-milled powder leads to a $(Th,U)O_2$ pellet having a high sintered density and uniform distribution of U and Th, compared to the dry-milled powder. The sintered density of a $(Th,U)O_2$ pellet tends to decrease by increasing the content of $ThO_2$. The thermal conductivity of $ThO_2\;and\;(Th,U)O_2$ pellets was measured by the laser flash method. The thermal conductivity of the $ThO_2$ pellet is higher than that of the $UO_2$ pellet, and the thermal conductivities of $(Th,U)O_2$ pellets containing $65wt\%\;and\;35wt\%\;ThO_2$ pellets are lower than that of the $UO_2$ pellet.

• Nuclear Engineering and Technology
• /
• 제53권12호
• /
• pp.4052-4059
• /
• 2021

The microstructure of the fuel pellet plays an essential role in fission gas buildup and release and is critical for the safe and continued operation of nuclear power stations. Structural analysis of uranium dioxide (UO₂)-molybdenum (Mo) composite fuel pellets prepared at a range of sintering temperatures from 1300 to 1800 ℃ was performed. Mo micro and nanoparticles were used in making the composite pellets. A systematic investigation into the influence of processing parameters during Spark Plasma Sintering (SPS) of the pellets on the microstructure, texture, grain size, and grain boundary characters of UO₂-Mo is presented. UO₂-Mo composite show significant differences in the fraction of general boundaries and also special/coincident site lattice (CSL) boundaries. EBSD orientation maps demonstrated that <111> texturing was observed in the pellets fabricated at 1500 ℃. The experimental investigations suggest that UO₂-Mo composite pellets have favorable microstructural features compared to the UO₂ pellet.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 2002년도 춘계공동학술발표회요약집
• /
• pp.233.1-233
• /
• 2002